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Hi,What value/s would you guys recommend in bypassing 1uF/400wvdc output caps in a phono preamp for better bass? Thanx.
Follow Ups:
Bypassing is kind of a "last resort" for those situations where you're stuck with a big cap value. But 1 microfarad is hardly a huge value, so just replace it altogether with something better.
Thanks. But what value can I use without altering other values in the circuit?
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Assuming the current output coupling cap is properly sized I don't think paralleling (aka bypassing) with another cap will make a significant enough different in the bass."Bypassing" usually means that you are paralleling the existing cap with a relatively small cap, maybe .1 of the original value or so. This is done to help out the high freqs. Even doubling it to move the -3db down probably won't do much assuming its big enough to start with and it may actually hurt - its entirely possible to have too much IMHO. Whats the input impedance of the next stage and the output impedance of the phono pre?
IMHO you may be able to get enough of an improvent to suit your tastes by *slightly* tweaking components in the RIAA curve circuitry to tip the lf response up a db or so. Try it and see. Another variable is the cartridge - some do LF subjectively better than others in any given system, just like tubes can. Maybe this is worth exploring too. -jd
Hey-hey!!!,
I don't think a bigger cap will do much good. The input impedance of the linestage is large compared to the impedance of that cap. which is aout 8k Ohm at 20 Hz. You could try doubling it, but better results will probably be had by bypassing with a good film/foil cap or maybe a 1.5 uF polypropylene/tin type of comparable voltage. As long as your linestage has imput impedance on order of 100 k Ohm you won't get much more from a bigger cap, though a slightly bigger and better quality one will help. Try one of the Russian TFE caps in .o56 size from KWTubes, I put one of those across the 3uF solens in the output of my linestage and get smooooth restult( a quality the Solen is not known for).
regards,
Douglas
Thanx for the advice Sector-7G. I just want to mention again that the preamp is phono, not a linestage. If I bypass them with 0.056uF Russian Teflons, it may become smoother, BUT would it also IMPROVE BASS significantly?
I did understand the amp in question is a phono pre. The input impedance of the linestage is the important thing. At 20 Hz it must be large compared to the 8 kOhm impedance of the 1 uF cap. 100 kOhm is probably enough, but, the linestage folks with 100-200k imput impedance amps still want around 3uF of output capacitor. Just try a 20:1 ratio,so your linestage will want about 150 k Ohm impedance, if not then increase the cap size and use a good one. SCR Tin and polyprop is a good palce to start and they come in 1.5 uF size. The internal circuit mods may be necessary if this( 20:1 linestage input impedance to cap impedance ratio at 20 Hz) does not help, as I would then say that it's not the cap causing poor bass response.the small TFE will probably not help bass much as you mentioned but I'd try it anyway if they are relatively easy for you to get, the better performing the cap the better the sound.
regards,
Douglas
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