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

[Spanzor]

I've reached at the step where I calibrate my unit.  It powers on, passes signal, and overall tone sounds really good on the vocal I have it inserted on.  On to calibration.   


It's a Blue Stripe.

PSU tested and working perfectly.  When I calibrate it, the output knob hitting the 11dBu mark seems extraordinarily low for the knob, down near the bottom of the range.  My Q bias adjustment is probably 20% from all the way counterclockwise.  Upon adjusting the R75 null pot together the trim pot on the front, my meter sits nicely at 0 and everything is good up to this point. 

Upon adjusting for the meter tracking, I begin to notice an issue.  My output knob reaches .775VAC, which is near "48" on the output markings (very low).  When I use the input pot to try and trim the output up to 2.44VAC, I run out of room.  The pot is maxed out around 1.659VAC.

Another thing I notice, which may be related, is that the two lower ratios don't seem to be showing compression on the VU meter.  The top two ratios show significant reduction just with the test tone, but the lower two I can't get the move.  I have metered every single one of the risistors on the ratio board and they all reflect what the schematic shows they should be.

Thanks for the help!

Spencer

 

[Echo North]

I've reached at the step where I calibrate my unit.  It powers on, passes signal, and overall tone sounds really good on the vocal I have it inserted on.  On to calibration.   


It's a Blue Stripe.

PSU tested and working perfectly.  When I calibrate it, the output knob hitting the 11dBu mark seems extraordinarily low for the knob, down near the bottom of the range.  My Q bias adjustment is probably 20% from all the way counterclockwise.  Upon adjusting the R75 null pot together the trim pot on the front, my meter sits nicely at 0 and everything is good up to this point. 

Upon adjusting for the meter tracking, I begin to notice an issue.  My output knob reaches .775VAC, which is near "48" on the output markings (very low).  When I use the input pot to try and trim the output up to 2.44VAC, I run out of room.  The pot is maxed out around 1.659VAC.

Another thing I notice, which may be related, is that the two lower ratios don't seem to be showing compression on the VU meter.  The top two ratios show significant reduction just with the test tone, but the lower two I can't get the move.  I have metered every single one of the risistors on the ratio board and they all reflect what the schematic shows they should be.

Thanks for the help!

Spencer

Start with the TP21/22 test as shown below.

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

 

[Jacob123588]

Your signal is dying  between TP1 and TP15.

This stuff is in the box labeled "Signal Preamp" in the lower corner. Check all of your components and soldering there including the output pot soldering.

Mike

Hey Mike, So after fixing a few solder points, I get tone through the compressor and musch high through the output. now my readings are as followed

-Input XLR + -- 0.775
- TP1 -- 0.150
- TP15 -- 4.29
- TP17 -- 0.813
- Output Transformer BRN -- 0.156
- Output XLR -- 0..285

now a new problem has come up, the output knob changes volume ok until 12 o'clock, from then on it jumps in volume up and down and wile turning the knob from -48 to 0 the tone changes quite a bit and at various random points. it also seems to take a second to "settle into" a volume position. sorry I'm a bit late following up this has made me want to bang my head against a wall hahaha thanks!

 

[Echo North]

Hey Mike, So after fixing a few solder points, I get tone through the compressor and musch high through the output. now my readings are as followed

-Input XLR + -- 0.775
- TP1 -- 0.150
- TP15 -- 4.29
- TP17 -- 0.813
- Output Transformer BRN -- 0.156
- Output XLR -- 0..285

now a new problem has come up, the output knob changes volume ok until 12 o'clock, from then on it jumps in volume up and down and wile turning the knob from -48 to 0 the tone changes quite a bit and at various random points. it also seems to take a second to "settle into" a volume position. sorry I'm a bit late following up this has made me want to bang my head against a wall hahaha thanks!

You've got an error somewhere in your "Signal Line Amp" section. It's labeled on the PCB.

Check all joints, all components.

