All things G1176 - the new "repost" thread.

[rbaker]

If you're using the input transformer you need the other parts as well, or at least when you're using the luhndal transformer. I can't imagine it's any different with the oep. As far as the cap on the far right, that's not a cap for the input section and doesn't follow the same *** rules as the others---jakob said it's optional (regardless of input method) but that it really should be there.

I should probably delete that file to avoid any confusion about it.

 

[astrovic]

Don't delete it - it alerted me to a possible issue I hadn't previously contemplated. Every little bit helps!

Methinks I'll return to reading this post (again) to see if anything jumps out at me.

 

[mnats]

7. I just thought of this - my wires connecting 18 & 21 from the main board to the ratio board are the same colour.

I'm sure it's been covered before but it is worth mentioning again - my boards have two possible connections for pad 18 depeding on what size trimmer you used for R81. The later revisions have an <18> pointing to the two possible holes, but you still must choose the correct one to use.

Choose the wrong one and your attack/release pots are essentially out of circuit which will probably cause it not to work as it should :wink:

BTW, I've added this to my 1176 FAQ.

 

[astrovic]

Thanks for the suggestion, Mnats, but unfortunately its not that - I have that part right. I'm also now certain I have R18 and R21 in the right way.

But something is not quite right, dammit! :grin:

I'm gonna have to shelve it for the rest of the week, so I can actually concentrate on work (or something else, at least) and come back to it with a fresh mind.

Thanks guys

 

[stefan]

I have exactly the same problem as You, sound but no compression. please let me know if You find out what´s wrong. hmmmm... I changed my mind Read my next one and You may realize that I have compression after all, not as much as I would like, but compression it is.

 

[stefan]

Since I´ve never used an original 1176 I´m kind of wondering what to expect, should it have massive pumping almost distortion type of compression in the 20 setting? I have one up running now and the sound is fine, no hum after cutting two traces, all the controls seem to work properly, and I will certanly solder my other one together cause I realize that it will be higly useful in the studio, but still I´m kind of surprized by the humble action of the unit when everything´s is turned full CW. Should this not result in an almost useless mess? What I´m really wondering is if my unit is working properly or if the Bias (or something else) is wrong. I don´t have a meter in the unit yet so I really don´t know what the meterreadings look like, I just adjusted the Bias with an external meter. One question ´bout the adjustment, and this is a stupid one but I ask it anyway: where is the Biaspot supposed to be when I check for +1dB out of the unit?

 

[MattiasC]

I'm wiring the primaries on my toroid in parallel, but I don't know whether to connect the "start" of each winding to live or neutral. I would assume live, but I'm confused by the two graphs below. If I follow Avel Lindberg's site, it seems to show the blue/violet (start of the winding) would be connected to 0 (neutral, I assume) on the IEC connector. Mark Burnley's graph shows the these two primaries being connected to Live.

So which is it?

 

[gyraf]

whether to connect the "start" of each winding to live or neutral

..Shouldn't matter..

 

[astrovic]

The one advantage to living a 45 minute train ride from work is that I have lots of time to read the entirety of this post, and anything else I can find on this project :grin: I'm sure my fellow travellers look at me strange when I unfold my A3 sized copy of the schematic, though!

I'm now pretty confident I know what my problem is - BF245A. One of my problems was a lack of compression (my audio signal is fine, but no limiting occurs at any setting and the attack and release pots have no effect), and if I have it right, if Q1 has died then there's no chance of that. I just tested the audio path using a signal detector (mark Burnley's wonderful little creation) and I have audio up to pin D on Q1, but not pins G or S. I take it pin S goes to ground, so I don't expect audio there, but pin G heads to the attack and release pots (via R7 and point 7), so I assume that without anything passing that way, there ain't gonna be no compression.

Along the way my zero adjustment trimmer stopped having any effect (in GR mode, the needle just slams to the right and won't move, but when I first fired up I could adjust it with the zero trimmer) and my needle stopped responding at all to anything. That's gotta be Q10, methinks.

Can anyone fault me on my logic? Of course, there may be other problems lurking in the background once I replace Q1 and Q10 (note to other newbie's - when buying parts for this project, buys lots of BF245A, so you have spares when your first lot die on you, and so you can match them as has been explained elsewhere in this thread), but do I sound like my error-sourcing is on the right track?

Chris

PS My Vu meter definitely works - I connected it in series with a 3k6 resistor to my best piece of test gear - a 15 year old Sony Walkman :thumb: All good!

 

[astrovic]

Well, I've ordered a bunch of BF245A's which will hopefully arrive early next week. I've also ordered a couple of 2x6 lorlin switches, as someone else in this thread described a similar problem to me and found it was a faulty switch. If I'm wrong, then the spare switch goes into the 2nd channel or the GSSL that I intend to build

I'll report back next week when the parts come in - hopefully with a grin on my face!

 

[mnats]

3. I haven't calibrated the unit yet. Do I need an oscilloscope to do this, or is there a workaround that will get me there?

You can do the "Q" Bias Adjustment and Gain Reduction Meter Tracking using your built-in VU meter. But because the G1176 rotary switch does not allow you to both observe the output or gain reduction on the VU meter and allow you to switch off the gain reduction, you will need a workaround.

Every time the calibration section of the 1176 manual says "Attack = full CCW (switched to OFF position), simply short pad 22 on the main board to ground (use a link with alligator clips or similar). This has the same effect as switching off the gain reduction using the Attack pot on the original unit. Every time it says to turn the Attack ON, just remove the link.

But you need a properly working unit before moving on to calibration, of course.

4. I when I put a signal through, and put the meter in Vu mode, the meter generally follows the strength of the signal, but never gets very "high" (i.e close to 0Vu)

What are you using as a test signal? The 1176 has loads of gain and even with a -20dB input you should be able to easily peg the VU meter.

