Topic: m148 bill of materials?

[Digital Quality]

Can anyone diect me to a list of materials in the (Shoeps version) m148? I'm curious in particular exactly which transformer model and active parts were used.

Well, thanks for any help you can offer - 'preciate it.

[thegreatgumbino]

Can anyone diect me to a list of materials in the (Shoeps version) m148? I'm curious in particular exactly which transformer model and active parts were used.

Well, thanks for any help you can offer - 'preciate it.

All of the info I've been able to find is compiled in this thread.  I don't think you'll ever find out the exact parts though.  First, Doug removes the part numbers from his work, and second, as time evolves and parts become obsolete or newer ones come along Doug changes things.  Good luck in your search.

http://taperssection.com/index.php?topic=52730.0

[Digital Quality]

Thanks man, I saw that.  Just messin 'round in spice right now. Do you know if it's a FET design?

[thegreatgumbino]

Thanks man, I saw that.  Just messin 'round in spice right now. Do you know if it's a FET design?

I don't think the M148 has any FET's.  It's a pure transformer based design to lower the noise floor and add a bit of warmth.

[Chuck]

You're not moving to the dark side are you?

Hey, Harrison has one. Maybe he knows the details.

This is what I know:

Descrete transistor front end into a Jensen transformer.
I used to know the model #. Maybe I can find it.
The ( 6v batteries provide the clean phantom power. He pours some goop over the guts before he ships them, so knowing all the various parts may be difficult.

I have just recently thought about making a good transformer based pre-amp myself. I've been tinkering with a cheap transformer and like the lack of noise in it. The battery thing is the easiest part as far as providing phantom power. I know Jensen has a few pre-amp designs based on their transformers on the Jensen site. I'd be surprised if the M148 isn't based on one of those designs...

[Chuck]

Thanks man, I saw that.  Just messin 'round in spice right now. Do you know if it's a FET design?

I don't think the M148 has any FET's.  It's a pure transformer based design to lower the noise floor and add a bit of warmth.

I know that there is some active circuitry in there. When Harrison had to change the batteries he noticed that Doug had a tap running off the middle of the battery cluster.

[Digital Quality]

You're not moving to the dark side are you?

I'm supposed to be getting a FedEx today.   I broke about a day before they started showing up on the yard sale.  

I'm not really trying to duplicate the brick as much as work on something with quality components and play around with some different discrete topolgies. I saw the talk of $200 Jensens but it didn't look to me like the $200 ones were as applicable for a pre as maybe for direct in or ground loop boxes.

[Digital Quality]

Descrete transistor front end into a Jensen transformer.

Are you sure it's not the other way around? I was thinking more of a transformer front end and a cascode gain stage.

It's interesting to play around with and talk/think about. I didn't really consider that I would maybe be stepping on Doug's toes, that's not my intent.

[Chuck]

You're not moving to the dark side are you?

I'm supposed to be getting a FedEx today.   I broke about a day before they started showing up on the yard sale.  

I'm not really trying to duplicate the brick as much as work on something with quality components and play around with some different discrete topolgies. I saw the talk of $200 Jensens but it didn't look to me like the $200 ones were as applicable for a pre as maybe for direct in or ground loop boxes.

If this thread is seen by enough people, someone will know the transformers he uses. I may have that info at home. If you do find the right materials, I'd like to work on it with you. I have an idea for a transformer based pre-amp that also has two line inputs that can be blended with the transformer outputs. A very simple design. It would work as a high quailty pre-amp on it's own, or a line . mic mixer when needed. The line inputs could be passive or possibly switchable to keep noise out of the circuit. I was starting to put together a MarkerTek order for the chassis parts, maybe I'll hold off. We could save on shipping etc... if we buy all the stuff together...

[Chuck]

Descrete transistor front end into a Jensen transformer.

Are you sure it's not the other way around? I was thinking more of a transformer front end and a cascode gain stage.

It's interesting to play around with and talk/think about. I didn't really consider that I would maybe be stepping on Doug's toes, that's not my intent.

It's too bad the old Oade tapers section is down, because I know he talked about this in a few threads. You might be right about the transistors after the transformer. But, I have it stuck in my head they came before. With the microphones input directly into transformers, there is no need for nasty coupling capacitors in the signal path at that stage.

[Digital Quality]

I'd say don't wait on me. It sounds like I'm a bit behind you and I'm going to be moving slow on account of my NC gf showed up and is taking a lot of maintanence time right now. She is supposed to be getting a job -- or leaving me for good, before too long and I'll have a little more time on my hands then. I ordered a little book with some topologies, and I'm heading over to storage to pick up some old engineering bookds today.

