[BUILD] FET/500 Official Support Thread

[Echo North]

I'm reporting back:

UNIT#1
* Input transformer pad 1
390mVAC

* (-) neg side of C7
0.5mVAC

* Output transformer brown wire
0.5mVAC


UNIT#2
* Input transformer pad 1
387mVAC

* (-) neg side of C7
0.5mVAC

* Output transformer brown wire
0.5mVAC

measured with a Fluke 179

Sorry, I wasn't getting notifications on this thread.  I reset the notifications so it should work now.

On the F you need to check the VAC with the above conditions at C9 instead of C7.

Post your readings at C9. Also post for R6.

Thanks,

Mike

 

[hasanova]

Sorry, I wasn't getting notifications on this thread.  I reset the notifications so it should work now.

On the F you need to check the VAC with the above conditions at C9 instead of C7.

Post your readings at C9. Also post for R6.

Thanks,

Mike

UNIT#1 RevF. FET/500
Input: 12 O’Clock
Output: 12 O’Clock
Attack: Full CW
Release: Full CW
Ratio: 20:1
Meter: GR OFF
Signal: Sine 1kHz @  0.780 VAC across input + and -

With DMM, measure AC at the following test points, using the anode (+) of D4 as reference (black probe):

* Input transformer pad 1
391mVAC

* (-) neg side of C9
1.58VAC

* Output transformer brown wire
0.4mVAC

* R6
upper side: 90.4mVAC
down side: 76.9mVAC

* OUPUT:
5.16VAC
---------------------------------------

UNIT#2 RevF. FET/500
Input: 12 O’Clock
Output: 12 O’Clock
Attack: Full CW
Release: Full CW
Ratio: 20:1
Meter: GR OFF
Signal: Sine 1kHz @  0.776 VAC across input + and -

With DMM, measure AC at the following test points, using the anode (+) of D4 as reference (black probe):

* Input transformer pad 1
389mVAC

* (-) neg side of C9
1.71VAC

* Output transformer brown wire
0.5mVAC

* R6
upper side: 87.8mVAC
down side: it varies around 10mVAC

* OUPUT:
5.46VAC

 

[Echo North]

UNIT#1 RevF. FET/500
Input: 12 O’Clock
Output: 12 O’Clock
Attack: Full CW
Release: Full CW
Ratio: 20:1
Meter: GR OFF
Signal: Sine 1kHz @  0.780 VAC across input + and -

With DMM, measure AC at the following test points, using the anode (+) of D4 as reference (black probe):

* Input transformer pad 1
391mVAC

* (-) neg side of C9
1.58VAC

* Output transformer brown wire
0.4mVAC

* R6
upper side: 90.4mVAC
down side: 76.9mVAC

* OUPUT:
5.16VAC
---------------------------------------

UNIT#2 RevF. FET/500
Input: 12 O’Clock
Output: 12 O’Clock
Attack: Full CW
Release: Full CW
Ratio: 20:1
Meter: GR OFF
Signal: Sine 1kHz @  0.776 VAC across input + and -

With DMM, measure AC at the following test points, using the anode (+) of D4 as reference (black probe):

* Input transformer pad 1
389mVAC

* (-) neg side of C9
1.71VAC

* Output transformer brown wire
0.5mVAC

* R6
upper side: 87.8mVAC
down side: it varies around 10mVAC

* OUPUT:
5.46VAC

The output seems fine on both. Looks like they are passing signal fine.

Are you able to set the qBias?

 

[hasanova]

The output seems fine on both. Looks like they are passing signal fine.

Are you able to set the qBias?

UNIT#1 RevF. FET/500
1 Q-bias is set!

2 VU meter calibration
peak meter:
output: +4.88VAC --> top 2 LEDs are lit and remain lit, no matter how I rotate "GAIN TRIM" trimmer!


UNIT#2 RevF. FET/500
* OUPUT: dropped again, very low.
1 Q-bias NOT set
I turned the Qbias timmer CCW until I heard a "click"
Output = 500mVAC; it keeps fluctuating around 500mVAC, it doesn't stand still on one value. After a minute It dropped even more, to 11.0 mVAC, no more fluctuation.

I'm back at my first post... this is very strange.

BTW, I'm in central Europe, so I reply with a bit of delay...

 

[Echo North]

UNIT#1 RevF. FET/500
1 Q-bias is set!

2 VU meter calibration
peak meter:
output: +4.88VAC --> top 2 LEDs are lit and remain lit, no matter how I rotate "GAIN TRIM" trimmer!


UNIT#2 RevF. FET/500
* OUPUT: dropped again, very low.
1 Q-bias NOT set
I turned the Qbias timmer CCW until I heard a "click"
Output = 500mVAC; it keeps fluctuating around 500mVAC, it doesn't stand still on one value. After a minute It dropped even more, to 11.0 mVAC, no more fluctuation.

I'm back at my first post... this is very strange.

BTW, I'm in central Europe, so I reply with a bit of delay...

Ah sorry.  I've discovered that the newer LEDs were using, the rev F need a different resistor at R203. Something closer to 90KΩ. That is why you can't get that red light off.  I can send you a 90K resistor if you need.  You should be able to still calibrate the rest of it. Sounds like Unit 1 might be working...other than needing a lower resistor at R203.

