1n34a .... active components off Merivale

 

Thanks!
Big enough demand that they have them in stock?
I'm assuming the only market for them is guitar effects...

 

If they don't need to have a high mA rating, I can send you a Ge and a red LED.
On the house.

 

just a small signal diode ( no real load capability )

1n34 ger = .3 v
1n914 sil = .6 V

either should work
and the red diode is about 1.8V (depends on mfg)
green about 3.2V

 

yes , call the store first ( they don't stock a lot)

 

Website says in stock but we'll see...
Ever use an IR diode? They look to be 1.4 or so, a smidge less than red.

 

I can mail some 1n34s if you want, pm me.

 

IR no ... if you're looking at Guitar V , it easily goes over 2V and that's what you're clipping / modding.
and in Ottawa , IR much harder and $$ to get.

BTW , small signal units are fast switching.

about 3 places to get components in Ottawa , one flies the skull and crossbones.
The rest are hit and miss (or need to order $25 worth of each)

if you get into building a lot ( start to stock parts ) there is Mouser Canada and
Amazon ca. stocks some pieces too.

 

Digikey is in Canada and has cheaper shipping than Mouser. Mouser sends almost everything from the USA. I buy my Germanium stuff from European eBay sellers in Russia, Ukraine etc...

 

Digikey is in Canada and has cheaper shipping than Mouser.

Just to caution that the cheap flat rate shipping from Digikey will only show up if you are set to Canadian funds on the .ca site. I got stuck once and couldn't figure out why the shipping had gone up, then I got it sorted out. And it's really fast shipping too, the Mouser cheap option can take weeks.

 

I can probably spot you some. In many instances, one or two Schottky type diodes (which are often easier to find and cheaper than germanium) can satisfactorily sub for germanium, depending on the needed forward voltage. If you need a higher clipping threshold, using several silicon-type in series, or sticking a resistor in series with silicon diodes, can yield a higher and potentially softer clipping threshold.

I think people often make too much of diode-type in clipping/distortion circuits. Yes, they have different conduction "knees" (speed of conduction), but all too often, those knees occur at speeds well above what guitarists need/use. In a universe of high-speed signal switching, it makes a difference if a diode starts conducting in 150 nanoseconds vs 80. Notsomuch for guitar, though. What matters far more is the forward voltage required for conduction (i.e., clipping threshold), and the signal current applied to the diodes (dictated by any series resistance, rather than by the diodes only).

But I have to ask, which model of Bandit is it, and which diodes are you planning to change?

 

Mhammer I appreciate the advice!
It's the 65, and I have the schematic. There's a post on another site about a series of mods to improve the 65 to make the saturation circuit less harsh. I'm going to try the 2 mods to the clip circuit.
If I understand the circuit correctly there are both feedback clipping diodes, and a pair to ground. One mod is to create asymmetrical clipping in the feedback pair by replacing one si diode with germanium. The other is to double up the other diode pair.
I think the ge is needed because it has a lower voltage threshold then Si, not because its ge. If I'm getting it right I think an LED there would decrease feedback and increase gain, and it has enough gain as it is. I just learned last night that schottkey diodes could also work.
The other mod doubles the diode pair that go to ground after the gain stage. I figure 2 red LEDs will be as good as 4 Si diodes (or 2 IR diodes if they are lower V then red.. )
I'm not looking for any magic, just messing around to learn stuff.
I have 2 bandit 65s so I can compare them side by side too.

 

There are multiple sets of diodes in the amp, and changing something earlier in the signal path can have counter-intuitive effects further along. There's also the not-so-innocuous aspect of preventing fizz buildup. I've modded two solid-state Fenders to address that with some degree of success. Feel free to discuss here or offline.

Using this schematic as reference, what is it you want to change, or were recommended to change? Is there any particular tonal change you're looking for, or hope would result from the suggested mods?

 

Chzge cr3 yo Ge diode
Change cr5 cr6 to diode pairs.

