[BUILD] 1176LN Rev D DIY

[Echo North]

Just a reminder, in case you have a unit available!
FET bias is adjusted correctly, I suppose the distortion occurs because of a superimposed ripple on the control (gate) voltage.

Did somebody ever measure the distortion at 40 Hz, with a gain reduction of 4 or 5 dB?
With a bass guitar I get audible distortion, even at longer release times.
Just curious...

(In the 'off' position, - so with the signal going through the circuit-, the distortion is very low.)

I can do it, but it'll be a 1-2 weeks as our units are on loan at the moment.

Mike

Hoping to get our units back this week!

 

[bxershrts]

I just thought I would share this. I found a plastic drawer in the shop with about 40 of these " F BC27 2n5457" Fets. I felt a sense of butterflies as I presumed I came across a source of FETS that I could match for future builds. Upon measuring them - they are absolutely not the same as the ones Mike supplies (GSD) These ones , although indicating 2n5457, have a different pinout and the source and drain seem to be interchangeable (DGS) as I measure them. Provided is a picture - the right one is what is provided from Mike @ Hairball

 

[Echo North]

Not sure what those are. Lots of companies have made 5457's through the years. Though that looks like a fairchild. Also they 5457 can measure wildly differently. Which is why they need to be matched. There certainly a lot of fakes out there too.

It's important to note that the now discontinued 5457 was never used in the 1176. They used a custom part and the 5457 is just one of many options that can be used. In fact, there may be a in production FET that sounds better. Something we're exploring.

Mike

 

[bxershrts]

Thanks for your reply Mike.

As I measure these alternate 5457's - they are in the 'range' of the ones I purchased from you.  I am sitting here thinking about trying these out  and making a socket to accommodate the pinout.

This brings me to these next questions.

I measure the same at the source and drain as I flip them around.  Data I read online about older 5457's with a center gate is that they are in fact S,D interchangeable.

The Fairchild ones I have purchased from you measure vastly different when flipped. Which makes me question if I wire a socket would these even work.....

Now if they would work , and I can match a pair of these - should these be biased accordingly?

Thanks

 

[Echo North]

Thanks for your reply Mike.

As I measure these alternate 5457's - they are in the 'range' of the ones I purchased from you.  I am sitting here thinking about trying these out  and making a socket to accommodate the pinout.

This brings me to these next questions.

I measure the same at the source and drain as I flip them around.  Data I read online about older 5457's with a center gate is that they are in fact S,D interchangeable.

The Fairchild ones I have purchased from you measure vastly different when flipped. Which makes me question if I wire a socket would these even work.....

Now if they would work , and I can match a pair of these - should these be biased accordingly?

Thanks

I don't see why not. Certainly wouldn't hurt to try them as, calibrate, and see what you end up with.

Mike

 

[babaorum]

Do you get a -DC V at pad 7? Does it change when you rotate qBias?

I sent a 1000 sine signal at input and measure at pad 7 when I rotated qbias ==> no changes ...

 

[Echo North]

Do you get a -DC V at pad 7? Does it change when you rotate qBias?

I sent a 1000 sine signal at input and measure at pad 7 when I rotated qbias ==> no changes ...

Under the same conditions you see a change at PAD 18? If so you have a wiring error.

Mike

 

[RuudNL]

This morning I took a look at the schematic of the 1178.
I noticed that the timing capacitor (attack/release) in the 1178 is 1 uF instead of 0.22 uF in the 1176.
This will of course change the behaviour, and (probably) also reduce the distortion at low frequencies.
Any ideas about this?

 

[babaorum]

Do you get a -DC V at pad 7? Does it change when you rotate qBias?

I sent a 1000 sine signal at input and measure at pad 7 when I rotated qbias ==> no changes ...

Under the same conditions you see a change at PAD 18? If so you have a wiring error.

Mike

Yes ! I see changes on pad 18 ! ok I have to check the wiring.
But could you say if this is on ratio pcb or not ?

 

[babaorum]

Here is my wiring of ratio_pcb vs main_pcb and attack; release knobs :

 

[babaorum]

So I think 7 is wrong an should be at grey output of the main.
And ground of my meter is connected to wht/red instead of violet (ground) of main.

 

[babaorum]

Ok in fact my Meter / main_pcb's  wiring was completely wrong !
I fixed it and will check if I could calibrate now.

 

[babaorum]

Houra amazing , I just could adjust qbias !!!!!
I'm so happy !

But for the step 2 I can't have 0 with the meter by adjust R71, needle doesn't move.

I just changed the trimmer by another one but it's the same, needle doesn't move ...

Thanks for your help.

 

[Echo North]

Do you get a -DC V at pad 7? Does it change when you rotate qBias?

I sent a 1000 sine signal at input and measure at pad 7 when I rotated qbias ==> no changes ...

Under the same conditions you see a change at PAD 18? If so you have a wiring error.

Mike

Yes ! I see changes on pad 18 ! ok I have to check the wiring.
But could you say if this is on ratio pcb or not ?

Could be on the attack/release pots.

 

[babaorum]

It was on ratio and meter but now I try to calibrate part 2 (set 0 to needle) but it doesn't work needle doesn't move ... with R71
(qbias now calibrated after re-wiring)

 

[bxershrts]

Hello All,  I am looking for another set of eyes and another brain.

I have a problem in the GR Meter section of the build.  I have cross referenced my measurements with the provided sheet and have scratched my head for the past week.
Any ideas are appreciated.

Here is what I have :

Q11
D=21.9v  !!!!


Q12
C=    21.9
B=    -5.92
E=    -.6

Q13
C=  21.15
B=  -.008 
E=    -.57

Thanks for your ideas.

 

[babaorum]

It was on ratio and meter but now I try to calibrate part 2 (set 0 to needle) but it doesn't work needle doesn't move ... with R71
(qbias now calibrated after re-wiring)

I have tried to change the FETs but without success, R71 doesn't move the needle, do you have an idea ?

 

[Echo North]

It was on ratio and meter but now I try to calibrate part 2 (set 0 to needle) but it doesn't work needle doesn't move ... with R71
(qbias now calibrated after re-wiring)

I have tried to change the FETs but without success, R71 doesn't move the needle, do you have an idea ?

How are the voltage isn that section VS the schematic with voltages?

Mike

 

[Echo North]

Hello All,  I am looking for another set of eyes and another brain.

I have a problem in the GR Meter section of the build.  I have cross referenced my measurements with the provided sheet and have scratched my head for the past week.
Any ideas are appreciated.

Here is what I have :

Q11
D=21.9v  !!!!


Q12
C=    21.9
B=    -5.92
E=    -.6

Q13
C=  21.15
B=  -.008 
E=    -.57

Thanks for your ideas.

Check for shorts or bad resistor values.

Those are way off.

 

[bxershrts]

Good afternoon Mike and all DIY'ers

I am still scratching my head with this REV D.

checked the GR pcb no shorts(solder connections) all correct resistors.
checked the GR Meter Driver Section - Confirmed each resistor is correct and no shorts.

I am able calibrate the Q Bias
I have swing on the Null adjust and on R71 - But I still +3 volts at the end of the trimmer and the needle at +3VU

Pad 28 and 29 show high volts of +21vdc.

What is the typical volts at pad 28 and 29 with the GR PCB disconnected?

I am trying to find other avenues to look down for build errors based on what I have.

Any hunches or thoughts would be appreciated.