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FDP Forum / Amp Mods, Repairs, and Projects / Reverb Feedback Issues

Hammond101
Contributing Member
*

So. Cal. USA

May 25th, 2012 12:41 AM Edit Profile Print Topic Search Topic
I'm working on a DR clone with an EVM-12L speaker installed. Complaint is too much reverb and reverb feeds back. I tamed it by reducing the value of the 1 meg resistor on the grid of the reverb driver. That reduced the reverb to an exceptable and more useable level but it still feeds back.

I traced that problem to the large magnet on the EV-12L. When I move the tank out of the cab (just behind it) there is no more feedback. I swapped tanks for good measure with the same results.

Anyone have an idea of how to shield the tank from the huge amount of magnetic flux from the EV? The owner of the amp is in love with the EV speaker and also will not want to run an external reverb unit or pedal.

I have a 12L in my personal DR clone and I don't have this problem however my tank feeds back in this amp as I made a second tank swap. I rolled a couple of driver and return tubes through it with no joy. My EV does have a factory heat sink on it. The problem speaker does not.

I actually can get my amps reverb to feed back but the reverb level needs to be darn near dimed and it's way to much to be used even in a surf tune as all the definition of the notes goes away.

The old good news, bad news senario here me thinks.
(This message was last edited by Hammond101 at 12:48 AM, May 25th, 2012)

rfrakes331K
Contributing Member
*

IL USA

RonHalen Jokingly He Says
May 25th, 2012 01:34 PM Edit Profile Print Topic Search Topic
You would think that the metal box the reverb tank is in would be enuf to deflect the magnet. Do you have a piece of scrap metal you could test in between the speaker mag and the tank?

Peegoo
Contributing Member
**********
**********

That chicken

is WRONG, baby.
May 25th, 2012 04:48 PM Edit Profile Print Topic Search Topic
An aluminum sheet might solve the problem. You can buy that stuff cheap in roll form at a builder's supply. Look in the roofing materials for "flashing."

Hammond101
Contributing Member
*

So. Cal. USA

May 25th, 2012 06:56 PM Edit Profile Print Topic Search Topic
I don't know if aluminum will do it or the flux/field will pass straight through. I'm thinking a of galvanized flashing might work. Thanks for the suggestion.

Home depot here I come.

rfrakes331K
Contributing Member
*

IL USA

RonHalen Jokingly He Says
May 30th, 2012 05:21 PM Edit Profile Print Topic Search Topic
Hammond, did it work?

Hammond101
Contributing Member
*

So. Cal. USA

May 30th, 2012 06:46 PM Edit Profile Print Topic Search Topic
I have explained and demonstrated the issue to the owner of the amp and he wants to leave it as it is for now. It is greatly improved with the grid resistor change and you are good 'till about 4 on the reverb dial. It is fairly surfy by then so he wants to call it good.

And here I was all set to give the tin snips a work out.

While all the voltages are in spec but on the high side I should have run Riverside's buck transformer on it before letting it go. The PT is a 110V spec clone. Might have shed some light. A cap of the proper value on the driver might have cured it too. I have a feeling it will be back.
(This message was last edited by Hammond101 at 07:21 PM, May 30th, 2012)

buckshank

usa

Jun 2nd, 2012 08:33 AM Edit Profile Print Topic Search Topic
Im playing through a newer deluxe amp and Im getting a high pitch squeal from the reverb. It always starts to happen late in the gig when the amp is hot. why is this happening and what can be done to stop this.

ampman91510

USA

Jun 3rd, 2012 02:24 AM Edit Profile Print Topic Search Topic
Jeez. Did the reverb have a bag? It shouldn't feed back with an EVM, I have a DR with an EVM-12L in it and it doesn't feed back at all. So, you said DR "clone", so I was just wondering what parts of the clone were non-standard.

I happen to be working with the reverb right now, I'm doing several custom builds and the reverb is what's happening.

I have one where the reverb is physically mounted on the actual chassis, what I did was take the pan (with the springs) out of the original box, and mounted the springs directly onto the chassis with four long binding-post type screws. I started with a Hammond organ tank, so very similar to the usual 17" Fender tank. I get two types of feedback: a) the usual low-frequency stuff that comes up from the speaker through the amp cabinet and into the amp chassis where it vibrates the springs, and b) if I take the amp out of the cabinet and place it vertically directly in front of the speakers (so the speaker is pointing longitudinally at the spring) I can get some nice high-frequency howling starting at about "4" on the reverb control. To mitigate these issues, I found some foam-on-nylon nut covers that happen to fit perfectly between the tank and the mounting screws, and that alleviates 100% of the first problem and about 50% of the second.

FDP Forum / Amp Mods, Repairs, and Projects / Reverb Feedback Issues

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