[BUILD] 1176LN Rev D DIY

[Nedrum]

I was doing my homework for a stereo rev D build and I saw on the schematic that Q5 and Q6 are to be matched. However, the only thing I can find related to this is a question posted by mnats back in January, 2007, for which I find no answer (despite searching for q5, q6, etc.):

Since someone keeps raising the matching question does anyone have an idea why the schematic suggests matching Q5, the small signal transistor and Q6, the medium power output transistor (circuit posted on page 2 of this thread)?

I'm assuming matching these is not required since I see no discussion about it. But I'm curious why the schematic included this and what was meant by it.

 

[Chryst]

maybe start with double checking component values when you say ...

What I did notice however that it was extremely hard to get the right output voltage as the output pot seemed extremely sensitive. I've tried to measured its resistance and I only get 125 ohm instead of 250.

If your output level pot R23 is 250 ohms for real (249750R difference on paper from the suppost to be fitted value 250K with a log taper) this alone would explain a lot. There might be other, or just be more exact with your numbers, dimensions or multipliers.

Hey Harpo, thanks for your kind help. I'm sorry, but I'm not sure I fully understand you. I'm not sure about the resistance of the output pot as I only measured it 'in circuit' which is unreliable per definition. But let's say the pot is 250 ohm as specified in the BOM, but it's too steep. Could this have an influence on the way the compression response is right now? It seems unlikely to me as I thought that the output circuit is independent from the metering and the GR circuit isn't it? Or am I wrong?

Should I start checking component values in the GR section? I'm pretty sure the original values were right because they were checked going in, so it comes down to desoldering and looking for defective components I guess.

If somebody knows an alternative strategy, I would be delighted. I've build quite a lot of these guys and this is the first one that's really not cooperating. Thank you very much for your help! It's being much appreciated!

 

[Harpo]

..But let's say the pot is 250 ohm as specified in the BOM,

It is not. Maybe look again.
250K=250000 ohm with log/audio taper wanted. This is a 249750 ohm difference to your 250 ohm pot.

Could this have an influence on the way the compression response is right now? It seems unlikely to me as I thought that the output circuit is independent from the metering and the GR circuit isn't it? Or am I wrong?

Yepp, wrong.

 

[Chryst]

..But let's say the pot is 250 ohm as specified in the BOM,

It is not. Maybe look again.
250K=250000 ohm with log/audio taper wanted. This is a 249750 ohm difference to your 250 ohm pot.

Could this have an influence on the way the compression response is right now? It seems unlikely to me as I thought that the output circuit is independent from the metering and the GR circuit isn't it? Or am I wrong?

Yepp, wrong.

I'm so sorry for being so sloppy with the values. I meant 250k. I haven't had much sleep lately and it's coffee that keeps me going. However I guess that because there could be an influence, it's maybe better to change the pot anyway just to be sure. It has a very steep curve to begin with, so I guess changing it out will improve that anyway. It's a pot from the Hairball kit.

 

[Chryst]

Just to be sure: replacing the 5k back with 2k trimmers shouldn't help right..?

 

[Philipp127]

I have a problem with the VU meter of my 1176 rev D built from MNats/Hairball parts.

The VU meter works just fine when only the XLR Input is connected : in GR mode the meter goes up to Zero, when i switch to +4 or +8 Output mode the meter goes hard left.

When i start using the 1176 as an insert and start connecting the XLR output as well the VU meter starts behaving very strange: in GR mode the meter also goes up to zero, but when switching to +4 or +8 Output Mode the meter tilts and goes hard right .

Anybody has an idea what could be wrong with the unit? The unit is calibrated just fine, passes audio and compresses without any problems, but it would be usefull to know what output is going on....

 

[Echo North]

Just to be sure: replacing the 5k back with 2k trimmers shouldn't help right..?

For the GR tracking?

No, the 5K will do everything the 2K does and more.

 

[Echo North]

I have a problem with the VU meter of my 1176 rev D built from MNats/Hairball parts.

The VU meter works just fine when only the XLR Input is connected : in GR mode the meter goes up to Zero, when i switch to +4 or +8 Output mode the meter goes hard left.

When i start using the 1176 as an insert and start connecting the XLR output as well the VU meter starts behaving very strange: in GR mode the meter also goes up to zero, but when switching to +4 or +8 Output Mode the meter tilts and goes hard right .

Anybody has an idea what could be wrong with the unit? The unit is calibrated just fine, passes audio and compresses without any problems, but it would be usefull to know what output is going on....

Are you sure you have the meter connected to the right pads on the meter PCB as well as pin 2 and 3 on the XLR?

 

[Philipp127]

The VU Meter is connected to the meter PCB and XLR OUT Pin 2 and 3

Eveyrthing is working fine as lone as i have no external XLR cable attached.

When attaching an external XLR cable the GR mode is still working , but in +4 and +8  Output mode the meter is slamming to the right and not moving  :'(

 

[s2udio]

Has the XLR'S you are using have switching contacts on them ?
Continuity checks are easily made with the unit powered off.
Check with a dummy plug inserted and with it removed.