Let's talk though, your design sounds interesting. I was more after just a mic pre with fixed gain to simulate play around with. This was my least great skill in school though so hopefully I'm a little smarter now

[balou2]

I'd say don't wait on me. It sounds like I'm a bit behind you and I'm going to be moving slow on account of my NC gf showed up and is taking a lot of maintanence time right now. She is supposed to be getting a job -- or leaving me for good, before too long and I'll have a little more time on my hands then.

A true taper.

Good luck with everything man.

[Chuck]

I am just a few parts way from having a passive (transformer based) mic pre that I'm cobbling together from a Rolls PB223 phantom power supply. I started with that, as it already provides phantom power, so that part is already designed. I have some very cheap impedence matching transformers that provide approx. +12 db of gain with the MSH-1O's i plan to use it with. My idea at this point is to add a basic transitor circuit (after the transformers) that will help blend in the line inputs when needed. I have severel mixer schematics that will work on 9-12v dc power, which is what the Rolls box runs on. Right now, I just need a descent dual 10k audio pot and a couple of RCA panel mount jacks and I'll have it done. The cheap transformers could easily be replaced in a later design with quality units. After the prototype, I figured I'd make a real nice one in a Hammond or similar enclosure. Maybe even make an integrated or removable 8x 6v DC small SLA battery pack for the phantom power, like Doug uses.

All it takes is time and money... I have time, with some motivation the money would come as well...

[Chuck]

2 gfs... I feel yer pain...

[Digital Quality]

A true taper.

Good luck with everything man.

Oh yea, my life is a 3 ring circus right now,, it's all good though. Thanks for the kind words.


Edit: Only one at a time, thanks!

[it-goes-to-eleven]

The Jensen version of the Reichenbach's in the Aerco are about $60 each, fwiw. From the specs, I guess they are 1:1 windings. I would have thought it would be better to get a little gain from the xformers and the rest from the gain circuit.

I think I have Doug's transformer posts archived.

[Chuck]

The Jensen version of the Reichenbach's in the Aerco are about $60 each, fwiw. From the specs, I guess they are 1:1 windings. I would have thought it would be better to get a little gain from the xformers and the rest from the gain circuit.

I think I have Doug's transformer posts archived.

What is the part number on the transformers in the Aerco and the coorisponding number on the Jensens? Again, this is from memory, but I think the gain in the m148 is all from the transformers. 1:10 is what I remember on the windings to achieve +20db gain.

[Digital Quality]

Ok, now I see, you pick your transformer based on the input impedance of your amplifer circuit. See the little blurb below the selector guide on Jensens site.

So, should we pick the amp to match the transformer we want or the other way around? Which contributes more to the sonic properties??

[RebelRebel]

this site will help..

http://www.diyaudio.com/

http://www.studio-central.com/DIY-projects.htm

http://1176neve.tripod.com/id10.html

gyraf provides excellent products.. http://www.gyraf.dk/gy_pd/g9/g9pd.htm

http://www.seventhcirclestudios.com/SCA/SCA.htm  another popular company..

[it-goes-to-eleven]

So...... Digging through my packrat archive of stuff..  Funny how you still need to save web stuff for later.  You never know when those web pages will suddenly disappear..  Who's your packrat daddy!

Jerry ala AERCO...

"There are two options for the input transformer so you can have 0 - 50 dB gain for rock & roll or 20 - 70 dB for nature recording."

So... To have 0dB of gain as an option, you must have a 1:1 input xformer (or do BS attenutation). Since my Aerco is 0-50 model, it is a 1:1.

Not sure who posted this but it was in regard to the aerco:

reichenbach mb-c input tranformers! (my google search equated these with the jensen jt-mb-c)

I'm sure Jerry would tell you what xformers you might use and he maybe even sell you some. He says the 48v circuit is by far the most complex aspect of the box.


Misc Doug Stuff:

Hi!
The transformers Jensen sells for mics have gain. It is very clean gain with no electronic artifacts as there are no electronics in transformers. Naturally if you add electronics, they can enhance or limit performance. This step is key to good sound or you can use one that needs no electronics. You also avoid the need for capacitors to block the phantom voltage and most caps add a good deal of noise and or distortion. You can use the Jensen JT-110K-HPC without a buffer or op amp for additional gain and it provides an amazingly clean 18 dB of gain. Very good sound that is easy to build.
Add 9 volts batteries for P48, a case with connectors and you have a very good preamp for under 300.00.
Jensen also provides detailed schematics for mic preamp circuits using their transformers that are at or near state of the art.
...Doug

http://www.jensen-transformers.com/mic_in.html
http://www.jensen-transformers.com/apps_sc.html

