I have a really nice little 5E3 clone thats a gas to play thru, But, I am in need of a nice harp amp. These were pretty legendary with a lot of old blues players.
The Problem is, no matter how large the room is, If I raise the volume over 1/10th I get terrible feedback. Even at over 15ft away.
Is there a simple mod to corect this type of thing?
5E3 schematic
I have no experience with this type of setup, But it seems to me it shouldnt be to hard to correct if I knew where to look.
Trout
The Problem is, no matter how large the room is, If I raise the volume over 1/10th I get terrible feedback. Even at over 15ft away.
Is there a simple mod to corect this type of thing?
5E3 schematic
I have no experience with this type of setup, But it seems to me it shouldnt be to hard to correct if I knew where to look.
Trout
Hello Trout!
I've read somewhere an article about guitar -> harp conversion in tube amps, but I don't remember, maybe I'll post it later if I find it.
However, I would try adding some negative feedback, in general that always helps against acoustic feedback.
Also, try to limit frequency response of the amp: with the harp you don't need such low notes and high ones. So if with guitar you need about 50Hz - 10kHz, I would cut anything lower than 100Hz and anything higher than 5kHz.
Try some negative feedback from the output transformer secondary to the cathode of the first section of the 12AX7 in the schematic. Use a resistor (a pot) to set a variable resistive divider in conjunction with the 1500ohm cathode resistor of that stage.
Hint: if the amp starts to oscillate this way, without input, swap output tubes anode connections to the OTP.
I've read somewhere an article about guitar -> harp conversion in tube amps, but I don't remember, maybe I'll post it later if I find it.
However, I would try adding some negative feedback, in general that always helps against acoustic feedback.
Also, try to limit frequency response of the amp: with the harp you don't need such low notes and high ones. So if with guitar you need about 50Hz - 10kHz, I would cut anything lower than 100Hz and anything higher than 5kHz.
Try some negative feedback from the output transformer secondary to the cathode of the first section of the 12AX7 in the schematic. Use a resistor (a pot) to set a variable resistive divider in conjunction with the 1500ohm cathode resistor of that stage.
Hint: if the amp starts to oscillate this way, without input, swap output tubes anode connections to the OTP.
And keep in mind that it is not the amp that feeds back, it is the system. The ultimate cause of feedback is the mic picking up what comes out the speaker and sending it back through the system.
So a lot can be done simply by working with the amp placement as well as with proper mic technique.
Obviously lowering the gain of the amp will make it less likely to feed back, but the conditions for feedback have to be in place for it to occur.
So a lot can be done simply by working with the amp placement as well as with proper mic technique.
Obviously lowering the gain of the amp will make it less likely to feed back, but the conditions for feedback have to be in place for it to occur.
Thanks for all the great replies,
I think possibly I have located a possibility as to why at least part of the feedback may be occuring.
When I built the amp, I only installed 2 inputs instead of 4.
Making them basically a bright and normal setup.
Looking back at the original 5E3 layout and schematic I omitted the lower set of microphone inputs.
They should be wired like this.
The lower 2 jacks are actually wired different than the upper pair.
The jacks I used are Cliff Jacks ( Marshall style) that are switched (normally closed). So it looks to me like part of the problem is the 1 meg resistor?
When a plug is inserted into the lower jack, it opens the switch and has no 1 meg resistor from tip to ground, or at thats what I think I am seeing?
I have a second amp here with all 4 jacks, The lower pair both have less output than the upper pair.
I am however still needing to run 12AT7's instead of the 12AX7's. The Normal channel is working better than the bright channel which is to be expected.
Trout
I think possibly I have located a possibility as to why at least part of the feedback may be occuring.
When I built the amp, I only installed 2 inputs instead of 4.
Making them basically a bright and normal setup.
Looking back at the original 5E3 layout and schematic I omitted the lower set of microphone inputs.
They should be wired like this.
An externally hosted image should be here but it was not working when we last tested it.
The lower 2 jacks are actually wired different than the upper pair.
The jacks I used are Cliff Jacks ( Marshall style) that are switched (normally closed). So it looks to me like part of the problem is the 1 meg resistor?
When a plug is inserted into the lower jack, it opens the switch and has no 1 meg resistor from tip to ground, or at thats what I think I am seeing?
I have a second amp here with all 4 jacks, The lower pair both have less output than the upper pair.
I am however still needing to run 12AT7's instead of the 12AX7's. The Normal channel is working better than the bright channel which is to be expected.
Trout
Miking a harp for PA sounds a truely horrendous task!, the harp itself isn't really very loud, but it is BIG - so you can't get the mike too close, or the closest strings will be louder than the further ones.
If you have the mike further away, the gain needs turning up further, and feedback is almost unavoidable!.
Did PA last Christmas for my daughter (bass) and Charlie (guitar), plus two vocal mikes - but both bass and guitar were acoustic with in-built mikes. It was SO difficult to try and get enough volume without feedback, so we had a LOT of feedback throughout the night!. I told them afterwards, "we're NEVER doing that again!" - did another 'acoustic' duo gig a couple of weeks back - didn't take acoustic guitars, used electric ones instead!
If you have the mike further away, the gain needs turning up further, and feedback is almost unavoidable!.
Did PA last Christmas for my daughter (bass) and Charlie (guitar), plus two vocal mikes - but both bass and guitar were acoustic with in-built mikes. It was SO difficult to try and get enough volume without feedback, so we had a LOT of feedback throughout the night!. I told them afterwards, "we're NEVER doing that again!" - did another 'acoustic' duo gig a couple of weeks back - didn't take acoustic guitars, used electric ones instead!
Enzo said:
It would seem so, But there is a marked difference in the sound. I am actually able to get the mic input working fairly well on the standard 4 input version, I just wish I had not omitted the 2 jacks in the other one.
Normal channel seems better than the bright channel on the microphone as far as feedback goes, But I like the sound of the bright channel better.
Trout
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