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

[dmp]

Rob, thanks for sending the manual & good to know those are the trusted schematics. The Waltzing bear schematics have confused me a few times.
The rev A Plosives thread has a lot of discussion on the differences between revs also, for others who are trying to follow this.  I have a bit of reading to do when I start a rev A build, but what I understand at this point is that several mods / component changes are possible to mnats boards to match the rev A schematic in the manual, which includes adding R31 & C13.
Thanks for your reply!

 

[ChrioN]

Which pictures have you guys used for guides when wiring the push button version?
One of the pics have excluded pad "22", "GRN" and "BLK" on the meter board. Are those not used in the REV A?

 

[mnats]

Which pictures have you guys used for guides when wiring the push button version?

As I mention at the bottom of my Rev A page, you should refer to the original schematic if you have any questions about wiring. Most of the various drawing circulating are for other versions or are not applicable to the current board layout(s).

But if you're really stuck, you might have to wait for me to finish the new wiring guides I'm currently working on for the pushbutton versions using Hairball components.

 

[ChrioN]

Which pictures have you guys used for guides when wiring the push button version?

As I mention at the bottom of my Rev A page, you should refer to the original schematic if you have any questions about wiring. Most of the various drawing circulating are for other versions or are not applicable to the current board layout(s).

But if you're really stuck, you might have to wait for me to finish the new wiring guides I'm currently working on for the pushbutton versions using Hairball components.

Feels like it would take hours to figure it out. Rather wait for a proper guide. Any idea of when this will be ready?
Thanks.

 

[Echo North]

Which pictures have you guys used for guides when wiring the push button version?
One of the pics have excluded pad "22", "GRN" and "BLK" on the meter board. Are those not used in the REV A?

Those are the bypass switch connections.  There are a few different places to put the bypass but ultimately those three wires should be on a SPDT switch.

It is on the original schematic

(Note: This is a clip from the rev F schematic.  I used the F because the copy was easier to read so be aware some surrounding labeling may differ.  The same switch is in the rev A but the schematic was very blurry.  The attack is R77 on the F and R55 on the A).

 

[mnats]

Feels like it would take hours to figure it out. Rather wait for a proper guide. Any idea of when this will be ready?

Longer than "hours".

 

[ChrioN]

Mr Hairball: that helped alot!  Didn't notice the traces in the schematic were numbered.

 

[ChrioN]

When looking at the picture, I don't get it. "GRN" and "BLK" are located on both push button PCBs. The link between them should be connected all the time?

 

[mnats]

When looking at the picture, I don't get it. "GRN" and "BLK" are located on both push button PCBs. The link between them should be connected all the time?

Have you read the switch board information PDF posted on the Hairball site?

http://hairballaudio.com/docs/FET_Compressor_PCB_Board_Info_V2.pdf

 

[ChrioN]

When looking at the picture, I don't get it. "GRN" and "BLK" are located on both push button PCBs. The link between them should be connected all the time?

Have you read the switch board information PDF posted on the Hairball site?

http://hairballaudio.com/docs/FET_Compressor_PCB_Board_Info_V2.pdf

No I haven't. Spot on! I don't know how I've missed it. Thanks alot.

 

[evilcat]

Does this switch works for "bypass/GR/+4" operation ?

http://fr.mouser.com/ProductDetail/Alpha-Taiwan/SR2511F-0403-19R0B-E9-S-W/?qs=yA6kp8fx8Y4NY83z79h69w%3d%3d

The ratio switch should be 2 decks but not this one for the meter, right ?

Thanks

Ben

 

[ChrioN]

That switch works

 

[evilcat]

Wow, what a quick reply, I'm still on mouser !!!
Thank you very much.

 

[ChrioN]

The push button documentation from Hairball is great, however I don't know what this means:

"blk - connects to gr bypass terminal on the bypass switch along with a signal ground"

btw, i'm wiring the attack pot switch version.