Hi !
I have built all three of these :
AS018 JT-16-A in Single Stage Low-Noise IC Mic Preamp
AS019 JT-16-A in Single Stage Mic Preamp with Two DC Servos
AS083 Famous Twin-Servo 990 Mic Preamp Basic Circuit
They inspired me to design the M148, which does not use op amps, it uses discreet transistors but does use a Jensen transformer, to my ears the best made. I think the first design (AS018) is very good and a great place to start for a first project. I would NOT use the NE5532, it is great for pushing long cable runs, but most engineers today will not pass their signal thru one. Sub out an AD712 for a much better sound. It is also possible to bias the op amp for single ended operation ( i.e. no negative supply rail needed). Using the same powersonic PS605 batteries I use for the M148 will provide the voltage for the single DC supply op amp and the best possible source for phantom power, true DC. This will blow your mind, it will sound so good and YOU made it !
Enjoy ...Doug

Hi !
Consider using the INA163, Grace, Apogee and a host of others use this newest design from Burr Brown /TI. If you use this chip, you do not want to use the Jensen transformer, this will save you a lot of money. Sounds like you have CAD/CAM capabilities, perhaps even put together a PCB design to post. I know several tapers who built preamps like this, they are not too costly and fairly easy to build and of course, they sound very good. Rane uses this current feedback chip in their low cost mic preamp and they offer a peek inside !
enjoy...Doug

http://www.chipcatalog.com/TI/INA163.htm
http://www.rane.com/note148.html
http://www.rane.com/ms1b.html
http://www.rane.com/pdf/ms1bsch.pdf

[Digital Quality]

Sorry, you can't repeat a karma action without waiting 12 hours.

Thanks a ton! Google has some Cached pages too but it's tricky finding the right one. WTG!!

Thanks Teddy and all too!

[Chuck]

So...... Digging through my packrat archive of stuff..  Funny how you still need to save web stuff for later.  You never know when those web pages will suddenly disappear..  Who's your packrat daddy!

Jerry ala AERCO...

"There are two options for the input transformer so you can have 0 - 50 dB gain for rock & roll or 20 - 70 dB for nature recording."

So... To have 0dB of gain as an option, you must have a 1:1 input xformer (or do BS attenutation). Since my Aerco is 0-50 model, it is a 1:1.

Not sure who posted this but it was in regard to the aerco:

reichenbach mb-c input tranformers! (my google search equated these with the jensen jt-mb-c)

I'm sure Jerry would tell you what xformers you might use and he maybe even sell you some. He says the 48v circuit is by far the most complex aspect of the box.


Misc Doug Stuff:

Hi!
The transformers Jensen sells for mics have gain. It is very clean gain with no electronic artifacts as there are no electronics in transformers. Naturally if you add electronics, they can enhance or limit performance. This step is key to good sound or you can use one that needs no electronics. You also avoid the need for capacitors to block the phantom voltage and most caps add a good deal of noise and or distortion. You can use the Jensen JT-110K-HPC without a buffer or op amp for additional gain and it provides an amazingly clean 18 dB of gain. Very good sound that is easy to build.
Add 9 volts batteries for P48, a case with connectors and you have a very good preamp for under 300.00.
Jensen also provides detailed schematics for mic preamp circuits using their transformers that are at or near state of the art.
...Doug

http://www.jensen-transformers.com/mic_in.html
http://www.jensen-transformers.com/apps_sc.html

Hi !
I have built all three of these :
AS018 JT-16-A in Single Stage Low-Noise IC Mic Preamp
AS019 JT-16-A in Single Stage Mic Preamp with Two DC Servos
AS083 Famous Twin-Servo 990 Mic Preamp Basic Circuit
They inspired me to design the M148, which does not use op amps, it uses discreet transistors but does use a Jensen transformer, to my ears the best made. I think the first design (AS018) is very good and a great place to start for a first project. I would NOT use the NE5532, it is great for pushing long cable runs, but most engineers today will not pass their signal thru one. Sub out an AD712 for a much better sound. It is also possible to bias the op amp for single ended operation ( i.e. no negative supply rail needed). Using the same powersonic PS605 batteries I use for the M148 will provide the voltage for the single DC supply op amp and the best possible source for phantom power, true DC. This will blow your mind, it will sound so good and YOU made it !
Enjoy ...Doug

Hi !
Consider using the INA163, Grace, Apogee and a host of others use this newest design from Burr Brown /TI. If you use this chip, you do not want to use the Jensen transformer, this will save you a lot of money. Sounds like you have CAD/CAM capabilities, perhaps even put together a PCB design to post. I know several tapers who built preamps like this, they are not too costly and fairly easy to build and of course, they sound very good. Rane uses this current feedback chip in their low cost mic preamp and they offer a peek inside !
enjoy...Doug

http://www.chipcatalog.com/TI/INA163.htm
http://www.rane.com/note148.html
http://www.rane.com/ms1b.html
http://www.rane.com/pdf/ms1bsch.pdf

Thanks Freelunch, that's the thread at the Oade site I was thinking about. +T
From that , it sounds like Doug uses a transistor stage after the transformer.

[Chuck]

Well, I've been doing some thinking... dangerous , I know...
Anyway... I'm going to start with the phantom power supply first. Since a very clean phantom power supply is very useful on it's one...

