Peavey Bandit 65 mods, anyone have any good mods?

[Slobrain]

Hi Slobrain,
I did try to make a recording using my iPhone when I had both the modded and original Bandits but the mic really isn't good enough to differentiate the tonal changes. You just end up hearing the room acoustic.

I can try to give a better description of the overall change though.

1. My aim was to get rid of the shouty/barky nature of the amp. I wanted more of a fender sparkle. I always thought the normal tone was a bit dull and the 'bright' setting was too harsh. Changes to the 'bright' setting were aimed at taming the mid and adding slightly more high frequency.

2. Similarly, I usually found myself running the amp in 'normal' (non bright) with the presence set very high. So, I modded the presence control to have a bit more boost at maximum and (similar to bright mod) a little less high/mid boost.

3. The use of asymmetrical diodes in the pre-gain circuit (not Sat circuit) worked with the mod to R5 increase their clipping effect. As I say, in stock format, it was possible to run this stage so the op-amp clipped which gives the nasty hard clipping distortion that no-one cares for. I like this tone for classic rock stuff. The addition of the Inductor and resistor in parallel with R18 served to give a mid bump at full pre-gain. This was an attempt to ape the mid boost of the tube screamer. Granted, the result is no tube screamer but it is better than stock.

4. Series clipping diodes in the Sat circuit increase the output of the preamp at full Sat (as swing is limited to 1.4Vpk rather than 0.7Vpk). This still allows plenty of 'gain' but with a bit more of the original guitar tone to make it through as the waveform is less clipped. I fairness, PV worked this out for themselves in subsequent designs. I think the Bandit was among the first to use this pre-amp. The switched 100nF cap in parallel with the clipping diodes makes for a nice creamy tone at full sat rather than the nasty buzz tone.

I don't think I have made a 'better' amp than the original. I.e. I am no smarter than any of the guys who did the original design. All I ave done is attempt to modify the tone for modern tastes. I'm pleased with the result. If the original design had been poor though, there was not way a few small changes like these would make so much of a difference.

As for style of playing, I play rhythm guitar in an indie/rock band. Main guitar for this is my Gretsch hollow body with P90 pickups. That said, the changes I have made to the amp allow a nicer scooped tone if Presence is run high and the Sat tone is also much nicer so I reckon it would be an improvement for metal too.

Hope that helps,

iep

Hey iep,

Yes, I can understand trying to use a iphone or similar to record with... they are decent but not that good. I do want to thank you for the work you have done with the Bandit. I really wanted to finish getting my electronics degree back in 89 to do stuff like you have but sometimes things are just not in the cards. I do electronics repair but I don't know how to engineer circuits. I know tubes amps pretty darn good as I did a lot of modding back in the 90s but that was also with the help from the guys at the old Ampage forum. I built SLO 100 clones too and can build a tube amp.

I think for what the bandit is its a good amp for any club use. even recording too. after all the tone one chooses to use is in the ears and the desired use. Heck, Tony Iommi used a small amp with a ripped speaker to record his lead on the song Paranoid...

Over all I like to repurpose stuff when possible and I think there are a lot of good old amps that can be done with. All the new stuff coming out are just twists on old designs.. accept the modeling stuff which can be good or bad depending on the use. I find its mostly musicians that are critical to sounds. Back in my club days I used SS amps and tube amps and really no one in the bars or clubs ever really knew the difference except other guitarists.

Cheers

[J M Fahey]

Any germanium you can get will do.

And I doubt any are made anymore, last batch (say, from 1980 something) will still last years or decades, given the level of consumption.

So all should actually be NOS, even if not so labelled.

[patlaw]

iep, where do you find OA90s? What other germanium diodes would be useful for this application? 1N34? 1N60? I shudder to think how many I threw away years ago. Then again, the current manufacturing processes for germanium semiconductors should cause them to be better parts than the old ones. That's the theory, anyway.

[iep]

Hi Slobrain,
I did try to make a recording using my iPhone when I had both the modded and original Bandits but the mic really isn't good enough to differentiate the tonal changes. You just end up hearing the room acoustic.

I can try to give a better description of the overall change though.

1. My aim was to get rid of the shouty/barky nature of the amp. I wanted more of a fender sparkle. I always thought the normal tone was a bit dull and the 'bright' setting was too harsh. Changes to the 'bright' setting were aimed at taming the mid and adding slightly more high frequency.

2. Similarly, I usually found myself running the amp in 'normal' (non bright) with the presence set very high. So, I modded the presence control to have a bit more boost at maximum and (similar to bright mod) a little less high/mid boost.

3. The use of asymmetrical diodes in the pre-gain circuit (not Sat circuit) worked with the mod to R5 increase their clipping effect. As I say, in stock format, it was possible to run this stage so the op-amp clipped which gives the nasty hard clipping distortion that no-one cares for. I like this tone for classic rock stuff. The addition of the Inductor and resistor in parallel with R18 served to give a mid bump at full pre-gain. This was an attempt to ape the mid boost of the tube screamer. Granted, the result is no tube screamer but it is better than stock.

