Hamlet+ problems

[Dawnofzion]

I have a Hamlet + project that I have been having issues with for awhile and I can't seem to figure it out. The pedal creates white noise whether it is engaged or bypassed. The output is also rather quiet. I bought the board already populated but have since replaced the Q2 with a pn4302 because I cannot seem to find a 2n5457.  I thought that was the issue but it is still there after this replacement.  My voltages are as noted below.  Any ideas where the issues could be coming from?

Pt2399
Pin 1-4.99v
Pin 2-2.50
Pin 3-0
Pin 4-0
Pin 5-2.64
Pin 6-2.45
Pin 7-1.13
Pin 8-1.18
Pin 9-2.50
Pin 10-2.51
Pin 11-2.51
Pin 12-2.50
Pin 13-2.50
Pin 14-2.50
Pin 15-2.50
Pin 16-2.50

Taptation
Pin 1-4.99
Pin 2-3.55
Pin 3-3.71
Pin 4-4.39
Pin 5-4.98
Pin 6-2.27
Pin 7-4.81
Pin 8-4.99
Pin 9-0
Pin 10-0
Pin 11-4.81
Pin 12-1.19
Pin 13-0.21
Pin 14-0

Mcp41100
Pin 1-4.99
Pin 2-0
Pin 3-0
Pin 4-0
Pin 5-2.45
Pin 6-2.45
Pin 7-0.30
Pin 8-4.99

Lt1054
Pin 1-1.12
Pin 2-5.0
Pin 3-0
Pin 4-0
Pin 5-0.14
Pin 6-2.54
Pin 7-1.41
Pin 8-9.25

Q1 - 2n5088
Pin 1-1.78
Pin 2-1.74
Pin 3-9.13

Q2 - pn4302
Pin 1-16.29
Pin 2-0.18
Pin 3-0

Q3 - bs170
Pin 1-0
Pin 2-2.24
Pin 3-0.29

Reg - 78l05
Pin 1-4.99
Pin 2-0
Pin 3-9.22

[Dawnofzion]

Pictures of the board.




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[Dawnofzion]

No ideas?

[midwayfair]

(a) Your PT2399's pin 7 and 8 voltages should not match. Pin7 should be closer to about 0.5V and pin 8 should be the opposite (IIRC; I don't usually have to measure pin . It's possible that white noise is constantly running through the chip, though, and that's dragging it down. (The voltage on those pins changes when signal runs through them.)

(b) You didn't label the pins on your transistors in a way that I can really tell which pin is which, but your JFET's voltages are wrong. You should have about 11V on the drain, 0V on the gate, and somewhere between 2V and 4V on the source (usually closer to 2V). Look up the datasheet, make sure you got the pinout right, and look for errors around there.

(c) Your 5088's voltages are impossible for an in-circuit bipolar junction transistor amplifier. The voltage drop between the base and emitter of a transistor can NEVER be less than 0.7V (the Fv of a silicon diode, which is what the base-emitter junction is). Your base and emitter are identical. This indicates a short, a missing connection, a bad transistor, or some other unusual problem.

[Dawnofzion]

I checked the pin out of the pn4302 and I did have it in backwards. I was able to get my hands on a 2n5457 and put it in place correctly.  After getting the 2n5457 in, I took new readings of all the voltages and have noted what each pin is.   Most voltages stayed the same after correcting the 2n5457.  I thoroughly looked over the board for any bridged solder joints, ect and could not find anything.  Getting frustrated with this one.

Q1 - 2n5088
Emitter Pin 1 -1.78
Base Pin 2-1.74
Collector Pin 3-9.13

Q2 - 2n5457
Gate-0
Source-1.46
Drain-3.76

Q3 - bs170
Drain Pin 1-0
Gate Pin 2-2.24
Source Pin 3-0.29

Pt2399
Pin 1-4.99v
Pin 2-2.50
Pin 3-0
Pin 4-0
Pin 5-2.44
Pin 6-2.45
Pin 7-1.13
Pin 8-1.18
Pin 9-2.50
Pin 10-2.51
Pin 11-2.51
Pin 12-2.50
Pin 13-2.50
Pin 14-2.50
Pin 15-2.50
Pin 16-2.50

[midwayfair]

Does your trimpot change the 2N5457's drain?

Use your multimeter to find out if you have continuity between the pins of the 5088. Remove it if you have to and take voltages where the pins would be. If there's no continuity between those pins and the voltages/connections aren't the same according to your multimeter (not your eyes), then the transistor might be bad.

[Dawnofzion]

I will check the trim pot and 5457 this evening.

I replaced the 5088 prior to taking the readings because I suspected it being bad. So unless my replacement was bad as well....?

[jkokura]

If they were both from the same source, that might potentially make both 5088's bad, although that's pretty rare. More often you'd have a bad jfet, and from the same source you could have both be bad.

Sometimes it's very hard to find bad solder joints. I recommend that you consider using some isopropyl alcohol and an old toothbrush to clean the solder side of the board carefully. Also consider that sometimes you'll get solder bridges on the part side of the board too, so inspect those joints carefully also.

This circuit isn't going to be deadly quiet no matter what, but it is designed to be clean delay. If you're getting white noise you should be able to find where the noise is starting using an audio probe. If you need some help with how to do that, please let us know.

Jacob

[Dawnofzion]

Ok I checked the voltage of the 2n5457 drain as I turned the trim pot and it went as follows...
Trim pot all the way down = 1.66
Trim pot all the way up = 17.84

I did noticed the voltage would slowly drop then finally settle in.

I probed around with an audio probe and found the following....
The noise was on Q1 2n5088 collector
It was found on the Q2 2n5457 drain
It was found on Q3 bs170 gate


The noise is actually more than white noise, It has a slight squeal to it. I noticed as I turned the trim pot the sound changed pitch. All the way up created a really high squeal in the white noise/hiss.

[jkokura]

Well that's interesting. Perhaps you have a bad cap in your power filtering section? Maybe check those?

Jacob

[midwayfair]

Your biggest problem is still that your emitter and base voltages on Q1 are the same. Regardless of what else MIGHT be wrong in the circuit, that is impossible for a working bipolar junction transistor and the cause must be located and solved.

[Dawnofzion]

Should I just replace the q1 again and see if that fixes the voltage discrepancy?


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[midwayfair]

Should I just replace the q1 again and see if that fixes the voltage discrepancy?


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Pull out Q1. Measure the voltages. Are they the same? Then there's a problem that has nothing to do with the transistor itself. Is the base reading some high voltage and the emitter at 0V? Then go ahead and replace the transistor and see if it helps.

Heck, breadboard the Q1 stuff and measure what you EXPECT the transistor's voltages to be, then drop it onto the PCB and see if they're the same! It's only 4 parts -- the transistor, a 4.7K, a 4.7M, and a 1K.

[Dawnofzion]

Ok I pulled the Q1 2n5088 and measured the voltages.
With the Q1 pulled I measured the pcb holes where it was supposed to go...
Collector - 18.55
Base - 3.7
Emitter - 0

I then installed a brand new 2n5088 and immediately remeasured and got the following....
Collector - 10.55
Base - 1.63
Emitter - 1.59

Not sure what is going on.....
Any ideas?

[midwayfair]

Did you try putting the same value components (from the same bag) on a breadboard? You need to systematically eliminate all variables, including the PCB. Q1 is only a couple parts, you should be able to breadboard it in seconds.