Hi all,
My preamp https://www.quasarelectronics.co.uk/Item/smart-kit-1215-stereo-line-level-audiophile-preamp-or-headphone-amplifier / https://www.quasarelectronics.co.uk/Item/smart-kit-1216-9-24v-1a-audiophile-dual-polarity-power-supply causes my speakers to pop (sometimes very loudly) when the mains supply is switched off. I am running it into a dual mono LM3875 Gainclone. It only happens when I switch the pre off first. If I turn off the power amp first and wait a few seconds, then turn of the pre it doesn't pop. Unfortunately, the power switch to the power amp is at the back of the cabinet, and my better half keeps forgeting (or so she says) to turn it off first.
Anything I can do to rectify this? Banning my wife/kids from using it is not an option 😉
My preamp https://www.quasarelectronics.co.uk/Item/smart-kit-1215-stereo-line-level-audiophile-preamp-or-headphone-amplifier / https://www.quasarelectronics.co.uk/Item/smart-kit-1216-9-24v-1a-audiophile-dual-polarity-power-supply causes my speakers to pop (sometimes very loudly) when the mains supply is switched off. I am running it into a dual mono LM3875 Gainclone. It only happens when I switch the pre off first. If I turn off the power amp first and wait a few seconds, then turn of the pre it doesn't pop. Unfortunately, the power switch to the power amp is at the back of the cabinet, and my better half keeps forgeting (or so she says) to turn it off first.
Anything I can do to rectify this? Banning my wife/kids from using it is not an option 😉
Assuming the switch is on the primary side of trafo, you can try putting a 22nF 630V polypropilen cap in parallel with the mains switch (i.e. bypass the switch with the cap).
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I shall give it a go. I would assume that I would get switching noise at both switch on and switch off though?
Is the mains switch OK ? Is it suitable for switching an inductive load such as a transformer. Have you tried pulling the mains plug (or a switched socket) to the preamp and seeing if it still makes the noise.
Mains switch is a 10A/250Vac switched IEC socket; exactly the same switch that's in my power amp. I've just pulled the mains plug from the wall socket and it makes exactly the same noise.
(I'm currently trying to model the circuit on SPICE after reading your guide. I'm struggling to find voltage regulators though.)
(I'm currently trying to model the circuit on SPICE after reading your guide. I'm struggling to find voltage regulators though.)
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Maybe it's a turn-off transient in the preamp circuit, not the switch itself.
Some preamps do require a muting relay at the outputs on power up/down to avoid noises.
to get rid of switch on/off "plop" , i would suggest a relay with time delay.
most possibly the "plop" comes from the input caps charging up.
You can possibly verify it,
there is a schematic in Your link.
according to that You got 2 input capacitors, C1 and C51.
see if Your source has any significant DC level, if not then You can short those caps out for a test run.
if the plops stop, then we have a winner.
allso do check if the problem is exsistent if You use the "REC OUT" to connect an amplifier.
most possibly the "plop" comes from the input caps charging up.
You can possibly verify it,
there is a schematic in Your link.
according to that You got 2 input capacitors, C1 and C51.
see if Your source has any significant DC level, if not then You can short those caps out for a test run.
if the plops stop, then we have a winner.
allso do check if the problem is exsistent if You use the "REC OUT" to connect an amplifier.
Thanks chaps. A time delay muting circuit sounds like it could do the job. Any ideas on a suitable design?
There are several based on a 555 timer floating around, I believe one was in Audio Amateur / AudioXpress.
TDA8560 pdf, TDA8560 description, TDA8560 datasheets, TDA8560 view ::: ALLDATASHEET :::
page 11 fig 7.
i'd assume it would need a buffer to drive relays, but i might be wrong.
i do not have time to check out.
You might want to change the 100 ohm ressitors in series with the reamp output to something like 1K ohm. If You short the preamp output otherwise it may damage it self with only 100 ohm load.
page 11 fig 7.
i'd assume it would need a buffer to drive relays, but i might be wrong.
i do not have time to check out.
You might want to change the 100 ohm ressitors in series with the reamp output to something like 1K ohm. If You short the preamp output otherwise it may damage it self with only 100 ohm load.
well this might be an over simplification but in my many years as a touring sound technician it was a strictly enforced rule:do not power down low level (preamp, mixer, effects) while high level (power amps) are on.
the rant was...at power up, low level first,high level last.at power down, high level first, low level last! and never "hot"patch (connect things while powered up. even speakers!)
it became a standard procedure to avoid turn on/off transients.
not saying that there isn't a work around to the problem but to me it's kind of like starting to weld without dropping your visor(go ahead but it's not a good idea!)
the rant was...at power up, low level first,high level last.at power down, high level first, low level last! and never "hot"patch (connect things while powered up. even speakers!)
it became a standard procedure to avoid turn on/off transients.
not saying that there isn't a work around to the problem but to me it's kind of like starting to weld without dropping your visor(go ahead but it's not a good idea!)
after a quick reread of the thread i think a relay to mute the output of the preamp at power down (no delay as you would want the output of the preamp to disconnect long before the supply starts to collapse)or relocating the amp's power switch is in order...
sorry if the previous post seems rant like.
sorry if the previous post seems rant like.
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Yes, definitely. Lest anyone be tempted to just leave the preamp powered on all the time, don't forget about power outages.
The trick with a 555 timer muting circuit (to make the relay close instantly upon switch off) is to use a normally closed relay,
and to connect a diode's anode to the timing capacitor, and the diode's cathode to the source of the 555 supply voltage
(not just across the timing resistor). This drops the timing capacitor voltage as quickly as possible. I'll post my version if I can locate it.
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Pleased you are finding the thread useful. I can't recall seeing any (simple 3 terminal) voltage reg models either. If you are trying to model the on/off behaviour of the circuit then I suspect you wont have much luck tbh. There are far to many unknowns to make a successful simulation of that.
Pulling the plug and you getting the noise is what I wanted to see.
Something like this could be adapted for a simple delay. There is a spice file in post #1 and a couple of video clips in post #24
http://www.diyaudio.com/forums/solid-state/224957-simple-universal-speaker-delay-using-triac.html
It could be a turn off transient...
Does the pop coincided exactly to the nanosecond 😀 you switch off, or is there a detectable time difference (no matter how small). If there is a time difference then a delay could work well, if its instantaneous then it suggests some other mechanism at work... we would have to investigate that separately.
There is a minute delay between switch off and pop, although I couldn't quantify it.
Would something like this fit the bill Audio Amplifier Circuit Output Relay Delay Audio | Audio Circuits and would I have to change the values R1 and R2 to acommodate my 18V transformer?
Chris.
Would something like this fit the bill Audio Amplifier Circuit Output Relay Delay Audio | Audio Circuits and would I have to change the values R1 and R2 to acommodate my 18V transformer?
Chris.
If it's 18VAC, the full wave rectified voltage is 24 VDC. A 24 VDC relay will be ok here.
Don't change the resistors. R1 is for timing. R2 is set low enough to saturate the transistor, and 2k should be enough.
Use a low leakage electrolytic.
A minutes delay 😀
That's just the circuitry throwing a wobbly as the rails fall away. Something like your linked circuit should work OK.
That's just the circuitry throwing a wobbly as the rails fall away. Something like your linked circuit should work OK.
Remember if using this circuit to short the preamp outputs, there should be a suitable series resistor before the relay,
the minimum value that the preamp can tolerate as a load.
Trust me to use a word that has three meanings. Damn the English language
Should have said miniscule 😉I have everything but the BC547 in my spares box. Could I use a D655F in place of the BC547 to save me a trip to Maplins?
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