Something much have a bad solder joint in the 2nd unit.  What is that C9 voltage now that your output died?

Mike

 

[hasanova]

Ah sorry.  I've discovered that the newer LEDs were using, the rev F need a different resistor at R203. Something closer to 90KΩ. That is why you can't get that red light off.  I can send you a 90K resistor if you need.  You should be able to still calibrate the rest of it. Sounds like Unit 1 might be working...other than needing a lower resistor at R203.

Something much have a bad solder joint in the 2nd unit.  What is that C9 voltage now that your output died?

Mike

Thank you Mike, let me see first if I can find a value close to 90KΩ resistor or make on with parallel resistors, before sending me one.

Unit#2:
Input = 776mVAC
C9 = 3.6mVAC
Output = 11.3mVAC

Hassan

 

[Echo North]

Thank you Mike, let me see first if I can find a value close to 90KΩ resistor or make on with parallel resistors, before sending me one.

Unit#2:
Input = 776mVAC
C9 = 3.6mVAC
Output = 11.3mVAC

Hassan

You signal is dying in that first stage.  See below.

Or your bias voltage is dying.

DO you still have 80ish mVAC on that one side of R6?  If so try removing Q1 carefully and see if that get's your signal back.

Mike

PS: I'm off to bed for the night.

 

[hasanova]

You signal is dying in that first stage.  See below.

Or your bias voltage is dying.

DO you still have 80ish mVAC on that one side of R6?  If so try removing Q1 carefully and see if that get's your signal back.

Mike

PS: I'm off to bed for the night.

Unit#1 = fully calibrated! (I've changed R203 to 91KΩ)

Unit#2: I'm getting 88.3mVAC on upper side of R6.

Hassan

 

[hasanova]

On a side note:
After calibrating "Unit#1" I put everything together. I noticed that a leg of R72 might be touching a #4 nut and/or 1/4" standoff. When I checked it with a DMM, it was so. Solved it by adding a bit of tape to the 1/4" standoff and #4 nut.

 

[Echo North]

Unit#1 = fully calibrated! (I've changed R203 to 91KΩ)

Unit#2: I'm getting 88.3mVAC on upper side of R6.

Hassan

The 88.3mVAC reading is good. What do you have on either side of R10?

 

[hasanova]

The 88.3mVAC reading is good. What do you have on either side of R10?

either side of R10 = around 12 ~13 mVAC

 

[Echo North]

either side of R10 = around 12 ~13 mVAC

How does that compare to the working unit?

 

[hasanova]

You signal is dying in that first stage.  See below.

Or your bias voltage is dying.

DO you still have 80ish mVAC on that one side of R6?  If so try removing Q1 carefully and see if that get's your signal back.

Mike

PS: I'm off to bed for the night.

After removing Q1 (on both units I use transistor holders) I don't get my signal back: 11.4mVAC on output.

 

[Echo North]

After removing Q1 (on both units I use transistor holders) I don't get my signal back: 11.4mVAC on output.

ya that stage seems fine.

It happening after C1 and before C9.

 

[hasanova]

How does that compare to the working unit?

I had to take the working unit apart. Here on either side of R10 I get a constant reading of 73 mVAC.

On the not working unit it was different on either side of R10 and jumping around between 12 ~ 17 mVAC.

 

[Echo North]

I had to take the working unit apart. Here on either side of R10 I get a constant reading of 73 mVAC.

On the not working unit it was different on either side of R10 and jumping around between 12 ~ 17 mVAC.

Something is happening at that R10.  Look at everything connected to it on the schematic.  Look for bad traces/joint...and triple check values.

Mike

 

[hasanova]

Something is happening at that R10.  Look at everything connected to it on the schematic.  Look for bad traces/joint...and triple check values.

Mike

I forgot to solder the leg of R6 connecting to R5!
I have correct output now: 5.4 VAC. I will proceed with calibration.  Goodnight Mike (Good morning for me, haha!) and thank you for your help.

 

[Echo North]

I forgot to solder the leg of R6 connecting to R5!
I have correct output now: 5.4 VAC. I will proceed with calibration.  Goodnight Mike (Good morning for me, haha!) and thank you for your help.

Nice!  Glad you found it.

 

[guismarquesrj]

Hey Mike,

It's been a year more or less since I built my two units of the Rev D here...

Sometimes a hum noise suddenly appears! Any idea? Nothing different about the usage... Always using it in the studio in the same lunchbox (Wes Audio Supercarrier II), not fully loaded... plenty of power available...

Any idea before I put it out and start to take a look on everything? lol

Thanks!

 

[Echo North]

Hey Mike,

It's been a year more or less since I built my two units of the Rev D here...

Sometimes a hum noise suddenly appears! Any idea? Nothing different about the usage... Always using it in the studio in the same lunchbox (Wes Audio Supercarrier II), not fully loaded... plenty of power available...

Any idea before I put it out and start to take a look on everything? lol

Thanks!

Hmmmm could be anything.  I would expect a ground issue.  Could be a bad solder joint, or a dirty edge card connector.  COuld really be a million things half of which are with the rack or connectors and cabling.

Mike