Ross Compressor and Ross Mixer DEBUG

[Moonibopper]

Help! I'm building a stompbox for my brother's birthday and I can't figure it out! I used the pcb layout by MarkM http://www.aronnelson.com/gallery/main.php/v/MarkMs-Gallery/album15/album76/ROSS_comp_LAYOUT.gif.html for the compressor and http://www.aronnelson.com/gallery/main.php/v/MarkMs-Gallery/album15/album76/ROSS_Mixer_LAYOUT.gif.html for the mixer. I also took at C3 and placed it on a SPDT switch for the Janglebox mod, and took out R20 and replaced with a pot for variable attack. I also jumpered from Q1's emitter to the appropriate place on the mixer layout. Here's the issue - I get a HORRIBLE GATED NOISY sound when it is engaged. Silent, and then when I strum really hard, the noise happens again. Here are the voltages:

(3904's C / B / E)
Q1: 7.34 / 2.66 / 2.3
Q2: 6.9 / 7.57 / 6.9
Q3: 9.58 / 0 / 0
Q4: 9.57 / 0 / 0
Q5: 9.22 / 9.58 / 9.08

CA3080E:
1 - 6.08
2 - 4.96
3 - 4.96
4 - 0
5 - 65mV
6 - 7.57
7 - 9.62
8 - 8.3

Can anyone please help? I spend 7 hours checking for solder bridges, cold joints, and can't come up with anything. Thanks.

[Moonibopper]

Thinking about this a little bit... I bought the CA3080E off of Ebay from Hong Kong. Could these voltages and audio symptoms be possible if the OTA is fake?

[PRR]

Voltages at Sustain pot and R19 leads?

Is there ANY chance you shorted pin 5 to pin 6 while testing? (That might pop the 3080.)

[Moonibopper]

At sustain pot
1&2- .78V
3 - 9.06V

At R19
65mV (lead closest to OTA)
.78V

Thanks!

[Moonibopper]

Also the OTA's look like http://www.ebay.com/itm/20P-CA3080-CA3080E-3080-op-amp-IC-ICS-Chip-NEW-A4-/280761912215?pt=LH_DefaultDomain_0&hash=item415eb6cb97#ht_2954wt_1139 but say "H 9834" instead.

[Moonibopper]

Also to answer your final question, I don't think I shorted the pins. I tried different OTA chips too. Again all identical and multiple purchased from Hong Kong in one transaction.

[Moonibopper]

Also some audio probe results after hooking up the pedal to a mp3 player.

3 and 4 of the OTA - clear audio
5 - clear audio but at much lower volume
6 - distorted audio at louder volume
7 - nothing
8 - identical to 6

I really hope someone can help. Thanks.

[PRR]

Verify voltage at C4 R2 R4. One end of each part should be the same, about 3V.

Turn "Sustain" the other way. Should get over 8 volts on pad 1+2, also at the high end of R19. Verify R19 is 27K. When you do this, does '3080 pin 6 voltage change?

> 5 - clear audio but at much lower volume

Poking 3080 pin 5 is more risk than it is worth.... but I can't think of any way it could have "clear audio". I hate to blame chips, hate to send you to the store. Re-check that 3080 pin 4 (ground) really is soldered-well, then I think you should get "good 3080" from a reputable source such as Small Bear.

[Moonibopper]

I really appreciate you taking the time to think through this:

One end of each of C4, R2, and R4 measure 3.4V.

Sustain turned all the way leads to voltage of 8.9V at 1&2 and at the high end of R19 (which I confirmed as 27K). However, the voltage of the OTA's pin 6 does not change when I turn the Sustain knob in opposite directions.

I purchased 10 of the OTA's from this seller. I've switched among all of them and still the same issues occur. Unfortunately Small Bear is out of the CA3080E so I have to look elsewhere. Thanks again.

[PRR]

> Small Bear is out of the CA3080E

Sorry for the bum steer.

And I bet if Steve can't get them, there are NO good 3080s around.

Argh. There's nothing IN a '3080. 9 transistors, 4 diodes. Some of them paired-up so it could be 8 parts. Someone with SMD skills could be frying-up '3080s from a small PCB and 79 cents worth of SMD.

Is LM13700 easier to get? (2 bucks at DigiKey, but <200 in stock.) Have to adapt 16 pins down to 6. There's a small difference in Iabc-pin action but no difference to the Ross. http://i.imgur.com/QAyZP.gif  

---wow. DIP-8 header now costs as much, and is as lightly stocked, as the LM13700. We used to use DIP headers for everything, even shimming wobbly benches.   DigiKey A101-ND

[Moonibopper]

Thanks. Just out of curiousity. Which part of the circuit layout determines the voltage at pin 6?

[PRR]

R3 to the 3.4V reference.

[Moonibopper]

Sorry for my ignorance but what does "3.4V reference" mean in terms of the layout?

[PRR]

Remember I asked "voltage at C4 R2 R4. One end of each part should be the same, about 3V."

The output of a happy '3080 won't fight an external voltage. In this circuit R3 to 3V "should" set the '3080 output DC to about 3V. This, and the sick voltage at Iabc pin, and Vout not varying with Iabc changes, make me think the chip may be a brick.

The layout is not great for understanding "how things work". The R2 R4 R3 network sprawls all over. If there is a well-drawn schematic (there are MANY but I'm too lazy to find the one which has the same part-numbers as this layout) it might be clearer how R4 R2 split the battery voltage and R3 tugs on '3080 output.

[Pettol]

I know it's an old thread, but I'm having the exact same problem. The same sound and odd voltages.

Did you find out what the problem was?

[R O Tiree]

Pin 8 of a CA3080 is not connected to anything inside the package, therefore, the voltage should be 0.  Neither is pin 1 connected to anything inside - that should be 0 as well.  Ergo, it's not a CA3080.

[Pettol]

You're right. Bought a new ca3080 and it worked right away. Don't mind a little debugging, but that's just ridiculous.

[R O Tiree]

Glad to be of service