[BUILD] 1176 Rev A - Back to the beginning...

[Echo North]

Try This:

 

[Moose]

THat's what I need -- thanks!


Edit to add -- that was the problem I was seeing. I bridged the junction of R1/R2 and it didn't work, but I needed to get it connected to the 10M so that it went to the switch, as well. The pad at R2 was not connected to the trace for some reason.

Voltages now run from -2.something to -6ish instead of almost -10V and I get gain reduction.

 

[jonathanmorbin]

Hi,

So i re-stuffed a PCB as the first one i built just didnt seem to work. I now have a different problem.

I first noticed that the voltage were not right (far to low) in my GR Meter circuit as the GR meter would not go up at all and the signal input was very low even when feeding a 0db sine wave. After a bit of looking around i have found that if i remove pad 7 the voltages are a little more accurate (but still a bit off,a little high) the signal level seems correct in this state and the GR meter goes up to around zero. As soon as i put pad 7 back in it seems to short it all out and the voltages go down, signal level drops to minimum and the GR meter is stuck at the bottom.

Both my ratio and threshold circuits function correctly with pad 7 out and in (although obviously the signal level is much lower with pad 7 in)

Any Ideas for where to look or what is going on?

Jon

 

[evilcat]

Hi there!

I'll make a combo with a VP25preamp and a revA compressor in the same box. I have an idea that I'd like you to concure : using the compressor Vu-meter to monitor the preamp output. I think using a DPDT switch to take the output signal on the compressor or the preamp, and still using the rotary switch for switching GR or VU. Is it correct, or do I need a sort of VU driver for the preamp output ?

Thanks,
Best,

Ben

 

[Stagefright13]

Ya prolly need A driver for the preamp VU but the 1176 doesn't seem to require that. You may be able to use A seperate tap from the pre's out transformer for that depending on what you use.

John

 

[evilcat]

A VU buffer like the JLM one's ?

http://www.jlmaudio.com/shop/index.php?_a=viewProd&productId=19

What do you mean by "use a different tap from the pre's out transformer" ?

Thanks,
Ben

 

[robotwilliams]

Hey, I'm trying to test the voltages on my power rails of the power supply, but every time I test with a multimeter the reading just goes to 0V. The unit is plugged in with the fuse in, and the power supply section of the pcb is completely stuffed. All resistors were checked prior to soldering. The rest of the pcb is mostly stuffed, although we still are waiting on R65, R50, R9, Q2, and Q4 to come in the mail. I think the problem is either in the way I'm testing for voltage with my multimeter or the partial stuffing of the pcb. Could someone please walk me through testing the power rails so I can double check with what I was doing, or if someone sees some obvious flaw please correct me. Thanks!

 

[Echo North]

Hey, I'm trying to test the voltages on my power rails of the power supply, but every time I test with a multimeter the reading just goes to 0V. The unit is plugged in with the fuse in, and the power supply section of the pcb is completely stuffed. All resistors were checked prior to soldering. The rest of the pcb is mostly stuffed, although we still are waiting on R65, R50, R9, Q2, and Q4 to come in the mail. I think the problem is either in the way I'm testing for voltage with my multimeter or the partial stuffing of the pcb. Could someone please walk me through testing the power rails so I can double check with what I was doing, or if someone sees some obvious flaw please correct me. Thanks!

You should see AC beween the secondary center tap and either of the 25V terminals.  At the -10V and +30V you should see DC between those spots and the CT.

 

[evilcat]

I'll have to use an external power supply for my next rev A : a JLM power station, 2 rails for the 1176, and 2 rails+48V for a VP25 preamp.

On the 1176 PCB, PSU section, what parts should I remove ?
What parts should I leave ?
Where should I connect my +30V and -10V ?

Thanks,

Ben

 

[robotwilliams]

You should see AC beween the secondary center tap and either of the 25V terminals.  At the -10V and +30V you should see DC between those spots and the CT.

Ok, I am getting AC readings between the secondary center tap and the 25V terminals, but I'm reading 0V DC between the -10V and 30V and the center tap. Any idea on what this means? I verified that all components are working in the power supply section of the PCB besides the capacitors. Thanks.

 

[Ton]

Hi everybody!
I'm new on the forum, but a follower for a long time.
I've just completed the rev. A 1.2.5 Hairball/Mnats project. Everything was Ok. Triple checked components and wiring. Voltages on power supply are fine. Also on the rest of the board, except on Q11, Q12 and Q13, where voltages are aprox half of those indicated on the schematic.
Powering up the unit, audio signal passes through and I have also signal on the output. Input and output controls work fine. The meter shows activity on +4 and +8. The problem is there is no compression. In GR mode, the vu meter is stuck, and I don't hear any compression effect at the output.
Any help would be much appreciated!

 

[mnats]

Ok, I am getting AC readings between the secondary center tap and the 25V terminals, but I'm reading 0V DC between the -10V and 30V and the center tap. Any idea on what this means?

Either your power supply doesn't work or you aren't using the meter properly. Check my FAQ; good components are only part of the equation.

I've just completed the rev. A 1.2.5 Hairball/Mnats project. Everything was Ok. Triple checked components and wiring. Voltages on power supply are fine. Also on the rest of the board, except on Q11, Q12 and Q13, where voltages are aprox half of those indicated on the schematic.
Powering up the unit, audio signal passes through and I have also signal on the output. Input and output controls work fine. The meter shows activity on +4 and +8. The problem is there is no compression. In GR mode, the vu meter is stuck, and I don't hear any compression effect at the output.

You probably have at least two problems. Fix the voltages by carefully checking the things listed in the dot points of my troubleshooting FAQ. Look at the original schematic and ensure that you are reading the resistor values correctly.

Mike did an earlier troubleshoot of no gain reduction. Work though it once you have the metering circuit working properly.

 

[outoftune]

is it possible to adjust the sensitivity of the input/threshold of the rev A? mine has been working fine for a few years and sounds great, but it seems i'm always around 9 oclock or lower and can't get much higher without a lot of GR, even with normal levels. is this normal?

 

[mnats]

is it possible to adjust the sensitivity of the input/threshold of the rev A?

It's been discussed a few times of the 1176 in general and I even put a place for an optional trim pot on my rotary Rev A switch boards. Did you do a search?

 

[outoftune]

had a tricky time finding the right serach terms...will keep lookin around. will check my rotary switch to see if it has the option. have had this thing running for years and finally getting around to tweaking this part of it.

 

[Ton]

After carefully inspection and double and tiple checking, my board and wiring are ok. Still no compression. I get right voltages except gate on Q2. Should be -2.22V, but I get positive voltage. Any ideas? Thanks in advance!

 

[dmp]

After carefully inspection and double and tiple checking, my board and wiring are ok.

First off, if it isn't working, this cannot be true. Right?

I get right voltages except gate on Q2. Should be -2.22V, but I get positive voltage.

This should be a positive voltage. There is no way it would be negative since you have a voltage divider R9/R10 from 30v to ground.
And the voltage on the schematic is positive on mnats copy online
http://mnats.net/1176_revision_a.html

If you pass signal correctly then the preamp and line amp are correct.
Check the GR controller - what is the Vbias set to?

 

[Ton]

Thanks for your help. I read 29.8V and -8.9.

 

[dmp]

The bias voltage for the FET (Q1/Q11) sets the bias for compression. The bias voltage should be just negative enough so the FET starts to conduct.
The bias voltage is set by the trimmer R59. It is a voltage divider between ground and -8.9v.
So, what is the voltage at the point labeled 18 on the schematic? And point 7.

 

[Ton]

I read -1.37 at point 18 and -0.20 at point 7