Peavey Bandit 65 mods, anyone have any good mods?

This is the full list from that thread:
"Component, Change, Effect
CR3, Single OA91, Assymetrical clipping of overdrive
R5, 470 up to 680, Increases diode clipping to reduce 'railing' of next stage. Sims showed that for high output guitar pickups,the first stage had inadequate headroom without this mod.
C6, Change to 330n, Additional Bass cut in full Sat mode which prevents the really buzzy breakup that occurs when the signal is reduced to a pure square wave. This was really prominenet with my Tele on the bass strings
C5, Change to 15n, Move 'Bright' to slightly higher freq. his made the amp 'sparkle' rather than shout (IMHO).
CR6, 1N4148 x2 series, Less harsh clipping (already implemented on the VTX)
CR5, 1N4148 x2 series, Less harsh clipping (already implemented on the VTX)
CR5, Parralel 100n cap shorting both dioeds to GND, Less high freq from distortion at full Sat. I used a panel mounted switch to select/de-select this feature). This really improved the Sat tone.
C10, 1u, Not essential, just tightens up clean channel
C11, 15n, Move 'Bright' to slightly higher freq. his made the amp 'sparkle' rather than shout (IMHO).
C17, 180p, Slight 1kHz 'scoop'. Or 220pF for less 1kHz cut
C18, 33n, More bass (post distortion stage)
R18, 47mH and 470R, Series Ind and Res in parallel with R18 gives addition mid 'bump' at full gain
C25, 20n, More high boost at full 'Presence'
R46, 1k, More high boost at full 'Presence'
C23, 10n, More high boost at full 'Presence'
... "

I'm not looking for anything specific except to see what it does. There are a lot of little mods there I was going to start with diodes to see what happens.

I've replaced the power supply caps in one amp and was going to do the same in the second, and try out a few of the mods listed.

 

BTW I appreciate your input. I just read a thread here from a few years back where you describe a lot about clipping diodes and the different distortion pedal circuits so I've learned a lot in the past few days that's for sure.
The preamp on the Bandit is very similar to the Special 130, and if I like these mods I was going to do them to the 130.
To really know if they work I'd need a good guitar player playing at live performance levels - not me in my basement.

 

My plan, selected from the full list

CR3, Single OA91, Assymetrical clipping of overdrive
R5, 470 up to 680,
C6, Change to 330n,
CR6, 1N4148 x2 series
CR5, 1N4148 x2 series
CR5, Parallel 100n cap shorting both diodes to GND

 

I'm not so sure that attempting to implement asymmetrical clipping that early in the circuit will be audible, given the several additional points where clipping is also introduced.

I do like the addition of the 100nf cap in parallel with CR5/CR6. I will suggest lifting the ground end of CR11/CR12 to remove some harshness and increase C14 to 680pf to "sand a little off the edges". Those three would make a useful, and easily reversible first step.

 

I'll try the Ge diode anyway to see what happens.
That first gain stage is odd with the concentric pots, one of them reversed. As the pot is turned the gain changes and the diodes are brought in more? Not sure...

CR11/12.. they look like clipping to ground but are they or are they overload protection for the amp stage? Lifting the ground removes them, so would replacing them with a string of diodes or LEDs also work?

I will add the c14 change to the plan. Sanding off edges is what it needs.

 

Yeah, I was wondering if CR11/12 were there to keep a lid on the level, but keeping the level sensible could also be done by gain adjustment in the preceding or following stage. And given how easy that would be to do, I figure Peavey were aiming for a little more bite/grit in the process. If level does become a problem, consider reducing R33 a bit, increasing R34, or both. Presently, that stage has a gain of a little over 4x. If R33 was 27k, and R34 was 12k, gain would drop to 3.25x with little change in bandwidth.

 

Thanks very much to oldjoat for dropping off a few Ge diodes and LEDs to try out. It'll be a few days before I can get to it but when I do I'll report back.