Which diode for tube sound fuzz?

[Rick899]

I am trying to eliminate a hiss from a tube sound fuzz. The attached layout shows a diode but the Anderton schematic shows no diode. The LO doesn't say which diode should be used. I used a 1N4148. If that is not the right diode would that cause the hiss?  Regardless of whether it would cause the hiss:   Which diode should be used ?   Thanks.

[PRR]

The diode is not the hiss.... it is in parallel with the 100uFd capacitor which would shunt any hiss from the diode.

The only function is to protect the chip if you plug a battery backward.

1N4148 is near-adequate for battery. If you plan on plugging strong wall-warts backward... don't. If you must, then 1N4007 is more certain to hold-up long enough to smoke the wart (or the 100 ohm resistor) before the chip.

As far as I know, this plan just hisses. The chip is MOS and MOS are notoriously hissy. The overall design has a LOT! of gain which will bring-up hiss.

Play loud, don't stop.

[ORK]

Increase the values of one of those 10pF caps or both to 22pF, 47pF, or even 100pF or more.

[Rick899]

Thanks for the replies.  Yes it sure does have a lot of gain. I can get some great sustain and controlled feedback from it.

In regard to the diode. I would rather smoke the 4049 chip which is a lot cheaper than a wall wart. So I'll leave that alone. I have a One Spot and I don't see how it can be plugged in backwards.

I already changed one of the 10 pf caps to 100 pf. I'll change the other one to 100 pf as well and see what happens.

Thanks again.

[petemoore]

  As long as the power supply is always correct, the diode doesn't really do anything.
   If there's a miswire of the power supply, the diode conducting whatever current the PS can deliver, will start cbaking, the power supply will also begin it's heat ramp up, which one dies or is damaged first is a match between 'the challenger' and 'the contender'. Power supplies take a little while to start baking so if you're careful [an LED indicator, plug in the input/PS defeat switch] you can test the power supply [DC] polarity correctness using the indicator LED, quickly switch the bypass switch...if it doesn't light...pull the PS immediately and begin to find out why...a good PS should be able to survive short shorts [a transient shorting condition when it is cool].
  But...
  Once the reverse DC gets into the circuit it can be a matter of no time at all to get the damages done [chip + anything else reverse polarized], making the debugging a series of messes to sort out.
   AC...make sure you don't have any AC WW's which can be plugged into DC circuits, AC can fry right through 'everything' polarized, protecting against AC 'manually' [don't ever connect it] is practical considering the complexity of alternatives AC circuit-protection-circuits.
  Having RP'd a couple circuit boards, I found out a reverse polarization mistake can be as easy as putting the left shoe on the right foot...as long as you check/verify the polarity every time the diode can't help anything. Fry the circuit or two and the diode strapped on the PS starts looking like the really easy way.
   I see big Si diodes in all kinds of equipment, they've proven themselves to be very cheep or free protection IME.

[DavenPaget]

Thanks for the replies.  Yes it sure does have a lot of gain. I can get some great sustain and controlled feedback from it.

In regard to the diode. I would rather smoke the 4049 chip which is a lot cheaper than a wall wart. So I'll leave that alone. I have a One Spot and I don't see how it can be plugged in backwards.

I already changed one of the 10 pf caps to 100 pf. I'll change the other one to 100 pf as well and see what happens.

Thanks again.

'till you realize that a 4007 will go first . Saving the power supply and the chip .

[Mark Hammer]

I run mine with 100k feedback resistors, and 330pf feedback caps, providing the gain via an op-amp input stage.  Negligible hiss.  Do try several different 4049s, though.  They can vary from unit to unit with respect to noise.

[Rick899]

Mark Hammer:  Thanks for the reply.  Which are the feedback resistors?    Which are the feedback caps?   As the layout shows there are two 100K, two 1M, and one 100R resistors.

[earthtonesaudio]

Play loud, don't stop.

Good advice in general!