[akgfan]

I built soft start and dc protection circuit with relay and have thump when powering on and off.
 
It's not a circuit issue because I disconnected input of this circuit and fed only output signal through relay. I tried large resistor between contacts but no change. I'm confused.
 
Relay is M1BS : http://www.gme.sk/_dokumentace/dokumenty/634/634-279/dsh.634-279.1.pdf .

 

[Avro_Arrow]

It sounds like to me that the thump is your output caps charging
when the relay closes.
Make sure you have a charging resistor right after the cap and
before the relay. 

 

[Avro_Arrow]

Check for DC offset too...

 

[akgfan]

I have relay after cap and resistor. When I connect output wire manually there is similar thump.
 
I tried different relay 24v with external power source and there is smaller thump when powering on but no thump when powering off. I guess that relay isn't good.
 
Is it possible to use relay just for connecting output to ground (or with resistor say 100 ohm or so) as in some tube amps? What would happen in Szekeres amp? That output cap always charge to output voltage after all. But Millet amps don't have it that way.

 

[nikongod]

Quote:

It sounds like to me that the thump is your output caps charging
when the relay closes.
 

The thump is the output caps *discharging* through the headphones when the relay closes. 
 
Quote:

Is it possible to use relay just for connecting output to ground (or with resistor say 100 ohm or so) as in some tube amps? What would happen in Szekeres amp? That output cap always charge to output voltage after all. But Millet amps don't have it that way.

I deleted the bit about the cap & resistor. If the resistor is before the relay (good! it should be) try a smaller resistor. In an amp like the szekers there is no reason to use a bleeder resistor larger than 1Kohms, and you may even prefer lower than 300ohms.
 
Another thing to look at is the size of your output caps. Larger caps store more energy, and typically have higher leakage than lower value caps. If you can use a size lower (470uf from a better family VS 2200uf from a fairly low-grade line, for common example) you might be QUITE happy with the results. flat response down to 20hz is over rated IMO, and bad caps suck at every frequency. 470uf still gets you plenty of bass with low impedance headphones.
 
To continue your idea of using the relay to ground the output better. Try hooking the relays up like this. 
 

 
This switches your headphones out of the circuit on power on, and the 32 ohm resistor to ground will bleed off the initial spike reallllllly fast. The 300 ohm resistor is still necessary to bleed off anything that leaks through if you unplug your headphones.

 

[akgfan]

I'll be trying tomorrow.
 
A 2k bleeder resistor is quite high value when my amp is for low impedance headphones. I agree with that.
 
But I don't get that thump when powering off. That relay is pretty bad when in comparing with my other relay. It shouldn't do any thump when dissconecting contacts.

 

[akgfan]

My other relay started doing the same. I don't get it. I tried everything and I'm confused.
 
I made a tube guitar preamp few years ago and there were six relays in signal path. And no problem...

 

[akgfan]

Well, looks like I'm very impatient person. The problem is that output capacitor isn't fully charged. That's the whole problem.

 

[Avro_Arrow]

Thats what I was trying to say....
 
Quote:

Well, looks like I'm very impatient person. The problem is that output capacitor isn't fully charged. That's the whole problem.

 

[Zigis]

I got very strange thump problem yesterday.
 
I built Aikido headamp/preamp. On preamp out i build half of ε12, time muting, increasing to about 30 sec. ε12 powered from a separate small 12-0-12V 300mA transformer. All work good, except wen I disconnect small transformer from mains, relay opened with loud thump. Wen I disconnect one wire from relay, don't matter +or-,everything  work perfect without thump. So problem is not in charging output caps, but in relay power somehow.
I tray regulated power, simple rectifier, with caps, without caps, with and without diode parallel to coil - the same result - if disconnect one wire to relay - silence, if disconnect transformer - thump.
B.T.W. ε12 schematic is not make a problem too, I make all experiments without ε12, just muting relay, connecting output to ground, wen not powered.
 
Then I build schematic with second relay, disconnecting + to muting relay a second before muting relay is powered off. Now everything work silent.
My schematic - 2 diodes rectifier connected to  relay 2, than via one more diode 3 to 470uF cap, than to mute relay. From 470uf + leg to mute relay go via relay 2 contacts.
Because diode 3, relay 2 not "see" 470uf cap and disconnected immediately, wen transformer is off, power in cap/muting relay is second or so longer.
 
This is only way, I can make it work.
However I have bad feeling, I am just solved problem's consequence, not problem itself. And I cant understand problem's/thump cause. Any ideas?