Can someone explain why substituting one op amp for another in a preamp stage (Musicman 130 210 combo, chassis 2275) would result in more gain through the preamp stage? I can't really square this with my understanding of how op amps work.
Specifically, I've been substituting LM307H op amps (which are the original spec for the circuit) with LF356N, which sound better, but also result in noticeably higher gain. I understand that any real op amp will vary from an ideal op amp in terms of frequency response characteristics, slew rate etc., but gain is pretty much gain... unless you were pushing the op amps to their gain limits, I would expect them to result in functionally very similar gain for a guitar audio signal.
So, for example, the -ve feedback resistors of r1 = 10K and r2 = 220K for op amp IC3 (channel 2) in that circuit should show result in a gain on the non-inverted input of 1 + (r2/r1) = 23. But substituting in the LF356N for the LM307H for this IC results in noticeably more gain.
This is just an example. Gain increases are also noticed when the LM307H ICs are subbed with LF356N in other stages of the preamp, e.g. IC4 and IC7.
Why would this be?
The schematic for this amp as a pdf can be found at http://www.musicmanamps.com/schematics/2475-130_and_2275-130.pdf in anyone is interested in the specifics of the circuit. The preamp section looks pretty straightforward to me, but there is always the possibility there's something I'm missing here.
BTW, the reason I've been experimenting with substitutions is because I quite like the sound of the of the LF356N -- a bit warmer and organic sounding to my ear than the stock LM307H. A little less noisy, too. But the extra gain is causing problems with the trem circuit (which is on channel 2), so I've gone back to the LM307H on channel 2 for the time being. But in any case, I'd like to understand the practicalities of op amps a bit more fully.
Specifically, I've been substituting LM307H op amps (which are the original spec for the circuit) with LF356N, which sound better, but also result in noticeably higher gain. I understand that any real op amp will vary from an ideal op amp in terms of frequency response characteristics, slew rate etc., but gain is pretty much gain... unless you were pushing the op amps to their gain limits, I would expect them to result in functionally very similar gain for a guitar audio signal.
So, for example, the -ve feedback resistors of r1 = 10K and r2 = 220K for op amp IC3 (channel 2) in that circuit should show result in a gain on the non-inverted input of 1 + (r2/r1) = 23. But substituting in the LF356N for the LM307H for this IC results in noticeably more gain.
This is just an example. Gain increases are also noticed when the LM307H ICs are subbed with LF356N in other stages of the preamp, e.g. IC4 and IC7.
Why would this be?
The schematic for this amp as a pdf can be found at http://www.musicmanamps.com/schematics/2475-130_and_2275-130.pdf in anyone is interested in the specifics of the circuit. The preamp section looks pretty straightforward to me, but there is always the possibility there's something I'm missing here.
BTW, the reason I've been experimenting with substitutions is because I quite like the sound of the of the LF356N -- a bit warmer and organic sounding to my ear than the stock LM307H. A little less noisy, too. But the extra gain is causing problems with the trem circuit (which is on channel 2), so I've gone back to the LM307H on channel 2 for the time being. But in any case, I'd like to understand the practicalities of op amps a bit more fully.