I just finished this pre-amp and have a constant hiss (too loud to ignore).
It does not change with the volume control.
I tried various PSU configurations, but it stays the same.
(HV MOSFET regulator, CRCRC, CLCRC)
On the PSU I have a 20mV 100Hz ripple and on the outputs I see a 40kHz 20mV ripple. I have no idea where that is coming from. It is not on the input, I also do not see it on the base or emitter of Q1.
Anyway, I don't think this is the hiss I hear, way too high for my ears.
I tried another set of valves as well.
I lowered the heater voltage also to 12V.
How can I fix this hiss noise?
Thank you for any help.
It does not change with the volume control.
I tried various PSU configurations, but it stays the same.
(HV MOSFET regulator, CRCRC, CLCRC)
On the PSU I have a 20mV 100Hz ripple and on the outputs I see a 40kHz 20mV ripple. I have no idea where that is coming from. It is not on the input, I also do not see it on the base or emitter of Q1.
Anyway, I don't think this is the hiss I hear, way too high for my ears.
I tried another set of valves as well.
I lowered the heater voltage also to 12V.
How can I fix this hiss noise?
Thank you for any help.
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Last edited:
On the PSU I have a 20mV 100Hz ripple and on the outputs I see a 40kHz 20mV ripple.
Is there also any audible hiss ?
Try to replace the CCS with a resistor to see if the hiss comes from the CCS (or from tube).
Good question audiowize. That load circuit is the first CCS I ever built. The HLMP 6000 series red from HP was the recommended part (for low noise) at the time.
If you have the parts handy you might try 100R in series with the base of each transistor and .1uF in across each of the LEDs.
Though it was quiet I soon opted for another circuit.
Somewhere in my playing with this circuit I also tried 47uF from the Vin to the base of each transistor at the junction of 100R and Base.
If you have the parts handy you might try 100R in series with the base of each transistor and .1uF in across each of the LEDs.
Though it was quiet I soon opted for another circuit.
Somewhere in my playing with this circuit I also tried 47uF from the Vin to the base of each transistor at the junction of 100R and Base.
What LED's? (They aren't all quiet)
Cheap, red, chinese ones. I will find some others and try them.
... but there are always room for improvement.
I now use another CCS, 2x DN2540 set to 17mA.
HISS is almost gone (slightly more then only the resistor, but MUCH less then the LED version) and the general sound is even better then before.
I also changed the heater supply to a 12V 3A SMPS. To get rid of the faint humm, I also implemented the "ground breaker" scheme, works like a charm.
I now use another CCS, 2x DN2540 set to 17mA.
HISS is almost gone (slightly more then only the resistor, but MUCH less then the LED version) and the general sound is even better then before.
I also changed the heater supply to a 12V 3A SMPS. To get rid of the faint humm, I also implemented the "ground breaker" scheme, works like a charm.
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I currently use this linestage with some Mullard 4-20's and Fostex FE207e speakers, which is very good but too sensitive I think.
With what can I replace them, not DIY up to £500.
Link to my amps: Mullard 4-20's
With what can I replace them, not DIY up to £500.
Link to my amps: Mullard 4-20's
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