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

[Echo North]

When I adjust the Q bias, the voltage does not move until I'm over half way. Then it's extremely touchie. Very hard to get 2.44 exactly. Is this a bad VR?

No, It's a touchy adjustment. Get it as close as you can. That sounds right.

 

[musicaudioworks]

Well when I turn the attack on, I still don't see the 10db drop. The output voltage stays the same as does the VU meter. The input control does not drop the voltage when increased.

 

[Echo North]

Does the trimmer on the front (R71) do anything when turned?
You were able to set the NULL?
You're getting a 10dB drop at the output?


Hey mike,

Thanks for getting back to me!

Yes yes and yes. All VR pots work. Null adjust moves the needle as expected.

Just went threw and calibrated it from scratch.

The VU shows no gain reduction when the input is increased with the attack and release full CW with 20:1 ratio and GR button depressed.

Could it be a short in a switch?

- If you're getting 10 db of GR, then the sidechain should be ok.

- If you we're able to NULL the meter, your transistors should be matched.

Start with the tracking adjust centered and set your unit to have 10dB of gain reduction on the output. With the unit in GR OFF (10dB on the output) trim the R71 zero adjust to 0 on the meter. Then switch to GR ON (0dB on the output) and adjust the tracking for -10.

Where does this go wrong for you?

Mike

 

[Echo North]

Well when I turn the attack on, I still don't see the 10db drop. The output voltage stays the same as does the VU meter. The input control does not drop the voltage when increased.

Then you have a sidechain (GR AMP) error.

Hold on one sec...

 

[Echo North]

A question about cleaning the solder side of the PCB on the FET rack. I've used 91% isopropyl alcohol, as well as tried some commercial flux cleaner spray.
I'm trying not to slather the stuff on. Just applying it with a Qtip or soft toothbrush and scrubbing.

They both seem to leave a filmy (slightly tacky?) residue behind. (as opposed to the more glossy, smooth top surface).

A. Is this normal?
B. Will this affect anything?

Is there a better way to clean it?

thanks
Carlos

Soak the bottom.

Hold it at a 90 degree angle to the sink and drench the bottom of the PCB so the cleaner runs off (keep the output transformer dry).

Scrub as it runs off. Let it sit and evaporate.

Mike

 

[Echo North]

musicaudioworks:

Set your unit to:
Input: 12 O’Clock
Output: 12 O’Clock
Attack: GR ON (Full CW)
Release: Full CW
Ratio: 20:1
Meter: GR
Signal: Sine 1kHz @ 0dBu

1. Using chassis as your ground reference, what is your AC V at TP22 for all 4 ratio settings.
2. Using chassis as your ground reference, what is your DC V at TP21 for all 4 ratio settings.

Mike

 

[musicaudioworks]

Then you have a sidechain (GR AMP) error.

Hold on one sec...

It must be. When the input is turned up, the VU meter does not move. It should obviously show db drop when the input is increased in GR mode.

I triple checked the components. Everything is correct. Solder joints look good.

 

[Echo North]

With GR Active you should see AC voltage.  Very small at 4:1 and larger at 20:1.

Check all of your ratio PCB solder points and the relay on the main PCB.  Also check the solder points for the Ratio to Main PCB connector.

Do that first.

If you still have nothing @ 22 ....then see what you AC is on either side of R78 with all of the same signal and control conditions as before....make sure GR is ON.

Mike

 

[csavetman]

Soak the bottom.

Hold it at a 90 degree angle to the sink and drench the bottom of the PCB so the cleaner runs off (keep the output transformer dry).

Scrub as it runs off. Let it sit and evaporate.

Mike

Thanks Mike. Just to clarify, you mean drench the bottom with CLEANER, (alcohol or the flux cleaner spray),  NOT WATER to rinse off the cleaner. Right?

Carlos

 

[Echo North]

Thanks Mike. Just to clarify, you mean drench the bottom with CLEANER, (alcohol or the flux cleaner spray),  NOT WATER to rinse off the cleaner. Right?

Carlos

I've always drenched with isopropyl alcohol.  If you have something more intense you might want to read its label.

 

[musicaudioworks]

With GR Active you should see AC voltage.  Very small at 4:1 and larger at 20:1.

