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

[Diamondj421]

Surely a bad component value or bad solder joint somewhere. Start be determining if the difference is in the amp stages or the sidechain.  Is there a level difference between the two units if both are in GR OFF and the in/outs are set the same?

Mike

Wow. Yea. The newest one is way louder in GR OFF.

 

[Echo North]

Wow. Yea. The newest one is way louder in GR OFF.

1. Make sure they are both QBiased properly.

2. Go through the top half of the schematic and check the DC voltages on both units. Signal and line amp.

http://mnats.net/files/1176REVD_VOLTS.pdf

Mike

 

[cl]

For the coupling capacitors (Rev A, Orange Drops): Is it possible to use a value other than 0.15uF, such as 0.1uF or 0.22uF? And without needing to change anything else in the circuit? Some brands of film capacitors are unavailable in 0.15uF values.

For the power supply: Can the 2,200uF capacitors be substituted with 1,000uF or 3,300uF? I remember seeing a 1176 schematic that was using 1,000uF in the power supply section.

 

[Echo North]

For the coupling capacitors (Rev A, Orange Drops): Is it possible to use a value other than 0.15uF, such as 0.1uF or 0.22uF? And without needing to change anything else in the circuit? Some brands of film capacitors are unavailable in 0.15uF values.

For the power supply: Can the 2,200uF capacitors be substituted with 1,000uF or 3,300uF? I remember seeing a 1176 schematic that was using 1,000uF in the power supply section.

I wouldn't change the value.  They filter DC, get too off the value and you're a) not filtering DC which leads to noise issues or b) start rolling off your low end.

The power supply caps are always selected based on voltage and current relationships for that particular circuit for max smoothing.

You should have no issues finding those values at a proper shop.

Mike

 

[cl]

I wouldn't change the value.  They filter DC, get too off the value and you're a) not filtering DC which leads to noise issues or b) start rolling off your low end.

The power supply caps are always selected based on voltage and current relationships for that particular circuit for max smoothing.

You should have no issues finding those values at a proper shop.

Mike

Thank you for helping a DIY newbie! I will stick with using the orange drops for now. I am learning a lot!

I've read that polypropylene film caps sound better than their polyethylene counterparts. Is this not always the case?

Does the capacitor begin failing to filter the DC when going down in value? And same for the low end roll off?

Can too much smoothing on the power supply be a bad thing? Adding extra capacitance here slows it down?

It looks like I have my electronics homework cut out.

 

[Echo North]

Thank you for helping a DIY newbie! I will stick with using the orange drops for now. I am learning a lot!

I've read that polypropylene film caps sound better than their polyethylene counterparts. Is this not always the case?

Does the capacitor begin failing to filter the DC when going down in value? And same for the low end roll off?

Can too much smoothing on the power supply be a bad thing? Adding extra capacitance here slows it down?

It looks like I have my electronics homework cut out.

You can google the rest of the stuff, but saying one capacitor sounds better than another is just plain wrong. They all sound different, and we select capacitors based on how they compliment the sound we're looking for. One sounding "better" than the other is just one persons taste. It's like saying one EQ setting sounds getter than another. The rev a is a gritty unit, it's full of color, especially when pushed in to saturation. The orange drops compliment that wonderfully.

IMO the orange drops are part of the finishing touch on the A. I for one would hate to see them switched out, but that's your call.

Mike

 

[cl]

You can google the rest of the stuff, but saying one capacitor sounds better than another is just plain wrong. They all sound different, and we select capacitors based on how they compliment the sound we're looking for. One sounding "better" than the other is just one persons taste. It's like saying one EQ setting sounds getter than another. The rev a is a gritty unit, it's full of color, especially when pushed in to saturation. The orange drops compliment that wonderfully.

IMO the orange drops are part of the finishing touch on the A. I for one would hate to see them switched out, but that's your call.

Mike

Glad to hear. Thank you for all the info!

 

[Diamondj421]

1. Make sure they are both QBiased properly.

2. Go through the top half of the schematic and check the DC voltages on both units. Signal and line amp.

http://mnats.net/files/1176REVD_VOLTS.pdf

Mike

First off, I need to increase the volume of my test signal between the two units to get them to .775VAC. I assume that, since it's being measured right at the input, .775VAC should be .775VAC as it's not affected by the circuit. Is this correct? The new unit was the first to be calibrated and the test signal which read .775VAC on that unit was .740VAC on the first build.  This lead me to think that it could be a faulty cable so I checked all connections and everything seems fine. Moving on...

