"The Pre"
Yeah, I like it! 😎
Happy to know you enjoyed the build.
Happier to see your mention of SIG. While incorporating this live H2 control with minimal output level variation using solely BJTs was one of my personal design goals that was met, it also gradually came to me that its perceived effects, are somewhat divisive. So whenever someone says the SIG works, I feel ecstatic!
Hi all, I got my pcb all populated, not cased in yet but it seems I got a ground loop of some sorts because I got the famous 50hz buzzing.
I'm using the Purifi 1et400a as power amp with a Khozmo relay attenuator before the input and I don't got the buzzing with the DAC straight in (DAC has both balanced/unbalanced outputs). The Pre has the buzzing even without connected to an input source.
Please forgive my (probably) stupid question: should I set the ground of the pcb to earth ? it's not earthed yet
Any suggestions are highly appreciated
Thanks all,
Adrian
I'm using the Purifi 1et400a as power amp with a Khozmo relay attenuator before the input and I don't got the buzzing with the DAC straight in (DAC has both balanced/unbalanced outputs). The Pre has the buzzing even without connected to an input source.
Please forgive my (probably) stupid question: should I set the ground of the pcb to earth ? it's not earthed yet
Any suggestions are highly appreciated
Thanks all,
Adrian
Hi Adrian. Sorry for late response.
In case the problem persists, yes you should. Preferably via a network of 10ohm+100nF ceramic in parallel.
Hi Shaun,
I have a problem which I think has developed on the pre-amp. I am getting a sound which I can describe as white noise coming through the when the amp is in use. I can move between channels and is there even when the volume is set to minimum. The volume can go up and down and also at times disappear completely just to return as the musical enjoyment is at it's height! I have changed it out foe a passive I have and the sound is OK. Any ideas please?
I have a problem which I think has developed on the pre-amp. I am getting a sound which I can describe as white noise coming through the when the amp is in use. I can move between channels and is there even when the volume is set to minimum. The volume can go up and down and also at times disappear completely just to return as the musical enjoyment is at it's height! I have changed it out foe a passive I have and the sound is OK. Any ideas please?
Hi Colin.
Turn on everything and connect a test speaker to the amplifier, not main speakers.
Take a screw driver and slowly turn the trimmers VR1 to VR4 just about a mm or so. If the noise goes away or comes back intermittently as you turn, then the trimmers are bad. I have had this static-like noise problem in the preamp a couple times.
The best solution is to turn off the preamp, give it 5 minures for the caps to drain completely, measure the VR1-4 trimmers between pin 1 and 3 individually, remove each trimmer and replace with fixed resistors of the nearest value available. Don't worry about the offset/bias, it will not change too much to affect performance.
Turn on everything and connect a test speaker to the amplifier, not main speakers.
Take a screw driver and slowly turn the trimmers VR1 to VR4 just about a mm or so. If the noise goes away or comes back intermittently as you turn, then the trimmers are bad. I have had this static-like noise problem in the preamp a couple times.
The best solution is to turn off the preamp, give it 5 minures for the caps to drain completely, measure the VR1-4 trimmers between pin 1 and 3 individually, remove each trimmer and replace with fixed resistors of the nearest value available. Don't worry about the offset/bias, it will not change too much to affect performance.
Hi Shaan, Set it up with other amp and speakers but not making the "static" noise I described. On switch-on loud wheeeeing then drops off but no other sound. Haven't connected a source yet. what is the problem using my other amp and speakers? They are Musical Fidelity power amp and Linn Majik140 speakers. If you think it better to measure and replace the trimmers with fixed resistors that is what I will do.
Are you turning the preamp on after the power amplifier? The preamp should be first “on” and last “off”. Power amplifier is last “on” and first “off”. This sequence eliminates transients from being amplified as the preamp stabilizes from power up. This sequence should be followed with any preamp/amp combo
Hi Shaan, Followed your suggestion above and seems all OK now. It was when I turned VR2 that the sound disappeared for me! Thanks again.
