Vibrations and Effects on Amps

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bhobba

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Vibrations and Effects on Amps
« on: 20 Sep 2010, 01:39 am »
Hi Hugh and All

Mike Lenehan has just posted some interesting comments on the effects of vibrations on amps. Check it out:
http://www.stereo.net.au/forums/showthread.php/26992-DAC-Shootout/page17

Hi all

this is the experience I had when we ran the Mac501's against the VAC PHi200s the day after the DAC shootout. Craig Steve and I listened to a track from Brother Four . Male vocalists, firstly I heard a very smooth communicative upfront delivery with reasonable detail.

After about 45seconds we stopped the track ( Steve Craig and I all concur that when in the groove ! pun intended ! we don't need much more time) Steve and Craig within that time both agreed the VAC was way ahead of the Mac's. I did not agree though , my thoughts are as follows.
The VAC sounded very communicative smooth and emotional but at the same time I could here a marginal slurring in the power range area (125 to 300hz) which manifested as a foreshortened soundstage and upfront presentation. The soundstage lived in the fore aft plane between the speaker baffles and the listeners ears. This was one of Steves discs that I love and had played it to death on the MAC's.
My memory of the Mac presentation was of less husk and marginally less forwardness in the vocal area with a soundstage that seemed larger and much deeper. Having said that I was very drawn to what had impressed Craig and Steve so much ! beautifully timbral sounds in the vocals and significant engagement.
The ladds spoke of supreme openness and communicability ! and yes I heard what they were saying . BUT I had an idea, The MAC's had 3hz isolation and I was intimately aware of what something so simple does. I ran out into the factory and grabbed a calibrated spring set and hoped I could get them to work on the VAC. The VAC by the way was simply put directly on the carpeted concrete floor.
My bright spark idea was that the resonance from the slab was producing the added husk and slurring distortion I was so sensitive to. Holey smoke the improvement was in my mind huge ! all of a sudden the VAC sounded much more like the Mac's , more dimensional more transparent more ! warning non valve word about to be said !! NEUTRAL !
Now I looked over to Steve and Craig but this change did'nt elicit as big a response as it did for me.
Just Tonight I measured the area where the VAC was sitting with an accellerometer but could only pick up moderate 40 to 60hz activity probably from the ML3's floor firing vent or perhaps the main mechanical feed through from the ML3's spikes slab interaction. But the very significant difference was there so I guess It shows how small an interference resonance is required to significantly upset the signal finally sent to the speakers. The ears is still better than measurement gear Huh.

Here's a few things to ponder

1. was the resonance from the concrete floor injecting the equivelent of even order harmonic distortion into the music signal and making the VAC sound even more romantic and forward in the power response range ?

2. Are there two types of audiophiles ? The they are here audiophiles ! and then the ! We are there audiophiles ?

3. Are the ! They are here Audiophiles ! the romantic sounding valve amp guys ? and are the ! We are there audiophiles the SS and accurate valve amp guys ?

4. Is it possible that what floats your boat regardless of what sounds like real live acoustic music will be defended to the death ? When one is emotively activated I can assure you reality could go out the door.

I believe the VAC could perhaps knock over the Mac's ! on the Isolation springs the VAC sounded magnificant but directly on the deck it was flat planeing and very enveloping ! by that I mean it sort of wrapped itself around you like a blanket ! cuddly but not like real music for me. We just did'nt have the time to compare back to the Mac's but given the obvious potential of the VAC a pair of 200watt Mono VAC PHi200's could be my next reference amps.
This thread should live forever ! Here Here !!!

Best Regards Mike Lenehan LenehanAudio

Thanks
Bill

gaetan8888

Re: Vibrations and Effects on Amps
« Reply #1 on: 20 Sep 2010, 03:40 am »
Hello Bill

The VAC PHi200, like all tube amps and preamps, can be subject to a microphonic effect in the tubes, some guys use tubes dampeners rings but if there is a strong low frequency vibration it may not be enough. Using a calibrated spring set was a very good ideas.

Transistors amps are quite insensitive to microphonic effect, except if some parts are defects or with some capacitors if the foil into the can are not wound tight enough. I have some old big mylar capacitors that you can squeeze because they are wounded lose.

Bye

Gaetan
« Last Edit: 20 Sep 2010, 07:49 am by gaetan8888 »