I'm thinking that (5) of the 9 v DC (actually 9.6 v nominal) NiMH batteries would work well to supply the phantom power and the juice the active part of the circuit will require. The problem is... If I wire them all together in series... how to charge them correctly... I'm waiting from a response from Thomas Dist. as they sell the batteries I am looking to use.

BTW, using the 9v NiMH batteries is about 50% less expensive than buying the eight 6 v cells Doug uses in the M148. They don't have the storage capacity (about half) but they can be cycled more times and are smaller and lighter in the end. I'll post again when I get the charger circuit figured out...

[it-goes-to-eleven]

I don't know anything about combining nimh batteries.. But I thought internal resistance was a problem with wiring in series?  Or is that with lions?

Jerry at Aerco made a comment that straight battery 48v can suffer from low frequency noise due to variable chemical reactions.  I'm not sure how significant that is or how it varies between battery type. My gut says lead would be more stable than nimh.

[Chuck]

Hmmm... Those issues never crossed my mind... I wonder if they are valid concerns?
I guess I could look at lead, but there is a reason they call "the Brick" the Brick. Also assembling a charging circuit for lead batteries is easier...

[mhibbs]

You're not moving to the dark side are you?

I'm supposed to be getting a FedEx today.  I broke about a day before they started showing up on the yard sale. 

I'm not really trying to duplicate the brick as much as work on something with quality components and play around with some different discrete topolgies. I saw the talk of $200 Jensens but it didn't look to me like the $200 ones were as applicable for a pre as maybe for direct in or ground loop boxes.

If this thread is seen by enough people, someone will know the transformers he uses. I may have that info at home. If you do find the right materials, I'd like to work on it with you. I have an idea for a transformer based pre-amp that also has two line inputs that can be blended with the transformer outputs. A very simple design. It would work as a high quailty pre-amp on it's own, or a line . mic mixer when needed. The line inputs could be passive or possibly switchable to keep noise out of the circuit. I was starting to put together a MarkerTek order for the chassis parts, maybe I'll hold off. We could save on shipping etc... if we buy all the stuff together...

Search the Oade forum (old and new) and you should be able to find the part number on the Jensen transformers.  They were out there at one point...I've seen it...but I can't remember what they were.  The only thing I've never seen any part number info on is all of the stuff on the board covered up by the goop.  That design is what is so closely guarded, the transformers are fairly common knowlege.  I'll try to search around and see if I can find them too.


mitch

[Church-Audio]

A true taper.

Good luck with everything man.

Oh yea, my life is a 3 ring circus right now,, it's all good though. Thanks for the kind words.


Edit: Only one at a time, thanks!

I love it when people try to reverse engineer products, but why don't you ask him what he uses for a transformer? Tell him what you want to do. Maybe he will say yes, maybe he will tell you to get lost. But I would be upset if I knew someone was reverse engineering my designs with out asking me. Just my two cents.

[Digital Quality]

Not reverse engineering the m148. Only curious which transformers were used but thanks anyway.

[RebelRebel]

Doug wouldnt tell anyway, dont believe. I also asked him if hed train someone up on how to build them as he couldnt anymore, but he said no.

I like the 148 a lot, but the fixed gain is a deal killer for me. I found that the Neve Portico sounded nearly identical (not in silk mode, but normal) but of course had variable gain..if I was still doing rock concert taping, id have the Portico. I love that sound and that of the brick.

A true taper.

Good luck with everything man.

Oh yea, my life is a 3 ring circus right now,, it's all good though. Thanks for the kind words.


Edit: Only one at a time, thanks!

I love it when people try to reverse engineer products, but why don't you ask him what he uses for a transformer? Tell him what you want to do. Maybe he will say yes, maybe he will tell you to get lost. But I would be upset if I knew someone was reverse engineering my designs with out asking me. Just my two cents.

[Church-Audio]

Doug wouldnt tell anyway, dont believe. I also asked him if hed train someone up on how to build them as he couldnt anymore, but he said no.

I like the 148 a lot, but the fixed gain is a deal killer for me. I found that the Neve Portico sounded nearly identical (not in silk mode, but normal) but of course had variable gain..if I was still doing rock concert taping, id have the Portico. I love that sound and that of the brick.

A true taper.

Good luck with everything man.

Oh yea, my life is a 3 ring circus right now,, it's all good though. Thanks for the kind words.


Edit: Only one at a time, thanks!

I love it when people try to reverse engineer products, but why don't you ask him what he uses for a transformer? Tell him what you want to do. Maybe he will say yes, maybe he will tell you to get lost. But I would be upset if I knew someone was reverse engineering my designs with out asking me. Just my two cents.