4. Series clipping diodes in the Sat circuit increase the output of the preamp at full Sat (as swing is limited to 1.4Vpk rather than 0.7Vpk). This still allows plenty of 'gain' but with a bit more of the original guitar tone to make it through as the waveform is less clipped. I fairness, PV worked this out for themselves in subsequent designs. I think the Bandit was among the first to use this pre-amp. The switched 100nF cap in parallel with the clipping diodes makes for a nice creamy tone at full sat rather than the nasty buzz tone.

I don't think I have made a 'better' amp than the original. I.e. I am no smarter than any of the guys who did the original design. All I ave done is attempt to modify the tone for modern tastes. I'm pleased with the result. If the original design had been poor though, there was not way a few small changes like these would make so much of a difference.

As for style of playing, I play rhythm guitar in an indie/rock band. Main guitar for this is my Gretsch hollow body with P90 pickups. That said, the changes I have made to the amp allow a nicer scooped tone if Presence is run high and the Sat tone is also much nicer so I reckon it would be an improvement for metal too.

Hope that helps,

iep

[Slobrain]

Hi, I did eventually complete this work and actually did a whole load more to my Bandit 65. Good news is that they more or less used an identical preamp on many amps so these changes could (at your discretion) be used on the VTX. The final result was, to my ear, a real improvement on the original design. Cause I am a bit daft (and frankly obsessive) I even picked up a second Bandit 65 locally for £20 and used it to A/B the mods. Now I'm probably biased on this so I asked a couple of other guitarists to see what they thought and one went as far as to buy the un-modded amp from me in order to make similar changes himself.

Of course, your mileage may vary but the mod list and original schematics schematics for reference are attached.

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'

All these mods had an effect but I was particularly pleased with the 100nF short of the SAT clipping diodes, and improvements to the Presence and Bright controls.

I also ultimately upgraded the speaker to a Jensen C12K (which is superb) but the sound was still hugely improved with the original Scorpion.

I should add that playing around with alternative op-amps yielded no discernible results (to my ear).

The mods sounded good with both my Tele 27 Custom RI and Gretsch P90 hollow body.

[ATTACH]33097[/ATTACH]

Cheers,

iep

I guess were in an age now that we can use a PC simulator program to actually help somewhat redesign certain amps to make them better. Not sure what the Peavey engineers were using back in the early 80s but This gives me hope for modding a few of my Peavey amps now.

I do want to ask iep, what style music are you playing thru the Bandit 65? Reason I ask is that I'm more a rock and metal guy.

Thanks

[Silvertone Jockey]

Many thanks for the update iep, and for doing the legwork as well your very informative and descriptive posts.

Unfortunately my OP amp rolling ended badly as I managed to silence my VTX by plugging in only half of the legs of one of the OP amps which damaged something in the pre-amp when I powered it up. Haven't made time to dig my scope out to troubleshoot it yet, but looking forward to moving on to try your mods at some point after I repair it...........again

[Slobrain]

Hey IEP,

Can you post a video of you playing thru the Bandit to show the sounds of it now? I would appreciate that. I feel these are sleepers. They just needed the right person to bring new life to them.

Thanks

[iep]

In case you don't already have it:

peavey_heritage_vtx.pdf

Cheers,

iep

[iep]

Hi, I did eventually complete this work and actually did a whole load more to my Bandit 65. Good news is that they more or less used an identical preamp on many amps so these changes could (at your discretion) be used on the VTX. The final result was, to my ear, a real improvement on the original design. Cause I am a bit daft (and frankly obsessive) I even picked up a second Bandit 65 locally for £20 and used it to A/B the mods. Now I'm probably biased on this so I asked a couple of other guitarists to see what they thought and one went as far as to buy the un-modded amp from me in order to make similar changes himself.

Of course, your mileage may vary but the mod list and original schematics schematics for reference are attached.

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'

All these mods had an effect but I was particularly pleased with the 100nF short of the SAT clipping diodes, and improvements to the Presence and Bright controls.

I also ultimately upgraded the speaker to a Jensen C12K (which is superb) but the sound was still hugely improved with the original Scorpion.

I should add that playing around with alternative op-amps yielded no discernible results (to my ear).

The mods sounded good with both my Tele 27 Custom RI and Gretsch P90 hollow body.

PV Bandit 65.pdf

Cheers,

iep

[Silvertone Jockey]

Excellent! less buzzy is what I'm looking for. I will be performing these mods on a Classic VTX instead of a Bandit. And yes 'ugly but functional' is the plan. I was thinking of using dip switches paralleled up with the diode strings so I could selectivity short out individual diodes. Then I could leave in the Si's and add the Ge's all in series and quickly go back and forth by throwing the dip switches to short out the unwanted types. I also have obtained the "desirable" type of FET op-amps to experiment with those as well. Thanks for the great info JM!

