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Old 10th November 2011, 02:13 AM   #1
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Default harmonica amp feedback

Ok so i am askin the experts before I start, any ideas how to reduce feedback when using a guitar amp for harmonica. my current amp is a 5e3 clone I built, (but am really lookin forward to the results of the 100 buck challange, for my next amp.) it works ok at home when i practise, but when we jam at the local pub (room like a box lots of echo) and i hav to turn it up a bit to be herd it feedsbak sumfin arwfull. I hav thought of using capasitors to block the unused freqs, but is there a better way?
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Old 10th November 2011, 05:50 AM   #2
Enzo is offline Enzo  United States
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Where is the speaker in relation to your microphone? Feedback is caused by the energy from the speaker being collected in the microphone and fed back through the system. Before looking for brute force solutions like notch filters, try working with amp placement. If it is behind you, try putting it in front of you like a floor monitor. Try putting it more beside you than in line with you. Aim it away. Try reversing the speaker leads - hey, can;t hurt.

You say you have to turn it up to be heard at the gig, and it feeds back. Specifically, do you have to turn it up so YOU can hear it on stage? Or do you have to turn it up so the AUDIENCE can hear it, but you can still hear it yourself? If it is not a matter of hearing yourself, instead of relying on the amp to cover the crowd, put yourself in the PA for them, and just use the amp on stage for tone and sound for just you.
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Old 10th November 2011, 06:24 AM   #3
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Hi there Enzo the room we gig in is fairlly small, but we like to play loud. there is no where in the room i can put the amp where i can hear it and not get feedback once the band cranks up. it usally sits on top of the pa speaker, but there is sooo much bounce back off the walls. it is a narrow L shape block construction. bad acustics but good beer. I can acctually get more volume at home where curtuins and things stop the echo.trying to mic the amp in this invirament is hard to as there is very little room we basically play IN the audiance lol.
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Old 10th November 2011, 10:15 PM   #4
GloBug is offline GloBug  Canada
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Keep your gain or "pre" turned down, and the master volume up, this will make it less sensitive.

If you have the first volume cranked, and the second volume low, you will have a similar output power wise, but it will be shreaking all over the place. This also introduces distortion, which might be desired in small amounts.

Pre = on 1 or 2
Post= as loud as you like/
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Old 10th November 2011, 11:25 PM   #5
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by GloBug View Post
Keep your gain or "pre" turned down, and the master volume up, this will make it less sensitive.

If you have the first volume cranked, and the second volume low, you will have a similar output power wise, but it will be shreaking all over the place. This also introduces distortion, which might be desired in small amounts.

Pre = on 1 or 2
Post= as loud as you like/
Hi,

It doesn't work like that, total gain is gain wherever you put it.
A specialist microphone might help or making the speaker more
directional, its hard to say if it doesn't work well at all.

Going through the PA and using the amp as a monitor might help.

rgds, sreten.
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Old 11th November 2011, 12:03 AM   #6
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re:'good beer' - not if it's Speight's...
Harp Surgery Hey There, What’s That Sound? – Microphone Feedback
& tell the bloody guitartist to turn down....
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Old 11th November 2011, 12:21 AM   #7
GloBug is offline GloBug  Canada
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Quote:
Originally Posted by sreten View Post
Hi,

It doesn't work like that, total gain is gain wherever you put it.
A specialist microphone might help or making the speaker more
directional, its hard to say if it doesn't work well at all.

Going through the PA and using the amp as a monitor might help.

rgds, sreten.
Actually using guitar amps, including the Fender 5E3, for about 20 years, I can tell you that's how it works.

Ask any guitar player to show you how to make a guitar amp clean or dirty.

You can make your guitar feedback at bedroom levels, or use the same amp to crank clean, clear acoustic guitar type sound at a live venue.

That's how you can get "Heavy metal" or "Clean" sounds out of the same amp. The clean settings will be far less sensitive to feedback vs. a high gain setting.

As far as special microphones, forget it, you'll kill the tone. Some of the best harp sounds come from an OLD Astatic JT-30 or the like.

You could try moving the amp around or standing behind it, see if that helps.

It is my understanding that you want a bit of grind (distortion) when playing those things.

No offense of coarse, Lot's of "voodoo" involved in music amps, even more so then HiFi!!

I think it basically has to do with how sensitive the first stage or preamp is. Turn it down, it takes more sound to excite a response through the microphone, makes it less vulnerable to feedback. The second stage (power amp) just amplifys the sound the first stage is creating.

Turn the first stage up high enough that a mouse fart can be recorded, well then you can see why the speaker would feedback through the sensitive microphone.

Hope this clears the air a bit.

Last edited by GloBug; 11th November 2011 at 12:29 AM.
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Old 11th November 2011, 04:05 AM   #8
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K should hav said hav moded the amp so that chanel one loops bak thru chanenl 2 so i can turn down chanel 1 and turn 2 up, this did help a lot. but and please correct me if i'm wrong here the volume pots are after the valve so the feedbaks alrdy in there.I also use an old sure vocalmaster (400 watts peak output) which has notch filters,with this feed bak is way less ,but its too dmn big to lug to jam sesions.

But what a want to know is whats in an acustic amp (eg marshal soloist100) that makes them not feedbak.
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Old 11th November 2011, 05:02 AM   #9
GloBug is offline GloBug  Canada
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I explained above, it's how much gain is at the first tube.

The more you raise it, the more feedback and distortion you get.

Acoustic amps are tame in the preamp section. Also they usually have less gain sections, whereas a "Metal" amp has more stages cascaded together.

Yes the volume or gain pot's are after valves, but the feedback is being created in the first valve, IT"S THE ONLY ONE THAT CAN "HEAR" YOUR MICROPHONE. Turn it down then.

Compensate for volume loss with the post or "Master"volume control.

That is why music amps are designed this way.
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Old 11th November 2011, 03:29 PM   #10
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by GloBug View Post

The clean settings will be far less sensitive to feedback vs. a high gain setting.

Hope this clears the air a bit.
Hi,

And why is that ? because overdrive, like a compressor, adds gain to
the loop, and overused will acerbate any feedback problems that exist.

I agree a clean sound at the same speaker level as a very clipped and dirty
sound will be far less likely to feedback, that is due to less loop gain overall,
not swapping input and output gains which I thought you implied, but in
fact your saying different, don't use high gain overdrive at the input.

rgds, sreten.
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Last edited by sreten; 11th November 2011 at 03:32 PM.
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