Check all of your ratio PCB solder points and the relay on the main PCB.  Also check the solder points for the Ratio to Main PCB connector.

Do that first.

If you still have nothing @ 22 ....then see what you AC is on either side of R78 with all of the same signal and control conditions as before....make sure GR is ON.

Mike

Figured it out! Working. Sounds amazing!  Thanks for your help. Feel better!

 

[Echo North]

Figured it out! Working. Sounds amazing!  Thanks for your help. Feel better!

Whoop!

Thanks, I'm going to go to bed for like 30 hours.

 

[csavetman]

I've always drenched with isopropyl alcohol.  If you have something more intense you might want to read its label.

Thanks Mike.
Sorry to be thick on this...last thing.  I shouldn't use water to rinse off the alcohol right? Just straight alcohol and let it dry?

thanks
Carlos

 

[Echo North]

Thanks Mike.
Sorry to be thick on this...last thing.  I shouldn't use water to rinse off the alcohol right? Just straight alcohol and let it dry?

thanks
Carlos

No water,  alcohol is a volatile liquid.  It'll evaporate in seconds.  Water will just sit on there.

 

[mrbobbailey]

Greetings.

I'm confirming that the resistors at R210 and R211 on the Active Link are 10R and not 10k.  Unfortunately I received (2)10k.

Thanks

 

[Echo North]

Greetings.

I'm confirming that the resistors at R210 and R211 on the Active Link are 10R and not 10k.  Unfortunately I received (2)10k.

Thanks

There are 2 10Ω and 2 10K resistors on the PCB.  Official BOM:

http://mnats.net/files/fetrack/fet_rack_link_doc_v1.2.pdf

Mike

 

[Einestad]

What PCB version do you have?  1.11? Is your trim pot short and square?

The PCB you provided, the trim pots are like the ones in your build guide for the latest version of the rev d (short and square) But the question remains, is there something wrong with the trimmer pads on the pcb? Considering that the build guide says the trimmers should fit easily and two of them does. Its the bottom left holes in two of the slots that are plugged, so could i perhaps use a needle two enlarge them or should i use the other pads on those trimmer slots?

Thanks!

 

[Echo North]

The PCB you provided, the trim pots are like the ones in your build guide for the latest version of the rev d (short and square) But the question remains, is there something wrong with the trimmer pads on the pcb? Considering that the build guide says the trimmers should fit easily and two of them does. Its the bottom left holes in two of the slots that are plugged, so could i perhaps use a needle two enlarge them or should i use the other pads on those trimmer slots?

Thanks!

I'm not sure what you mean.  You have pads that are filled with solder?  Can you post an image here?

 

[Diamondj421]

I'm pretty sick right now so I can't do comparative tests on this end today.

That's about a 3dBu difference and might have more to do with input/output pot tolerance. I can't remember if the pots are 10% or 20% but that can account for that.

Try adjusting one input so you have the same voltage at TP1. See if you're output is within a dB now. How much did you have to adjust it? Like a half dot or less? if so then that's just pot tolerance. Try just adjusting the output how far do you need to adjust that one keeping the inputs matched?

Because of all the tolerances in the unit every unit is going to be a little different. 

Also before doing that make sure the input and the output skirt line on each unit lines up perfectly with "0" on the scale.

3dB seems a bit high, but confirm those pots are lined up and adjust the input (and output) a little to get them to match. See how far you have to adjust the knobs.

Whenever you use a pair on something there is always a little trimming to be done. It's 60's analog gear.

Mike

Hope you're feeling better!
I had to turn the older units input up about 2/3 of the way from 24 and the next dot (22 since each dot is 3 units). 
Older unit: 6.63VAC
Newer unit: 9.98VAC

With the inputs matched, I had to turn the output of the older unit up to what would be 17 (1/3 between 18 and the next dot)

Let me know what you think!

 

[csavetman]

Hey Mike,

Just a small discrepancy I noticed in the FET Rack build guide. In the assembly section, the third photo shows the ratio card installed with one orientation (switches solder tabs facing out), then a little later on, it shows it differently (switches solder tabs facing in towards the meter card).

I was having a little issue with getting the ratio buttons to center themselves properly in the panel, then I noticed the latter picture, flipped the card and voila!

Just figured you might want to know, in case anyone else has a little difficulty.

Carlos