I called him and he told me but I am not allowed to tell anyone 

[Chuck]

I have been thinking about this project and really want to continue this discussion. I have attached a schematic that Jensen has on their site. Doug Oade recommended this as a good place to start. The circuit uses an AD797 op-amp. Doug suggested using an AD712 instead. I have built several op-amp based microphone pre-amps. One problem with op-amps is DC offset. Another is the need for a bi-polar power supply. Maybe we could modify this circuit to bias the op-amp for single supply operation?

[Digital Quality]

That's a single supply schematic. Am I missing something??

Some other stuff on biasing http://www.analog.com/UploadedFiles/Application_Notes/42621535592205AN581.pdf Our drive current shouldn't be very high...

[Chuck]

That's a single supply schematic. Am I missing something??

Some other stuff on biasing http://www.analog.com/UploadedFiles/Application_Notes/42621535592205AN581.pdf Our drive current shouldn't be very high...

I actually read that Analog Devices paper today. Rodney, I'm not familiar enough with transister circuits to design a pre-amp circuit with them, like Doug Oade did. You mentioned using transistors in the begining. Maybe that's the way to go. If we can build a good circuit.
I don't see on the Jensen schematic that powering the IC is addressed.

[Digital Quality]

IC or descrete stage, they are about the same except the IC takes care of getting nicely matched devices and reduces the problem of stray capacitance.

These ICs can be run in dual or single supply. The AD712 for example is a 9V to 36V device. You can use + or - voltage to come up with a combination in that range.

The ground is shown in the schematic, the positive V is not super important as long as it's at least 9v (for the AD712) and so long as the output signal is still within line level V. The next thing in the chain will then have a DC blocking cap (I believe) to take care of our biased output.

[Chuck]

The aluminum box to the left is 7.5" x 4.75" v 2". I believe that is the same size box used on the m148?
I have the rest of the stuff around from other projects. The bigger box (on the left) cost me $4.95 at a local surplus parts place. It has some holes already drilled in it, but I'll fill those and it will work great. I also think I may use the Neutrik NF2D-B-9 and NF2D-B-2 for the outputs, rather than the XLR's.

I may just go with the 6v SLA batteries after all. Building the charging circuit will be easier. Does anyone have the lowdown on the cheapest place to buy the PS605's?

Edit:
After looking at photos of the insides of the m148, I found it's the same Hammond case I have, 1590D. It turns out that my local surplus electronics store made a mistake and only charged me $4.95. That's the price without the matching top. Anyway, I'm going the start filling the holes and get it ready to drill holes in the right spots for the XLR connectors.

[Digital Quality]

Looking good!

[Chuck]

I really like the idea of using the recessed RCA jacks for the outputs.

I e-mailed Doug with some questions and told him I was going to build a microphone pre-amp similair to the M148, based on the Jensen AS018 design. He told me that the SLA cells would supply the cleanest phantom power. It's true that it would be much easier to build a charger circuit for the SLA's. He also encouraged me to use op-amps after the transformer. If I socket the op-amps, It will be possible to swap op-amps to find the best one, or provide different sonic characteristics.

[Church-Audio]

I really like the idea of using the recessed RCA jacks for the outputs.

I e-mailed Doug with some questions and told him I was going to build a microphone pre-amp similair to the M148, based on the Jensen AS018 design. He told me that the SLA cells would supply the cleanest phantom power. It's true that it would be much easier to build a charger circuit for the SLA's. He also encouraged me to use op-amps after the transformer. If I socket the op-amps, It will be possible to swap op-amps to find the best one, or provide different sonic characteristics.

Hey Chuck how much gain do you need? I would suggest for an opamp the opa2227pa and also check out the TLO82 and NE5532 they are all very good sounding opamps I see them alot in preamps. Also check out that transformer company here is a link much better prices then Jensen and half the price. http://www.sowter.co.uk/ also check these guys out I dont know what the prices are like though. http://www.stevens-billington.co.uk/index.htm These guys build very good transformers I have used the Sowter transformers and found them to be much better then the Jensens for most applications.

[F.O.Bean]

awesome chuck

[Chuck]

I really like the idea of using the recessed RCA jacks for the outputs.

I e-mailed Doug with some questions and told him I was going to build a microphone pre-amp similair to the M148, based on the Jensen AS018 design. He told me that the SLA cells would supply the cleanest phantom power. It's true that it would be much easier to build a charger circuit for the SLA's. He also encouraged me to use op-amps after the transformer. If I socket the op-amps, It will be possible to swap op-amps to find the best one, or provide different sonic characteristics.

Hey Chuck how much gain do you need? I would suggest for an opamp the opa2227pa and also check out the TLO82 and NE5532 they are all very good sounding opamps I see them alot in preamps. Also check out that transformer company here is a link much better prices then Jensen and half the price. http://www.sowter.co.uk/ also check these guys out I dont know what the prices are like though. http://www.stevens-billington.co.uk/index.htm These guys build very good transformers I have used the Sowter transformers and found them to be much better then the Jensens for most applications.

