Peavey Bandit 65 mods, anyone have any good mods?

[Slobrain]

Hey Steve,

Did you mean a Peavey Special 130? I never seen a bandit 130 before... right now I have an 1982 Special that's 120 watts, then I got the Bandit 65 which is cool when I run my Boss ME50 thru it. I like Peavey amps even though I have a few Fender tube amps and a Marshall 1987X full stack to boot. I guess I sort of have G.A.S....lol I have owned too many SS and tube amps over many years, they were all good.

Imho I think any amp can serve a purpose, heck it depends on what you can get out of it. After all Dime played on Cowboys from Hell with a Randall SS amp.

I can bet that many folks used SS amps in recordings we hear on the radio. Didn't John Fogerty use a Kustom SS in some of his recordings? Brain May used a SS amp for some stuff too.

I cant afford to be a snob to the SS realm when I used SS amps in clubs for years before affording a really good tube amp.

In the very early time of my guitar and band playing I used Peavey SS amps at many party's and no one ever said, darn that was some sorry arsed guitar tone you got... It was a 1980 Peavey (the century) with a home made 2x12 cab using eminence generic 12s.

besides I seen Brent mason playing a Peavey special and getting really cool tele tones from in it. Lots of Nashville guys like the Peavey amps.

my first 4 amps when I started to play in Oct 1979, Univox U65RN for learning, then a Fender Tremolux 40 watt tube head with a 2x10 Fender cab, (Sunn Beta series 2x12 Horrible amp), and then the Peavey The Century 100 watt head with home made 2x12 cab. Then in 1982 I got a Peavey Bandit till 1984, in 85 I got my Peavey Renown amp. That was a good club workhorse. Its still out there somewhere being used...in 1986 I got a Marshall model 1987 50 watt non master head that was made in 72 or 73 with a Marshall late 60s 4x12 loaded with 30 watt celestion greenback if I remember correctly I paid the guy $250 for the rig but had to put a new power transformer in it and new tubes too. Awesome amp.

[Steve A.]

Hey Steve, Did you mean a Peavey Special 130? I never seen a bandit 130 before...

You are absolutely correct. I must hide my face behind this Help sign and say 100 Hail Mary's.

Tube amps are great in the studio or a small bar where you can really hear the finer qualities. If everybody is playing loud people aren't going to notice the subtleties. If you are able to crank the tube amp loud enough for power tube distortion and that magical interaction between OT and output tubes and speaker, go for it!

SS amps are easier to lug around and less likely to be stolen. And if they do get stolen you should be able to find something comparable for not too many bucks. And no need to worry about finding the perfect tubes for it.

On the downside, most of the OD channels on SS amps are pretty lame- but you could say the same about a lot of the tube amps from Fender and Peavey! I only buy SS amps that have a nice sounding clean channel and use a pedal if I want some dirt.

Steve

P.S. Line 6 amps used to sound terrible if you were more than a few yards from the stage. What sounded so cool when you were right next to the amp would dissipate into mud as you got further away from it. "Whaddaya mean you didn't like the way my guitar sounded? I thought it sounded great!"

[Chuck H]

Line 6 amps used to sound terrible if you were more than a few yards from the stage.

Which was an upgrade to how they sounded up close! Now, with improvements they sound terrible from anywhere in the room

[Slobrain]

You are absolutely correct. I must hide my face behind this Help sign and say 100 Hail Mary's.

Tube amps are great in the studio or a small bar where you can really hear the finer qualities. If everybody is playing loud people aren't going to notice the subtleties. If you are able to crank the tube amp loud enough for power tube distortion and that magical interaction between OT and output tubes and speaker, go for it!

SS amps are easier to lug around and less likely to be stolen. And if they do get stolen you should be able to find something comparable for not too many bucks. And no need to worry about finding the perfect tubes for it.