Here are my readings for the DC voltages of the newest unit [measured (expected)]:

Unit 1 (First Unit)
Signal Preamp
Q2  B=1.07v (1.05v)
          C=1.78v (1.75v)
          E= 0.57v (0.54v)
Q3  C= 12v (12.58v)
          E= 1.19v (1.15v)
Q14 E = 11.44v (12v)

Signal Line Amp
Q4  B= 1.01v (1.02v)
        C= 4.3v (4.2v)
        E= 0.433v (0.46v)
Q5  B= 3.30v (3.25v)
        C= 24.9v (26.18v)
        E= 2.74v (2.72v)
Q6  C= 27.6v (25.13v)
        E= 2.21v (2.2v)

Unit 2 (Newest Unit)
Signal Preamp
Q2  B=1.07v (1.05v)
          C=1.79v (1.75v)
          E= 0.58v (0.54v)
Q3  C= 12.3v (12.58v)
          E= 1.19v (1.15v)
Q14 E = 11.69v (12v)

Signal Line Amp
Q4  B= 1.02v (1.02v)
        C= 5.17v (4.2v)
        E= 0.453v (0.46v)
Q5  B= 3.36v (3.25v)
        C= 25.7v (26.18v)
        E= 2.82v (2.72v)
Q6  C= 25.7v (25.13v)
        E= 2.82v (2.2v)

 

[Echo North]

No the input impedance of the unit will slightly change the level at the input. The input impedance is effected by the position of the input and it's tolerance. 

Try this:
nput: 12 O’Clock
Output: 12 O’Clock
Attack: GR OFF
Release: Full CW
Ratio: 20:1
Meter: GR
Signal: Sine 1kHz @ 0dBu

What is the ACV for each unit at these points:

TP1, TP15, TP17, Output Transformer Brown.

Mike

 

[Diamondj421]

No the input impedance of the unit will slightly change the level at the input. The input impedance is effected by the position of the input and it's tolerance. 

Try this:
nput: 12 O’Clock
Output: 12 O’Clock
Attack: GR OFF
Release: Full CW
Ratio: 20:1
Meter: GR
Signal: Sine 1kHz @ 0dBu

What is the ACV for each unit at these points:

TP1, TP15, TP17, Output Transformer Brown.

Mike

Older Unit
TP1 =.111VAC
TP15 = 2.00VAC
TP17 = .304VAC
Brown = 7.42VAC

Newer Unit
TP1 = .132VAC
TP15 = 2.36VAC
TP17 = .360VAC
Brown =10.32VAC

 

[Einestad]

Hi, im new to building DIY equipment and got a question for the pros.
Im populating the PCB on my 1176 rev D and got a problem with the slot where my trim pots are supposed to go. There are 7 pads on each slot for the 4 trim pots but only 2 of the slots for the pots have holes in all 7 pads. This means that i cant insert two of the trimmers the correct way.. But i looks like the pads are connected on the bottom of the PCB so could i just bend the trimmers and use the other pads with holes in them? Aren't all pads supposed to have holes in them or im a missing something here?

Thanks!

 

[Echo North]

Older Unit
TP1 =.111VAC
TP15 = 2.00VAC
TP17 = .304VAC
Brown = 7.42VAC

Newer Unit
TP1 = .132VAC
TP15 = 2.36VAC
TP17 = .360VAC
Brown =10.32VAC

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

 

[Echo North]

Hi, im new to building DIY equipment and got a question for the pros.
Im populating the PCB on my 1176 rev D and got a problem with the slot where my trim pots are supposed to go. There are 7 pads on each slot for the 4 trim pots but only 2 of the slots for the pots have holes in all 7 pads. This means that i cant insert two of the trimmers the correct way.. But i looks like the pads are connected on the bottom of the PCB so could i just bend the trimmers and use the other pads with holes in them? Aren't all pads supposed to have holes in them or im a missing something here?

Thanks!

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

 

[mrbobbailey]

File this under [im an idiot], but in the photo I have my the PCB boards to both of my Rev As.  As you can see, in the bottom PCB, I have oriented my output transformer incorrectly.  I'm sure this is a good reason not to work on these projects at 2AM.  My leads are all correctly placed.

Does it go without saying that I should de-solder and correct this or is it acceptable if there is clearance for the bottom plate of the unit to be attached?

 

[Echo North]

File this under [im an idiot], but in the photo I have my the PCB boards to both of my Rev As.  As you can see, in the bottom PCB, I have oriented my output transformer incorrectly.  I'm sure this is a good reason not to work on these projects at 2AM.  My leads are all correctly placed.

Does it go without saying that I should de-solder and correct this or is it acceptable if there is clearance for the bottom plate of the unit to be attached?

Whoops.

You'll have to see if there is clearance.  If there is you could leave it like that.

Mike

 

[musicaudioworks]

Hello,

I'm building two rev d racks. One calibrated properly. But the other one is giving me some trouble.

While calibrating the tracking adjustment, the VU stays at -10 when the attack is turned on or off. This is after adjusting for the 10db drop with the front panel R and tracking adjustment R.

Meter functions normally when in +4 or +8.

Any ideas?

 

[Echo North]

Hello,

I'm building two rev d racks. One calibrated properly. But the other one is giving me some trouble.

While calibrating the tracking adjustment, the VU stays at -10 when the attack is turned on or off. This is after adjusting for the 10db drop with the front panel R and tracking adjustment R.

Meter functions normally when in +4 or +8.

Any ideas?

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?

Mike

 

[musicaudioworks]

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?

 

[musicaudioworks]

I just checked every component in the GR meter driver amp section. Everything looks correct. All the pots are functioning properly.

Could it be my matched transistors?

 

[csavetman]

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