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!