Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 2nd April 2006, 06:19 PM   #1
diyAudio Member
 
mschwilson's Avatar
 
Join Date: Jun 2005
Location: N.E.England
Send a message via AIM to mschwilson
Default Preamp hum.

Hi.
I use a Perreaux PMF2150B power amp with matching SM2 pre.
I have two slight problems.
The first is that when the pre is on top of the amp,I get loads of hum.
I got round this by moving the pre away,but I would like to know if there is a way to get rid of it rather that just make do.
The transformer is a huge block type,and the top of the amp is made of what appears to be some kind of cardboard with cork on the inside(search me why).
Anyway,the second problem is that when switching the amp on,it "sucks" the bass cones of my speakers in(quite normal)but a grating noise,rather like the noise you get from a noisy volume pot comes from the cones.
I recently re-coned the drivers and know they are pretty much perfect,and have also tried other speakers with the same result.
This is only brief and after the initial surge,cannot be heard again.
The amp works perfectly and I hammer it regularly,but is this a sign of something about to give in.
Please help.
Thank's,
Simon.
  Reply With Quote
Old 2nd April 2006, 07:07 PM   #2
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi,
the amp is not working perfectly but it may be working normally.

It has a large DC output offset at start up, which is pretty common.
Most manufacturers will either eliminate the temporary offset or fit an output relay to hide the symptom.

You will find it easier to hide it.

Your reconed speakers are not pretty much perfect.
From your description it sounds like the voice coil is scraping against the pole piece or top plate. This is probably due to an offset in the voice coil from true geometric centre.

Recheck your cone setup. If glued at both surround and spider then you have to fathom out a fix. If it is bolted at one or both you should/may be able to recentre the voice coil more accurately.
__________________
regards Andrew T.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Tube Preamp Popping on Source Input Change (?) / 6DJ8 Preamp On Chip Amps MartyM Tubes / Valves 3 16th October 2008 04:52 AM
Guitar Preamp = MIC Preamp = other preamp ,,are they all same? Paswa Solid State 1 12th March 2008 05:16 PM
twisted pear Preamp/other suggestions for Preamp kit LukeDuke Chip Amps 1 1st February 2008 09:57 PM
Electret mic preamp - will phono preamp work? darthmullet Analogue Source 6 12th October 2007 07:32 AM
wiring preamp outs on a preamp bonsai171 Solid State 4 22nd March 2004 10:13 PM


New To Site? Need Help?

All times are GMT. The time now is 07:41 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2