Hello everyone! I saw loads of schematics for 18-20W guitar amplifiers using two EL84 tubes, but I can't find any schematics for a bass guitar amp.
I have most of the necessary parts, so I'm looking for an amp schematic that uses two EL84s to produce about 20W.
Can anyone help me? Thanks!
I have most of the necessary parts, so I'm looking for an amp schematic that uses two EL84s to produce about 20W.
Can anyone help me? Thanks!
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Hi,
quite a lot of info available for the Traynor YBA-1 Bassmaster.
rgds, sreten.
That would be a tiny bass amp.
But look at and steal the circuit of:
Peavey Classic 20
Fender Blues Junior
Crate V18-112
Vox AC15
And so on. If you hold them at arm's length and look at the overall circuit, they are all pretty much the same.
perhaps you already saw all of those. Finding an amp specifically for bass using those tubes will be tough, but really, the amps don;t care what you play through them.
You could use DUncan's Tone Stack Calculator to adjust the center frequencies of the tone controls to be more bass friendly. You could increase some coupling caps to reduce low end rolloff. But you also run into the bottom end demands running this tiny amp out of breath.
But look at and steal the circuit of:
Peavey Classic 20
Fender Blues Junior
Crate V18-112
Vox AC15
And so on. If you hold them at arm's length and look at the overall circuit, they are all pretty much the same.
perhaps you already saw all of those. Finding an amp specifically for bass using those tubes will be tough, but really, the amps don;t care what you play through them.
You could use DUncan's Tone Stack Calculator to adjust the center frequencies of the tone controls to be more bass friendly. You could increase some coupling caps to reduce low end rolloff. But you also run into the bottom end demands running this tiny amp out of breath.
At that sort of power level, a pair of EL84s will be distorting quite a bit. If that's the sound you're after, which is less usual for bass, fine, if not, consider a pair of EL34s instead.
EL84s distort early, in terms of (power)/(rated max power), so bear this in mind.
Not mentioned so far is that the power you can put through an output transformer without running into saturation of the magnetic core depends on frequency. The lower the frequency, the lower the power. Bottom E on a guitar is 82Hz, on a bass, 41Hz.
Roughly speaking, this means you can put 1/4 the power through a given transformer at 41Hz than at 82Hz, for a given level of transformer distortion. A 20w "guitar" output transformer will not be so good for 20w of bass.
High power valve bass amps are usually dangerously heavy. Having helped cart an Ampeg SVT into and out of gigs in the dim and distant past, I'd say, if you like valve sound for bass, use a small one and take a di into solid state when you need more volume.
EL84s distort early, in terms of (power)/(rated max power), so bear this in mind.
Not mentioned so far is that the power you can put through an output transformer without running into saturation of the magnetic core depends on frequency. The lower the frequency, the lower the power. Bottom E on a guitar is 82Hz, on a bass, 41Hz.
Roughly speaking, this means you can put 1/4 the power through a given transformer at 41Hz than at 82Hz, for a given level of transformer distortion. A 20w "guitar" output transformer will not be so good for 20w of bass.
High power valve bass amps are usually dangerously heavy. Having helped cart an Ampeg SVT into and out of gigs in the dim and distant past, I'd say, if you like valve sound for bass, use a small one and take a di into solid state when you need more volume.
Hi,
FWiW nearly all small classic valve bass amplifiers, (identified basically
by having more iron in the output transformer than for guitar), have
been appropriated by guitarists for their "thicker" distortion sound.
If you have the bits TBH an effective 20W guitar amplifier is easier
as you can make it far louder with a guitar versus bass speaker.
rgds, sreten.
TBH for bass I'd prefer BJT's in a degenerated setup with no overall
feedback other than some form of optical soft limiting, YMMV.
FWiW nearly all small classic valve bass amplifiers, (identified basically
by having more iron in the output transformer than for guitar), have
been appropriated by guitarists for their "thicker" distortion sound.
If you have the bits TBH an effective 20W guitar amplifier is easier
as you can make it far louder with a guitar versus bass speaker.
rgds, sreten.
TBH for bass I'd prefer BJT's in a degenerated setup with no overall
feedback other than some form of optical soft limiting, YMMV.
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And the EL84 usually has a thinner bottom end than, say a 6V6, even for guitar. What output transformer are you thinking of? The previous replies are right about needing a lot more iron for bass. Also the reason bass amps were popular with guitar players is the manufacturers sized the transformers for the frequency response of a guitar in guitar amps but they did it with clean output in mind. Of course guitar players ran them distorted, with wimpier output transformers they would sometimes 'fart out'. A sign of needing a bigger transformer.
Nothing wrong with your plan. Traynor YBA-2 came in a EL84 (actually 6BQ5) version as well as 6V6. Schematics for all vintage versions here:
Velvet Black - Models
Velvet Black - Models
Yes,
20W is plenty for a bass amp except for stadium, very large room gigs. The "trick" is at least one and better with two off 12" speakers.
Cheers,
Ian
20W is plenty for a bass amp except for stadium, very large room gigs. The "trick" is at least one and better with two off 12" speakers.
Cheers,
Ian
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