SSL9K both channels back alive! now on to the HUMMMM

update:  OK, this thread is getting old. I have been trying to complete these pres since July, and finally got both channels working but still got some grounding issue (HUMMMM).. see later posts... thanks to everyone who's helped out..

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OK, so, this is my first build, and I finally got the thing together. Sort of. Right now it looks like the son of frankenstein (metalwork is killing me)  and I get no audio output from it at all. As soon as I turn it on (actually 1-2 seconds later) all I get is a hum, and a bit of hiss in the background, with a mic connected or not.  Could this be a ground issue?  Everything looks ok, but... obviously something's wrong. 

Last night when I first tested it, I had the pot wired all wrong. I forgot Ra and Rb, and grounded it like a volume pot instead of wiring like a vari resistor. My first clue is that gain didn't change, the pot just hissed and crackled and stuff.  I should have checked the schematic first. Maybe this messed things up?  I got that sorted (now it raises and lowers the HUM, albeit like a very bad pot, hissy, scratchy, sound cuts out while moving), but once left in place the pre gives the same noise as last night.

Also, last night I was getting 1-1.5V DC on the output pin 2. Pin 3 had nothing. Just checked again and it was close to zero (+_.002V)

My ground wiring (I admit I don't really understand grounding as well as I should):

The audio input ground (on the PCB) is going to input pin 1, which was grounded with ouput pin 1 to the star ground.  I lifted this but had the same hum.

The audio out ground on the main PCB goes to the ground of balance board input.

Balance out ground goes to output Pin 1, which goes to the star ground along with input pin 1.

The 0V from PSU all go to star ground separately.

The 0V from both mainboard and balance go to star ground.


Could this be anything else? I have more 5534s, I figure I could start pulling them out and replacing one by one, but I don't have any way of knowing if one is working or not, so it seems kind of like roulette.  Is there an easy way to test these?

So far the only thing I know works is my PSU. I get all the right voltages within .25V.

I think that's it for now, if someone has an idea, I appreciate it.
Thanks in advance..

For starters, what voltages are you getting at pin4 and pin 7 of all of the 5534's? -Before you start looking for signal, start looking at your DC.

Then if you don't have a scope, use an audio probe (a 0.1µF capacitor in line with a wire connected to a fairly high-impedance quiet amplifier) and listen from the first stage onwards, see how far the audio makes it.

Keith

Hi Keith,
thanks for the reply.. I just checked the voltages.. they seem mostly ok.
Readings at IC 23,24,30 (middle two and the one next to the TL052) were +18.05 and -17.98.

IC22 is at -16.90, + 17.34,
IC29 read -16.76, +17.20
Is the discrepancy normal?

The TL052 seemed normal also. +-15.2 at 1 and 8

No scope... thanks for the probe idea. gonna try that next and let you know the results..

ok just tried it... soldered a .1uF cap to a wire and the other end to an RCA jack. Plugged the RCA to an amp. Then hooked up an sm58 to the pre and turned it all on. I went through touching pin 6 of each 5534, but just got loud hum. The same as when I took the line out to an mbox last night, although this was slightly louder.

Funny thing is, when I ran the line out from a PC soudncard to the amp through the cap I got nothing. Without the cap, of course, I got sound. What is the purpose of the cap?

ok, I'm gonna take another look for any solder bridges and maybe swap the 5534s...

Does my ground wiring description sound ok?

thanks again..

you are going to need ot feed a test tone into the pre. Not a mic signal. I usually use the signal generator from Pro Tools through a direct box to the mic in. Then i use my signal tracer to search along the audio path and find out where the signal stops,

I was afraid of that. I don't have a sig tracer, but I guess it's time to make one. That'll be next week though since I have to go to the big city to get stuff.

For what it~s worth, I went through and rechecked every solder joint and they seem OK.

I'm curious though, why would I be getting +-17V at ICs 22 and 29 when the others are getting +-18?

ok, hopefully I can get my hands on some test equipment around here. Otherwise, if anyone has any ideas I'm open...

thanks..

I am not sure if it can be said enough. Double and triple check ALL your components for value and orientation.

I had an issue with one of mine being quite noisy and super low gain. Had 51k's instead of 51 ohm's on the balancing board!!

Check all diodes are in the right way too!!

mm

On my first GSSL comp I mistakenly installed 130 ohm resistors instead of 100K ones. The colour banding is valid for both if you read them back-to-front (brown-black-black-orange-brown). Can be really easy to do if you're not on your toes...or assembling it at 3am in a dimly lit shed!

[quote author="marshman"]I am not sure if it can be said enough. Double and triple check ALL your components for value and orientation.

mm[/quote]

I hear ya. I checked every component with a meter prior to installing. And I just checked everything again. All the opamps, electrolytics, and the Mat02 are oriented properly. Everything is the right value. But, I did have two resistors that read low on my meter and couldn't tell why from the schemo.

r117 is in fact a 50K resistor but reads 11k measured.
r113 is a 4.22K but reads 1.9k

I have a lot to learn about all this. I told myself I wasn't going to rush anything, so it's helped not get frustrated. I appreciate all the help.

