Thanks.
The circuit will be connected after the PSU regulator. Will I still need the resistor, and what is the purpose of fitting it?
Trust me to use a word that has three meanings. Damn the English languageShould 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?
That looks fine for this circuit.
If there is a detectable delay before the noise i.e. the switch has opened silently, then the circuit should fix it. If the noise seems to coincide with the switch opening then its more than likely something else such as burst of RF somehow entering the chain.
I'm not familiar with that transistor tbh. Only reference I can find is SD655F which is only 15 volts C to E rated. Not enough.
Normally you would short the audio circuit's signal output after a series resistor. Do you want to short the voltage regulator output instead?
Trust me to use a word that has three meanings. Damn the English language
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?
D655F NTE Equvilent NTE315
TRANSISTOR NPN SILICON
100V IC=1A MEDIUM POWER AUDIO AMP
http://nte01.nteinc.com/nte%5CNTExRefSemiProd.nsf/$all/05D503F0BF9FADAE852579100080D714?OpenDocument
I just need to disconnect the output of the pre amp on switch off. Are you suggesting a high value resistor to ground before the relay (on the signal line)?
The usual way to do this is to have a series resistor at the preamp's output, between the
line amplifier and the RCA jack, and to short the center pin of the RCA jack to ground.
This will not damage the preamp because of the resistor, and will mute the output to the amplifier.
This is safer than breaking the circuit.
the cuircuit i did link from the dataheet does:
slowly ramp up voltage on power on.
instantly let voltage down on power down.
i did suggest 1K ohm resistor in series with the output, before the relay.
relay should ground the output of the preamp while off.
and will delay the relay of about 1-200 ms time.
why would a 555 timer be needed for this ?
slowly ramp up voltage on power on.
instantly let voltage down on power down.
i did suggest 1K ohm resistor in series with the output, before the relay.
relay should ground the output of the preamp while off.
and will delay the relay of about 1-200 ms time.
why would a 555 timer be needed for this ?
It can be more precise over a wide range of time, but in this case you probably can just use a single NPN transistor.
A timer can be used for a turn-on delay, also.
Attachments
When power is disconnected from a power transformer, the transformer turns into a spark coil, generating a pretty high voltage transient. It's the nature of any inductor. If the transient only or mostly happens when the unit is turned off, not so much when it turns on (that's a different transient mechanism), then this is probably what's happening. Putting a .01uF 1kV cap (ceramic is fine) across both the primary and secondary of the tranny can reduce this by quite a bit. I also put these same caps across the AC line in (hot and cold to earth ground), and one across the power switch.
The trouble with the simple delay circuits is that most aren't fast enough for this particular issue. I use those too but more for the turn on transients. Adding these caps will minimize the problem, but I still leave my preamps on 24/7 and just turn off the poweramps when I'm done using the system. Most preamps draw so little current that I don't care if they help heat the room a little when idling.
The trouble with the simple delay circuits is that most aren't fast enough for this particular issue. I use those too but more for the turn on transients. Adding these caps will minimize the problem, but I still leave my preamps on 24/7 and just turn off the poweramps when I'm done using the system. Most preamps draw so little current that I don't care if they help heat the room a little when idling.
You can try it both ways, but your version isn't guaranteed to eliminate noises.
BTW, does your preamp cause a noise if turned on after the power amp is turned on?
There are 1.5nF caps across the transformer secondaries to filter out any transformer nasties. The mains switch itself doesn't seem to be affecting the cicuit.
Although a relatively low powered amp, the output transistors ar biased into class A, so I am loathed to leave it on for any length of time. It gets as warm as the power amp if I leave it on for any length of time.
Hopefully I will be able to build/fit a simple delay this evening and see if it makes a difference. I shall report my findings.
Although a relatively low powered amp, the output transistors ar biased into class A, so I am loathed to leave it on for any length of time. It gets as warm as the power amp if I leave it on for any length of time.
Hopefully I will be able to build/fit a simple delay this evening and see if it makes a difference. I shall report my findings.
hmmm, can You post the actual schematic ?
stuff+psu.
might even happen You need some bleeding resistors across the powersupply.
stuff+psu.
might even happen You need some bleeding resistors across the powersupply.
hmm maybe something like the Carvin AC120s might do the trick it has programmable on/off sequencing....
i have no doubt that it is a very nice psu,
but i think it is far too complicated,
took a look at the datasheet of lm337/lm317 datasheet,
i would not be surprised if the regulators would be playing some tricks on You.
I'd hazard a plain old 7815/7915 regulator pair build as per datasheet application would have been just as good enough.
I fail to see the benefit of that powersupply, while i sortha can see how it could play some tricks on You.
You might get away with some dummy load on the powersupply board.
can be like 1K ohm from rail to ground / rail.
right at the output.
wish if You had some other powersupply to test if the problem remains,
while the schematic looks to me error free,
if You get "pop"-s far after shutting down power, then i would suspect the psu more.
amplifier turn on/of pops are "instant" when You flick the switch.
if the thing pops long after turning it off, then i would assume a ripple big enough to kick the pre-amp back into action, then when the caps are "empty" it is shutting down again.
this kind of stuff is very likely, if You tunr only the preamp off, and after a longer period You hear 2 short "plops" one after the other.
one for preamp kick back on, and the nextone very soon afterwards, pre-amp shutting down.
the problem will be solved with a delayed relay setup.
keep in mind that You can not ground the output of Your pre-amp , it needs at least 600 ohm load. (1K would be better), and not sure if the poweramp would like to see a floating input then a relay slammming at it.
but i think it is far too complicated,
took a look at the datasheet of lm337/lm317 datasheet,
i would not be surprised if the regulators would be playing some tricks on You.
I'd hazard a plain old 7815/7915 regulator pair build as per datasheet application would have been just as good enough.
I fail to see the benefit of that powersupply, while i sortha can see how it could play some tricks on You.
You might get away with some dummy load on the powersupply board.
can be like 1K ohm from rail to ground / rail.
right at the output.
wish if You had some other powersupply to test if the problem remains,
while the schematic looks to me error free,
if You get "pop"-s far after shutting down power, then i would suspect the psu more.
amplifier turn on/of pops are "instant" when You flick the switch.
if the thing pops long after turning it off, then i would assume a ripple big enough to kick the pre-amp back into action, then when the caps are "empty" it is shutting down again.
this kind of stuff is very likely, if You tunr only the preamp off, and after a longer period You hear 2 short "plops" one after the other.
one for preamp kick back on, and the nextone very soon afterwards, pre-amp shutting down.
the problem will be solved with a delayed relay setup.
keep in mind that You can not ground the output of Your pre-amp , it needs at least 600 ohm load. (1K would be better), and not sure if the poweramp would like to see a floating input then a relay slammming at it.
I did wonder why the PSU had a 337/317 regulator, but then the voltage is adjustable by means of replacing the zenner diode rather than the regulator.
I get a barely audible click at switch on (I presumue switch contact noise), and a large single pop somewhere between 500mSec and 1 second after switch off.
I was thinking along the lines of shorting the output to ground through a 47k resistor, prior to the relay contacts. Once the relay contacts open, any residual power will be expended through the resistors. The power amp is stable enough.
I get a barely audible click at switch on (I presumue switch contact noise), and a large single pop somewhere between 500mSec and 1 second after switch off.
I was thinking along the lines of shorting the output to ground through a 47k resistor, prior to the relay contacts. Once the relay contacts open, any residual power will be expended through the resistors. The power amp is stable enough.
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