 

[Philipp127]

The XLRs have no switching contacts on them...

 

[StudioJakubka]

So I am all business now, +4, +8 and GR shows OK, compression switch works just fine and I am getting visible (on scope at least) compression. However with 0.775VAC on input I am getting audible distortion on every compression rate when GR meter shows -1 to -2dB compression. When off (attack fully CCW) the audio out is good and without distortion, when attack on it doesn't matter if I am fully CW or 12 o'clock, distortion is there. Any idea what is wrong?

Did you check your voltages against the schematic with voltages?

Yes I did, and all seems OK apart from Q8, down about 0.5V (14.31V, 29.9V, 14.95V) and the main problem is, I think, Q14, where I can not get the right voltage (10.91V, 29.9V, 11.52V) which is 1V bellow. Should I try to put resistor/ trimmer parallel to  R14 and try to set voltage up to match 12.58V there?

I am not sure if my idea is doable. Is 1V bellow on Q14 the cause of distortion? When I  bypass (Attack fully CCW - off position) there is no distortion and level is OK.

I am attaching Scope on return with Attack Fully CW/ release full CW, GR 20:1, when attack off then signal return is almost identical as signal in, signal in is measured at 0,775V.

Any idea why am I getting so high distortion?

 

[dbonin]

so it only distorts with GR on? 

I am attaching Scope on return with Attack Fully CW/ release full CW, GR 20:1, when attack off then signal return is almost identical as signal in, signal in is measured at 0,775V.

Any idea why am I getting so high distortion?

 

[s2udio]

The XLRs have no switching contacts on them...

Then recheck the continuity of your wiring, folowing the schematic on each side of the meter.
The path for the +4 and +8 is a very simple circuit.
You must have a problem around the meter selection switches.

 

[StudioJakubka]

so it only distorts with GR on? 

I am attaching Scope on return with Attack Fully CW/ release full CW, GR 20:1, when attack off then signal return is almost identical as signal in, signal in is measured at 0,775V.

Any idea why am I getting so high distortion?

yes , when bypassed I.e. Attack full CCW signal goes thru ok.

 

[Harpo]

The VU Meter is connected to the meter PCB and XLR OUT Pin 2 and 3

'X' and 'Y' on meter pcb connect to XLR-out-pins2/3. If you have the VU meter connected directly between XLR-out-pins2/3, the series resistors R16 or R77 in between would be missing, causing this hard right slammed behaviour.

 

[Chryst]

I'm still not able to really pinpoint the problem with my 1176. I've build lots of them without any significant problems, but this one keeps bothering me. The compression on this one seems too low and as far as I can see, it's probably not a meter problem. As a last attempt I'm posting the voltages. There a bit low, but I can't figure out if this could be because the of problems with the last calibration step.

I already replaced the 2N3707 FETS. Should I also replace the 2N5457 FETS? Any help is greatly appreciated. If anybody has any other strategy, please tell me! Thank you very much!


Q
2 0.55/1.77/1.06
3 1.16/0.00/1.77
4 0.44/3.97/1.02
5 2.77/24.91/3.31
6 27.41
7 3.95/14.93/4.50
8 14.30/29.98/14.93
9 2.88/16.96/3.46
10 16.40/29.98/16.96

CR6 -9.83
R87 29.98

 

[Alexmc1988]

I seem to have not received the white plastic power connector for my Rev D show here.

http://www.hairballaudio.com/blog/wp-content/uploads/2013/09/IMG_0278.jpg

Can I just solder the corresponding wires together instead? It sounds like it just connects from one side to the other.

 

[Echo North]

I seem to have not received the white plastic power connector for my Rev D show here.

http://www.hairballaudio.com/blog/wp-content/uploads/2013/09/IMG_0278.jpg

Can I just solder the corresponding wires together instead? It sounds like it just connects from one side to the other.

Ya you can just solder them together and cover with shrink tube.

Or email us and get us to send it to you.

 

[Echo North]

I'm still not able to really pinpoint the problem with my 1176. I've build lots of them without any significant problems, but this one keeps bothering me. The compression on this one seems too low and as far as I can see, it's probably not a meter problem. As a last attempt I'm posting the voltages. There a bit low, but I can't figure out if this could be because the of problems with the last calibration step.

I already replaced the 2N3707 FETS. Should I also replace the 2N5457 FETS? Any help is greatly appreciated. If anybody has any other strategy, please tell me! Thank you very much!


Q
2 0.55/1.77/1.06
3 1.16/0.00/1.77
4 0.44/3.97/1.02
5 2.77/24.91/3.31
6 27.41
7 3.95/14.93/4.50
8 14.30/29.98/14.93
9 2.88/16.96/3.46
10 16.40/29.98/16.96

CR6 -9.83
R87 29.98

If you're not getting enough compression, either your threshold voltage is off (- DC at pad 21) or your AC at pad 22 is too low or something in the GR amp stage.

I have some common Pad 22 and 21 voltages posted in this thread.