I'm aiming for 12db to 20db gain.
I am familiar with the op-amps you mentioned. The NE5532 is in a lot of gear, but I disgree with you on how it sounds. It's a good choice for driving long transmission lines, but I think there are better choices as far as sound quality. I wish I had the time/ money to audition all the various transformers out there. That, of course, would be the best way to go. The Jensens are a known quality transformer, that's why I think I'll go with those. I'll investigate the Sowters though. Cheaper is a very good thing, in my mind.

[Celac]

I'm aiming for 12db to 20db gain.
<SNIP>
 I wish I had the time/ money to audition all the various transformers out there. That, of course, would be the best way to go. The Jensens are a known quality transformer, that's why I think I'll go with those. I'll investigate the Sowters though. Cheaper is a very good thing, in my mind.

Hi,
...following your discussion with interest.  http://www.cinemag.biz/    = very similar form factor to Jensen, good reputation, and a competitve price.  Used in some pretty well respected stuff see: http://www.adesignsaudio.com/ . 
Celac.

[Chuck]

I gave those a look a while back. I wish I had a bunch of money, so I could buy them all. Run music through them and listen, to determine which is the best. The CMMI-2C on a quick look looks the closest to the Jensen JT-16-A.

Hey Celac, I don't see prices... do you know what price range these things are in?

[Church-Audio]

I really like the idea of using the recessed RCA jacks for the outputs.

I e-mailed Doug with some questions and told him I was going to build a microphone pre-amp similair to the M148, based on the Jensen AS018 design. He told me that the SLA cells would supply the cleanest phantom power. It's true that it would be much easier to build a charger circuit for the SLA's. He also encouraged me to use op-amps after the transformer. If I socket the op-amps, It will be possible to swap op-amps to find the best one, or provide different sonic characteristics.

Hey Chuck how much gain do you need? I would suggest for an opamp the opa2227pa and also check out the TLO82 and NE5532 they are all very good sounding opamps I see them alot in preamps. Also check out that transformer company here is a link much better prices then Jensen and half the price. http://www.sowter.co.uk/ also check these guys out I dont know what the prices are like though. http://www.stevens-billington.co.uk/index.htm These guys build very good transformers I have used the Sowter transformers and found them to be much better then the Jensens for most applications.

I'm aiming for 12db to 20db gain.
I am familiar with the op-amps you mentioned. The NE5532 is in a lot of gear, but I disgree with you on how it sounds. It's a good choice for driving long transmission lines, but I think there are better choices as far as sound quality. I wish I had the time/ money to audition all the various transformers out there. That, of course, would be the best way to go. The Jensens are a known quality transformer, that's why I think I'll go with those. I'll investigate the Sowters though. Cheaper is a very good thing, in my mind.

I only mention the sowters because its what Neve uses, they do not use Jensen and since Neve is the de facto standard in microphone preamps, you should take a serious look at them. I think Jensen is overrated and not nearly as good as the Sowters transformers are.

Chris Church

[Celac]

I gave those a look a while back. I wish I had a bunch of money, so I could buy them all. Run music through them and listen, to determine which is the best. The CMMI-2C on a quick look looks the closest to the Jensen JT-16-A.

Hey Celac, I don't see prices... do you know what price range these things are in?

Hi,
I called about mic split transformers and they were less expensive. I did not ask about mic input but the fellow I talked to indicated they were cost competitive across the line.  I don't think that given the value of the unit that you are home brewing a clone of the cost of the Jensen is a killer.  I would assume that the A-Designs people are using the cinemag xfrmr for its quality rather then price (given the cost of their products I'm sure they could use Jensen, Lundahl, or whoever they wished).  Neve is certainly a very respected name but not the only one.  Do the Portico pre's use Sowter?
Celac

[kskreider]

Neve is certainly a very respected name but not the only one.  Do the Portico pre's use Sowter?
Celac

[Church-Audio]

Neve is certainly a very respected name but not the only one.  Do the Portico pre's use Sowter?
Celac

I think they do, I know Sowter does oem work for Neve so I would say yes. I know Neve are not the only name in preamps, I have been a sound engineer for 20 years and in that time, nothing I have ever used comes close to the old neve 1173 eq/preamp. It is simply the most musical sounding preamp ever made IMHO.

[Chuck]

This ESP Project #13 circuit would be almost the ideal transistor section to place after the input transformers, since it's looking for a 600 ohm input which matches perfectly with the JT-16-A's.

I don't like the idea of electrolytic capacitors in the signal path, but this would solve the problem of needing a bi-polar power supply for an op-amp... I have never built a transitor based pre-amp circuit. Does anyone know if the transistors used here are the best for this application? I would set the gain lower than the current 32 db. Maybe use a fixed metal film resistor and put a quailty 5k pot in there to use as a trim control?

