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Old 17th Apr 2006, 5:20 pm   #1
Jim - G4MEZ
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Default Homebrew Reverb Unit

A little project that has been waiting far too long to have anything constructive carried out on it (except collecting components) finally came to fruition this weekend.

I have been wanting for some time a vintage sounding spring reverb unit to go with my Fender Champ guitar amp. I had tried all the modern digital effects units and found them a complete and total disappointment. I also acquired a Fender Frontman amp that despite looking vintage was a nasty semiconductor affair that sounded like a wasp trapped in a jamjar. It did however have a spring reverb tank and it kindly donated it to this project.

The task a pal and I embarked upon was to design and build a valve reverb unit that could have a guitar plugged in at one end and the Fender Champ plugged in the other and sound suitably vintage. The sound of a Fender Twin Reverb was the goal but without the volume.

It took two days and four complete revisions before we were happy with the result. It met it's design criteria and sounds really quite magical..

Of interest about the circuit is the ability to vary the reverb depth by varying the power supplied to the tank and the ability to mix the straight audio with the recovered reverb signal on one pot.

Building it was an object lession in how to build audio corcuits as hum is just a bad layout away...

I've attached the circuit and a picture of the completed (prototype) unit. I'm not showing the under chassis view as I will be accused of ratsnesting but after four revisions of the circuit it was inevitable it would end up scruffy. It is now going to be rebuilt on a new chassis properly and cased.

A weekend well spent? Yes!


Jim
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Old 18th Apr 2006, 7:57 am   #2
Mike Phelan
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Default Re: Homebrew Reverb Unit

What did you use for the spring line, and the transducers, Jim?

Hammond ones had moving-magnet transducers; the input was driven from a wirewound pot across the speaker, and the low impedance output went to a PNP germanium transistor, thence to the all-valve reverb amp.

There have been various designs in the comics using piezo cartridges.
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Old 18th Apr 2006, 9:29 am   #3
Jim - G4MEZ
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Default Re: Homebrew Reverb Unit

Quote:
Originally Posted by Mike Phelan
What did you use for the spring line, and the transducers, Jim?
Hi Mike,

I'm presently using a clone of the Accutronics Type 8 tank. It's a 3 spring compact tank with magnetic transducers at each end. The input side has an impedance of around 10 ohms and needs about 2 watts of audio drive power for full reverb. The output side has an impedance of around 2k. I'm not sure who makes the particular tank I'm using as I "borrowed" it out of the nasty little Frontman amp. I'm soon to buy a genuine Accutronics Type 9 tank so that I can put the Frontman back together and send it on it's way via and hopefully recover the cost of a Type 9 tank.

Link to the Accutronics Specs here: http://www.accutronicsreverb.com/prodspec.htm

I'm curious about making a reverb unit from a piezo cartridge. Tell me more!


Jim

Last edited by Station X; 18th Apr 2006 at 10:09 am. Reason: Quote fixed.
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Old 18th Apr 2006, 10:06 am   #4
Mike Phelan
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Default Re: Homebrew Reverb Unit

Quote:
Originally Posted by G4MEZ
Quote:
Originally Posted by Mike Phelan
What did you use for the spring line, and the transducers, Jim?
Hi Mike,

I'm presently using a clone of the Accutronics Type 8 tank. It's a 3 spring compact tank with magnetic transducers at each end. The input side has an impedance of around 10 ohms and needs about 2 watts of audio drive power for full reverb. The output side has an impedance of around 2k. I'm not sure who makes the particular tank I'm using as I "borrowed" it out of the nasty little Frontman amp. I'm soon to buy a genuine Accutronics Type 9 tank so that I can put the Frontman back together and send it on it's way via and hopefully recover the cost of a Type 9 tank.

Link to the Accutronics Specs here: http://www.accutronicsreverb.com/prodspec.htm

I'm curious about making a reverb unit from a piezo cartridge. Tell me more!


