[BUILD] 1176 Rev A - Back to the beginning...
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evilcat
Well-known member
Ok guys, I need you ! I'm building 2 units. The 2 worked at the 1st shoot but as I had some difficulties to calibrate the 1st one, I pulled off all the 2n3708 to measure and match the Hfe (since someone gave me a multimeter w/ Hfe tester), reloaded the PCB w/ matched transistors and now, the comp doesn't work well at all !
The main issue is that when I put the output pot full there's a strange noise and the Vu is going crazy, even in bypass mode, and it made the Q bias calibration difficult. When I put pad 22 to ground to bypass the GR, the sound become strangely distorded (like a robot on voice). And there's like "pop", still on vocals, when the attack is fast and when I compress more than 3-4 dB, whatever the ratio is. Of course, all these things don't happened on the 2nd unit. 1st I suspected the transistors so I put those of the 2nd unit in the 1st one and it didn't resolved anything. I also tryed with the input and output transformers, and the T-pad attenuator of the 2nd unit, with no success...
What can I try ?
The main issue is that when I put the output pot full there's a strange noise and the Vu is going crazy, even in bypass mode, and it made the Q bias calibration difficult. When I put pad 22 to ground to bypass the GR, the sound become strangely distorded (like a robot on voice). And there's like "pop", still on vocals, when the attack is fast and when I compress more than 3-4 dB, whatever the ratio is. Of course, all these things don't happened on the 2nd unit. 1st I suspected the transistors so I put those of the 2nd unit in the 1st one and it didn't resolved anything. I also tryed with the input and output transformers, and the T-pad attenuator of the 2nd unit, with no success...
What can I try ?
0dbfs
Well-known member
If you have a scope, you could try measuring and comparing at different points along the signal paths and comparing between any working units you have and the suspect unit.
Also the same with a meter.
That might help identify some differences which could lead down a path to a solution.
Best,
jonathan
Also the same with a meter.
That might help identify some differences which could lead down a path to a solution.
Best,
jonathan
evilcat
Well-known member
I'm not sure that the old scope that a friend gave me is still working but if it works with a multimeter, I will try this to find where my problem is. I stupidly don't remember ( 'cause I've done so much test in so much configurations), but I think that the problem is not on the main board but on one of the ratio or meter board : I think I tried to sweep the main PCB with success and I'm sure of my transformers and attenuator.
Anyway, thanks for the tip, I'll definetly try tomorrow.
Best,
Ben A.
Anyway, thanks for the tip, I'll definetly try tomorrow.
Best,
Ben A.
0dbfs
Well-known member
If you think it's on one of the ratio or meter switch boards you could also measure and compare resistance between different positions with the units powered down.
As part of my troubleshooting the ratio/meter boards, I hardwired some values according to the schematic and bypassed the switches/boards. Something was wrong with those boards in my case and I ended up doing some point to point switches following the schematics which worked out well. I damaged my lorlin's in the process and used some different switches that I had for a different project.
Sorry not to be able to provide better detail but If you got at least one working I believe that you can get this one going!
Best,
jonathan
As part of my troubleshooting the ratio/meter boards, I hardwired some values according to the schematic and bypassed the switches/boards. Something was wrong with those boards in my case and I ended up doing some point to point switches following the schematics which worked out well. I damaged my lorlin's in the process and used some different switches that I had for a different project.
Sorry not to be able to provide better detail but If you got at least one working I believe that you can get this one going!
Best,
jonathan
evilcat
Well-known member
0dbfs said:
Yeah, that's what I think too. When I think I had 2 working units and I had mess with one !!! :-\
Thanks Jonathan,
Best,
Ben A.
0dbfs
Well-known member
Well, At least you're fortunate enough to be in the position to figure out how to fix it!
If you never broke it (I mean fine-tune it) then this opportunity may have been lost forever (unlikely, I know).
Interested to see what it is tho... Seems like the switch pcb's provide people all kinds of opportunities.
Maybe also try disconnecting the switch PCB's from the main-board and swapping the known good with the suspect to narrow it down a little and isolate the problem a little.
Cheers,
j
If you never broke it (I mean fine-tune it) then this opportunity may have been lost forever (unlikely, I know).
Interested to see what it is tho... Seems like the switch pcb's provide people all kinds of opportunities.
Maybe also try disconnecting the switch PCB's from the main-board and swapping the known good with the suspect to narrow it down a little and isolate the problem a little.
Cheers,
j
evilcat
Well-known member
0dbfs said:
That's exactly what I wanna do first ! Be sure I'll let you know.
best,
ben
evilcat
Well-known member
Well, I switched the 2 main PCBs and it didn't resolved my problem. So I was sure that it was on the main board, not the switch or ratio ones.
The "pop" problem on every ratio varied when I changed the Q bias setting with the trimmer, so I began to suspect that the Q bias calibration was the problem, as bypassing the GR by putting pad 22 to ground isn't working (I don't now why !!!).
So I've calibrated the units by using the Vu meter of my console (real studio console with Sifam AL29 Vu meters) and the meter switch to bypass or not the compressors. And it seems to work !!!
I don't know why I'm no longer able to bypassing the GR with pad 22 to ground, it's weird, but I was able to achieve the calibrations and it works, that's all I need, isn't it ?
Ben A.
The "pop" problem on every ratio varied when I changed the Q bias setting with the trimmer, so I began to suspect that the Q bias calibration was the problem, as bypassing the GR by putting pad 22 to ground isn't working (I don't now why !!!).
So I've calibrated the units by using the Vu meter of my console (real studio console with Sifam AL29 Vu meters) and the meter switch to bypass or not the compressors. And it seems to work !!!