[Celac]

This ESP Project #13 circuit would be almost the ideal transistor section to place after the input transformers, since it's looking for a 600 ohm input which matches perfectly with the JT-16-A's.

I don't like the idea of electrolytic capacitors in the signal path, but this would solve the problem of needing a bi-polar power supply for an op-amp... I have never built a transitor based pre-amp circuit. Does anyone know if the transistors used here are the best for this application? I would set the gain lower than the current 32 db. Maybe use a fixed metal film resistor and put a quailty 5k pot in there to use as a trim control?

Hey,
Data sheet for the spec'd part may be here? http://www.datasheetcatalog.com/datasheets_pdf/B/C/5/4/BC549.shtml 

I will admit my transformer spotting skills may not be up to the test, but I can't read the nomenclature on the input.  The Portico brochure I picked up at AES just says "custom" transformer and obviously it could be mfg'ed by Sowter. Attached is a Sowter "Neve" line output.  The bobbins certainly look different. Were "Marinair" and "St. Ives" Sowter OEM products?   

I certainly respect your (Church Audio's) experience, and you are not alone in liking Neve. It was not my intention to advance the cause of one brand over another, or denigrate anyone else's opinions and ideas about transformers.  I was just suggesting another alternative to Jensen that I was aware of and that I knew was used by reputable mfg's in high quality products. 
Celac.

[Church-Audio]

This ESP Project #13 circuit would be almost the ideal transistor section to place after the input transformers, since it's looking for a 600 ohm input which matches perfectly with the JT-16-A's.

I don't like the idea of electrolytic capacitors in the signal path, but this would solve the problem of needing a bi-polar power supply for an op-amp... I have never built a transitor based pre-amp circuit. Does anyone know if the transistors used here are the best for this application? I would set the gain lower than the current 32 db. Maybe use a fixed metal film resistor and put a quailty 5k pot in there to use as a trim control?

Hey,
Data sheet for the spec'd part may be here? http://www.datasheetcatalog.com/datasheets_pdf/B/C/5/4/BC549.shtml 

I will admit my transformer spotting skills may not be up to the test, but I can't read the nomenclature on the input.  The Portico brochure I picked up at AES just says "custom" transformer and obviously it could be mfg'ed by Sowter. Attached is a Sowter "Neve" line output.  The bobbins certainly look different. Were "Marinair" and "St. Ives" Sowter OEM products?   

I certainly respect your (Church Audio's) experience, and you are not alone in liking Neve. It was not my intention to advance the cause of one brand over another, or denigrate anyone else's opinions and ideas about transformers.  I was just suggesting another alternative to Jensen that I was aware of and that I knew was used by reputable mfg's in high quality products. 
Celac.

Hi Celac the reason why the bobbins look different, as I am sure you are aware. The transformer in your picture is a chasis mount, the one in the portico is pcb mount. Sowter does make transformers for Neve, I would assume this is another Sowter transformer. Jensen is good but I think I would go with what ever Neve uses. I trust good old Rupert when it comes to preamp design And there maybe other preamps out there but there is only one Neve

[Celac]

Hi Celac the reason why the bobbins look different, as I am sure you are aware. The transformer in your picture is a chasis mount, the one in the portico is pcb mount. Sowter does make transformers for Neve, I would assume this is another Sowter transformer. Jensen is good but I think I would go with what ever Neve uses. I trust good old Rupert when it comes to preamp design And there maybe other preamps out there but there is only one Neve

Hey,
Well actually I never noticed the screw lugs for attaching it to chassis until you pointed that out. I was just looking at the frame and the bobbins.  I was kind of thinking that stamped or molded parts (things that could be mass produced to lower cost) might be unchanged even on a custom wound piece. 

Perhaps we could start another thread dealing with either a Neve clone or a powering scheme for field use of available modules (i.e., some kind of BAE style rack, except battery powered or a DC "lunch box").  This seems to have wandered OT and I don't want to dilute peoples focus... but a DC lunch box would be really cool though considering the # of API format pre's.
Celac.

[Church-Audio]

Hi Celac the reason why the bobbins look different, as I am sure you are aware. The transformer in your picture is a chasis mount, the one in the portico is pcb mount. Sowter does make transformers for Neve, I would assume this is another Sowter transformer. Jensen is good but I think I would go with what ever Neve uses. I trust good old Rupert when it comes to preamp design And there maybe other preamps out there but there is only one Neve

Hey,
Well actually I never noticed the screw lugs for attaching it to chassis until you pointed that out. I was just looking at the frame and the bobbins.  I was kind of thinking that stamped or molded parts (things that could be mass produced to lower cost) might be unchanged even on a custom wound piece. 

