All things G1176 - the new "repost" thread.

[Purusha]

EDIT AGAIN - it seems there's a coating on the Amveco leads and not copper. Have never seen this before on Transformers. Scraped the coating away, and all is well.

Happened to me too :shock: I was also thinking my toroid was gone ... :grin:

 

[gerardmanvuca]

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[gerardmanvuca]

It's cool , I'm looking at Greg's BOM and it specifies the voltage for each component.

:idea:

 

[gerardmanvuca]

Hey everyone,
I've condensed the ''All things G1176 - the new repost thread'' to 2 pages, if anybody has hard time searching through the whole post, this might
make your life a little easier.

enjoy.

http://www.buythebeats.com/1176%20Thread%202%20pages.rar


peace.

 

[gyraf]

Great initiative!! :thumb:

Jakob E.

 

[Siegfried Meier]

Ok, I finally finished a pair of these and am on to Calibration. Lots of info, lots of posts and I'm still trying to work out exactly what to do. However, I have noticed that in +4 mode of my Mnats Rev J versions, I don't get a VU signal (on either unit). I was under the assumption that +4 was output level, and the +8 was removed and the switch used as an attack off button. I've checked and rechecked, and I don't think I've wired anything wrong - at least if I did, I did it to both units.

Otherwise, the units seem to be working really well, and no serious noise issues that I can immediately tell.

Thanks for everyone's help on these (too many people to mention), and on the Pultecs as well. It's taken a while to finish it all, but well worth it.

PS - Gerard, your link doesn't work.

thanks,
Siegfried

 

[Siegfried Meier]

Also noticed tonight, that along with the VU not working on +4, the second unit I finished, when bypassed, is probably around 5-6 dB quieter than the first unit. Everything was built identically, with the same lundahl ins and outs. What would cause the decrease in volume? Could the input and output pots really have that much tolerance?

Thanks,
Sig

 

[Siegfried Meier]

Ok, I see now that the Mnats pushbutton boards are reversed, and +4 is actually in the +8 location on the front panel, and +4 is actually GR Disable. Still have a small level discrepancy, but I think it is just potentiometer tolerance now, as it's not that huge. Working on calibration, and I realize that I need a real millivolt meter, not just the inexpensive guys for general work.

Thanks,
Sig

 

[dustbro]

Hey guys. Need some help getting my G1176's up and going. I built 4 units side by side, and all 4 have the same problem... No compression.
Input and output appear to be working properly. Meter (sifam AL29WF) works properly when set to +4, and it even rests at 0VU when I set it to GR. All voltages seem to match the schematic. I just checked all of the resistors around the ratio switch and everything seems to be in order.
When I check the voltage at the Gate of Q10 with my multimeter, I hear gain reduction, and the meter starts to show gain reduction. When I remove the leads from the gate, the gain reduction stops. And the recovery of gain reduction after I remove the leads even seems to follow the position of the release knob.
I cant imagine it being a solder bridge somewhere since it does the exact same thing on 4 units. It almost seems to be that the threshold is just set too high.
I can get thru the Q Bias adjustment when calibrating, but moving the attack knob to "fast" and adjusting the Tracking pot does nothing. These FETs have been matched using the PRR rig.
Thanks for any help
Dan

 

[gswan]

Dan,

What exactly is your test and setup procedure? I haven't seen one that requires the attack pot in the 'fast' position (ie fully CW).

Geoff

 

[Siegfried Meier]

That sounds pretty odd, and I would say it's definitely something you've done, because you've done it 4 times. Is the meter completing the circuit somehow, and is it possible you've forgotten to solder something in place? Just a thought.

I have a strange issue with the output pot on my second unit, and it's not the pot as I swapped it with the good one and it still happens. It sounds kinda scratchy, and the output level shoots out a burst at over +4 vu, and the speakers just push like mad when it happens - seems like maybe some kind of a DC problem? Any ideas what to check?

Thanks,
Sig

 

[dustbro]

[quote author="gswan"]Dan,

What exactly is your test and setup procedure? I haven't seen one that requires the attack pot in the 'fast' position (ie fully CW).