Mike

 

[Diamondj421]

Hey Mike,
Got the FETs already. You're the man! So these are replacing q1 and q11, correct? Thanks again!

 

[Echo North]

Hey Mike,
Got the FETs already. You're the man! So these are replacing q1 and q11, correct? Thanks again!

yes

 

[rubberband]

Hello<

I completed my REV A Version 1.14 last night and had the following issue:

When calibrating the Q Bias, the AC voltage between (out +) and (out -) was  0 .391 with the setup configuration as published:

Input = "24" mid rotation
Output = "24" mid rotation
Attack = full CCW (switched to off position)
Release = full CW
Compression ratio = 20:1
Meter mode = "GR"
Q-bias adjustment = full CW (Higest Output)

With the output full clockwise, AC voltage measures 2.43, at full counter clockwise it is 0.0

AC voltage at test pad (1) (with output full clockwise) 0.136, Test pad (15)  0.192, Test pad (17)  0.030.

everything in the preamp section is in order: re-folwed joints, all correct resistors etc.

could this be a problem with Q1 FET?
Ideas?

Thanks!!!

 

[Spanzor]

Start with the TP21/22 test as shown below.

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

Thanks Mike,

My test points read as follows:

TP22 at ratios 20,12,8,4, respectively

2.21, 2.04, 1.525, 0.733, all measurements in AC

TP21 at ratios 20,12,8,4, respectively

-5.87, -3.23, -2.4, -1.57, all measurements DC


Best,

Spencer

 

[bcwiz]

Hi Richard,

One difference between your FET/RACK and a vintage unit...the input pot (t-pad attenuator) on the original units had a very odd taper. It’s not a taper you commonly see in potentiometers today. Your input attenuator has a more common taper, which leads it to be a little “hotter” earlier in the clockwise pot turn. Even compared to out old blue T-pad.

That said 7 o'clock seems low.  I suspect it's a combination of the hot input pot and our meter having a little more over shoot than the originals.  They have $150 meter in them, we decided not to go that route.  We feel like out meter is 90% as good at a fraction of the cost.

The meter should be a little more accurate in the full CW position and should show you less compression. Hard to say what is right because I don't know what your input level is compared to ours.

Mike

Mike

Can I replace the Hairball Rev A input attenuator with an original 1176 600 ohm t-pad? I prefer that taper to the more common standard.

 

[Echo North]

Can I replace the Hairball Rev A input attenuator with an original 1176 600 ohm t-pad? I prefer that taper to the more common standard.

Absolutely.

 

[Echo North]

Hello<

I completed my REV A Version 1.14 last night and had the following issue:

When calibrating the Q Bias, the AC voltage between (out +) and (out -) was  0 .391 with the setup configuration as published:

Input = "24" mid rotation
Output = "24" mid rotation
Attack = full CCW (switched to off position)
Release = full CW
Compression ratio = 20:1
Meter mode = "GR"
Q-bias adjustment = full CW (Higest Output)

With the output full clockwise, AC voltage measures 2.43, at full counter clockwise it is 0.0

AC voltage at test pad (1) (with output full clockwise) 0.136, Test pad (15)  0.192, Test pad (17)  0.030.

everything in the preamp section is in order: re-folwed joints, all correct resistors etc.

could this be a problem with Q1 FET?
Ideas?

Thanks!!!

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

With your DMM measure your AC at the following test points using the chassis as you reference (black probe).

-Input XLR +
-TP1
-TP15
-TP17
-Output Transformer BRN
-Output XLR +

 

[Echo North]

Thanks Mike,

My test points read as follows:

TP22 at ratios 20,12,8,4, respectively

2.21, 2.04, 1.525, 0.733, all measurements in AC

TP21 at ratios 20,12,8,4, respectively

-5.87, -3.23, -2.4, -1.57, all measurements DC


Best,

Spencer

Pad 22 seems really high.  Check all the resistors on the ratio PCB.  Make sure you don't have a 47K swapped with a 4.7K or something.

