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preamp causing amp to push woofer out at power-up

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Posted on January 26, 2023 at 08:35:35
BS64
Audiophile

Posts: 2451
Joined: July 17, 2000
 I have a Zero Zone C-J clone tube preamp. It works well, but one thing that has always bothered me is that when I power up the SS amp the woofer on my 3-way Gershman A-G's pulls in, pushes out, pulls in, then relaxes. Nothing audible, strictly visual.

I can run my Cary 303-300 cdp directly into the amp as it has volume control. In this configuration the woofer does not move at amp power-up.

So, what is it about the preamp that is causing the woofer to move at amp power-up? The preamp shipped with no-name 12AX7's. I have rolled in 12AU7's and 5751's and that made no difference.

Thanks in advance...

 

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Proper procedure for powering up any stereo with seperate components, posted on January 26, 2023 at 08:45:44
Ralph
Manufacturer

Posts: 4778
Location: Minnesota
Joined: April 24, 2002
 This is normal for most preamps ever made. To prevent it:

1) power up preamp and wait until it settles.
2) insure the volume is down.
3) power up whatever sources you're using
4) power up the power amplifier.

If the power amp is on before the preamp, regardless of the technology of the preamp, expect some sort of pop, thump, woofer excursion, hum, buzz and so on.

The power amps are always turned on last.

 

RE: and turn off your Amp first!, posted on January 26, 2023 at 09:09:08
jaynemo
Audiophile

Posts: 1881
Location: Connecticut
Joined: February 7, 2003
 never turn on or turn off an "amp energized" pre-amp or source(s).

 

RE: Proper procedure for powering up any stereo with seperate components, posted on January 26, 2023 at 09:32:39
BS64
Audiophile

Posts: 2451
Joined: July 17, 2000
 Perhaps I wasn't clear. Preamp is already on, wait about a minute, then the amp is powered-up.

 

+1 nt, posted on January 26, 2023 at 09:44:16
Ralph
Manufacturer

Posts: 4778
Location: Minnesota
Joined: April 24, 2002
 -

 

clarification: preamp is already powered-up, then the amp is powered-up, posted on January 26, 2023 at 09:45:57
BS64
Audiophile

Posts: 2451
Joined: July 17, 2000
 nt

 

This can happen if the B+ of the preamp isn't regulated., posted on January 26, 2023 at 09:47:32
Ralph
Manufacturer

Posts: 4778
Location: Minnesota
Joined: April 24, 2002
 When you power up the amp, the line voltage drops a bit and then recovers. This causes the B+ of the preamp to drop a bit and then recover too. Its a pretty long time constant, so you just see the woofer move a bit.

Regulating the power supplies in the preamp solves this issue- and usually the preamp will sound better for it as well unless the regulators have some sort of (solvable) problem.

 

RE: preamp causing amp to push woofer out at power-up, posted on January 26, 2023 at 09:51:00
Davey
 You'd need to do a little investigation on what amount of DC output your ZZ preamp has and how it's interacting with the power amp when you turn it on.

If you turn on/off/on your power amp with no input connected do you still get the cone movement?

I probably wouldn't worry about actually. :)

Dave.

 

RE: preamp causing amp to push woofer out at power-up, posted on January 26, 2023 at 10:02:52
BS64
Audiophile

Posts: 2451
Joined: July 17, 2000
 If I plug my cdp directly into the amp, turn the cdp on first and then the amp, no woofer movement.

 

RE: preamp causing amp to push woofer out at power-up, posted on January 26, 2023 at 12:53:57
Davey
 As I said, I probably wouldn't worry about it.

Your preamp probably doesn't have a (sufficient) bleed resistor after the output coupling capacitor. The turned-off power amplifier, being an indeterminant load, maybe allows a residual voltage to build up on that output capacitor. When you turn on your amplifier the load changes and that capacitor discharges and you see the result in your woofer cones.

That's one possible explanation. There are numerous other ones.

Dave.

 

RE: preamp causing amp to push woofer out at power-up, posted on January 28, 2023 at 09:33:37
Ugly
Audiophile

Posts: 2912
Location: Des Moines, WA
Joined: August 22, 2006
 Makes you wonder if it's a servo circuit kicking in when you power up your amp. If it is pulling things in to zero and you can't hear it, then it maybe it's working right.

As Davey seemed to be aluding to, that sort of reaction may even be caused by DC in the preamp output and if the cd player output didn't have as much DC in its output for whatever reason it may explain the behavior difference.

If you have a DMM you can measure to see how much DC output your devices have while playing a silent track.

 

Thanks, everyone..., posted on January 28, 2023 at 13:51:02
BS64
Audiophile

Posts: 2451
Joined: July 17, 2000
 Thanks for the insights, everyone. I packed my system away nearly 3 years ago for a couple of different reasons, so unable to take any DC measurements at this time.

We will be dropping off our younger son at Texas Tech this fall. After that, I will be taking back our media room and getting back into 2-channel listening in a dedicated room. The reason for my ZZ preamp concern is that I am considering a change in speaker approach. Getting away from 3-way boxes and going panels, which would allow use of the 2 SS amps I have. What affect could this DC "spike" have on a planar or stat speaker?

Also considering high-eff floor standers (Zu, for example) with a lower-powered tube amp. If I go this direction I would most likely go with a tube integrated and eliminate the need for the preamp. But again, if I end up using the preamp could the DC spike be detrimental to the speakers?

Thanks again for the insights, and for any further suggestions/recommendations you may have.

 

RE: Thanks, everyone..., posted on January 31, 2023 at 10:37:16
Ralph
Manufacturer

Posts: 4778
Location: Minnesota
Joined: April 24, 2002
 I doubt this will be a problem for any speaker since it apparently isn't a high power event.

 

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