PCBs for 1176-flavoured FET compressor w/ opamps - (almost) no wiring

[Ricardus]

Yes, attached 

The boards are still available. See the first post in this thread or email me at fripholm [AT] gmail [DOT] com for details on how to order.

I will definitely be in touch.

 

[Catrunes]

Yes, attached 

Thank you!
ill post some pics next week when i have time, but i'll be finishing mine tomorrow in time to use on jim bruer as a test. ha 

 

[pstcho]

Hello, guys, is there any help thread about this project ?  cant find so far

 

[TillM]

Hello, guys, is there any help thread about this project ?  cant find so far

This is the help thread ! 

 

[pstcho]

Alright, thanks for your fast answer

i received all the components this week and build it, as carefull as i could, when i fired up, i got a perfect sound controlled with input and output potentiometers, but no compression whatsoever, also i have all the leds ON, like if the compression was full full all the time, no change in by pass or without sound

any place i should check out where i must have F***ed up ?

 

[TillM]

Alright, thanks for your fast answer

i received all the components this week and build it, as carefull as i could, when i fired up, i got a perfect sound controlled with input and output potentiometers, but no compression whatsoever, also i have all the leds ON, like if the compression was full full all the time, no change in by pass or without sound

any place i should check out where i must have F***ed up ?

First: did you calibrate the unit ?

 

[pstcho]

i read -8.5V on the resistor R48 and if i turn the Qbias i can see the voltage go untill 0 if i go full but no difference in the sound

i replaced all transistors and op amp ( in case ) but no difference

if i remove Q3 the sound is great but way too loud ( removed it while the unit was powered, i forgot to close it )

the vu meter can be calibrated , i can change the gr nul and scale as i want, but i see no signal going there

 

[fripholm]

if i remove Q3 the sound is great but way too loud ( removed it while the unit was powered, i forgot to close it )

If you remove Q3 and the sound gets a lot louder, your JFET is biased so that it's already attenuating a lot. Readjust QBIAS until the volume drops just ~1dB. The input level needs to be very low when you do this - you don't want the unit to compress the signal. Re-read page 7 in the guide.

What type of JFET are you using?

 

[pstcho]

Qbias doesn't do anything to the sound

i tried J111 J112 2n5457 and bf245a ( that i had from other 1176 i made )

i suspected at first that the transistors were jammed, but all of them its a bit awkward

also no difference if i switch from bypass to compression

 

[fripholm]

Did you check the pinout of your FETs? The silkscreen on the board (D-S-G from top to bottom) is for J11x and similar types.

When inserted correctly, does the voltage at the FET gate change when you adjust QBIAS?

 

[pstcho]

For what Ive checked the pinout was ok for the j111 j112 and 2n5457, the ba were reversed

About the voltage I'll check tomorrow

 

[pstcho]

hello, gate is at 0 and stays at 0V  ( we talk about Q3 right ? )

qbias voltage varies at c37 till the 2 diodes D1 and D2, at the other side of those diodes there's no more voltage

 

[fripholm]

hello, gate is at 0 and stays at 0V  ( we talk about Q3 right ? )

qbias voltage varies at c37 till the 2 diodes D1 and D2, at the other side of those diodes there's no more voltage

Is your 'Slam' switch enabled when you try this? For calibration it needs to be turned off.

 

[pstcho]

ive made some tests at night, and it feels like the compression is huge all the time, even in bypass, even when i remove the slam switch or the ratio board

i cant find any short circuit anywhere

must have a wrong resistor somewhere i guess

 

[fripholm]

Don't remove the ratio board when calibrating as there are components on it which are necessary for correct biasing.

It's not the compression that's 'huge' - your FET is in full conduction (which results in a huge level drop) because the gate is at zero volts. It has to be negative (with respect to the source). The actual voltage depends on the FET your using.

 

[pstcho]

yeah i noticed the bias goes through the ratio board, but i needed to try maybe a short was on the board

im still trying to find out whats the path of the bias signal on the pcb, ill find it ( one day i guess )

could be the slam switch that is wrong

when i apply signal straight at Q5 the vu meter works properly

 

[fripholm]

could be the slam switch that is wrong

The SLAM switch just shorts out a couple of points (the same way as pressing all buttons on a real 1176 ratio knob assembly does). It shouldn't do anything at all when it's not pressed.

Do you have resistor R69 installed?

 

[pstcho]

yeah i do

when installed i mesure 124K

Colors are Brown Grey Green Gold, 1.8M

 

[fripholm]

yeah i do

when installed i mesure 124K

Colors are Brown Grey Green Gold, 1.8M

Huh?! 

When the SLAM switch is NOT pressed down, R69 is shorted out and should read zero Ohms. It's only in circuit when SLAM is enabled. In this case your value would make sense as it's in parallel with some other stuff around it.

 

[pstcho]

yeah when slamm is pressed, i have it at 0