On the downside, most of the OD channels on SS amps are pretty lame- but you could say the same about a lot of the tube amps from Fender and Peavey! I only buy SS amps that have a nice sounding clean channel and use a pedal if I want some dirt.

Steve

P.S. Line 6 amps used to sound terrible if you were more than a few yards from the stage. What sounded so cool when you were right next to the amp would dissipate into mud as you got further away from it. "Whaddaya mean you didn't like the way my guitar sounded? I thought it sounded great!"

I once opened up a small line 6 amp and the guts looked like a computer motherboard. I couldn't fix the issue... Steve I see you still have the Blue Guitar site up.. Good for you

Too bad T-boy wont go back to the old Ampage format... I used to have a blast on the Ampage site in the late 90s, so many cool folks to talk shop with...

[iep]

Hi, just found this thread and thought I'd share a few thoughts.

I've just bought a used Bandit 65 (not even had it delivered yet) and have set to work planning mods. I like the Peavey clean tone so don't plan to do much there but agree with many that the distortion leaves a lot to be desired. Even in when it was first designed it sounded crappy among its peers.

I've taken a look at the schematic for the amp that was provided in this thread:

http://music-electronics-forum.com/t16210/

and sketched out the gain/distortion stage in a simulation tool:



Ignoring the diodes I have circled in red. This is pretty much as per the schematic with the saturation knob set to its minimum and the Lead Pre knob set to its max (so max distortion achievable with minimum saturation). I used this schematic to run a simulation of the circuit with a 1kHz sine wave input signal.

The waveforms below give the actual output signal and an FFT showing the frequency content including harmonics out to 20kHz:



Looking at the signal this is an attempt to mimic overdrive rather than distortion where no signal clipping occurs but instead we see slew rate distortion. Essentially, gain is applied to small signals but not larger signal. It's a form of compression really. Seems quite neat until you check the FFT on the left. Basically, we are still seeing distortion totally dominated by odd order harmonics (3, 5, 7 etc). So, pretty noisy, not very musical and certainly nothing like the even order harmonics that you get from a nice Valve amp in break up.

Spin the saturation knob to the max and things get 'worse':



I say 'worse' because this is now just a classic distortion signal. Hard clipped top and bottom and totally dominated by the odd order harmonics again. This is actually okay if you are looking for a true distortion tone (it's more or less what the Boss Ds1 does). But it's a bit disappointing since, sonically, it's not really much different to to the tone with the saturation knob at its minimum.

Are there any easy mods to fix this? probably yes. I should add that I hae not been able to try them out yet but below is my own plan for my used Bandit 65:

Mods to the schematic:



All I have done here is to add two additional diodes to the feedback section (at the top) and one to the hard clipping section (at the bottom). The aim is to produce asymmetrical clipping which accentuates the even order (more musical harmonics).

What does it do?

Overdrive (saturation at minimum):



As you can see, the waveform is now asymmetrical about 0V and the result is that the dominant harmonics are now the 2nd and 4th, which are a lot easier on the ear. The dominance of these even order, lower frequency harmonics 'should' also lessen the buzzy wasps in a jar tone of the amp.

Distortion (saturation at maximum):



Again, asymmetrical waveform about 0V and greater even order harmonics. That said, it's meant to be a saturated tone so hard clipping is important so I have only added the one extra diode in order to maintain the 3rd and 5th order harmonics dominance.

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.

Want to go further? Replace each silicon diode (CR3, 4, 5, 6) with a pair of germanium ones (like OA90s). Of course, to maintain the mods described above CR3 would be replaced with 6 series germanium diodes and CR5 with 4 series germanium diodes. Germanium diodes can/do make a difference in clipping circuits. I have used them to good effect n the hard clipping stage of my Boss DS1.

Anyway, possibly a bit premature given that I have not completed the work yet but thought I would share.

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

[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

[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'.

[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?

[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]

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!

[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

[iep]

In case you don't already have it:

peavey_heritage_vtx.pdf

Cheers,

iep

[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

[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