SSL9K both channels back alive! now on to the HUMMMM

[signalflow]

Mitsos,

Reading your first post made me start to question the way I wired my gain pot. Was wondering if you, or anyone else, would mind letting me know which way to wire it up? Hopefully you can see the pic below, the diagram on the left is the way I have mine wired. The one on the right is what I understood from your description. Is the one on the right in fact the correct way or did I misunderstand.?

Sorry for butting into your thread.

-Casey

 

[mitsos]

[quote author="signalflow"]
Sorry for butting into your thread.[/quote]

haha, no prob. In fact, thank you for butting in. I am not sure I wired the pot right,since my pre is not working atm. At first, though, when itwas obviously wrong, I had it wired something like on the right. Now, it is more like what you have, the drawing on the left. But I am not sure it's right anyway, I just think that is the way you wire a pot like a variable resistor. "Wire the wiper with either of the other two leads together" seems to be the consensus on the world wide web of misinformation. No one here has confirmed it, but I found it in enough places that I bought it as truth. For now.

I take it you are building these as well? I hope yours are coming along better than mine.

by the way, in case you want to check your pre without worrying about whether the pot is wired right or wrong, PRR (I think) posted in an old thread in the 9K meta that, instead of the pot or switch you could solder a couple of resistors between the gain pads for fixed gain. Anyway, irrelevant, maybe, but I need to build me an audio probe and small amp. In the meantime, I'm gonna re-check my components...

 

[signalflow]

Right on, The one on the left was explained to me by the repair tech at my old job, so thats what I went with. I'm gonna leave it for now and see what happens. I'm waiting for my power supply now but everything else is wired up and ready to go.

-Casey

 

[mitsos]

ok.. so I should get more sleep I think.. or at least start soldering during the day. I took a closer look at the underside of the boards and holy shit. Pretty damn embarassing solder work, even for me. Interestingly, the first board was not too bad, a couple cold solder joints, the second was all over the place. I hope I found my problem. I am travelling for the weekend for a couple shows but I brought the pres with me cuz the're all I think of right now (don't tell my wife) and as I am without any way of testing myself, am going to meet some friends at a studio Friday or Saturday to pass some signal through them. Btw, besides looking aweful, my first clue was checking resistor values from the next pads over. I didn~t check them all cuz I need to get to sleep, but the ones I did check are now at the proper value, whereas before they sometimes were, sometimes were not. Will update later.. Thanks for the help so far.

 

[mitsos]

Good news is, I am now getting audio out... Bad news is, it's bad audio... Oscilation at both ends of the gain pot travel and crappy stuff in the middle. I am testing out of hte case right now, with grounds tied to star/earth ground. Sam G posted some tips in another thread, I am going to check negative feedback I guess now.. if anyone has any tips, please let me know. Appreciate it..

 

[mitsos]

Ok, an update... I rewired my with shorter, non-twisted cables. This seemed to fix some stuff, or maybe it was something unrelated.. who knows? Fact is, I am getting sound on one channel through an sm58. My voice, just testing and sounds fine. There is a hiss I need to fix, but I'll get to that.

The second channel pooped out on me while testing over the weekend. It was working as above, but I think a ground wire touched something it shouldn't since everything was unbolted out of the case. Not sure what could have happened? I assume some of the ICs could be fried? I hope not. I got no further sound out of it that day and all I get from it now is hum.

Back to Channel 1, I have a hiss. Also, when the pot is all the way counterclockwise (gain 0, right? I have hum and no audio. When I twist the pot just a bit, hum stops, signal comes in, but the hiss is there. Also, my gain doesn't quite work as it should. It seems there isn't much gain at all, and it seems as if it works backwards... before you ask, they are the Omeg 2K2 rev logs from AudioMaint.
Also, I have them wired as Signalflow's picture above, with the resistor on the left leg and the other two wired together and back down to the PCB. I am pretty sure they are wired correctly to the board, I checked and double-checked the schematic.

RE the hiss... I tried putting a resistor between input XLR pins 2-3.. no change. Anything else this could be?

I am back in my small town with not much more than a multimeter to my name. hope to sort this out soon.. thanks everyone..

 

[mitsos]

ok, I'm at my wits end. Of course, maybe that's not saying much..

I redid my pot wiring again like this guy (instead of the way Signalflow's diagram shows):
http://web.comhem.se/bergis/ssl9k/SSL9K.html

The resistor is inline with the wiper. After measuring the R of the pot I thought this would work. Maybe I should put the resistor on the CW soldertab instead?

