Topic: Church transformer based pre

[stirinthesauce]

Here is my outline for the product..

1- Flat frequency response from 20hz to 50k
2- Super low distortion
3- Hi pass filter with switch
4- Clip lights
5- Battery operation ( external??)
6- Size?
7- Cost effective
8- built like a tank
9- Phase switch
10- Mic pad -20 db?
11- 12 Stepped gain control
12- For gain I was thinking about 40db or so being the target but 60 is not impossible I just don't know how practical 60db of gain is for live concert recording..

Now we are getting to the meat of the matter 

These are my initial ideas but I am open to suggestions.

 



Reading through everyone's posts this morning I started thinking about that Simpsons episode.  You know the one where Homer discovers his brother who is a corporate exec for an auto manufacturer.  Homer's brother wants a common Joe to develop a car for the people.  Homer then proceeds to tell the developers everything that the people want.  All the bells and whistles to make life more enjoyable in the car and more pleasing to the eye.  When the car debuts at an auto show, it is an utter disaster and the brother's company goes bankrupt.  Moral of the story, leave the designs up to the experts (which I am not  ) and hope for the best.

My .000000000002 cents worth


Carry on....

[twatts (pants are so over-rated...)]

Nice!



T

[gratefulphish]

I was thinking about the output of the preamp it seems to me some people that are running things like MT'S are having problems with using external preamps. I was thinking about a output level controls as well as input level so that you could "tweak the output down" for what ever your connecting the preamp to. So you can run the preamp hotter with out over driving the input of the recording device. I know this is not an issue for interfacing my preamp with a recording console, but it is an issue for some recorders maybe I could offer that as an option.. I am just thinking out loud here...

Chris, This is a limited issue, principally with the MTs, and I have one as a back-up so I am not dismissing it, but could there just be an output switch that would just be an xxdb attenuator of the output for devices that need it.  Seems it would likely be smaller than another pot. 

Sizewise, a little smaller than the UA-5, and sounds like it could be smaller than a V3.  I don't think that most people want this to be a cigarette pack size device.  Once you build it, you could always come up with a tinier, superstealth version, incorporating the external power, external cable suggestions.

Meters, I still want some nice long meters, where you can really see what you are doing.  Too many of the current decks either have slow meters, or they are so compressed, particularly as you approach 0 db, that it really makes dialing in a lot tougher.  I, personally, don't like running anything where I just have a clip light, because up until then, you are virtually guessing where you should be.

For gain/ padding, something similar to the combo sensitivity knobs/trim control on the R-4 Pro.  Those really come in handy, and make life easy.  I doubt most anyone will need more than a 40db range.

Definitely build like a tank, a solid external housing all the way around top, bottom and sides, with connectors and controls slightly recessed in back and front.

Thanks for listening.

[Todd R]

Very interesting discussion -- and a big thanks to Chris to stepping into the ring on this!

I will say, I really think you need to decide what you want to do yourself and what you think the best market is.  Along the lines of the Homer-designed car, everyone will have different ideas on what is absolutely essential.  I remember a few years back either here or on the Oade board, an engineer at Zaxcom came on looking for input on what they could make for a stripped down recorder (stripped down from Zaxcom's perspective ) and how they could reach our market.  They got info pulling them in 10 directions at once, and not surprisingly never came up with that small, 2channel recorder they were discussing.

Maybe you should think about making a couple different preamps to meet different market segments, using the knowledge you gain from your R&D.  I'd imagine that the work you do on working out the internal voltage rails and 48v powering could easily apply to a couple different preamps -- one that is small for the stealth market, and one that is bigger to meet everyone's needs.

If you just want to make one and decide to go with a larger design, you'll be having a lot more competition. V2/V3, UA5, Oade modded all-in-one recorders like the ACM671 and HDP2, etc, etc.  Some of those options have other functionality you wouldn't be offering, like an A/D section or full recording capabilities, so your preamp will come up short for those people not wanting multiple boxes. 

From my standpoint, it seems like there is a open niche for a really nice sounding, very small preamp that people could use with a R09 or MT to do 24-bit stealth recordings.  But that is a very different animal than the feedback you're getting in this thread.  It seems to me there is a lot of interest in the PSP2, the Aerco MP2, the sonosax, etc that work in stealth and low-profile situations.

And making that major decision on market will drive a lot of other decisions.  Small stealth box = miniXLR connectors, minimal metering, internal battery.  Larger field preamp = full-size XLR connectors, full metering, external battery, etc.

Good luck, and looking forward to what you come up with!!