Jim
Hi Jim
As I remember, they had a strip of metal with a stereo turnover cartridge - maybe TC8M or H. Instead of the stylus, there was a straight steel wire sitting on the notch where the stylys was, and attached to a piece of fire element spiral as a spring.

I don't know the Accutronics unit, but the impedance of the two types of Hammond units would have been about the same.
The small one on the M100 and A100 organs type had two springs, tensioned horizontally.
The large ones on the PR40 tone cabinet (6 x EL84 !) had three springs hanging like a necklace.

If you noved the cabinet when powered up without locking the reverb, is made a noise like a hundred dustbins being dropped down a lift shaft!

I think the reason for more than one spring was to give a slight discord to avoid resonance.
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Last edited by Station X; 18th Apr 2006 at 10:11 am. Reason: Quote fixed.
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Old 18th Apr 2006, 12:23 pm   #5
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Default Re: Homebrew Reverb Unit

Yeah. Both my Carlbro Rebel Twin and my JHS 120W bass stack have twin spring reverb tanks.

I really liek them, and i dont think i can ever go back to solid state reverb.

And if you move it they do make funny noises .

I liek the way the bass sounds if you slightly overdrive the reverb circuitry.
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Old 18th Apr 2006, 1:21 pm   #6
Jim - G4MEZ
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Default Re: Homebrew Reverb Unit

Quote:
Originally Posted by Mike Phelan
Hi Jim
As I remember, they had a strip of metal with a stereo turnover cartridge - maybe TC8M or H. Instead of the stylus, there was a straight steel wire sitting on the notch where the stylys was, and attached to a piece of fire element spiral as a spring.


If you noved the cabinet when powered up without locking the reverb, is made a noise like a hundred dustbins being dropped down a lift shaft!
That's interesting Mike, I'm very tempted to try one of those piezo ones! How was the fire element spring excited?

I know the fantastic noise a rattled tank can make. During my development I had the tank resting on our tumble drier when a cup of tea was brought out to me. Cup placed down on the drier followed by the most almighty and deafening reverberating clang from the amp as the springs rattled Another great experiment is to feed a radio programme into a reverb unit. The result is pretty interesting...

Adi, I'm in the opposite camp and just love my clean tones and that is one thing I like about mine, it's as clean as a whistle with a very ethereal (sp?) quality to the reverb. There is just nothing to compare to the sound made by a spring reverb.
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Old 18th Apr 2006, 8:54 pm   #7
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Default Re: Homebrew Reverb Unit

The pics on the Accutronics website are a bit dark and dont show the spring lines very well. I have a two spring reverb unit which I was going to use with a Reel recorder for effects, Havent got round to it yet..
The one I have is similar in appearance to type 1 on the accutronics page. No makers name on it though.
The springs are connected each end to small boxes in which is the pickup unit. similar type to a cartridge. These boxes sit on a narrow strip of aluminium which is supported on each corner by 4 very small springs. So it is independently sprung.
The boxes are about the size of an oxo cube and have two wires connected to each box which are then connected to two tag strips and they have a screened wire on each..
I thought I had one of the other type using turntable type cartriges but I cant find it. Im sure that one had a makers name on it...
Hope my description is of some use.. Peter Reelguy
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Old 19th Apr 2006, 8:51 am   #8
Mike Phelan
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Default Re: Homebrew Reverb Unit

Quote:
Originally Posted by G4MEZ
That's interesting Mike, I'm very tempted to try one of those piezo ones! How was the fire element spring excited?
Jim
It just had a piece of piano wire sitting on the notch attached to the piezo elements where the stylus should be, and was then attached to the end of each spring.
This would need a fairly high impedance to drive it.
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Old 19th Apr 2006, 11:05 pm   #9
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Default Re: Homebrew Reverb Unit

I have a spring reverb unit, in its original Marshall case. Somebody - not me -
has replaced the original electronics with something made on Veroboard.

If anyone wants it for the cost of postage let me know.

Joe
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Old 20th Apr 2006, 6:34 am   #10
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Default Re: Homebrew Reverb Unit

Joe,

PM sent!
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