Retired:Symmetrical FET

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gt_jumper said:
Can i use n4007 in the place of Z10? I have a large bag of N4007s.

I am not really sure when the 10V breakdown voltage becomes relevant (22dBu?), so it could be interesting to hear from someone smarter than me.

I would use the zener :)

Gustav
 
Thanks for the answer.

This should do the trick yes?
http://au.rs-online.com/web/p/zener-diodes/0812465/
 
Just finished mine up. No dramas at all. Pleasure to build, thanks Gustav! Sounds excellent. I've owned a number of 1178's in my life and this is definitely made of the same stuff :)

Here's a couple of pics:

1_BIG.jpg


2_BIG.jpg


3_BIG.jpg



 
Nick Franklin said:
Just finished mine up. No dramas at all. Pleasure to build, thanks Gustav! Sounds excellent. I've owned a number of 1178's in my life and this is definitely made of the same stuff :)

Here's a couple of pics:

1_BIG.jpg


2_BIG.jpg


3_BIG.jpg

That build is insanely good looking...

What did you use for the FET?

Gustav
 
Gustav said:
Thanks G!

I used an NE5566!

Nick.



Nick Franklin said:
Just finished mine up. No dramas at all. Pleasure to build, thanks Gustav! Sounds excellent. I've owned a number of 1178's in my life and this is definitely made of the same stuff :)

Here's a couple of pics:

That build is insanely good looking...

What did you use for the FET?

Gustav
 
Even mine was finished today, and after days and weeks of Amateur mistakes, torture as well as half a dozen flashing 4R3, I finally did it. Thanks again for all your support  8)

I really learned a lot with this project.

 
Today with further calibration I realised a strange behavior. The balance even of the uncompressed signal changes, when I move the output knob and especially the release knob.

Lets say I have a kick and a snare. When turning the release knob from slow to fast (CW) the balance changes as if the slightly right panned snare walks to the left. And even worse, if I put the release knob to its maximum, the output volume is increasing about 8dbfs and the unbalance changes completely to the other side. Should that be in bypass?

Any ideas?
 
So, now changed ic's, incl npd5566.

The imbalance still there, but no shifting from left to right. The meters shows the balance difference  as well as the bars in the daw.

The difference changes by changung input/output volume, which indicates that the npd5566 should work as  expected.

Could this be a calibration problem? May I should rewire the pots, cause I used Molex for the connections.

May there is always an imbalance?

Beside that, the compressor seems to work fine and can make a bass track really growl if pushed into the red.
 
It's impossible to achieve 100% complete tracking  - but something like 1dB tracking up to 15dB GR should be within reach.

What are your differences, at what settings?

Jakob E.
 
Hello Jakob,

it doesn't matter at which settings. After calibration as Gustav describes it on the Website for the 1176, I have a really good stereo tracking. As soon as I change the threshhold via input, the imbalance appears.

I recently realized, that I used 20% tolerance trimmer for the qbias. May this could be the source of evil?  Thanks!
 
mike76 said:
Hello Jakob,

it doesn't matter at which settings. After calibration as Gustav describes it on the Website for the 1176, I have a really good stereo tracking. As soon as I change the threshhold via input, the imbalance appears.

I recently realized, that I used 20% tolerance trimmer for the qbias. May this could be the source of evil?  Thanks!

Mike - remember that the "calibration" I have in 4 steps without metering on my site for the Phat FET is not at all accurate. I feel its not overly critical on he 1176, but for this fellow´, digging out the manual and doing the calibration properly will yield much better results.

I also have a feeling some things could be improved with this design, based on feedback, but I am sort of sidestepping upgrading this project with a different take on a new unit I am working on with much more control and a basic DIY circuit that has been proven to be accurate. (I took the 1178 direct from schematic, not proven or tested in DIY).

Gustav
 
Gustav said:
(I took the 1178 direct from schematic, ...
There is no/nada/niente zener diode in the 1178 (IIRC the Urei house numbers Y10 were 1N914 or 1N4148).
Your 10V zeners at the audio rectifier might cause unexpected behaviour when driven harder.
As always YMMV.
 
Okay, thanks for your words,

I read the 1178 manual several times, got confused with dbm, dbu, Vrms, etc.

I send an testtone from cubase -18dbfs (my converters should be at this level) and set the meters to +1. Then GR mode, bypass off, Ratio 20:1, Release full cw. Then set the Qbias to 0db on the meters.

But the problem is: there is even an imbalande in bypass mode, and even without the npd5566 installed,  If I turn the Input volume up, the difference sometimes getting more (about 5db), sometimes less, varying no matter how much I turned the volume up. Two the same settings vary after turning the pot upside down.

I think, that can't have to do anything with the compression circuit, there has to be something in the input. When I turn up the output volume, the differenve stays pretty much the same without the GR activated.

I think, there should be something else, don't know if it is the pot that I've soldered with wires and molex.

I will check this first, when I got time. But I have to say, that I'm a bit frustrated  :mad:  Just want it to get working, it must not  be perfect. The other builders seemed to get it working almost properly. So much time and afford; I do not count the money anymore.

May I have to look for someone who has got more skills and knowledge.
 
Okay,

after testing several pots I came to the conclusion, that it is not in the circuit at all.

The pots shows more or less different values in each channel even without beeing connected. When I want to turn the axis, and I am at the point short before turning, differences in the balance appears when connected. slighlty touching the pots is enough to imbalance the sound. So far, so good.

This should be a mechanical problem with the omeg pots. 

But now I got another problem in one chanel. It is "popping" and distorting on higher volume to the rhythm of the bassdrum. I carefully knocked with the back of my skrewdriver on the pcb to see, if anything isnt proper soldered.

May this could be a transisitor or a cap?

getting closer :)
 
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