• These commercial threads are for private transactions. diyAudio.com provides these forums for the convenience of our members, but makes no warranty nor assumes any responsibility. We do not vet any members, use of this facility is at your own risk. Customers can post any issues in those threads as long as it is done in a civil manner. All diyAudio rules about conduct apply and will be enforced.

PeeCeeBee Preamplifier GB

Jump to Latest
#521
cln.white said:
Hi Shaan, I now feel obliged to show some pictures of my effort. I had a bit of a struggle to get it in the enclosure but at this time needs must. It was actually a passive pre I has spare so it was forced into service! I must say also that the SIG control works exactly as you have described in your paper. Thanks for providing me with so much fun and games!
Click to expand...
"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!
:spin::cheers::spin:
 
#522
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
 
#523
Hello Shaan,

Both boards arrived today. Everything is in order. Thank you very much !
 

Attachments

  • IMG_1576.JPG
    IMG_1576.JPG
    564 KB · Views: 251
#526
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?
 
#527
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.
 
#528
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.
 
#529
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 👍
 
#531
shaan said:
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.
Click to expand...
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.
 
You must log in or register to reply here.
Top Bottom