Crazy Fingers Lonely Hearts Fuzz

A

ac30irons

Active member
Hey all, I hope some one can help.

I’ve just built one of these having done a fair few before, without issue. On testing it sounds like a dying ZX Spectrum, or more accurately like it’s maybe not getting enough power. Hit a string and just glitches and disappears. The trim makes zero difference.

I have been through every component and all is as should be. Now, bizarrely if I reverse Q2 it works - just without any fuzz. Thinking that maybe if was a duff board, I did another and the exact same thing.

I am literally pulling what little hair I have left out.

I know you will ask for pics but brand new iPhone will not let me do bloody anything. IMG_9299.jpeg IMG_9300.jpeg
 
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Nostradoomus said:
What transistors did you use?
Click to expand...
Hey man, tried a few !!! 5088 in Q1 and 2N2222a in Q2. Also tried BC549c in Q2 (correct orientation) these are probably the 7th I have built of these and I have always used the 5088 and 2n2222a combo.

It’s confusing me that if I reverse Q2 ie pi the emitter where collector should go, it works - just as a really nice OD, not fuzz 😂 I think this tells me it’s not a power issue ?

On a better note, a load of pharmacist boards have just arrived - well worth the extra few $ for UPS to the UK.
 
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Do you have the right resistors for biasing the transistors? Ie Are they the correct value?

It really sounds like a bias issue on the transistor(s). Give the voltages a check and see - it will definitely help solve the puzzle.
 
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pbrommer said:
Do you have the right resistors for biasing the transistors? Ie Are they the correct value?

It really sounds like a bias issue on the transistor(s). Give the voltages a check and see - it will definitely help solve the puzzle.
Click to expand...
I’ve literally checked every resistor 3 times and they are all as per the BOM. The voltages across the transistors ‘seem’ ok to my amateur eyes. It’s really perplexing.
 
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ac30irons said:
Hey there, checked orientation a gazzilion times. Which would be the primary smoothing cap
Click to expand...
C11. Found the build doc and it looks correct. I had an issue with the smoothing cap once and the fuzz would almost slowly gate, depending on how hard you played. Turned out to be a bad cap(in C11s position).
Your description reminded me of that.

Check voltage at the emitter of Q2 while adjusting the trimmer to make sure it isn't melted I e V should change when turning trimmer.
Then post voltages for CBE of both transistors
Could audio probe at the base and emitter of each transistor as well...
 
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jwin615 said:
C11. Found the build doc and it looks correct. I had an issue with the smoothing cap once and the fuzz would almost slowly gate, depending on how hard you played. Turned out to be a bad cap(in C11s position).
Your description reminded me of that.

Check voltage at the emitter of Q2 while adjusting the trimmer to make sure it isn't melted I e V should change when turning trimmer.
Then post voltages for CBE of both transistors
Could audio probe at the base and emitter of each transistor as well...
Click to expand...
Thanks for this dude - C11 is orientated correctly but I have just swapped it out regardless - no better.

Voltages are:

Q1 E 2.08v, B 2.76, C 4.2

Q2 E 3v, B 3.7, C 3

When turn the trim it goes between 3.7 and 2.2
 
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Base voltage calculate right per the component values used.
Both are operating near cutoff--base <0.7v higher than emitter
Do you have a working one on hand to check voltages?
I kinda wonder if you have a resistor combo that just enough out of tolerance in the wrong directions that is causing one transistor to not turn on? Kinda throwing darts though.
Did you probe it? Guessing signal is good up to Q2?
 
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jwin615 said:
Base voltage calculate right per the component values used.
Both are operating near cutoff--base <0.7v higher than emitter
Do you have a working one on hand to check voltages?
I kinda wonder if you have a resistor combo that just enough out of tolerance in the wrong directions that is causing one transistor to not turn on? Kinda throwing darts though.
Did you probe it? Guessing signal is good up to Q2?
Click to expand...
@jwin615 Hey dude, gave it a good probing. It actually starts to get a little glitchy at Q1 collector - I’ve tried socketing r5 and tried a bunch of resistors to no avail ! Things just get progressively worse really. I’ve also whipped out C1 and C5 - nothing. Might have to admit defeat !!!
 
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