[J M Fahey]

Well, there is some sound change, basically gemanium has somewhat less defined clipping point/is lossy/both so waveform is somewhat more rounded and so less buzzy.

Roughly, from roundest to "squarest",you can clip with:
* germanium
* silicon
* Leds
* back to back series Zeners

I have not tried Schottkys or other exotic diodes, might be fun.

So in a nutshell, using germaniums there it will be somewhat smoother, but be aware that level will be less; that might be a problem.

Clipped squarewave will be around 700mV peak with silicon and less than half that (say 250 to 350 mV Pk) with Germaniums.

A single Si diode one way and either 2 Ge in series the other way may be interesting, or all 3 Si .
Let your ears be the judge, just remember to pamper the PCB, repeated desoldering can tear pads and track ends.

If you are not sure and want to go back and forth, I suggest you crush old diodes with pliers, straighten legs as if they were soldering posts and solder new diodes there, so you don't mess with the actual soler pads.
Ugly but functional.

[Silvertone Jockey]

Anyone else have any experience in switching the silicon diodes out for germanium in clipping circuits as suggested by iep? If so can you describe the effects on tone or distortion characteristics?

[Jazz P Bass]

Quote:"
The diodes I have messed with are CR3 (three in place of one) and CR5 (two in place of one). You can just use the same 4148 diodes already in the design."

I believe that you may have mislabeled the diode in question.
CR3 should read as 'CR4'.

[iep]

Hi,
I appreciate your points and certainly agree that the amp is pretty good out of the box. I also agree that most of the best musicians (and probably especially the guitarists) that I have worked with are the ones with minimal kit but just know how to play properly.

I would refute a couple of things though:

1. It was the best that could be done with the amassed knowledge and available parts/budget at the time. But that time was 35 years ago. Quite a lot has been learned since then and there is absolutely room for improvement or at least update in this design. More significantly though, the 'fashionable' amp sound has changed. The Bandit 65 sounds as they intended at the time, high gain, more distortion than overdrive. A small update to an old design can can often help bring out new tones.

2. When a product gets on the market there is no reason to believe it is the best that can be done with those parts on that budget. Instead those will be factors but so will other influences like market forces (what did the marketing team say it needed to sound like) and timescales (how many iterations of the design were allowed).

3. It is true that many mods do little or, worse, degrade sound and that is kind of the basis of my post. A lot of hot air and voodoo gets spoken on forums (op-amp rolling etc) so I hoped that use of FFTs etc might help a few people understand what actually happens when modifications are made (rather than giving purely subjective thoughts on the audible results). And yes, at the end of the day you need to listen to it to but the sims show you what to expect and help you avoid spending time on blind alleys.

The Bandit 65 is a great amp to modify because the basic design is solid and, well, basic. The distortion circuitry uses a nice simple combination of diodes in feedback for overdrive and for hard clipping on the output of the gain stage, it is easy to make small, effective mods to these. The PCB is also large and easy to work on and the chassis has plenty of space to add mini toggles to allow mods that can be switched in and out.

I'm not claiming (or expecting) to be able to create a Valve amp killing sleeper, but if you're curious, go and buy one of these amps for really very little cash and have a bash at modifying it. Worst case you can revert back to stock if you don't like the changes but more likely you'll enjoy the process and learn a few things.You might even end up with a sound you prefer (I'm confident that this at least is possible).

Cheers,

iep

[J M Fahey]

Didn't look at all your images, my eyes hurt (what's wrong with black on white schematics? ) but :

1) yes, unsymmetrical clipping sounds noticeably better than symmetrical, and is easy, so do it.
Just don't get carried away, besides simulation check often with the Ear-O-Meter[tm]

2) you have what you have, most (99.5%) "Internet Mods" are useless or destroy original sound.
Do you really believe that an unexperienced noob sitting behind a keyboard will know better than the thousands of man-years accumulated at Fender, Peavey, etc.?
Besides, they have some real heavyweight Guitar players hired testing stuff.

I'm quite certain that when a product (by them, can't speak about others) gets on the Market, it's already the best that can be done , with those parts, within that budget.

There's minor tweaking possible, such as cutting a little extra treble after a distortion stage that's perceived as buzzy, but you overdo it and it turns into mud.

I know tons of Pro players, I mean those hired by a singer for a single show or a tour or to record, or to be part of a commercial group which has some dates sold, those who can read music on first sight and don't need to play a song 1000 times to learn it and play it well, (that's PRO in my book) who happily use a Bandit or a FenderFM212 or similar because they are light, robust, and being inexpensive means they don't have to worry that much.
And in the event of a problem (not amp failure, but, say, dropping 10/15 feet from a plane cargo hatch onto the tarmac) they can be easily replaced.

And guess what? .... they sound killer with any of those amps

So I suggest you use that amp as a good platform, don't lose sleep about it, add as many pedals as you wish and enjoy