Modding a Bugera amp.

[TheGuitarist]

So i'm looking at modding my bugera 333XL.

I've swapped ALL the tubes out already but i feel it could benefit from a good once over with some parts replaced etc. I know their schematics come with a signature signed with blood that you will never ever even tell people what resistor value r15 is, so i can't just get a hold of one and go from there, but i figure, most caps have their ratings on them anyway.


Does anyone have any suggestions on what i could do and how i'd go about it. I actually like the sound of the amp, i just think it could be... better?

At the moment i'm just considering recapping. Should i just replace any non electrolytic caps? Or should i replace those too. I was going to use WIMAs wherever i could. I'll probably leave the transformers as it may change the sound too much.

FWIW The tubes i'm using are JJ's KT77s as power tubes, JJ 12dw7? (the one with 20 gain on one side and 100 on the other) then JJ's 12ax7s (pos 3 with gold pins) and pos4 is a phillips 5751? i think? I can't remember the number off the top of my head.

 

[rodabod]

Just re-capping will likely get you nowhere useful.

You either need a schematic, or need to trace yourself what is going on in the circuit I'm afraid. Also, consider what you'd actually like to change about it.

 

[toobdood]

Why?

 

[Junction]

It really depends on what sound you are chasing, if you want a modern edgy sound, you've probably got close to that I would guess, if you want a more organic vintage sound then you may consider replacing components, but the vintage tone comes from a combination of carbon comp resistors, caps, output transformer, choke and tube rectifier. If thats what you are chasing then it might end up being a total re-build. Just changing a few caps, the difference will be so subtle, you'll probably not even notice it.

What is it you want?

 

[TheGuitarist]

Well in particular i wouldn't mind improving the cleans, the retubing helped but didn't quite get it there (when i play a strat through my amp i want it to "sparkle" youuu know that sound), tightening the bass up would be nice as well. Its a tad loose at the moment.

That being said i've only run the amp through 3 diff cabs so it might just be those that are lacking (an Orange, Behringer and Krank). Basically i just wouldnt mind a overall performance boost.

And yeah as i said, getting the schematics won't happen.

And yeah, the sound i'm chasing is a modern edgy hard/pop/punk sound, Think, Blink 182 meets Nickelback meets Breaking Benjamin. Nice and crunchy when it counts. Oh and yes i've played around with all the controls on my amp, i actually quite like the eq despite the bass being a bit funny and the treble being a bit overpowering.

 

[rodabod]

Why?

Guitar amps are crude. Really crude. I don't worry too much about how the small components sound as much as how reliable they are. I hardly care about electrolytic cap distortion considering how distorted the amp will be, even when clean.

If you want to tighten up the bottom-end, consider rolling off some bottom early on, as long as you can compensate for this with eq later. This is partly how Marshall achieve a tight distortion sound.

However, with respect to your amp, I can't say anything as we know next to nothing about the circuit.

 

[TheGuitarist]

I can say it IS reverse engineered off a Peavey JSX.

So putting a high pass filter at around say... 60hz? might do the trick? Or possibly an adjustable one.

 

[abbey road d enfer]

Tightening the bottom end of a guitar amp is dependant at least at 50% on the speaker/cabinet. Is it a head or a combo?
In the latter case, I think replacing the ****** Behr... speakers is the way to go, if the former, what cabinet are you using, closed, ported or open-back?

 

[rodabod]

Just to be clear, I was referring to the distortion's response rather than the overall bass response. Distorted low-end can be wooly and farty, which is why rolling it off early gives you a clearer and "tighter" sound.

 

[Junction]

rolling it off early gives you a clearer and "tighter" sound.

He did say he tried it thru 3 different cabs, and I assume he did not find his tone, I would agree that rollin off the bottoms will tighten it up. One approach might be to try reducing the value of the cathode bypass capacitor, start at the first preamp tube, it could be a 10uF electrolytic, or thereabouts, try reducing the value or even removing it. A schematic would be useful - might be worth reverse engineering the schematic to work out what you have to play with.

Michael

 

[kooma]

Thats funny, I thought I saw schems in gmail...
imo. tubes and those ****** molex-connectors were the biggest problem. (And maybe double checkking every solderjoint etc. wouldnt hurt)

 

[JohnRoberts]

If the Bugger is already a modified something else, maybe mod it back more like whatever it was based on? Presumably a successful amp in it's own right.

JR

 

[TheGuitarist]

Well look at that, you find all kinds of things in that email... bloody hell. So i guess you can find the schematic somewhere


Hope that helps someone, i'm looking it over, but not 100% sure how much can help. I'm just trying to find the cathode bypass cap. I'm thinking it would be that 22/50 cap. A 22uf 50v electrolytic?


As i said, its not actually a bad sounding amp at all, i just think its cheap workmanship (thus the connectors and possible resoldering) incorrect biasing (which i had to fix straight away) And some parts that could be done better.

Other mods i'm considering are actually putting effects pedals IN the amp that just live permanantly on so i'll get to that if i feel that the amp stands up on its own. But i mean thats not hard in the slightest.

 

[Junction]

yeah thats the one, the 22uF electro, could try reducing the value, for example to 2.2uF, should tighten the flabbiness up a bit.
Michael

 

[TheGuitarist]

So just check i know what this is doing. By lowering the value i'm essentially putting a low shelf filter on the input of the amp. Would 10uf better? Just don't want to kill all the bass. In particular i only want to tame under 80hz. Actually while i get the cap... i might just buy a 3way switch. To see which i like best, and then just keep that value.



Does anyone have any other suggestions now the schematic is available?

 

[Junction]

Dont go desoldering the old cap and the solder in a new one and and repeat until you find the right one for you, because you will end up damaging the pcb, I will often use alligator clips and I can happily try different values until i find the right tone. Maybe a switch will be useful, for a 3 way, at a guess I would try .68uF, 4.7uF and 25uF.

Changing the bypass cap also changes overall gain, so u might find there is a trade off to be made here. For interest try a .68uF poly in there (aka marshall) and then anything in between that and your original 25uF and try remove the bypass cap totally and you'll hear the impact it has on gain.

You can also look at the coupling cap to the next stage, currently the 47n or .047uF(C70), can try dropping that as well, try a .022uF

Be careful though when you are working on this, tube amps can kill.

Michael

 

[TheGuitarist]

Yeah thats definately something i have to be careful with..


Actually, considering this is nearly a complete ripoff of the JSX (schematics at www.schematicheaven.com), might it be worth using JSX transformers? I guess that would be an upgrade from whatever chinese made ones are in it.

And you guys reckon replacing components with better quality ones will do little to know noticeable improvement? Saves me alot of work

 

[Sorr]

I would bypass C65 and change R120 to 1Meg, and remove C17

 

[TheGuitarist]

Can i ask why? just so i don't replace something for no reason.

 

[Sorr]

You dont need C65, the less caps in the signal path the better.
1M for R120 will reduce the loading on passive pick ups.
Removing C17 will give less HF roll off.