Also, as an aside, I'd really like to see the 24bit SBM1-type offering -- really small, internally powered box that does 24bit A/D.  Of course, if we ever get that, then it would be nice to have some more ultra small 24bit recorders with digital input other than the MT.  All of that is probably outside Chris' area of expertise, but I'd still like it!

[Brian Skalinder]

I think your proposed list looks pretty good: 

1- Flat frequency response from 20hz to 50k
2- Super low distortion
3- Hi pass filter with switch
4- Clip lights
5- Battery operation ( external??)
6- Size?
7- Cost effective
8- built like a tank
10- Mic pad -20 db?
11- 12 Stepped gain control
12- For gain I was thinking about 40db or so being the target but 60 is not impossible I just don't know how practical 60db of gain is for live concert recording..

I think 40 dB of gain is plenty for typical taper usage.  I only very rarely need to use > 40 dB, typically for acoustic or unamplified sound sources.

My $0.02:  KISS (Keep It Simple, Stupid).  Which to my mind means:

• level meters - don't bother, we already have them on our ADCs / recorders
• Y-cabling / mini-XLRs - forget it, just one more thing to lose / forget / break
• power - stick to an external power source, preferably a commonly available lockable connector with 6v - 12v VDC, allowing for standard, aftermarket battery usage...no need for a separate snap-on battery compartment or some such
• variable gain - nice to have, not critical
• stepped gain - probably more critical if running straight into a recorder
• phase switch - BFD, I can always switch it in post;  maybe more necessary for multi-channel stuff, though (but again, I'd just do it in post)
• HPF - nice to have, not critical (can always do it in post)
• size - as small as possible, without compromising sound quality
• output level adjustment - not necessary

As Todd R just suggested - pick your market and drive your design considerations accordingly.  But in any case, my main point wit hthis thread:  KISS.

[terrapinj]

perhaps you could have just a couple LEDs showing the signal at a particular db and then a clip indicator - most recorders have meters where one could do the detailed adjustments but that would allow the user to at least get the pre in a somewhat optimal range

interested to see how all this pans out 

[stirinthesauce]

I will say, I really think you need to decide what you want to do yourself and what you think the best market is. 

But in any case, my main point wit hthis thread:  KISS.

2 excellent points

[Church-Audio]

I think your proposed list looks pretty good: 

1- Flat frequency response from 20hz to 50k
2- Super low distortion
3- Hi pass filter with switch
4- Clip lights
5- Battery operation ( external??)
6- Size?
7- Cost effective
8- built like a tank
10- Mic pad -20 db?
11- 12 Stepped gain control
12- For gain I was thinking about 40db or so being the target but 60 is not impossible I just don't know how practical 60db of gain is for live concert recording..

I think 40 dB of gain is plenty for typical taper usage.  I only very rarely need to use > 40 dB, typically for acoustic or unamplified sound sources.

My $0.02:  KISS (Keep It Simple, Stupid).  Which to my mind means:

• level meters - don't bother, we already have them on our ADCs / recorders
• Y-cabling / mini-XLRs - forget it, just one more thing to lose / forget / break
• power - stick to an external power source, preferably a commonly available lockable connector with 6v - 12v VDC, allowing for standard, aftermarket battery usage...no need for a separate snap-on battery compartment or some such
• variable gain - nice to have, not critical
• stepped gain - probably more critical if running straight into a recorder
• phase switch - BFD, I can always switch it in post;  maybe more necessary for multi-channel stuff, though (but again, I'd just do it in post)
• HPF - nice to have, not critical (can always do it in post)
• size - as small as possible, without compromising sound quality
• output level adjustment - not necessary

As Todd R just suggested - pick your market and drive your design considerations accordingly.  But in any case, my main point wit hthis thread:  KISS.

The nucleus of the preamp the "guts" are going to be all me. But the outside knobs and switches are all you guys.. Because its not a big deal for me to say add a high pass filter or add a clip led or add a 20db pad. These things do not effect the performance of the preamp just add to ite flexibility.. I would like suggestions on gain switch settings what do you guys use. And if you had it your way what would you want in the way of gain "steps"

Chris Church

[ambo]

Hey Chris, you should run this idea by the folks on Gearslutz location recording board and Yahoo Nature recordists. While the Gearslutz folks, many of whom  are on this site will probably have similar requests, the nature recordists are also looking for a small self powered stereo pre. These folks are looking for field rugged, low noise and high gain. As well as the pro's and hobbyists, there are several film/audio school instructors who are always looking for inexpensive recording options for their classes. 

[Church-Audio]

low profile switches that can't be accidently turned off if this device is run out of a waist pack, or, confined area like a pocket.
It'll save me from having to grind the switch down, and then having you replace it after my grinding blunder.