I am not sure about the way I wired up the pot though. Can anyone verify: On the one gang, I have a wire coming from Gain B (close to IC30) to a 39 Ohm resistor and to pin 3 of the pot(looking at it from the front with the pins down, the right-most pin). I then wired the other two pins together and back to the other Gain B pad, next to IC23. For gain A, I went out from the pad closest to the MAT02, to the 27 Ohm resistor and then to pin 3 of the pot. Connected the other two and went back to the other Gain A. Does that sound right? I get a lot of scratchiness if I turn the pot.

OK, just tried it again after cleaning up some iffy solder joints but no change... tomorrow I'm gonna try to find a scope or probe...

i used a gain switch, but the pots shouldn't be scratchy.

OK, so I went ahead and built up the other channel. Disconnected the first channel cuz I didn't make more cables (used molex connectors) but hooked it up to channel 2 on the balance board. lo and behold... the same noise. :sad:

so you have checked all component values. Correct. If so try without the balance board. Here is where the signal tester will work wonders. Check and triple check component values again, especially resistors.

I would double check your input cable/signal. Maybe you are just not getting anything to the inputs??



mm

thanks for the replies everyone. I'm going to check my wiring next and find someone in town that has a scope or probe. I used a shielded mic cable and connected the shield to pin 1 and the ground on the pcb input. I then connected pin 1 to the star ground. Is this right?

I feel some ground loop issues with all those ground connections, but probably because I don't follow you well though...

I would just connect input XLR pin 1 and PSU pcb ground to star ground in a first step, then I would connect the SSL9k pcb ground to the PSU pcb ground
That should be sufficient for grounding, then I would test how audio goes through the circuit, making an audio loop in the DAW and connecting it at mike input with a resistors pad or with the DAW output level set very low

If it is possible for you to post a picture, it might help with troubleshooting.

I would've thought a grounding problem wouldn't have stopped both channels working altogether. Hum and buzz yes, but not loss of all signal. I'm thinking power supply...

Curtis.. I've checked my voltages every time I powered on. Other than that, what do you think could it be? I'm afraid I'm not too experienced with any of this stuff.

I should say that I haven't hooked up both channels simultaneously. I did try both channels of the balance board with each board, but no change.

Anyway, your post made me curious.. My PS is connected to a dual 20V secondary trafo. Everything looks right as far as placement, and I have each voltage going to a terminal on a barrier strip: http://www.radioshack.com/product/index.jsp?productId=2103983&cp=&sr=1&origkw=terminal+strip&kw=terminal+strip&parentPage=search

I have +18V, then took that with a few diodes to another block on the strip to get +15V. Did the same with the negative.

Thanks again for posting..

You mentioned earlier on that you had OK power supply voltages, but you didn't say if you verified they were measured on the correct pins of the IC's - pin 4 of all IC's should read negative, pin 7 of IC's 22, 23, 29, 30 should read positve, pin 8 of IC 31 should read positive. Also verify you have the IC's installed the correct way around.

The voltage measurements themselves seem OK. I would expect a little less voltage on IC's 22 and 29 (as you have discovered), as their supplies are derived from additional RC filters on each line which will drop a little bit of extra voltage.

What kind of power supply are you using? Schematic?

The measurements you made on R117 and R113 - did you remove them from the board to measure? Resistance measurements in-circuit can be influenced by other components, and to get accurate measurements they should be first removed from the board.

Hey Curtis,

I did check the voltage at pins 4 and 7 of the ICs on the first board. I should´ve been more specific. I do remember that I was always better at reading comprehension than writing....

Anyway, I admit I did not check the IC voltages on the second board, but all the ICs are in the right way around. I wasn't sure at first, because they don't have the usual notch, but rather a small circle in one corner on top, which I assumed indicates pin 1.

The two resistors, I removed the R113, and it measured 4k22. The other one I did not remove.

The PSU is keith's (ssltech), the one that comes with the SSL9k boards. No mods, except a lifted +18V pad due to stupidity. I just soldered the wire to the next pad, which is a C8.

link to PSU files
http://www.beatbazar.com/guests/ssltech/kps-1/index.htm

Also, the transformer I am using is this one:
http://www.antekinc.com/AN-0520.pdf

On the primary side, I connected same colors together (120V mains here) and used the two blues for 0V, the greens for 20.

Also, keith mentioned to input a signal and use a probe to listen at different points to see how far the audio gets. If I don't find one by this weekend, I'm going to build one from a simple design (google is my friend) BUT any idea where to place it on the circuit? Is it the output of each 5534? Or do I start at the input and go through the whole circuit, component by component?

Thanks again to all for bearing with me here...