Studio Supply Corp. PC 0004 Cards - Anyone heard of these? Spectra Sonics Clone

[EWalter]

I picked up 4 of these things because I thought they seemed interesting, and I thought I'd share.

Photos:
https://imgur.com/8yTcANC
https://imgur.com/4gYkcLv
https://imgur.com/EN1m9Pa
https://imgur.com/lTKBlKR

They seem very similar to the Spectra Sonics 110 cards. I'm trying to confirm the voltage these require (guessing +/-24V) as well as what pins 6, 7, & 8 are for.  My assumption is that these are for strapping a potentiometer for gain and I plan to test this out as soon as I get a chance. 

Pin Out (From trace side of board, connectors on left):
1. Com
2. -24V (I believe)
3. +24V (I believe)
4. N.C.
5. Audio In
6.
7.
8.
9. Audio Out
10. Com

Looking forward to hearing people's thoughts!


Cheers,
Erik

 

[emrr]

I have a half dozen or so of those in a DIY console, haven't done a drawing.  The output transistors on mine are 2N2270.  Mine have a 2K2 carbon resistor yours lack, and yours has one more electrolytic loaded than mine do.  Mine are on +/- 15 supply. 

 

[analogguru]

Beside their appearance this cards have nothing to do with spectra sonics 110 cards.

The circuit is a NPN-differential-amplifier followed by an PNP-differential Amplifier and an output driver stage.  Gain is fixed at 10.  Pretty standard circuit for that time, nothing really amazing.

Considering that the emitter resistors of the output drivers are 10 Ohm they will not be able to deliver an high amount of current.  Since they used 25V capacitors for the power rails I wouldn't run them on +/- 24V.  I would assume that they are intended to be used on +/-15V (or max. +/- 18V).

 

[EWalter]

I have a half dozen or so of those in a DIY console, haven't done a drawing.  The output transistors on mine are 2N2270.  Mine have a 2K2 carbon resistor yours lack, and yours has one more electrolytic loaded than mine do.  Mine are on +/- 15 supply.

Thanks for the info! Lemme know what you find. Do you like them? And do you have anything connected to pins 6-8?

The transistors on mine are:
FSE4021 231 (x 2)
F2N4249 150
2N2270-7245S (X2)

I couldn't find a part number for the orange ones.

Beside their appearance this cards have nothing to do with spectra sonics 110 cards.

The circuit is a NPN-differential-amplifier followed by an PNP-differential Amplifier and an output driver stage.  Gain is fixed at 10.  Pretty standard circuit for that time, nothing really amazing.

Considering that the emitter resistors of the output drivers are 10 Ohm they will not be able to deliver an high amount of current.  Since they used 25V capacitors for the power rails I wouldn't run them on +/- 24V.  I would assume that they are intended to be used on +/-15V (or max. +/- 18V).

Well that's a bummer - and here I thought I was getting some kind of a steal!

Do you think there's any kind of a mod to get variable gain? Swapping a resistor(s) for a potentiometer? I haven't had a chance to sit down and follow traces, but I'm curious if pins 6-8 might have something to do with gain.

I did think that the 25V caps might be cutting it close if it ran at +/-24, thanks for all the info!

Cheers,
Erik

 

[analogguru]

The transistors on mine are:
FSE4021 231 (x 2)
F2N4249 150 (x 2)
2N2270-7245S (X2)

I think it should look like this...

I couldn't find a part number for the orange ones.

If you are talking about the brown ones (with two legs) these are color coded capacitors.

Well that's a bummer - and here I thought I was getting some kind of a steal!

The Spectra Sonic cards are nothing special too because they can be (re)build in better quality for little money (if you are not an "I want the original"-fetishist)

Do you think there's any kind of a mod to get variable gain? Swapping a resistor(s) for a potentiometer? I haven't had a chance to sit down and follow traces, but I'm curious if pins 6-8 might have something to do with gain.

Currently the gain is set with the first horizontal resistor (1k, brown-black-red-gold) and the second vertical resistor to the right (10k, brown-black-orange-gold) beside the 110k resistor (brown-brown-yellow-gold).

If you want to make the gain variable this would be possible by lifting one side of the first horizontal resistor (1k) and connecting a (neg log) potentiometer (1kC, or 5kC) together with a series resistor of 100 Ohm to ground.  If you want to increase the gain further, you can lift one side of the second vertical resistor to the right (10k) and connect a e.g. 50k resistor between pin 7 and 8.  You can use a potentiometer here to, but it is possible that it will crackle.

 

[EWalter]

If you are talking about the brown ones (with two legs) these are color coded capacitors.

Ah - that's dumb of me - I didn't realize they only had two legs. I'm still learning... obviously

The Spectra Sonic cards are nothing special too because they can be (re)build in better quality for little money (if you are not an "I want the original"-fetishist)

That's good to know. What about the aged transistors here? Are these not cool?

Currently the gain is set with the first horizontal resistor (1k, brown-black-red-gold) and the second vertical resistor to the right (10k, brown-black-orange-gold) beside the 110k resistor (brown-brown-yellow-gold).

If you want to make the gain variable this would be possible by lifting one side of the first horizontal resistor (1k) and connecting a (neg log) potentiometer (1kC, or 5kC) together with a series resistor of 100 Ohm to ground.  If you want to increase the gain further, you can lift one side of the second vertical resistor to the right (10k) and connect a e.g. 50k resistor between pin 7 and 8.  You can use a potentiometer here to, but it is possible that it will crackle.

Very cool! I'll give this a try and see what it sounds like.

I'm kind of interested in making some kind of distortion box out of them or something like that. Just planning to experiment and learn new things. Do you think I'd burn my studio down if I connected all 4 in series?

 

[Bill Wilson]

These cards are from an early room equalizer that was Studio Supplies own design. I had a rack inherited from a customer in mid 70's.  This is why some components will differ on each card. A regular customer of mine bought his MCI studio package from Studio
Supply.  They had used one of theses amplifier cards on the reverb return. There was a 2300volt power line that crossed over the rear of the building at a 45 degree angle. This put 60hz hum on the reverb return & the 16 track tape machine. I had to turn the 16 track at a 45 degree angle  to cancel out the hum pickup. I replaced the SS card on the reverb return line with my copy of the neotek mike preamp, there was no more hum.

Personally I would just discard the cards & save yourself some trouble.                 

 

[EWalter]

Well that’s a bummer. At least I didn’t pay much for all 4 of them. I may just see what kind of distortion I can get out of them or something.

 

[emrr]

Mine were added to the custom console at a mid-70's rebuild for bus outputs.  No problems noted, but it's been awhile since that console was fired up. 

 

[jordan s]

I saw these on Reverb and almost bought them because of the claim of being close to Spectra Sonics. Glad I didn't. I hope you find something good to use them in.

 

[EWalter]

You should have bought them so I didn’t have to! I gave a very low offer and didn’t think it would get accepted, so I sorta got them by accident.