So I Realised the other day that almost all the noise from my amp is from the pre amp. Before I build a new pre, just wanted to check what people thought of using very high rating caps to smooth the supply... i.e. What about using 98000uF / 25V caps? Would I experience ruler flat dc measurements or are there down-sides I haven't thought off?
Same question for my power amp... if I change my 22,000uF caps for 47,000?
Same question for my power amp... if I change my 22,000uF caps for 47,000?
What size caps are in at the moment? Probably the issue is poor design rather than cap value. Hum can also be caused by bad grounding implementation or wiring.
If it's noise then that's a different issue, but may again be down to poor design.
22000uF in a power amp is way more than enough not to have a hum problem. Unless it's class-a.
If it's noise then that's a different issue, but may again be down to poor design.
22000uF in a power amp is way more than enough not to have a hum problem. Unless it's class-a.
Bob Cordell's book suggests splitting up your enormous filter capacitor bank into more than one section, with small-valued series resistors between sections. One of the recent Sutherland phonostage preamps carries this to an extreme, splitting it into N>10 sections with series resistors connecting the sections. Why do they do this? it reduces ripple and RFI. It also squanders supply headroom, which may be important in a power amp but not so important in a preamp.
I had the same issue once, but thought it was from a Sumo amp I had.
After unplugging everything but the bare essentials, I found out the noise was coming in through the catv ground, which was electrically connected through other equipment.
Turns out that the Sumo amp was sensitive to the ground noise, as soon as the catv was disconnected, the noise was gone.
Not sure if something like that applies to you, or if you have already disconnected all unnecessary devices, but if you haven't already then it is worth a try.
After unplugging everything but the bare essentials, I found out the noise was coming in through the catv ground, which was electrically connected through other equipment.
Turns out that the Sumo amp was sensitive to the ground noise, as soon as the catv was disconnected, the noise was gone.
Not sure if something like that applies to you, or if you have already disconnected all unnecessary devices, but if you haven't already then it is worth a try.
You say "noise". What do you mean by noise? White noise? hum? clicks and pops? All the ground loop stuff mentioned is quite real. Some you can fix, some are designed in. I would have to assume your preamp has regulated supplies, so large filter caps should not be needed at all. The trick of low value resistors separating smaller caps works great by the way. But that is not likely your problem. I was having a heck of a problem in my system that I tracked down to a poor HDMI switch.
How old is this stuff? Electrolytic caps are good for 7 to 10 years before they dry out.
Just doubling your filter caps is a good way to blow up your rectifiers. Newer caps tend to have lower esr to boot. If you do a little searching, there are many good pieces on how to properly size your filter caps.
How old is this stuff? Electrolytic caps are good for 7 to 10 years before they dry out.
Just doubling your filter caps is a good way to blow up your rectifiers. Newer caps tend to have lower esr to boot. If you do a little searching, there are many good pieces on how to properly size your filter caps.
Right, what kind of noise - is a very good question.
Anyway, if it is related to poor rails filtering, I would rather use a simple 1-transistor regulator rather than enormously high caps values. Much more efficient and does not increase inrush current. The drawback is loss of roughly half-a-volt, but this is normally something you can live with.
Anyway, if it is related to poor rails filtering, I would rather use a simple 1-transistor regulator rather than enormously high caps values. Much more efficient and does not increase inrush current. The drawback is loss of roughly half-a-volt, but this is normally something you can live with.
Yeah, I should point out it's pre-amp noise/hiss, and it's very minor.
In general the only part of my set-up I'm not happy with is my speakers, but with several DIY projects going on that's not really an issue much longer!
The main thing Is I have two amps, both Identical, except the power stage in one has gone.
Thought maybe I could improve my sound quality by simply adding capacitance, or even unplugging the PSU from one unit and using the other units PSU, so that the power was effectively isolated into a separate box.
The series resistance idea seams pretty neat and easy to implement, the rest of what's discussed here I'd need to put some more thought into... but it sounds like it could be a way to make a pretty decent low V PSU for the Pre without a lot of hassle?
In general the only part of my set-up I'm not happy with is my speakers, but with several DIY projects going on that's not really an issue much longer!
The main thing Is I have two amps, both Identical, except the power stage in one has gone.
Thought maybe I could improve my sound quality by simply adding capacitance, or even unplugging the PSU from one unit and using the other units PSU, so that the power was effectively isolated into a separate box.
The series resistance idea seams pretty neat and easy to implement, the rest of what's discussed here I'd need to put some more thought into... but it sounds like it could be a way to make a pretty decent low V PSU for the Pre without a lot of hassle?
I don't think that "hiss" is coming from your power supply.
There is a lot to be said for a super quiet power supply though.
There is a lot to be said for a super quiet power supply though.
You might try altering your gain structure. You will probably find a gain structure that greatly diminishes the hiss.
A simple resistor network ("voltage ladder") between the preamp and power amp will accomplish this.
Since I know nothing about the circuits you are using, I would recommend trying 3 dB at a time. Once you hone in on your target, try 1 dB at a time.
You probably won't have to get it exact to realize a major reduction in hiss. Make sure to leave yourself enough headroom. 😉
A simple resistor network ("voltage ladder") between the preamp and power amp will accomplish this.
Since I know nothing about the circuits you are using, I would recommend trying 3 dB at a time. Once you hone in on your target, try 1 dB at a time.
You probably won't have to get it exact to realize a major reduction in hiss. Make sure to leave yourself enough headroom. 😉
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This is called a capacitor multiplier and is used in many power amps to clean up the IPS/VAS rails. They work even better than the resistor separated idea but are a tad more complex needing board space, where you can retrofit and "fly" the passive version.
BUT, a preamp is likely to have a regulated supply making this unnecessary.
Back to hiss. I agree, probably not the power supply. Hiss, or white noise as it is called, is usually from the input stage of the preamp or the input stage of the power amp. Everything generates Johnson noise if there is a current going through it. Unless this is new, indicating a failure, it is probably design based. We would need to know a lot more about the units involved.
Some older IC regulators can produce objectionable hiss. You haven't shown us the power supply circuitry. It's probably just old poor design.
Shouldn't a local bypass capacitor clean that up? A good design will have a local bypass or trap circuit.
Yes, an m derived pi filter or proper power supply resistor-capacitor decoupling just depends on the current draw to get good regulation. Really good ripple reduction sometimes requires multiple stages like the RONAN regulator.
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