aikido thump

[jayme]

Anyone else get a loud thump when turning off their aikido-based preamp?

Just wondering if the issue is with my PSU section...

 

[ray_moth]

It is reportedly common practice, among those who use separately powered preamps, to switch off the main amp first, wait a second or two, and then switch off the preamp.

 

[jayme]

Yeah...I am familiar with that practice...but I'd like to look for an overall solution other than a guideline (my wife likes to shut everything off at once...)

 

[Burnedfingers]

I put an idiot sheet next to the equipment. It spells out the turn on and off procedure.

Problem solved

 

[Andypairo]

I use a relay that shorts out the output (after the cap) with its NC contacts.
I energize the relay after a delay at turn on and de-energize it immediately at turn off.

No thumps.

Cheers

Andrea

 

[triode_al]

Anyone else get a loud thump when turning off their aikido-based preamp?

Just wondering if the issue is with my PSU section...

jayme
In my Aikido I have a 1.200 micro farad capacitor at a 215 V. It takes some time to load and similarly - to unload.
The result is: no thumps on turning on, and no thumps on turning off. It just fades (the tubes are cold befor the power line really drops).

I switch my power amp with the power switch of the Aikido. My power aplifier is transistor (LeMonstre) and would really show up any odd issues. Maximum at turn on is 3 volts for 1 second at turn on (after 30 sec) and none at turn off. For safety, you should really add Andy's relay.


success
albert

 

[jayme]

How would I implement a relay? Just have a switch which shunts B+ thru a resistor to ground?

I don't need the protection at start-up...I use a 5AR4 rectifier, which gives me a slow ramp up.

My PSU doesn't have a lot of big caps: it is CLCLC with 3.3uF, 20uF, and 40uF caps, respectively. I use some big 15H chokes for the inductors.

 

[Klimon]

I put an idiot sheet next to the equipment. It spells out the turn on and off procedure. Problem solved.

 

[Andypairo]

How would I implement a relay? Just have a switch which shunts B+ thru a resistor to ground?

I don't need the protection at start-up...I use a 5AR4 rectifier, which gives me a slow ramp up.

My PSU doesn't have a lot of big caps: it is CLCLC with 3.3uF, 20uF, and 40uF caps, respectively. I use some big 15H chokes for the inductors.

I was talking about shunting the output (=signal) after the coupling cap.

Cheers

Andrea

 

[Bill*B]

My own Aikido has a subsonic output at turnoff - you can see the speaker cones thrust out, although there's no sound. I've never tried to track down the source, although I (like you) suspect that it is the power supply - I used a regulated unit and I'll bet the voltage surges when the voltage reference falls out of conduction.

 

[jayme]

Bill*B,

Do you have AC or DC heaters?

And, do you know the voltage magnitude of the turnoff thump? Can you check with a DVM?

I am getting about a 20V pulse for about 1/2 second during turnoff. I am assuming that this is high enough to potentially damage my tube amp/speakers.

 

[Bill*B]

Heaters are AC. I don't have a good way to measure the magnitude. My only concern re: speakers is that it could stress the litz wires leading to the voice coil. Rather than try to track it down, I've just started shutting off the amp first.

 

[jayme]

Oddly enough, if I try to shut off my tube amp first, I still get some major speaker woofer movement, but no audible thump.

It's only slightly less dramatic than when I shut off the pre first...

 

[Bill*B]

My old Citation 12 sand amp used to give the speakers quite a goose when I turned it on - subsonic, but you could see the speaker cones thrust out.

 

[kor952]

My 2 cents..

Do you have bypassed your turn on/off switch with filtercaps to suppress sparks while turning your pre off? It will help!

Ciao,

Ronald.

 

[jayme]

My 2 cents..

Do you have bypassed your turn on/off switch with filtercaps to suppress sparks while turning your pre off? It will help!

Ciao,

Ronald.

I tried that. Didn't help.

It seems my culprit is that I am running lean on filter capacitance. I have a CLCLC.

3.3uF cap
15H choke (60R)
20uF cap
2 15H chokes/one per channel (60R each)
2 20uF caps/one per channel

The voltage drops dramatically once the power is switched off...faster than the heaters can cool. At least that is my current theory. I'm going to pick up some test clips, and try adding in an extra 100uF cap for each channel of that last "C" to see if that helps. (It also might help damp my PSU...I get some low level freq motorboating around 12Hz)

Off-topic: Is there any way to shunt the low-level AC(12 Hz stuff) on the B+ before it hits my signal circuit?

 

[kor952]

jayme wrote:
Off-topic: Is there any way to shunt the low-level AC(12 Hz stuff) on the B+ before it hits my signal circuit?

I once did built a EL34 PPP power amp that also had a motorboat problem. I figured out that my Electrostatic speakers where the problem (a too high capacative load), as soon as I mounted a resistor (100 ohm) parallel to the speakers the motorboating did disappear.

Ciao,

Ronald.