Main Forums >> Guitar Technology
        Print Thread

Pages: 1
UneducatedWeasl



Joined: 24/02/07
Posts: 85
Loc: Leeds, West Yorkshire
Microphonic Feedback (possibly)
      #1029315 - 18/01/13 07:55 PM
Hi all.

I'm getting a high pitched squeal from my amp whenever I get close to the head. I've had the issue occur in the studio, when the cab is in the live room, amp in the control room, and the feedback seems to be due to proximity to the head, irrelevant to the cab. I've even had it squeal in this setup with nothing coming through the monitors, the amp is loud enough that I can just about hear it do this through the wall. It's a Selmer Treble and Bass, though the treble side has been gutted, fairly messily. I've tried tapping the preamp tubes, and they don't seem to make a sound, so I don't know if they've gone microphonic, but it sounds like that kind of feedback.

The fact that it doesn't seem to be volume related, and is proximity related, is what is throwing me. Any thoughts, before I drop it off with a tech? any diagnosis I can do is bound to make his job easier

--------------------
Freelance Engineer / Musician / Nerd


Post Extras: Print Post   Remind Me!   Notify Moderator     Back to top
Hugh RobjohnsAdministrator
SOS Technical Editor


Joined: 25/07/03
Posts: 22417
Loc: Worcestershire
Re: Microphonic Feedback (possibly) new [Re: UneducatedWeasl]
      #1029316 - 18/01/13 08:13 PM
Can you control or vary it by changing the angle of the guitar relative to the amp? It could be magnetic coupling from the amp's output transformer to the pickups.

H

--------------------
Technical Editor, Sound On Sound


Post Extras: Print Post   Remind Me!   Notify Moderator     Back to top
UneducatedWeasl



Joined: 24/02/07
Posts: 85
Loc: Leeds, West Yorkshire
Re: Microphonic Feedback (possibly) new [Re: Hugh Robjohns]
      #1029326 - 18/01/13 10:42 PM
Tends to vary in pitch as I move around. Initially it was amusing, rising in pitch as I ducked if I was near the amp. Now it's just annoying!

--------------------
Freelance Engineer / Musician / Nerd


Post Extras: Print Post   Remind Me!   Notify Moderator     Back to top
Nico 3313



Joined: 12/07/06
Posts: 100
Re: Microphonic Feedback (possibly) new [Re: UneducatedWeasl]
      #1029350 - 19/01/13 09:00 AM
Did anyone think of the possibility of inductive coupling of the Output Transformer and the pickup coils?
I remember the phenomenon, but not with what guitar, bass or amp.

--------------------
Preamps are Class A by default


Post Extras: Print Post   Remind Me!   Notify Moderator     Back to top
UneducatedWeasl



Joined: 24/02/07
Posts: 85
Loc: Leeds, West Yorkshire
Re: Microphonic Feedback (possibly) new [Re: UneducatedWeasl]
      #1029372 - 19/01/13 12:06 PM
Based on the little bit of research that I've done on the subject (hard to find much, with a quick google, annoyingly) that does seem a likely culprit. Anything that I can do to resolve the problem, or is it time to bite the bullet and call my tech?

FWIW, when I got the amp I took it to my tech for a checkup, it being from the late 60s, and a bit of a homebrew (it's just the chassis, in a handbuilt enclosure) and he said that inside is a mess, hence why it's a noisy thing. Luckily I play loud, fuzzed up rock, so a bit of noise becomes fairly irrelevant in a hurry. At some point I might be able to afford to get it pretty much rebuilt, but we'll see.

--------------------
Freelance Engineer / Musician / Nerd


Post Extras: Print Post   Remind Me!   Notify Moderator     Back to top
Goddard



Joined: 04/04/12
Posts: 960
Re: Microphonic Feedback (possibly) new [Re: UneducatedWeasl]
      #1029537 - 21/01/13 02:21 AM
Quote UneducatedWeasl:

Tends to vary in pitch as I move around. Initially it was amusing, rising in pitch as I ducked if I was near the amp. Now it's just annoying!




Ah, that describes "Moog-ophonic" not "microphonic" feedback.

Does this pitch variation also occur if you approach the amp without a guitar?

And, does this amp have a "tremelo" or "vibrato" section by any chance?


Post Extras: Print Post   Remind Me!   Notify Moderator     Back to top
Pages: 1

Rate this thread

Jump to

Extra Information
1 registered and 7 anonymous users are browsing this forum.

Moderator:  David Etheridge, James Perrett, zenguitar, Martin Walker, Forum Admin, Hugh Robjohns, Zukan, Frank Eleveld, SOS News Editor,  
Forum Permissions
      You cannot start new topics
      You cannot reply to topics
      HTML is disabled
      UBBCode is enabled
Rating:
Thread views: 1949

January 2015
On sale now at main newsagents and bookstores (or buy direct from the
SOS Web Shop)
SOS current Print Magazine: click here for FULL Contents list
Click image for January 2015
DAW Tips from SOS

 

Home | Search | News | Current Issue | Tablet Mag | Articles | Forum | Blog | Subscribe | Shop | Readers Ads

Advertise | Information | Privacy Policy | Support | Login Help

 

Email: Contact SOS

Telephone: +44 (0)1954 789888

Fax: +44 (0)1954 789895

Registered Office: Media House, Trafalgar Way, Bar Hill, Cambridge, CB23 8SQ, United Kingdom.

Sound On Sound Ltd is registered in England and Wales.

Company number: 3015516 VAT number: GB 638 5307 26

         

All contents copyright © SOS Publications Group and/or its licensors, 1985-2014. All rights reserved.
The contents of this article are subject to worldwide copyright protection and reproduction in whole or part, whether mechanical or electronic, is expressly forbidden without the prior written consent of the Publishers. Great care has been taken to ensure accuracy in the preparation of this article but neither Sound On Sound Limited nor the publishers can be held responsible for its contents. The views expressed are those of the contributors and not necessarily those of the publishers.

Web site designed & maintained by PB Associates | SOS | Relative Media