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Turning a guitar amp into a bass amp

#41
True. Well hopefully we can get a 'review' soon from a poster who has this head and bass gear to test it out with. So far it seems promising. It's low powered so I am not sure what would need changes other then the pots/ resistors in the tone 'stack' since it doesn't seem to do much. Probably because it just rolls off high end, which really isn't as present with a bass.
 
#44
I have a valve jr that I use with my various vintage and new cabs. It only has one power and one preamp tube. So it is kind of fun for tube rolling. You get a better picture of how a vintage RCA tube compares to a new EHX tube when its the only small signal tube in the circuit. There are also a ton of mods for these out there. Though I am so backed up on soldering projects I haven't done any of the mods myself. Well that, and I have 1.5 bajillion pedals.
 
#45
Biszkhopt said:
That's a bummer that they don't wanna help out. It would be super nice if someone with technical knowledge could point out all necessary modifications.

As far as my (next to nothing) knowledge and research goes, to make it more bass friendly we would have to change:

- output transformer (preferably bigger one :D)

- heater fuse (so it can handle some bigger tubes)

- some caps (?)

I'm really tempted by the price, in Europe it costs same as Valve Junior...
Click to expand...

Tranny is fine; fuse is fine; caps are the only thing you would need to change. Basically, you're looking to "voice" the amp differently and you can do that with a couple swaps. Having no schematic to work from makes this part guesswork for me at this moment, but there are three pinkish orange caps from the right of that board that would be quick swaps and that would probably make a world of difference.

they may be .022 or .047 uf and bumping them up to .1uf should do the trick.
 
#49
found a mod thread on this over at Invalid Link Removed

looks like the bypass caps on V1 are 4.7uf - they need to be bumped up to 25uf

The coupling caps all seem to be close to what you need. You may want to bump up the preamp coupling caps to .1uf as suggested, but it might make it "woofy"

You're talking less than $10 in mods there that would make a world of difference.
 
#50
I have't read the whole thread so I don't know if this has been suggested yet, but I recorded this and this with this Invalid Link Removed http://www.musiciansfriend.com/amplifiers-effects/jet-city-amplification-jca20h-and-jca12s-half-stack I find that it can sound quite nice for bass. (It's one of my brother's guitar amps) As long as you don't plan on really pushing it you probably won't need to do anything to it. Crank the master and use the gain as your volume to get a cleaner sound, turn the bass knob up, just a touch of mids, and keep the treble and presence zeroed or close to it.
 
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#51
jimmy rocket said:
found a mod thread on this over at Invalid Link Removed

looks like the bypass caps on V1 are 4.7uf - they need to be bumped up to 25uf

The coupling caps all seem to be close to what you need. You may want to bump up the preamp coupling caps to .1uf as suggested, but it might make it "woofy"

You're talking less than $10 in mods there that would make a world of difference.
Click to expand...

Hey Jimmy, are these your suggestions or what the guys over at TDPRI are saying ? I was browsing there thread and didnt see anything about running bass through, just guitar.

I have seen a couple mod threads for harmonicas too, not sure if they need closer or further away from what a bass needs haha
 
#52
No, there's nothing about bass specific mods on there, but it did tell me what's in there. The suggestions are mine from my experience in building amps.

The two places where bass frequencies are generally attenuated in amps like that are in the bypass caps on the first preamp tube and in the coupling caps between stages. Guitar players are generally doing the opposite of what I'm suggesting. For instance, I just lowered the coupling caps in my Princeton because too much bass was getting through.
 
#55
This looks like a fun little project. +++++1 on the traynor amps. I have a bass mate. Beautiful mod platform, and a tighter power amp than my bassman1 (its build like the VHT like a guitar amp) I put the .1uf bypass caps on it and the bass blooms out of its huge little 40 watts
 
#57
jimmy rocket said:
found a mod thread on this over at Invalid Link Removed

looks like the bypass caps on V1 are 4.7uf - they need to be bumped up to 25uf
Click to expand...


What?? That R/C combination gives a breakpoint of ~ 23 Hz. What do you expect to accomplish boosting down to 4 Hz? If anything, I'd make it smaller.
 
#59
jimmy rocket said:
found a mod thread on this over at Invalid Link Removed

looks like the bypass caps on V1 are 4.7uf - they need to be bumped up to 25uf

The coupling caps all seem to be close to what you need. You may want to bump up the preamp coupling caps to .1uf as suggested, but it might make it "woofy"

You're talking less than $10 in mods there that would make a world of difference.
Click to expand...

Thanks for opinion man. The amp itself cost brand new Invalid Link Removed which is 150$, so I'm too very tempted

aetheriac said:
Here's part of the Special 6 at High Power, Boosted through a 2x10 Hydrive.
http://soundcloud.com/aetheriac/btsample-special6-210-115

Unfortunately the 1x15 was cut from the track on mix down.
The mic is crappy and my playing is mediocre, but there it is.
Click to expand...

Well it gives us some idea, thanks man. With right cabinet and mods it might turn out to be very interesting little practice amp indeed.
 
#60
JGR said:
What?? That R/C combination gives a breakpoint of ~ 23 Hz. What do you expect to accomplish boosting down to 4 Hz? If anything, I'd make it smaller.
Click to expand...

My bad, it looks like I was working off of a schematic with some changes already penned in. This thing is friendlier with bass than I imagined.


With those 1k5 resistors 4.7uf is fine. I wouldn't go down to 2.2uf though because you're raising the cutoff to 48 and rounding off the bottom end of 4 string land.

you could raise the resistor to 1k8 and then the 2.2uf would bring you in ~40hz and tighten that up.
 

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