I have audio up to pin D on Q1, but not pins G or S.

I wouldn't expect (much) audio on the gate of Q1, since it is fed DC from the Gain Reduction Control Amp (see CR3 and CR4). But with Gain Reduction ON, you should have plenty of audio at, say, the emitter of Q15 just before rectification. If not, something is wrong upstream.

That's gotta be Q10, methinks.

Seems very unlikely that both your FETs are faulty. More likely that the common circuit controlling them is where the fault lies.

Try removing Q1 and seeing what that does to your output strength. This will allow you to test the Signal Preamp and Line Amp without any sidechain circuit interaction. Once you're sure this is working properly, move on to the Gain Reduction Control Amp circuit.

 

[stefan]

My first 1176 is up and running and everything seems to be working OK soundwise. The only problem is that when I set the switch in "GR" position the needle goes down to -20 and stays there regardless of how I adjust the trimmers. The meter(Sifam AL19) is working just fine in VU mode (as far as I can tell) but in GR nothing happens. where should I start?

 

[mnats]

where should I start?

Here. Start in the lower left hand corner of the schematic or around IC1 (TL071) on the PCB.

 

[astrovic]

What are you using as a test signal? The 1176 has loads of gain and even with a -20dB input you should be able to easily peg the VU meter.
...
Try removing Q1 and seeing what that does to your output strength.

Using a 1KHz signal, at approx 0dB (measuring AC at my input read 0.777 VAC), which was loud enough to send my mixer skyrocketing I never got the meter moving much/at all.

With Q1 in, I adjusted the output so the meter on my mixer is reading 0dB. I then pulled Q1, and got the exact same level on the mixer. I changed between modes (i.e bypass, GR and VU) and ratios, and the output strength never changed :?

I get the impression my compression sidechain just isn't getting activated at all.

But with Gain Reduction ON, you should have plenty of audio at, say, the emitter of Q15 just before rectification. If not, something is wrong upstream.

No audio there, unfortunately. I re-checked my power supply voltages (all good), and the voltages at Q12-15, and still all good.

Seems very unlikely that both your FETs are faulty. More likely that the common circuit controlling them is where the fault lies.

Could it be a faulty Q-Bias trimmer? I am looking in the right area for the common circuit?

I'll keep hunting! Unfortunately I only ever seem to get about 10-15 mins at a time with it :sad:

Thanks for the help, Mako

 

[mnats]

Using a 1KHz signal, at approx 0dB (measuring AC at my input read 0.777 VAC), which was loud enough to send my mixer skyrocketing I never got the meter moving much/at all.

I'm not quite understanding your signal chain. You are feeding your 1kHz, 0dB test signal into your 1176 and the output of the 1176 to your mixer? If you are saying that the mixer at the end of the chain was skyrocketing and the meter in your clone was not registering much when the rotary switch was set to VU, there is something wrong with either the VU meter (which you said you had tested earlier) or the connections feeding it. In other words, if your actual audio output meets or exceeds 0dB you should at least be able to see it on the meter since it is tied directly to the output when switched to the VU setting.

Get the VU meter working properly and ditch the mixer for now.

No audio there, unfortunately. I re-checked my power supply voltages (all good), and the voltages at Q12-15, and still all good.

The circuit that controls both FETs is the Gain Reduction Control Amp in the bottom middle of the schematic. You have no audio from the last stage of that amp when the clone is not in bypass. So start from pad 15 on the main board and trace the signal to pad 4 on the ratio board out to pad 22 back on the main board (which is the input of the control amp), then through the GR control amp circuit until you find out where the signal stops. Then apply Jakob's rule.

 

[stefan]

something is strange, I don´t have the -10V, I´ve soldered out C24,C26,R45,R82,R57,R56,R52,Q10 and pulled the TL071 out of it´s socket and changed the zener and still I have only around -4.5V! if I remove the zener and measure before it I have around -12V, am I measuring wrong or what is it? I thought that the unit was working soundwise and that the meter was the only problem but I´m not so sure anymore...

 

[astrovic]

Stefan

What voltage do you get at R85?

 

[astrovic]

...and it's "working" - not perfectly, but man, it's great to hear it compress something :green: :green: .

My problem was, of course, a failure to properly apply Jakob's rule :grin: :shock: :grin: Some free time, a strong light and hey presto - all the poor soldering job's on my board started leaping out at me.

Though I cleaned up some others, it looks like my problem was a poor solder joint on one leg of my tracking trimpot...now she goes!!!

A couple of questions about its operation, though:

1) It is meant to compress in Bypass mode, or does bypass just turn off the meter? At moment, in bypass there's no compressing going on, and the ouput level is significantly higher than when in Gr or Vu mode, which would make sense if bypass mode bypass the whole sidechain and not just the meter

2) In Vu mode, the meter still barely moves no matter strength signal I put through it. This can't be right?

I might try a new u meter at some stage (I blew up the light in this one ) to see if the meter isn't doing its job properly, but it seems to work ok in GR mode

Thanks Mnats for all the help - you're a legend!!!

:green: :green: :green:

 

[stefan]

[quote author="astrovic"]Stefan

What voltage do you get at R85?[/quote]If I unsolder The first 1K resistor (R86 I think) in the PSU and measure right after the 1N4003s I get only around -12V measured to ground is this right? I do not understand why I don´t have -30 or so, but I might be missing something obvious??

 

[astrovic]

I take it you meant -10, not -30?

I checked for -10 after R85 rather than checking after the 1N4003's. This is the spot to check - see here. I'd work through the first part of this dealing with getting the PSU section right to see if it throws any light on your situation.