I recently completed a tube power amp build (Pete Millets DCPP) and though it works great I do get three little annoying pops somewhere 30 seconds after turning it on.
I have had this issue with other builds before. In those instances the designs were preamps though, I implemented a simple 555 timer relay setup to short the outputs to ground for the first 30 seconds following startup.
I am not sure how to implement a mute circuit on a tube power amp though (???). I don't think shorting an output transformers secondary windings together (to ground) is advisable when the output tubes are conducting.
How does one implement a mute circuit for startup on a tube power amp?
I have had this issue with other builds before. In those instances the designs were preamps though, I implemented a simple 555 timer relay setup to short the outputs to ground for the first 30 seconds following startup.
I am not sure how to implement a mute circuit on a tube power amp though (???). I don't think shorting an output transformers secondary windings together (to ground) is advisable when the output tubes are conducting.
How does one implement a mute circuit for startup on a tube power amp?
This is one solution, https://diyaudiostore.com/collectio...oducts/high-voltage-delay-for-tube-amplifiers
Would a relay work if used so it initially connects a dummy load and then switches to speaker feed. So just a standard DPDT relay and timer. There could be a few milliseconds when no load is connected as the contacts move but would that be a problem in practice.
You could also use two overlapping delays, one to open the dummy load after the speakers connect. I would guess the dummy load need not be all that low in resistance either.
You could also use two overlapping delays, one to open the dummy load after the speakers connect. I would guess the dummy load need not be all that low in resistance either.
I do want to implement a HV delay eventually but I dont know if a HV delay is what would fix my "problem" here (???).
There is zero problem by shorting the speaker outputs in a tube amp. Open output on the other hand, which will occur during switching load, is asking for problems.
One should however identify and fix the cause of "annoying pop". Schematics cold be of help here
I've little to no practical experience on valve amps and that was something I had wondered as it is the easy and obvious method.
Would there be any 'noise' or unwanted behaviour in a short time interval after the short was removed?
My thinking was that the feedback loop seems to be taken from the secondary of the output transformer and I wondered what the amp might do under those conditions.
Well here is a video of the pop so you can hear it! It occurs about 20 seconds after being turned on. Always the same noise and sequencing of pops.
That sounds really odd to me. Silly question but does it do that with shorting plugs in the inputs?
That is two seconds after power-up? Go look for a time constant in the schematics, somewhere an RC circuit is causing this time delay. What happens when you turn the power off. Can you publish your schematic, and we have a look see. Is the problem identical on both channels?
Schematic:
http://www.pmillett.com/file_downloads/dcpp_sch.pdf
http://www.pmillett.com/file_downloads/dcpp_sch.pdf
Let me try this and report back!
The noise occurs about 18 seconds after start up. I shortened the video to highlight just the noise.
I see three different time constants in the power supply alone, could this contribute to the problem?
What happens if you turn the power off just after you heard the plop and then on again, is there a plop, sooner than 18 seconds or maybe not at all?
I would suggest that the HV is turned on only after the other voltages has settled, i.e. use your current mains switch as a "standby switch" and switch the HV on and off as if it was the mains. Valves takes some time to operate, only after the heaters have stabilized anyway would it be very annoying to you to place a time delay in the HV circuit as a suggestion and delay it by say 18 seconds.
The screen voltage is delayed more than the HV according to the schematic, should it not be the other way round.
Screen voltage is spotted. No it must not be turned on before plates. But the time seems to fit. Could be oscillation
that occurs when g2 is applied. Shorten timeconstant ( reduce R33 to half and see if sounds comes at half time. )
that occurs when g2 is applied. Shorten timeconstant ( reduce R33 to half and see if sounds comes at half time. )