[BUILD] New FET/RACK Official Help Thread - Please read first post!

[jgremlin]

Anode of CR2 is AC.  Are you measuring DC there?

Ok that might explain something then. I measured DC because when I measured AC, I got essentially zero (like 0.001mv) for all ratios.

 

[Echo North]

Is this with GR ON?  With GR ON and the test setup in the trouble shooting guide, you should see that AC there as noted, if not you have an issue in your GR AMP.

With GR OFF you should see no AC.

Mike

 

[jgremlin]

Found it. I went over the GR amp section again. My Mr Magoo (TM) brand eyeballs didn't see it the first time but the Q8 base and collector legs were cut a bit high and were bent enough to touch. Trimmed the legs down and resoldered and everything calibrated as it should. Thanks for the help!

 

[Echo North]

Found it. I went over the GR amp section again. My Mr Magoo (TM) brand eyeballs didn't see it the first time but the Q8 base and collector legs were cut a bit high and were bent enough to touch. Trimmed the legs down and resoldered and everything calibrated as it should. Thanks for the help!

Awesome!

 

[Sinkia]

Hi Mike !
I have ordered a RevA 2 weeks ago. It arrived last week and was build within the next 48h!
I have now the comp fully working and calibrated, but I think I might have an issue..

We (me and an other engineer with whom I'm working) found the input really hot... like to compress "how it should be" we need to put the Input Knob at 7h..

Is it a bad calibration or it can come from somewhere else?
Many thanks in advance !

 

[alex_dempsey]

Ya that's way too much voltage. If you have a Rev A, you need something like -1.00 VDC at one side of the trimmer and -1.75VDC at the other side. You'll never get compression with what you're seeing.

Stuff to check:

C21 oriented correctly
CR2 and CR3 oriented correctly
C19 and C20 oriented correctly
All resistor values and soldering on the ratio pcb
Resistors and caps on the attack/release PCB
R60/R83 values/soldering and the QBias trimmer.

Mike

Thanks for the help. On resistor R60 I measured about 360R instead of 680R like its supposed to be. I assumed that was the problem and requested the replacement part. I put it in absolutely positive that it was a 680R resistor but once in the circuit, it still reads about 360R. What could be causing this? I also just found that R76 is reading about 4K instead of 18K like it should. What am I missing?

Alex Dempsey

 

[Echo North]

Hi Mike !
I have ordered a RevA 2 weeks ago. It arrived last week and was build within the next 48h!
I have now the comp fully working and calibrated, but I think I might have an issue..

We (me and an other engineer with whom I'm working) found the input really hot... like to compress "how it should be" we need to put the Input Knob at 7h..

Is it a bad calibration or it can come from somewhere else?
Many thanks in advance !

It's a combination of the Rev A being REALLY hot by design, the natural analog meter overshoot, and the original t-pad being very hard (impossible) to mimic.

You can lower the amount of signal you send to it, or in about 1 week we are going to be posting a mod to also adjust that issue.  Basically you increase the value of R78, R19, R20, R21 to lower the amount of signal entering the side chain. Increase them all by about 5-10 x their current value to your taste.

Mike

 

[Echo North]

Thanks for the help. On resistor R60 I measured about 360R instead of 680R like its supposed to be. I assumed that was the problem and requested the replacement part. I put it in absolutely positive that it was a 680R resistor but once in the circuit, it still reads about 360R. What could be causing this? I also just found that R76 is reading about 4K instead of 18K like it should. What am I missing?

Alex Dempsey

Those resistors are in parallel with other components so you have to mathematically consider everything interacting with it.  You need to lift one leg of the resistor off the PCB to accurately measure it.

 

[alex_dempsey]

Those resistors are in parallel with other components so you have to mathematically consider everything interacting with it.  You need to lift one leg of the resistor off the PCB to accurately measure it.

Ah that makes sense. I've now gone through a bunch of other trouble shooting and found some other things I can quite explain or don't understand. I retested the power supply first and I'm reading about 50VDC instead of 30VDC like I got the first time. I can't find anything plugged in incorrectly that might cause that. Obviously if I'm running 50V through the circuit, it doesn't matter if the trim pot works or not cause I'll be blowing way too much voltage through it. What could be causing that to change to 50V?