Ch1, (working but hissing before) now barely works. It only passes audio (albeit louder than before, but still with hiss) in a small portion of pot travel. The rest of travel is hum, and sound still comes in and out while turning.

Ch 2, only hum as before and louder. I redid the pot as above, and swapped all the ICs on the main board, but still no audio. MAT02 dead? The weird thing is, the gain works. I mean, it makes the hum louder as I turn the gain up, but on the other board, the pot doesn't work.. weird cuz I checked all connections, no cold solder, etc.

QUESTION - Does anyone have any idea why Ch2 stopped working? Could a MAT02 die?

ALSO - Can someone who has this working please confirm the pot wiring?

thanks to all..

 

[mitsos]

ok.. so I measured +4V dc on the Gain B side of the pot, not the side with the resistor. I guess this is what's causing the scratchiness. What's causing the DC though?

 

[gltech]

ALSO - Can someone who has this working please confirm the pot wiring?

Look at this schematic (rotate it so the text is oriented properly):
http://www.beatbazar.com/guests/ssltech/9k/9k-schem.pdf

The pots are oriented so that the wipers move up as the pots are rotated clockwise.

Here's another way to look at it:

 

[mitsos]

wow, GL... thanks... that helps a bunch. It's weird cuz the picture didn't show up when I first looked at our post. Funny, I had it that way until I saw that other guy's site, but thought I'd change it since the pre's not working. Oh well, redo it tomorrow.

I finally got my hands on a passive DI (IMP2) and tried to run a 1K test tone and probe around the circuit, BUT I get crazy (oscillation?) at minimal gain. It's like feedback, and it almost made me deaf.. Weird cuz the DI works going into the mbox pres, but not through this pre into the Mbox line ins. What is this?

I also measured DC on the opamp outputs (pin 6 to ground on the 5534).. I got more than enough to go around. Holy crap, look what I got:
IC22 : 2V
IC 29 : 2V
IC 23 : 10V :shock:
IC 30 : 5V
IC 24 : 14V :shock:
IC 31 : -13.8 on both pin 1 and 6.

Any ideas on this? Sorry for all the questions, seems like it never ends. This is my first serious project after some small amps and it's turning out to be a handful. Thanks to all.

 

[mitsos]

OK, I just measured DC on all input/output pins of the opamps. They are all over the place. I am fairly certain this is my problem, or rather, whatever is causing this is causing my problems. But I am not sure what components/junctions I should check. My guess is I should start with the beginning of the circuit, since there is DC on the first opamp inputs, which would then get amplified/passed on, right?

Anyway, here goes: If anyone can point me in the right direction, I'd appreciate it.

IC 22
2 +12.4 VDC
3 +12.4 VDC
6 -2.07

IC 29 pin 2 and 3
2 +12.4
3 +12.4
6 -2.13

IC 23
2 -0.04
3 -0.04
6 -16.06

IC 30
2 -0.59
3 -0.59
6 16.93


IC 24
2 4.06
3 4.76
6 +17.25


IC 31 - tlo52
1 -13.87
2 -16.58
3 -0.00
4 -15.2
5 -13.79
6 16.1
7 -13.83
8 +15.2

 

[mitsos]

OK, I shelved this project for a while... went on vacation, came back got some 312 (almost) working perfectly, which got my hopes up and feeling all happy, I thought I would tackle this depressing beast. I've almost got a case for it, so I'll try to get some pics up if anyone thinks it'll help. It's still in the same place as before... One channel passing "audio" ... sort of. I re-read voltages, and accidentally shorted pins 3-4 of the TL052, now the -15V rail reads 0V... I see pin 3 is grounded in the schemo, could they have shorted inside the IC?

I scoped it, ran a 1000K tone out of PT through a DI into the pre, and while I can hear what sounds like a 1K tone coming back into PT, the scope is all over the place. It reads from 500Hz then 2K, then 58K, etc, just all over the place. I did scope the tone coming out of PT and it read 1K, so I guess the scope is ok. 

Also, the old symptom of the gain "working" only 1/3through rotation and then cutting out, is still there. After that I only hear hummmmmmm, which doesn't get louder with increased gain.  But now I am worried I just fried my TL052. So, I'll have to swap that out, but the symptoms haven't changed since I fried it.

If anyone can help I'd appreciate it... thanks!

