DIY project for these parts?

[pmroz]

Hello, I've been here reading all day, the info is infinite...

Never tried a DIY project but have done soldering (cables and output jacks mostly) and trying to learn electronics theory from a couple Radio Shack books. In the meantime, thought I'd try to put something together from scratch. After reading here, it seems like the Paia kits are a good place for me to start... along with the Craig Anderton book. I was wondering what people thought of the Sound of the finished Paia dual mic-pre w/ phantom kit? How might compare in the world of brand-spanking-new products, and how it would compare to the green pre and/ or other projects? The Paia kits seem to be my skill level (feeble) but I don't want to build something that wouldn't be better than the pres on my soundcard (aardvark q10). If they're just okay-sounding, I'll build the theremin kit into an old 35mm film box laying around... also I know there are many 'flavors' of pre, would this be the neutral or colored flavor?

3nd question (4th?)... speaking of laying around, I also have a metal box which I'm guessing is an oldish (70's?) analog/video switcher/monitor... 4 channels w/ both m&f XLR, some coax i/os labeled pgm,1,2,3, all hooked up to a 10 position rotary switch. Also vol pot, vu meter, and int/ext switch to choose 1/4 headphone or built-in Altec 405a 8ohm speaker. I tried to fire it up, but the power plug needs resplicing... do that manana. The parts look in good shape (but not electronically tested) and i was wondering the viability of making a mic pre of the parts.

The parts (as far as I can tell, note question marks) are:

Power transformer: Triad Utrad f-93x Huntington, Ind. brown paper on coil, white ink on top says 17-7619... connects to a black hexagonal relay? with either an m or w in the middle... 4 posts, +/- are grounded to chassis via 2 metal cylinders marked 500mf, 25v, tt25x500a. These are about 1 1/2in longx3/8in. diameter.

Input Transformer: Opamp Labs Model 423, the power goes to 2 ceramic resistors, yellow/purple/tan/silver, don't have the Radio shack book here for ref. Also 2 more of the above metal cylinders connected to different pins of the octal socket, along with a two smaller resistors and a smaller can-type cylinder that reads 8022a + .

Output Transformer?: UTC A-18 15k/80k max level +15dbm. Found some info on this somewhere on the web

Output Power Transformer?: Triad-Ultrad S-79z 20w, 16ohm pin connected to speaker/headphone switch, com pin to UTC. Also paper-wrapped, print on paper.

Rotary switch: Janco 2amp 115v has numbers 1-12 on the back, but i could only get 10 positions. 48 connections.
Volume pot: A/B Type J, 100k ohm (jain200p104aa)

Also 10 fXLR, 5 mXLR, 5 coax, most are wired to the switch, 1 mallory tcn-5010 with ff printed on it, paper cylinder, another metal cylinder 2"x3/4" with no markings between speaker/headphone switch and headphone.

It seems to my small brain that this box contains almost all the pieces hooked up for a single mic or line pre, and I could lose the rotary switch, speaker, and zillion connections, and maybe add phantom somehow? And would it be any good, usable for a DAW front? Does anyone know of a DIY mic pre build that utilizes any/all of these components? Maybe I could save some shopping. Also, I read some reference to the usefulness of the rotary switch for volume vs. pots... would the switch (with resistors) work better for pre volume than the pot listed above?

Long post, sorry. Any help/info welcome. Sorry if all these parts=crap, you can just reply with 'it's all crap'... if not I'll get a meter and test them. Don't even know what the metal cylinders are... are they caps? i read somewhere UTC's are spendy, the opamp 423 is $50 on their site... that's only why I asked, doesn't mean they're useful for a mic pre... if helpful I can unmount the components again and give exact pinouts, or try a diagram, but i've no idea how to draw a switch like that... thanks in advance...

 

[Svart]

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=3278&item=3758986699&rd=1 ????

 

[pmroz]

... yes, but this one has the 'decorative opamp cover'... thanks, i copied and pasted that description for future reference...

so is it 'a true classic'? can't go by what they say on the eBay, I figured here I could get the low-lowdown... also it's not worth anything if it won't go in something useful, and I'm faaaarrrr from designing from scratch. I'd need a design to follow... and how 'bout the other stuff? UTC etc.?

 

[Svart]

I'm not sure if any or all of that stuff can be put together without some solid research on all the parts. you have I/O transformers and an opamp.. sounds like you could have a mic pre on your hands to me.

I'll go ahead and say what others will surely say.. Search for preamps and find some of the more simple designs using this type of setup and Try it! I'm not educated when it comes to the A*P*I and N*e*v*e stuff that has a trafo in- gain stage- trafo out, but i would think that would be a good start for ideas to model your design after.

just an idea. I'm sure someone will come along shortly with better insight than I have.

and welcome to the forum!

