Attempt to build a UA-1108 mic pre

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Feb 18, 2006
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8
Hello,

I have decided to embark on making my own UA mic pre. I found a schematic that looks fairly simple for the most part and I have located most of the parts or parts that will function just as well as the replaced model. Here is the link to the schematic http://www.waltzingbear.com/Schematics/Urei/UA_1108.pdf I understand most of it except where to the gain knobs and any other knobs go?? I can prolly make a guess but I am for the most part clueless. If anybody cares to help me label and locate the different knobs that would be awesome!

Also, if anybody knows of anywhere to get those same transformers or ones that will work just as well, please let me know :)

Thanks!

Fill
 
the output transformer is quite unusual, or better, it's teh same one used in the class A original 1176.. with that particular tertiary feedback.. it's the UA-5002 and almost impossible to find one original.. Purple Audio use a custom reproduction made for them by what i think is Cinemag, maybe you can give them a call.. it will not be that cheap as you might think.
 
I really wish I knew! :? I know the pre supplies 48v of phantom power, I think the gain is +-45-55db. http://mixonline.com/mag/audio_revision_history/index.html theres a little bit of history on the pre, I couldnt exactly pull much info on the transformer on it. https://www.ued.net/ued/addItems.do?itemCode=PNRUA5002 theres a place to buy the UA-5002 transformer....

Heres a PSF of the new model derived from the 1108 http://barryrudolph.com/mix/pdfs/ua2108.pdf

Im sorry thats all the info I was able to get from the net. If it helps, cool! :) If not im sorry :?

Thanks.

Fill
 
Thanks for the info, Kruz! I dont know exactly how crucial it is to have that exact model of transformer, im willing to make some compensations. If you can think of a xformer that will do the job it should be fine.

*edit* better yet... If anybody knows of a good DIY pre thats entry to midlevel difficulty around 200$ let me know! :) Im not exactly looking for a kit, Id like to search around and build it from scratch. I currently have an all digital setup and am looking for something to take the ice out of my digital recordings. A tube amp might be more in my alley but personally id opt for a good SS.

Fill
 
[quote author="BlackHatRecording"]If anybody knows of a good DIY pre thats entry to midlevel difficulty around 200$ let me know! :) Im not exactly looking for a kit, Id like to search around and build it from scratch.[/quote]

Well, the Green Pre is supposedly very good and cheap too - good for beginners.

I currently have an all digital setup and am looking for something to take the ice out of my digital recordings.

I don't think something like the green pre would sort this... Have you tried other mics? Ribbons work well with digital systems for some circumstances.
 
i would say you should try an api 312 style circuit. you can get some good input and output transformers from cinemag, and there isn't much to the circuit. you could even start off with an inexpensive chip opamp like the opa604 or opa134 at first, then put in some kind of discrete opamp later.

i also hear that fabio has a board he calls the "fetboy" that might fit what you're looking for.

compared to those two, the 1108 is a relatively complicated circuit, and the output transformer is hard to get and not cheap. start with something else and work your way up to it.

ed
 
Thanks Ed,

That circuit looks interesting, and indeed, not too difficult. How much could I buy the xformers needed for the API 312? I looked on cinemag, but couldnt find prices, id have to e-mail them. Im also looking for a very budget friendly 8 channel pre setup, perhaps the opamps would be good for that.

Thanks,

Fill
 
cinemag don't list prices on their website. you can email them, but in many cases it is best to just call. you'd want the CMOQ-2S for the output, and something like the CMMI-8 or CM-75101 for the input. i'd guess one input and one output would be about $80 or less together. if you call and talk to them, you can find out what quantity discounts are available if you are making 8 channels.

have a look at the boards offered by fabio:

http://www.thediypill.phx.com.br/buyboards.htm

and good luck.

ed
 
Awesome, I just recently looked at the DIY Pill stuff, very interestign and helpful... I think I will do the 312, it looks a lot easier than the 1108 because I dont have to draw my own PCB board. I also ran across the 312 V1 parts list, where all the parts are acounted for with price, total cost for 100% completion is 250ish. The output Xformer is 78 bucks though! :shock: I might have to give cinemag a call, and look into somethign cheaper... (if anybody knows of a xformer that will work and is 30-50$ lemme know :) :) ) Overall the build looks straightforward and easy, the PCB is very well laid out. If it is 250$ per channel i will have to only build one its too much for 2 let alone 8 unless I can scrape it down to 200 or less which I hope to do, then I could maybe afford 2 channels.

