I am looking to improve the sound of my cheapie Peavey Basic 50 guitar amp. It currently uses 4 x RC4558 opamps. I am considering OPA627($$$$), OPA827 ($$), or OPA2134($). Has anyone been able to compare these, or other FETs, for preamp usage?? This is primarily for pedal steel guitar.
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Perhaps, but the noise specs of the TL072 are quite a bit worse than the lowly 4558, and MUCH MUCH worse than the other ICs I mentioned; THD is worse as well. I don't know if this translates well for a pedal steel guitar amplifier, but a lot of players who have installed the "Ken Fox" mods to their Peavey amplifiers seem to think that the ICs DO make a difference. Are you saying that ANY old op amp will sound the same in a circuit with negative feedback?? I can't remember seeing ANY opamp circuit that doesn't use negative feedback; so I guess I am missing your point.
I am playing DIY-amps for a lifetime, and did many tests with op-amps.
If you are looking for low-noise in most cases you will find the circuitry the limiting factor with 100kOhm-pots, hi-impedance feedback networks and so on. Noise performance of most real circuitry is far away from physical limits.
And if you are looking for distortion - this is not hi-fidelity. Any OPA from TL072 upwards will to the trick.
Over the years I had built myriads of solid-state amps, and the signal path often had to pass a bunch of TL072/NE5532 or similar.
This never had been a problem. Occasionally I was asked which tubes I put into my amp - and the answer was zero - niente - nada
Nonetheless I am picky with noise. And I modded any guitar that I put my hands on: Electrostatical shielding, stacked humbucker pickups and an in-built buffer-amp - that is what I consider real progress in sound.
Just my 2c.
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If you are looking for something that sounds more like a tube preamp, try this:
The JFET Bender Preamp
You may have to joint the forum to see the attachments.
Many of the Peavey opamp preamps use a variable gain first stage that is not compatible with the idea of using a JFET in the feedback network to create distortion.
The JFET Bender Preamp
You may have to joint the forum to see the attachments.
Many of the Peavey opamp preamps use a variable gain first stage that is not compatible with the idea of using a JFET in the feedback network to create distortion.
What I would do is put a TL072 or LF412 in place of just the 1st 4558. Using high dollar op amps in a guitar amplifier is silly, given all the electrolytics and other caps shaping and limiting bandwidth. LF412 measured well in a Bob Cordell paper, so gfy to those who want to discuss the "sound" of op amps.
What did you use for shielding? Mu-metal foil, maybe? And what components for your buffer?? I just noticed the OPA1642--even less expensive (~$3) than a 2134, and better specs. And I will probably put film caps in place of the electrolytics.I am playing DIY-amps for a lifetime, and did many tests with op-amps. If you are looking for low-noise in most cases you will find the circuitry the limiting factor with 100kOhm-pots, hi-impedance feedback networks and so on. Noise performance of most real circuitry is far away from physical limits. And if you are looking for distortion - this is not hi-fidelity. Any OPA from TL072 upwards will to the trick. Over the years I had built myriads of solid-state amps, and the signal path often had to pass a bunch of TL072/NE5532 or similar. This never had been a problem. Occasionally I was asked which tubes I put into my amp - and the answer was zero - niente - nada
He said "Electrostatical shielding". That means a good conductor - probably aluminium sheet. Mu-metal is for magnetic shielding.
Don't replace electrolytics with film caps unless you are sure that the circuit does not rely on ESR to damp any local resonances. And you are sure that the physically larger film caps will not create unwanted extra stray capacitive coupling, thus adding hum or instability.
Guitar amps are not hi-fi. Even in hi-fi opamp swapping is more a fad than serious engineering.
Don't replace electrolytics with film caps unless you are sure that the circuit does not rely on ESR to damp any local resonances. And you are sure that the physically larger film caps will not create unwanted extra stray capacitive coupling, thus adding hum or instability.
Guitar amps are not hi-fi. Even in hi-fi opamp swapping is more a fad than serious engineering.
Copperfoil or any other metal foil that is solderable are fine.
Mu-Metal has never been an option here.
The buffer maybe an JFET Opamp, but I do prefer discrete JFET buffer because current consumption can be set to several 100uA for long battery life.
In the signal path of a guitar PreAmp there is no need for electrolytics with coupling capacitances below 1uF so I normally use film caps here.
that is your opinion.
Nonsense for my opinion.
Should I post you a guitar sound sample and you tell me the electronics in the signal path?
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There are plenty of guitar amps without opamps in the signal path.
Download the book in this thread: Teemuk's Book about solid-state guitar amplifiers
Download the book in this thread: Teemuk's Book about solid-state guitar amplifiers
Certainly there are. But I am sure you could not discern whether there are OPAs in the signal path or not.
It is simply irrelevant.
Any outstanding Guitar sounds are produced by outstanding guitar players.
Period.
Btw, Teemuks Book ist a must read!
OpAmps sure can have their place in a guitar amp like in the first stage (as a "booster"), certain types of tone controls, buffers, level shifters, effect loop drive and return circuits (including integrated spring reverb), etc.
But for the core stages where the characteristic distortion and compression is happening it is much easier to work with simple discrete semiconductors.
But for the core stages where the characteristic distortion and compression is happening it is much easier to work with simple discrete semiconductors.
jfetrer's comment was to have a discrete SS amp WITH ONLY LOCAL FEEDBACK.
STFU if you don't understand.
This forum turns more and more into a dead letter box for people who actually understand the discussion every day
The hard clipping of an OPA with local feedback is not the kind of distortion most guitar players are after, including me.
The non-linear element should be something with a smooth transition to clipping, like JFETs, Diodes, differential pairs etc.
Something like this sound sample of light overdrive...
The non-linear element should be something with a smooth transition to clipping, like JFETs, Diodes, differential pairs etc.
Something like this sound sample of light overdrive...
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