advertisement


Ideas re Thump

R

retrospective

pfm Member
I have an A and R a60ap which has a pronounced 'Thump' on shutdown only, if i remove the Din shorting plug prior to shutdown there's no thump i've changed the smoothing caps which has improved the amps performance but has had no impact on the thump.
Ordinarily this wouldn't concern me too much but having spoken to other owners of the same amplifier they report no spkr thump.

I'm looking for ideas on what to check/change next or reassurance that it will do no harm to my speakers.

Many thanks
 
Have you checked the DC offset at the speaker terminals? (Use the lowest voltage setting you have on your meter and put the probes in the terminals with no speakers connected.) It should be less than plus or minus 50mV. Do the test with your shorting plug in and then again with it out. Is there a difference?
Actually, I do not understand what the ''shorting plug'' is or does, can you explain?

Is the 'thump' on both channels?
 
The amplifier is split pre/power the shorting plug (din plug) allows it to be used as an integrated or a normal A60

Yes the thump is the same on both channels
 
Cheers,i'll check the dc offset later and post my results with/without the din shorting plug.

The din shorting plug uses the aux input would it be ok to use the tape input with no load connected to test the offset?
 
retrospective said:
Cheers,i'll check the dc offset later and post my results with/without the din shorting plug.

The din shorting plug uses the aux input would it be ok to use the tape input with no load connected to test the offset?
Click to expand...

Eh? You don't need an input to check the DC offset and it's at the speaker terminals anyway... Very unlikely to be any problem with offset.
 
retrospective said:
if i remove the Din shorting plug prior to shutdown there's no thump
Click to expand...

What does the shorting plug do?
If it connects the preamp to the power amp, then the thump is caused by the preamp.
Maybe you increased the value of the smoothing caps for the power amp and this has resulted in the preamp supply rail(s) going down before the power amp supply?
 
I was under the impression that it was necessary to ensure that the amp was switched to aux with nothing connected in order to test..the fact that this amp doesn't have an aux made me query it.

Cheers
 
I've checked the dc offset after approx 10 minutes of settling.

with the shorting plug in place

22.8mv ..left
24.4mv ..Right

Without the shorting plug the readings are the same.
 
Hi,
The following reference states how the A60AP works :
https://www.manualslib.com/manual/9217/AAndr-A60.html?page=5#manual

So, when the plug is connected in, there is a thump. The plug connects the preamp section to the power amp section.

When the plug is removed, then the AP connection can be used as a power amp input, bypassing the pre-amp. When you disconnect the DIN shorting plug there is no thump.

So as others have stated - it is the pre-amp that is causing the thump.

So, when you replaced the smoothing capacitors, did you use the same values as previous ones, and did you connect the right way around ?.

Did you make a mistake such as a solder bridge or other in some way ?

Did this amplifier have the thump before you changed the smoothing capacitors ?? (just checking).

Regards,
Shadders.
 
I used the same values as fitted i believe the old caps were the originals and the Thump was evident prior to changing the smoothing Caps that's the reason that i changed them. The only difference i've noticed is that with the old caps there was a bit of a delayed thump on the right channel now both channels thump in unison.
 
Hi,
OK - your initial post was read that you changed the capacitors and this was now causing the thump.

If the amplifier has always done this, and given it is decades old and continues to do the same even with the capacitor change, then there is no need to worry.

Regards,
Shadders.
 
There's a muting circuit on the output of the preamp after the volume control. It might be worth looking into how this works (I don't know...)
 
You must log in or register to reply here.


advertisement


Back
Top