As for what Xformer to get id like one with a more low end, and less hi-fi sounding.

Thanks!

Fill
 
[quote author="BlackHatRecording"]As for what Xformer to get id like one with a more low end, and less hi-fi sounding.[/quote]

Say no more! Something like an Edcor WSM600/600 will probably do you good. Specially if a little dirt is what you're looking for, and most specially if price is an issue.

http://www.edcorusa.com/

Peace,
Al.
 
i'm pretty sure the cinemag CMOQ-2S is $30 or less.

if you go edcor (which is not a bad idea for $12) try asking for the XSM 600/600 which is a bit bigger than the WSM series, and will fit the cutout in fabio's board. if you call edcor, see if you can order the XSM without the channel frame mounting bracket, and with screw holes through the core, so that it will drop right into the hole in fabio's board. edcor is generally good about custom orders, so if you explain what you are trying to do, they can usually hook you up.

ed
 
Thanks Guys! :)

Thats right up my alley, price is fantastic. Having a direct fit into Fabios board would be a major plus, i will have to call them up and see what they can do. Quick question though, Al stated the WSM had the tonal qualities I was after, does the XSM series posses the same general sound the WSM does, or is it slightly different? Because of the pleasing price of the Edcor boards, I might as well throw two channels in it. There I might want a more Hi-Fi sound in the next one for a little bit of options, well unless I wanted to do stereo pair work... Then it might make it sound lopsided, or blend in nicely:roll: if anybody has any idears on that lemme know! :)


*edit* Besides the Edcor Xformer for the input, what would I use for output? Again, low price = good :)

Thanks!

Fill
 
Hey Fill,

The WSM or XSM are suitable for output... unfortunately Edcor only really do output or interstage transformers.

For input Cinemag do some of the best around, look on their website for CM75101's (used in the past by API), their CMMI-7c, or 8c. Or check out ed's post in the black market:

http://www.groupdiy.com/index.php?topic=13462

You'll have to check what transformers fit Fabio's boards - or you'll have to make an adaptor...

Justin.
 
the main diff between the XSM and WSM series is that the XSM series uses the same size core as most other output transformers you will see (EI625 size lamination) such as jensen, cinemag, sowter, and the WSM is a bit smaller. but the material is the same, the WSM just has a bit less of it. so, the WSM will be easier to saturate and get that transformer distortion sound. you can still get that with the XSM, you just have to push it a bit harder.

for the input transformer, it looks like fabios boards will accept the CM75101 or the CMMI-8PCA, which means that the transformers i'm selling would work also.

ed
 
Way cool! :) I e-mailed Cinemag just to get a price quote on the CM75101. If I calculated it all right, I can get 2 pres for around 250$, I dont know much much the PSU will cost in the end, hopefully no more than 50-100$. Which would excellent! I still have to add up shipping! :( I think I will get a WSM and an XSM, XSM for vocals and WSM for guitars for a litle bit more grit in the line.

Just a little bit more planing and lining up all the damn little parts I can begin purchasing and building! :cool:

Thanks for all the help.

Fill
 
If you are going to use a 2520 opamp, use a 150:600 or 75:600 transformer for more headroom and free gain, instead of 600:600. The original was wired as 75:300, but I think 150:600 is the perfect choice for a 2520 output. Some people likes to wire the original it as 75:675 but that´s not really needed.
 
Can I also ask you to bear in mind that our hosts www.groupdiy.com (top left button on the screen) - sell Sowter transformers for API input and output
http://www.groupdiy.com/SearchResult.aspx?CategoryID=120
 

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