The voltages are now:
IC 22
2  +12.4 VDC
3  +12.4 VDC
6  -2.07

IC23
2  4.25V
3  4.25V
6  9.43V

IC24
2  4.25V
3  4.25V
6  13.34V

IC 29
2 +12.4
3  +12.4
6  -2.13

IC 30
2  -0.045V
3  -0.045V
6  -4.8V

IC31
1  -14V
2  13V
3  0V
4  was -15V now is 0.66V  (this "rail" was working. I accidentally shorted pins 3-4 with my DMM probe, saw a small spark and now no voltage)
5  0.12
6  0.14
7  14.72
8  15.48

 

[Harpo]

replace the failed open diode (whichever of the probably 5 ones in series decided to die fastest when dead shorted to ground) in your voltage dropping string from -18V to -15V. (just ohm it out). The TL052 servo amp may or may not have survived this arcing.

 

[mitsos]

Hey man, thanks for that! Did the trick... Now my voltages are ok, but the pre is still in the same state... Any clues on how to trouble shoot this?? I am getting desperate with this. Especially after hearing a real SSL pre recently.. Fell in love, and really wanna get this to work...

 

[mitsos]

OK, after hearing an SSL fx 383 pre (I loved it) I am crazy to get this thing working. I am going to pull everything (or mostly everything) and re-solder to try to get to the bottom of it..

One question.. I tested my MAT02s for HFE and one side reads 460, the other 780... Aren't they supposed to be matched? Did I get a bum one or did I hurt it somehow?

thanks!

 

[Harpo]

OK, after hearing an SSL fx 383 pre (I loved it) I am crazy to get this thing working. I am going to pull everything (or mostly everything) and re-solder to try to get to the bottom of it..

One question.. I tested my MAT02s for HFE and one side reads 460, the other 780... Aren't they supposed to be matched? Did I get a bum one or did I hurt it somehow?

thanks!

from MAT02 datasheet current gain match delta HFE is typically 0.5%, up to max. 2% for type EH or max. 4% for type FH, so this doesn't sound right.

 

[mitsos]

I checked the datasheet but didn't see that info.. bad eyes I guess. Well, this sucks.. one $10 transistor in the trash.. I'm gonna go through the rest of the circuit and hopefully all will be ok in the end..
Thanks for the info...

 

[khstudio]

OK, after hearing an SSL fx 383 pre (I loved it)

Sorry to ask but what does the SSL fx 383 have in common with this 9k pre other than the name "SSL"?

Did I miss something here?

I thought those SSL FX 383, 384, etc... are from the 4000 "G" series stuff.

 

[mitsos]

I

OK, after hearing an SSL fx 383 pre (I loved it)

Sorry to ask but what does the SSL fx 383 have in common with this 9k pre other than the name "SSL"?
Did I miss something here?
I thought those SSL FX 383, 384, etc... are from the 4000 "G" series stuff.

I think that's the desk they're based on..anyway they just sounded awesome that's all. I just "heard" them recently on acoustic guitar. (Martin steel string, AKG 414, into PT). They sounded awesome, not clean by any means.. sort of sweet. I don't know how to describe sound so there. But I liked them so much that it got me all excited to get my SSL9Ks done to see if there was any similarity in the sound (I haven't the luxury of recording on an SSL9000 desk so I have no idea).  I would guess the 9Ks can only be better. Anyway I just rechecked all my resistors, they are OK, and I will check the caps, and then I'll throw in an LM394 to see if the MAT02 was the problem.

Has anyone ever built this with 2 separate but HFE-matched transistors (like 2x BC550C as in 2520)??  I'm thinking of doing this until I know the circuit is working, so I don't blow another $10 hole in my wallet.


BTW, Kevin, did you get my PM about the night EQ?

 

[khstudio]

BTW, Kevin, did you get my PM about the night EQ?

No PM showed up.

I'm wiring up my 4ch 9k pre right now. I'm also excited to here them. A good friend of mine said "your gonna kick yourself in the ass for not building them sooner... they sound GREAT"
He also said they are "Clean... but not clean, BIG sounding & that they almost give you the "Sense" that there could be tranny's in there. He also mentioned having a "Color" or "Sound" to them... unlike what some others have said about them JUST being "Clean"... so, I'm very excited to hear for myself. ;D He also said they are one of his top favorite Vocal & Snare Pre's.

I haven't been following your problem too much but if you tested your HFE correctly & they're off that much... I'd just replace the MAT's. Even if they don't end up being the problem, they're worth money & can EASILY be sold.

Good luck man.