 

[Echo North]

Ah that makes sense. I've now gone through a bunch of other trouble shooting and found some other things I can quite explain or don't understand. I retested the power supply first and I'm reading about 50VDC instead of 30VDC like I got the first time. I can't find anything plugged in incorrectly that might cause that. Obviously if I'm running 50V through the circuit, it doesn't matter if the trim pot works or not cause I'll be blowing way too much voltage through it. What could be causing that to change to 50V?

Hmmmm, maybe a measurement error or improper grounding (check all those L Brackets).

 

[alex_dempsey]

Hmmmm, maybe a measurement error or improper grounding (check all those L Brackets).

What am I looking for with the L brackets? They all measure nothing against ground.

 

[Echo North]

What am I looking for with the L brackets? They all measure nothing against ground.

Are they all screwed into the PCB and Chassis?  At least one is how your chassis get's grounded to the circuit.

Mike

 

[Sinkia]

It's a combination of the Rev A being REALLY hot by design, the natural analog meter overshoot, and the original t-pad being very hard (impossible) to mimic.

You can lower the amount of signal you send to it, or in about 1 week we are going to be posting a mod to also adjust that issue.  Basically you increase the value of R78, R19, R20, R21 to lower the around of signal entering the side chain. Increase them all by about 5-10 x their current value to your taste.

Mike

Damn ! I guess I'll just wait for the mod !

Is it gonna be something to get from you @ Hairball, or we will be able to just buy the part at our locals seller (I'm only concern of the shipping time to France !)

BUT ! the sound of the unit is so ******* great ! I love it !!!
Only concern about this HOT HOT HOT input  8)

 

[Echo North]

Damn ! I guess I'll just wait for the mod !

Is it gonna be something to get from you @ Hairball, or we will be able to just buy the part at our locals seller (I'm only concern of the shipping time to France !)

BUT ! the sound of the unit is so f**king great ! I love it !!!
Only concern about this HOT HOT HOT input  8)

Just changing those 4 resistor values. I'm sure you can find them locally.

 

[alex_dempsey]

Are they all screwed into the PCB and Chassis?  At least one is how your chassis get's grounded to the circuit.

Mike

They all seem to be attached and tight to the chassis.

 

[Echo North]

They all seem to be attached and tight to the chassis.

With the power off.  Check that you have continuity between the chassis and middle pad of the 5 pin connector where the power transformer connects to the main PCB.

 

[rubberband]

Damn ! I guess I'll just wait for the mod !

Is it gonna be something to get from you @ Hairball, or we will be able to just buy the part at our locals seller (I'm only concern of the shipping time to France !)

BUT ! the sound of the unit is so f**king great ! I love it !!!
Only concern about this HOT HOT HOT input  8)

Hey Mike:

Do you have some suggested resistors that have worked well in testing for those spots? R020-021 @56K R019@ 68K  and R078@ 47K. To be clear, for example R078 would be replaced by a 470K.

Thanks! Love the unit, but usually have to clip gain down way too much to get it in the spot I like.

 

[Echo North]

Hey Mike:

Do you have some suggested resistors that have worked well in testing for those spots? R020-021 @56K R019@ 68K  and R078@ 47K. To be clear, for example R078 would be replaced by a 470K.

Thanks! Love the unit, but usually have to clip gain down way too much to get it in the spot I like.

Still trying to get time. However, I think if you increase those 4 resistors by 10x you'll get what you want. So 56K change to 560K and so on. Just like you said.

Report back!

Mike

 

[Sinkia]

Still trying to get time. However, I think if you increase those 4 resistors by 10x you'll get what you want. So 56K change to 560K and so on. Just like you said.

Report back!

Mike

I havn't switch mine yet ! If you do it i'm interested in the report as well  8)

 

[alex_dempsey]

Are they all screwed into the PCB and Chassis?  At least one is how your chassis get's grounded to the circuit.

Mike

So I checked all of the L brackets and they seem to be all tight and good to go. I rechecked all the grounding points and I think I fixed an issue because now I am reading the correct 30VDC from the chassis to CR8. But now I'm only reading a couple of millivolts from the chassis to CR9. What could be causing that?