Fender FR-12 preamp mod : The Hissterectomy

WKSmith said:
One of them was acting weird when I posted it.
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Seems fine now. Idk

WKSmith said:
The FR-12 can play pretty flat with the eq dialed in. It just naturally has a curve in the response with the eq knobs on 5.
I really like how that curve sounds as a backline though.
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It would be interesting to see a frequency graph after your crossover mod and with the knobs set in such a way as to make it as flat as possible. That's just purely for curiosity's sake though.
 
WKSmith said:
Yeah my eq is 3 filters instead of 4. I may try it both ways. But I am trying the cut knob after the high pass xover to attenuate just the compression driver.
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Ahhh. That makes sense! IMO the cut knob is the most useful part of the EQ section. And that's purely for its tonal control and not even considering the hiss reduction.
 
2204JCM said:
Yeah, but on the other side do you actually think you can hear the difference between metal film and carbon film resistors?
If you told an engineer that he'd laugh.
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Maybe not. But typically, tolerances are tighter on metal film resistors. That means less variation from build to build, with more accurately predictable results. The circuit you get is closer to the circuit you designed.
 
2204JCM said:
Yeah, but on the other side do you actually think you can hear the difference between metal film and carbon film resistors?
If you told an engineer that he'd laugh.
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I like a hybrid of both of if the budget is tight.
Metal Film when it's in the audio path and feedback loop, and carbon film if it goes to ground.
Same for caps. The ones that go to ground can be less expensive . Sonically they are not critical there, but tight tolerances often are.
 
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Rex said:
Maybe not. But typically, tolerances are tighter on metal film resistors. That means less variation from build to build, with more accurately predictable results. The circuit you get is closer to the circuit you designed.
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Metal film are for precise low noise circuitry such as in instrumentation.
The tolerances in carbon film are plenty good these days. There's no way you would hear a noise difference in an audio circuit.
I understand using them in personal builds. But for mass production consumer stuff its just a waste of $$$.
 
2204JCM said:
Metal film are for precise low noise circuitry such as in instrumentation.
The tolerances in carbon film are plenty good these days. There's no way you would hear a noise difference in an audio circuit.
I understand using them in personal builds. But for mass production consumer stuff its just a waste of $$$.
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But buying 12,000 resistors at a time, the cost for metal film was not much more.

Maybe pricing has changed in 10 years though from what I remember. But it was a fraction of 1¢ difference.

I would prefer they save money elsewhere in the design, that actually does kill the hiss. And then buy metal resistors for the audio path , and lower tolerance caps.

For the V2 preamp design, it's on my list of mandatory spec. Because my name is on it.
 
2204JCM said:
Yeah, but on the other side do you actually think you can hear the difference between metal film and carbon film resistors?
If you told an engineer that he'd laugh.
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Carbon comp resistors are well known for shot noise issues, especially at higher voltage potentials across the resistor (like in tube amp preamp plate resistors). It's measurable, and even carbon film resistors are less noisy and tighter tolerance. Metal film are even less noisy as well as generally tighter tolerance than carbon film. Certainly any decent engineer would be knowledgeable on the topic of parts quality....
 
2204JCM said:
Metal film are for precise low noise circuitry such as in instrumentation.
The tolerances in carbon film are plenty good these days. There's no way you would hear a noise difference in an audio circuit.
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Phase inverter circuits driving the power amp tubes don't have much gain between them and the speaker output, and can get away with noisier resistors, but the cascaded high gain preamps in guitar amps multiply everything - guitar signal and noise - that comes into their inputs, and demand careful attention to noise entry into the audio....
 
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