2. amps-preamps
  3. 1273520086

amp clipping or low freq causing pumping speakers

My cd source plays back fine at loud volumes with modest amplfication. My analog MC setup needs much more volume and until I switched out my premap from a Dodd battery powered to my present highly resolving
Doshi Alaap I had little to no pumping / displacement in my bass drivers (Salk HT3's).

Now they noticably vibrate in and out with some breakup distortion. Not as much with jazz but more so with dense rock music. Unfortunately quieter passages are too far in the background when played requiring higher volumes (perhaps I need more preamp gain). CD's with their higher compression sound fabulous on the Doshi and with less volume required

I have seen this once before when at an audiophile meeting a friend brought over an Infinity pre that went down to subsonic frequencies and my speakers were vibrating

my dilema is I need to turn my turntable up louder than my cds(which sound great and don't clip).

Could it be the added dynamic range and more low end of analog sending the speaker into viration mode

Or is the amp clipping not being able to reproduce the load sent to it?

I have a Moscode 401 HR amp, I have a higher powered BAT VK600 with a friend 1200 miles away.

thanks

Tom
128x128audiotomb
audiotomb's avatar
audiotomb OP
1,112 posts
 
thanks guys

seems the record with the most trouble was a slightly warped one. I went back and lowered the volume a little and haven't had the pumping effect. It's mostly very demanding passages - doesn't get overloaded on jazz like it does on some rock records

I have a ZYX Artisian outboard phono pre and will try that in one of the line imputs on the doshi - perhaps there is a roll off in the low freq end of the phono stage

it doesn't do this with cds

I'll touch base with Nic Doshi and get his comments on gain and low end frequency

I believe I do have that test record

thanks

Tom
onhwy61's avatar
onhwy61
5,136 posts
 
Have you tried repositioning your turntable? You might have it placed in a room node peak.
audiotomb's avatar
audiotomb OP
1,112 posts
 
woofers only seem to be over-extending on fairly loud playback or warped records

could be a room mode 15' depth - speakers 3
from back wall
acoustat6
357 posts
 
Hi Audiotomb, What did Nick have to say about this?
Perhaps you are just listening too loud? How loud are you listening?
Bob
atmasphere's avatar
atmasphere
11,574 posts
 
The Triplanar and the ZYX is a good match- I use that in my own system and there are no pumping effects.

One thing that can effect this is low frequency bypass in the preamp or amp. An extreme example is when the filter caps are failing in the power supply, and the amp or preamp 'motorboats', which is a woofer-pumping phenomena. But if the amp or preamp is insufficiently bypassed in the power supply, this can still be a problem at higher volumes.

If this is what is going on, it points to the amp or line stage, not the MC preamp.

Improper tone arm setup can cause this too. The Triplanar is equipped with multiple arm weights, so you can choose a combination that allows the mass to be closer to the arm pivot or further away, which allows you to tune the effective mass of the arm a bit. If the effective mass is too high, woofer pumping can be a problem. The solution is to choose a heavier set of weights that can be used closer in to the arm pivot. I would not track the ZYX less than about 1.8 grams.
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