I don't know why I'm no longer able to bypassing the GR with pad 22 to ground, it's weird, but I was able to achieve the calibrations and it works, that's all I need, isn't it ?
Ben A.
0dbfs
Well-known member
If it's working for you then it's working.
I'm looking at the schematic/board-etch file, following the signal, and just talking out loud here.
Pad 22 is the input to the GR ctrl amp (C17). That is normally fed from the output pot through the S4A (voltage-divider) and the GR-OFF switch to C17 via the pad 22 shielded jumper wire.
If you ground pad 22 that means the GR amp should not be receiving audio signal at C17.
I believe that the Q Bias trim-pot adjusts the -10V DC offset at the output of the GR amp (for -bias V of Q1/11) and both C7 & C17 should be blocking any DC fed into the GR ctrl amp (which could cause pops). Maybe C17 is failed or backwards?
I would check that C17 is properly oriented and not failed and see if you can locate where the audio comes from that gets into the GR amp when pad 22 is shorted to gnd (while disconnected from S4A). Also probe around those points (C7, output pot, C17, pad22) for any DC.
Best,
j
I'm looking at the schematic/board-etch file, following the signal, and just talking out loud here.
Pad 22 is the input to the GR ctrl amp (C17). That is normally fed from the output pot through the S4A (voltage-divider) and the GR-OFF switch to C17 via the pad 22 shielded jumper wire.
If you ground pad 22 that means the GR amp should not be receiving audio signal at C17.
I believe that the Q Bias trim-pot adjusts the -10V DC offset at the output of the GR amp (for -bias V of Q1/11) and both C7 & C17 should be blocking any DC fed into the GR ctrl amp (which could cause pops). Maybe C17 is failed or backwards?
I would check that C17 is properly oriented and not failed and see if you can locate where the audio comes from that gets into the GR amp when pad 22 is shorted to gnd (while disconnected from S4A). Also probe around those points (C7, output pot, C17, pad22) for any DC.
Best,
j
evilcat
Well-known member
0dbfs said:
Thanks a lot Jonathan. As a newbie, I'm not sure to understand what you mean by "Also probe around those points (C7, output pot, C17, pad22) for any DC". Do you mean that there's a problem if I measure any DC curent here ?
Thanks again,
best,
Ben A.
0dbfs
Well-known member
I believe that there should be no DC in those positions because there are caps on both sides of that wire/path. Those caps should block the DC.
Check with your DMM for DC and see if there is any there. Also confirm that the caps are good and with the +/- sides oriented correctly. The only reason I mention that is because you mentioned "pops" and adjusting the Qbias changed that behaviour.
If you have pad 22 grounded (and disconnected from the GR/Ratio switch) then it should not be compressing as expected. That tells me that signal (or some other signal) is getting into the GR CTRL AMP via some other means.
I'm just throwing stuff against the wall to see what sticks.
Best,
j
Check with your DMM for DC and see if there is any there. Also confirm that the caps are good and with the +/- sides oriented correctly. The only reason I mention that is because you mentioned "pops" and adjusting the Qbias changed that behaviour.
If you have pad 22 grounded (and disconnected from the GR/Ratio switch) then it should not be compressing as expected. That tells me that signal (or some other signal) is getting into the GR CTRL AMP via some other means.
I'm just throwing stuff against the wall to see what sticks.
Best,
j
Attachments
Evilcat, are you using a proper VU meter or just a d.c meter with a moving needle ? The 1176 requires a proper VU meter with a diode rectifier bridge in it like the sifam AL29 (still not really a proper VU, but will definitely work).
aistobasbistoc
Member
hello,
i wired my dual 1176 (purusha case) the same way as the picture on mnats site. Rev J But i cant find any information about wiring the bypass - comp switch ( under the VU - meter on the front panel )
So i dont agree the bypass - gr - vu switch, this is well documented.
can anyone help me?
Thanks!
i wired my dual 1176 (purusha case) the same way as the picture on mnats site. Rev J But i cant find any information about wiring the bypass - comp switch ( under the VU - meter on the front panel )
So i dont agree the bypass - gr - vu switch, this is well documented.
can anyone help me?
Thanks!
Stagefright13
Well-known member
That is just an extra hole that was put on by mistake. It is unused. I stuffed it with 1/4" trs sockets.
John
John
evilcat
Well-known member
Thanks again J for your help ! I will check for DC at those points.
Hi Rob. I'm using the Hairball Vu-meter. I assumed that it's not a REAL Vu meter but it should work, isn't it ?
Again I'm not sure to understand : I have to ground pad22 of the main board and disconnect the Meter board (wich fed pad 22) ?!!! When I looked at the calibration video on Mnats site, I thought that he just grounded pad 22 without disconnected the wire between meter and main boards. Am I missing something ?0dbfs said:
Rob Flinn said:
Hi Rob. I'm using the Hairball Vu-meter. I assumed that it's not a REAL Vu meter but it should work, isn't it ?
so i got the second of two units complete with the hariball matched transistors and transformers. Everything seems to work but on the second unit the meter does not fall when the gain reduction is switched off, and the gain reduction does not bypass. I checked the bypass switch wiring 6 times now. it is fine. I everything looks like the first unit, the amp works fine, i just cant figure out what to do. I tried changing the transistors in the gain reduction circuit, no help. any ideas?
Echo North
Well-known member
The meter should "0" with GR off.
With GR off use an ohm meter and see if pad 22 on the main PCB is shorted to ground. It should be.
Mike
With GR off use an ohm meter and see if pad 22 on the main PCB is shorted to ground. It should be.
Mike
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