Perhaps we could start another thread dealing with either a Neve clone or a powering scheme for field use of available modules (i.e., some kind of BAE style rack, except battery powered or a DC "lunch box").  This seems to have wandered OT and I don't want to dilute peoples focus... but a DC lunch box would be really cool though considering the # of API format pre's.
Celac.

Yes the api stuff is very nice but it requires a split supply of atleast 15+ 15- to run correctly.

[Chuck]

From David at CineMag:

The CMMI-2C is $60.85 each plus $8 shipping.
Maybe it's worth trying?
It's also a 200 ohm input /600 ohm output 1:2 quality audio transformer.

[Church-Audio]

From David at CineMag:

The CMMI-2C is $60.85 each plus $8 shipping.
Maybe it's worth trying?
It's also a 200 ohm input /600 ohm output 1:2 quality audio transformer.

The specs are not very good why did they measure distortion at -10 db? at 20k to get a reading of 0.03% wonder what that would be at +8 ? hummm I have only one word to say SOWTER. 

[Chuck]

Chris, I don't see a viable Sowter to use... Maybe I missed something...
200 ohm input, 600 ohm output 1:2 turns ratio is what I need.

[Church-Audio]

Chris, I don't see a viable Sowter to use... Maybe I missed something...
200 ohm input, 600 ohm output 1:2 turns ratio is what I need.

Check this one out Sowter model # 3257 150+150/600CT Input/Output Transformer

[Chuck]

Chris, I don't see a viable Sowter to use... Maybe I missed something...
200 ohm input, 600 ohm output 1:2 turns ratio is what I need.

Check this one out Sowter model # 3257 150+150/600CT Input/Output Transformer

OK, I will, Thanks.

[it-goes-to-eleven]

So.. the m148 is 20dB of gain.  Any idea how much is from the transformers vs. the discrete transistors?

I was doing some preamp testing the other day and was struck by how quiet the aerco is at 0db gain vs. 10dB.  At 0, you're not running through the op-amp, etc.  Though I don't have a schematic so I don't know for certain what the path is for 0dB.  It raises the possibility of running the aerco at 0 for the "transformer sound" and then using another pre for the actual gain.. The opamp in the aerco is very good and very quiet, just yet another combo option..

The aerco comes in two basic flavors.. 0-50dB of gain with a 1:1 transformer.  And a 20-70 version that gets the first 20dB from the transformer.  I wonder how the two versions compare when each is run at 20dB?

I am really itchin' to start building and tweaking a pre.

[Church-Audio]

Anyone making any progress on projects?  Closest I've come lately is moving the Mouser catalog into the bathroom as a reminder to put together an order...

Anyone have any thoughts on whether transformers make a preamp more sensitive to bass vibration than non-t designs?

Thats too funny I have the digikey and mouser catalog in my bathroom too my wife loves it

[Digital Quality]

I got a pair of Jensen transformers and some LM4562 op amps gathered up but that's about it so far. The transformers just showed up the other day. I picked out the JT-16A for my project. The 11K-APC matched my noise figure better but the spec said that it was for ultra low noise current app and my opamp isn't that low on the noise current side. Plus, I wanted to get the version with the bracket for nicer mounting.

So now I'm deciding how to power it. I wouldn't mind using the same cells as Doug used but it would be nice to come up with some sort of switchable power bus so the cells could be charged in parallel instead of in series. A 6V or 12V charger would be so much nicer to deal with than 52 or so....


I think Chuck might have his amp done already - is that right man?

[Chuck]

Yup, parts catalogs in the bathroom here too

I have the hammond case and I started drilling holes in it last weekend. My project has changed, many times. I really need a field mixer at this time more than I need a transformer based microphone pre-amp. So, I'm making a four in, two out mixer. The first input will be XLR or RCA awitchable, so that when I'm ready to add the transformers for the mic pre, it'll be set. I plan to use a very simple summing mixer to mixe the line inputs, so It will look very close to the Jensen pre-amp design we have been talking about. To muddle things further, i just bought a Rolls MX28 that I plan to modify, so Eventually that will be my line mixer and the project in the hammond enclosure will be a mic pre-amp. I'm assembling the parts , like good film capacitors, metal film resistors, panel mount jacks etc when I see them cheap on eBay or anywhere else. I have most of the parts, except the transformers for the mic pre-amp part.

One more thing to add... Jon, over at Naiant Studio has a summing mixer that he is working on it looks like it can run on 12v DC. He's looking for some more folks to maybe go in on a group buy of the circuit boards. I'm probably going to use the circuit he designed as the summing part of my project, with the Jensen transformers (eventually as the impedence matching and a bit of gain) for the mic pre-amp section. Give him a shout. I've found him to be very easy to work with.

Chuck

[Nick's Picks]

you geeks!
i'm so jealous.  I wish I had someone close by w/solid EE skills so I could learn something new.
i'm stuck in such a run w/my projects.  much desire, desired outputs.  excellent plan...but no skill to implement it.
I was born for middle management.