I might use locking toggle switches but they are freakin expensive. I might use slide switches except they suck.. So I might have something put on to the front of the preamp to protect the knobs like two metal plates. I am thinking about a bunch of things now. Once I get the panel layout done I can figure out the best way to protect it. I don't think this is going to be something that will fit in a fanny pack this will be something that's going to be inside a recording bag. I don't know how much I would have to worry about switches there. Any thoughts?

[Todd R]

I would echo Brian's advice of KISS.  Especially since if you put everything possible into the design, then it's going to end up costing more and you'll be competing with higher level devices.

Some recommendations I'd make, all presuming you're talking about audience concert taping:

- gain -- 25-35db should be fine, even for amplified acoustic music, since the recorder/AD should be able to give you another 10-20 db of gain as well.

- metering -- maybe just a couple LEDs for signal present (-18db or so) and approaching clipping (say -2db before clipping).  Separate meters for each channel

Phantom power -- selectable on/off.  For just a 2ch preamp, I'd guess one switch for both channels would be sufficient

Gain steps -- again, users will probably have detailed gain available on the recorder/AD, so 5db or 6db steps should be fine

HPF -- personally, I like this option, but it may not be needed (post production).  6db slope, maybe 60-75hz

Mic pad (-20db) -- I wouldn't bother, many mics already have it availble on the mic

Inputs/Outputs -- seems driven by your market.  Open taping = full size XLRs on both in/out.  Stealth, not sure, not all stealth mics will be XLRs anyway, so building full-scale XLRs would mean converter cables will be needed with those mics.  RCAs or miniXLR on output for a stealth preamp would be smaller on the outside for the user and on the inside for your real estate needs.  No real need for full size XLR outputs for stealth (recorders probably won't be using XLR inputs)

[Chuck]

I have mixed thoughts on this...

Here they are:

Oade modified UA-5's are popping up in the Yard Sale for around $400 now. That gives you a good pre-amp plus an A/D converter and the ability to mix two line sources with two microphone sources in one box! That's a whole lot of features for not much money.

I see a market for a high quality (perhaps transformer coupled) microphone pre-amp that costs less than say $600.  But that thing better sound real, real good, or have a bunch of features not available on similar pre-amps that are already available.

The old Oade pre-amps still retain their value, because of the sound and simplicity. The internal batteries and their use for supplying the super clean phantom power in the m148 make it unique and still viable, and sought after, in the taping community.

Ultimately, it is going to be price vs performance and features that will determine how succesful this product will be. If it were me, I'd incorporate a feature or two that no one else offers. I don't have any one, specific feature in mind, but for example only, something like a four line/ mic in, two line out mixer. Two transformer pre-amps and two solid state preamps in one box maybe. This would be useful for the 4 channel crowd. Perhaps you could make it whatever "flavour" the specific owner wanted, by swapping out op-amps or using transistors after the transformer side.

Chris, I'm glad you are listening to some of the opinions of the folks that are going to be purchasing this pre-amp. I wish you luck.

[J.T.L]

...Perhaps you could make it whatever "flavour" the specific owner wanted, by swapping out op-amps or using transistors after the transformer side.

...just a thought, but having a model that is also user-upgradable would be sweet for the DIY crowd. Run a flavor for a while then switch out for another. Can this be done without sacrificing path quality?

EDIT: to say I guess real DIY'ers would probably make their own pre 

[Gizby]

All I can really say is that I love the input sensitivity knobs on the UA-5. Recording digitally into a MicroTrack, those things are a godsend when I compare it to my time running ATs > battery box > MT, where the signal was running much too hot.

I've only ever had the UA-5 for a preamp (and the MT is my second recorder after a minidisc recorder), so I don't quite know what to put forth in terms of suggestions. I've never run a separate ADC, nor do I really know what they cost or really what they are off the top of my head.

I guess all I'd really need in a preamp is a better built UA-5. I like outputting digitally, but if I needed a separate ADC, so be it. I like to record in 24 bit (even if it's not really 24 bit). The RCA jacks for patches are nice, though I don't use them very often.

But yes, there is definitely a market for the sub-$600 taper preamp. Make it well and they will spend. I greatly look forward to how this will shape up.

[Nick's Picks]

IMO..., and in the tradition of keeping it simple..(sometimes), i'd stick w/original idea of a straight up transformer based preamp.
that is the unique part.  that is the "hard to find" elsewhere allure.

we already have 3 "flavored" sub $500 premaps (that include a very good A/D in them as well, plus all the other UA5 bells and whistles).

the apogee miniMP is also available in this price range.  and that will be hard to top (except for ergonomics and foot print).

a cheap 148 is what this crowd wants.  everything else is already available.