:guinness:

 

[CJ]

www.vacuumbrain.com

A-18 would make a cool innerstage transformer for a Pultec-EQP-1A.

 

[pmroz]

also I found
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=50597&item=5728542705&rd=1&ssPageName=WDVW

for the UTC A18 ($200 a pair nos?), and $10 on several Triad power transformers, though not the model above.

 

[pmroz]

Wow, the vacuumbrain pics are great... i have a Pultec EQ emulation on a UAD card in the DAW...definitely need to bone up on schematic reading for that one...

A Mic pre would be more use to me, as I have several comps (RNC, Ashly sc-50, dbx118, no 'boutique') plus the UAD emulations (which I like, though no way to A/B with the originals), but only two Rane pres (plus the q10 pres...). So a pre of a 'vintage' flavor might be nice for variety... I'll search for 'API/Neve' type designs as mentioned, see if there's anything with these parts...

looks like the next step is fix the power, see if it fires up/makes noise & what kind, get a tester, and if it tests/works see if I can rewire it to just 1in/1out without the speaker, switch and dozens of i/os...

any opinions on the Paia pres?

 

[Svart]

well I'm not saying that those parts you have match anything used by any certain product, but you can compare the spec'd parts and the part you have to decide if what you have can be used. It would be cool to figure out how to use what you have to build something unique!

Cheers!

 

[pmroz]

thanks svart, you guys are very helpful, i know these basic questions are probably not mind-expanding for you in the least, but still, you're helping a lot... searching now for info on a-18 applications, haven't found much for opamp 423, leads me to believe it's not a great opamp... also found a few mentions of handy rotary switch applications (the gyraf ssl looks like a great unit)

Best-case scenario: replace plug, then it fires up and passes audio to headphone jack. Then I can get on with testing parts,simplifying it, and changing the box, meanwhile research and perhaps replace opamp/other parts... worst-case, I can use a few pieces like A18 in a new project. Also searching for DIY pre projects with the same voltage requirements (I'm assuming from the power transformer this is 25 (24)v but should probably test). The nice thing is, the box is here in front of me begging to be tinkered with, so that motivates me to actually think about how it works.
.... more post reading and back to books...

 

[Svart]

That opamp has an octal base.. I bet you could work out an adapter to the footprint of most other discrete-based opamps so that you could design for one of those but try your opamp too.. you never know you might come up with something that sounds great for a certain use or even many uses!

:thumb:

 

[rafafredd]

I would use the UTC A18 in a vari mu compressor.

 

[PRR]

> is it 'a true classic...'

Yes, but it is not a treasure unless you are maintaining 1970s boxes. It really will make 10+watts into a loudspeaker, handy for talkback amp; except if you have to re-wire it for the purpose it would be easier to go find an old 10W PA amp in the thrift-stores. The only real use is as a plug-in quick-fix for some essential box that uses the 423.

As a mike-amp: it needs an input transformer (which you do not have) for balancing and step-up, and if I recall the guts of the 423 it has a nasty output stage that will distort low-level signals even though the full-power THD may be acceptable.

What you have is a monitor system, to listen to any of five Line Level signals, adjust volume, and drive speakers/headphones. As such it could be useful today, except it is MONO.

You may have a decent +/-15V power supply and lots of jacks pre-mounted. But I think everything else goes in a museum.

The 10/12 position switch may have a pin in it, to limit the stock 12-pos mechanism to the 10-pos actually needed here. Find that, yank it, and you get a 12-pos switch. If this is really 4-pole 12-throw, that is a very expensive switch to buy today. And not real useful at full 4P12T capacity.

 

[pmroz]

rafafredd, pm'd you back, but don't know if I did it right.... nice plans for the pultec pre on your site BTW. Still no roommate and car so no power...

 

[rafafredd]

Forget about the MB1. I like this project but we do not have a PCB for it, and if you must go tube you should go G9. It´s safer then a PtoPt project...

Gustav has high quality boards for a very nice price. Have a look at the Black Market...

 

[pmroz]

thanks for the reply PRR, sometimes when reading threads here and you come in with the business-end of whatever is discussed i almost grasp what the heck you're all talking about...also PRR you win best picture IMO.

trying to stay in the wings here instead of blurting stupid questions... wanted to say after reading SMG audio thread not all 'lurkers' have bad intent. I've not much creatively to contribute here, but i'm just starting. thank you for online manuals links. this group has greatness,

worked out a trade deal with rafael for input xfmrs, putting a couple 312-style boards together... with Forssell i hope? 2 sets of parts = at least 1 board? hopefully won't go above this ratio. back to study, thanks again on this.