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onis_uk 29th June 2010 05:49 PM

Curing Arjen helder amp power off pop !!!
ive build an amp now using an arjen helder ta2020 mk3 board and a mk2 valve preamp ! i have also fitted a small relay board which he sent me to cut the speaker wires to "cure" the on off pops!!
it cures the power on pop but not the power off thud i get!?!?

i have attached a small pic to show what i mean but if i disconnect the buffer amp signal i get no power off thud !!!!!! so this tells me the pop is being generated from the preamp, so now how do i cure this problem?!?!?!? its rather annoying not to mention its damaging my speakers :(

cheers Dom

teamacc 29th June 2010 07:25 PM

the relay at the speaker cable should also be interrupted on 230v drop. (power off)
So: if you reroute the relay route, with a 230v relay in between, and put this after the on/off switch, and make sure there are enough buffer caps to power the board for at least 0.5 seconds, there should be no pop-off noise.

onis_uk 29th June 2010 08:55 PM

ok i'll try this, but what is causing the pop ? a dc/offset between the 2 amps ?

the 240v relay coil to be powered by the live and neutral or live and earth ?!

teamacc 30th June 2010 07:28 AM

Never use earth for connections like that!
always use neutral!

This method makes sure your speakers are disconnected before the amp or buffer powers down, as they run a while on the buffer caps before shutting down.

And yes, it most likely is the dc offset.

ArjenShenzhen 30th June 2010 08:48 AM

Hi there Onis,

Sorry for seeing your post so late!

Ive made a small board to solve this issue, its got 2 relays that are switched on delayed and they are put in between the speakers and the amplifier board.

this board is available free of charge for everyone that has bought a pre-amp from me, just mail me, and ill check and send.

the little board is connected as follows:

the new version of the tube buffer uses a delay circuit that's similar, a charging cap over the base of a transistor, and the transistor in his turn driving the Mosfet's gateto slowly open. the POP is caused by the DC-DC converter that whacks up the voltage so fast that the buffer capacitors are charged quickly, passing it on to the amplifier that passes it to the speakers, especially in sensitive speakers can then give a annoying POP.

ill send one off to you!


Arjen Helder

teamacc 30th June 2010 11:13 AM


Originally Posted by onis_uk (
...i have also fitted a small relay board which he sent me to cut the speaker wires to "cure" the on off pops!!...

He has an issue with the pop-OFF sound, the pop-ON is already taken care of by your board...

ArjenShenzhen 30th June 2010 03:54 PM

Ah i see, i didn't see that just now !

I've hooked it up back here and when switching it off the pop is very small, not noticeable for me,because i don't have huge super efficient speakers. but i also know that many switch mode power supplies actually give a spike when switched off, that means in your case it could be allot bigger than what I'm measuring here.

The big caps on the board delays the switch off it a little, I'm quite sure that if we use a double pole switch for the power and the relay board the relay board should be fast enough to disconnect the speakers before the pop emerges.

best bet is use the double pole switch for the positive wire to the PCB and the negative black wire that runs to the relay board.

only option for soft start and stop on a DC-DC converter would be a MCU with programming, i will look in to this.

i have made a change for the boards now so that they do a soft start, the soft stop still needs to be considered.


Arjen Helder

onis_uk 30th June 2010 05:22 PM

yes as teamacc said i've fitted the board you sent me (many thanks) and it cured the power on pop. i have a feeling this is coming from the smps i have... i will try powering the amp iva a 12v battery. if i get no pops then its a power supply problem !
cheers guys

onis_uk 30th June 2010 05:49 PM

ok what would be a very good power supply to use for this set up other than a smps ?!?!?

how about this ??
cheers Dom

teamacc 30th June 2010 08:03 PM

nope, it has a 22v AC main power output, which is approx 30v DC, but also an aux 12v AC line, which is about 15v DC.

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