Mike

 

[rubberband]

Hi Mike:

The AC is a s follows:


-Input XLR +  0.385
-TP1                  0 .184
-TP15                2.016
-TP17                0.313
-Output Transformer BRN  5.073
-Output XLR +                              4.861

 

[Echo North]

Hi Mike:

The AC is a s follows:


-Input XLR +  0.385
-TP1                  0 .184
-TP15                2.016
-TP17                0.313
-Output Transformer BRN  5.073
-Output XLR +                              4.861

That seems normal.

What's your AC between out + and out - under those same conditions?

Mike

 

[rubberband]

That seems normal.

What's your AC between out + and out - under those same conditions?

Mike

Mike,

I put a load on the output and got 8.5 VAC. The unit then calibrated normally.

In running some material through it, It is too hot on the input, understanding the taper issue with the potentiometer. With a vocal track, I couldn't get it to the first dot before 20 db of compression, on other lower amplitude material of bass and acoustic guitar I am having the same issue. Essentially it is either on or off with the full range of input between full CCW to 48.

Thanks !

 

[Spanzor]

Pad 22 seems really high.  Check all the resistors on the ratio PCB.  Make sure you don't have a 47K swapped with a 4.7K or something.

Mike

Thanks Mike-

These seem okay, biggest discrepancies I could find on the ratio board were R63 metering at 1.23k ohms instead of 1.5k, and R64 metering 1.62k instead of 2.2k.  I checked these against similar values on the main PCB to make sure nothing was switched around and it seems like they're okay.  Let me know if you think I should get a few resistors closer to 2.2k for R64 and I can drop that in, or if it's something different.  Really appreciate your help man!!

Best,
Spencer

 

[Echo North]

Mike,

I put a load on the output and got 8.5 VAC. The unit then calibrated normally.

In running some material through it, It is too hot on the input, understanding the taper issue with the potentiometer. With a vocal track, I couldn't get it to the first dot before 20 db of compression, on other lower amplitude material of bass and acoustic guitar I am having the same issue. Essentially it is either on or off with the full range of input between full CCW to 48.

Thanks !

Sounds like your source material might be too loud.  The input is a 40db attenuator.  It it's having problems attenuating in the normal range, my guess is that the the source needs to be turned down.

Also if your release is slower, the meter will kind of bottom out and never make it back.

Mike

 

[Echo North]

Thanks Mike-

These seem okay, biggest discrepancies I could find on the ratio board were R63 metering at 1.23k ohms instead of 1.5k, and R64 metering 1.62k instead of 2.2k.  I checked these against similar values on the main PCB to make sure nothing was switched around and it seems like they're okay.  Let me know if you think I should get a few resistors closer to 2.2k for R64 and I can drop that in, or if it's something different.  Really appreciate your help man!!

Best,
Spencer

If you're measuring them in circuit, often the value will be lower than you expect. This is because the resistors are in parallel with other components in the circuit.

 

[Echo North]

Thanks Mike-

These seem okay, biggest discrepancies I could find on the ratio board were R63 metering at 1.23k ohms instead of 1.5k, and R64 metering 1.62k instead of 2.2k.  I checked these against similar values on the main PCB to make sure nothing was switched around and it seems like they're okay.  Let me know if you think I should get a few resistors closer to 2.2k for R64 and I can drop that in, or if it's something different.  Really appreciate your help man!!

Best,
Spencer

Your Qbias went fine right?

Try the same test as Rubberband above.

Mike

 

[MeesterZee]

Hi all, finally got my build completed and calibrated. Everything is sounding great.

However, I'm having some trouble with the knobs not sitting flush to the face. I have large gaps of different widths. It seems that some of the pots have a longer shaft that others, preventing the knobs from sitting closer. After spending so many hours on the internal build, I want the outside to look clean too! Any solutions?

Pics here:
http://i.imgur.com/mLtbrhN.jpg
http://i.imgur.com/RR55QDn.jpg

Thanks!