 

[phatmateo]

this is your wiring for the bypass switch.  GRN and BLK are for the on/off function.  When 22 is connected to ground(BLK), then the GR is bypassed

 

[ChrioN]

that i get. what i don't get is the "along with a signal ground" part

 

[phatmateo]

I don't have my 1176 in front of me, but I think you can just connect BLK to that terminal.  Do you have a continuity tester on your multimeter?  Make sure that BLK is connected to ground, otherwise, hook one up so that it does.  I cant remember off hand how I have it hooked up.  If you look at the schematic, you can see that the signal preamp ground and R22 are connected to that point on the GR disable switch

 

[0dbfs]

Finally got around to wiring up my dual RevA.

My problem at the moment is that when the unit compresses the signal sounds distorted. Not compressed.

If I bypass the GR it sounds nice and clean. That tells me that the signal get's through the input/output amps fine but with the GR amp section enabled the signal is distorted. That is with tone, acoustic gtr, and vocals.

I can get to the calibration point of setting the Q bias to 1db of drop but cannot get the voltage across R74 down to 0.00V. Only as low as 0.75V.

So, moving forward I have left the mater cal to the side for the moment and been focusing on getting the unit to compress as expected.

I swapped the initially installed 5088's in the GR section (Q7,8,9,10) to 3708's with hfe of about 350. That should be fine. I started out using the rotary boards included by mnats and went to a P-to-P wiring on the ratio & meter lorlin's as well as the attack/release pots. I rewired one side of my dual in this fashion last night, still had the distortion, and re-checked this AM. I expect that when I move on to sorting out the meter cal I will swap Q12&13 from 5088's to 3708's (although I did initially match the HFE in Q12/13 to 386 for one unit and 399 on the other unit according to my notes)

Whenever I scope or DMM probe around Q1 (the audio-path GR 5457) it affects the signal, so it's hard to get an accurate reading. I can however see the GR signal (pad 7) modulate with some small waveform as I increase the input pot (hairball 600 ohm T-Pad). Moving the release pot to-and-fro shows the GR signal (pad 7) move up and down. The DMM shows the pad 7 signal to change between about -0.7V to -1.1V when the release pot is moved CCW to CW. Audio signal does not appear to affect the voltage at pad-7 much (at least in that same range on the DMM).

I have spent some considerable time tracing the signals around the circuit and am coming up short on a solution.

If anyone has some pointers or additional tests that may lead down a certain path, I would love to help share the ultimate solution in this case.

Best,
jonathan

 

[0dbfs]

Ok. Sorted that problem. Wiring error!

Decided to take another detailed look at my wiring and identified that I had Pad-22 (input to the GR Ctrl Amp) fed directly from the output of the signal preamp (pad-15) instead of after the ratio network, AND that I had connected the control voltage -6V source (Pad-20) to the ratio network (where PAD 15 should have been!) instead of to the threshold network...

Seems to be compressing much more cleanly now and I can see the control signal on pad-7 behaving as expected with peaks.

Now, the secondary issue I have is to get the GR function in the meter working as expected.

I'll focus on testing both of my main boards with this current wiring implementation so that I can have a point of reference between the two units before moving on to sorting out the GR metering issues.

Thanks!

Best,
jonathan

 

[0dbfs]

I have discovered a problem in my case when powering two RevA boards (dual unit in 2RU) with the mnats stand-alone PSU board.

When I power both units (no signal passing, just sitting and doing nothing) they both start to oscillate at a low frequency and thump at the output. The 30V rail starts sagging in unison along with the thumping. The LED on the PSU board also flashes in tandem.

If I disconnect either board from the 30V rail, the thumping stops...

Not sure if I need a different PT with a higher VA rating (I think I used the 30VA Avel Lindberg trafo used by others here) or if the 30VA should suffice and I probably have a fault elsewhere. It seems to work fine with only one main-board powered by the stand-alone PSU.

Any insight is much appreciated.

Best,
jonathan