Geoff[/quote]
Hey Guys. Thanks for the replies!
Turning the attack pot CW is actually the 3rd step in doing the tracking calibration (according to the original manual)
-apply 1K and switch meter to +4
-turn output level CW until meter reads 0VU
-turn attack control ON (CW) and observe drop in meter
-adjust input level till meter reads -10

Thats as far as I can get cause turning the attack control ON causes no gain reduction, and neither does adjusting the input level.

Whatever I have done I did in all 4 units. I'm using BF245A FETs... these are the proper ones to use, right? It seems to have the ability to compress but I'm not quite hitting the threshold yet.
[quote author="Siegfried Meier"]Is the meter completing the circuit somehow, and is it possible you've forgotten to solder something in place? Just a thought.[/quote]
Interesting thought... not exactly sure what to look for though. Would the meters actually affect the compression?

 

[gswan]

A scratchy sounding pot is a good sign of DC across it. Check your coupling capacitors (you didn't use tantalums, did you).

Also check your wiring on the ratio switch. If you crossed some of them then it's possible to feed the bias DC onto the output pot.

Geoff

 

[gswan]

[quote author="dustbro"]
Turning the attack pot CW is actually the 3rd step in doing the tracking calibration (according to the original manual)
-apply 1K and switch meter to +4
-turn output level CW until meter reads 0VU
-turn attack control ON (CW) and observe drop in meter
-adjust input level till meter reads -10[/quote]

Dan, turning the attack pot 'on' means turning it in a CW direction until the switch turns on. BTW, it doesn't really matter what setting the attack pot is at during calibration since we are dealing with a steady-state input anyhow.

[quote author="dustbro"]
Thats as far as I can get cause turning the attack control ON causes no gain reduction, and neither does adjusting the input level.

Whatever I have done I did in all 4 units. I'm using BF245A FETs... these are the proper ones to use, right? It seems to have the ability to compress but I'm not quite hitting the threshold yet.
[/quote]

If you get no gain reduction the you have either not setup the FET into conduction yet (the Qbias step), or your input signal is too low (lower than the threshold) or the input control is too far CCW. Start with the input control at around half way.

 

[dustbro]

[quote author="gswan"]
If you get no gain reduction the you have either not setup the FET into conduction yet (the Qbias step), or your input signal is too low (lower than the threshold) or the input control is too far CCW. Start with the input control at around half way.[/quote]
I'm sending 1K @ 0dB from a sine wave generator for the Qbias adjustment. Would you suggest sending +6dB or more?

 

[gswan]

No, 0dBu is fine. The threshold is around -20dB. Where's the input pot set at? The input pot needs to be up around halfway or so to have enough signal at the GR amp to trigger compression.

 

[syn]

[quote author="dustbro"]...and all 4 have the same problem... No compression...
Dan[/quote]


O.K., this is probably not the case, but have you connected your fets properly (pinout wise)? I've read somewhere around, that if you do that the wrong way , audio will still be passed, but no compression will occur...

cheerz

 

[Siegfried Meier]

[quote author="gswan"]A scratchy sounding pot is a good sign of DC across it. Check your coupling capacitors (you didn't use tantalums, did you).

Also check your wiring on the ratio switch. If you crossed some of them then it's possible to feed the bias DC onto the output pot.

Geoff[/quote]

Which coupling capacitors are you referring to? I may have used Tantalums, so what would the problem be with that?

Thanks,
Sig

 

[gswan]

[quote author="Siegfried Meier"]
Which coupling capacitors are you referring to? I may have used Tantalums, so what would the problem be with that?

Thanks,
Sig[/quote]

The stage coupling caps pre and post the output pot. These ensure that there is no DC across the pot.

Tantalum caps are horribly fragile and often fail s/c. If they do you will have DC across your pot.

 

[Siegfried Meier]

You're referring to C9 and C11, both electrolytic 47 uF/40V, correct? Those seem to be ok. I guess next would be rechecking the ratio pushbutton board, which I've done at least a hundred times now. The answer must just be eluding me.

Thanks,
Sig