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Spring Reverbs again

Started by phatt, November 26, 2012, 08:21:49 AM

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phatt

Hi all,
        I have been re-visting Reverb circuits so I thought I'd share my findings.

I scoured an old bit of junk a Ross 5 channel powered mixer. A rather poor performer for audio but did have a 3 spring 9 inch rev tank.  The tank has high Z transducers at both ends. bum. :grr
My Maxiverb circuit will only drive the lower Z units so I came up with a plan and it certainly works way better than I expected. <3)

My original Maxiverb needed two supply voltages and had a rather oddball output but
This circuit only needs split 15 volt rails and lower parts count so it would be much easier to build.

So if you have one of those high Z reverb tanks this might just be the ticket for a very good Reverb unit that won't break the budget.

The small Output/Line Transformers should be easy enough to find and likely dirt cheap.
The DC reading is around 190 Ohms / 330 Ohms. The Resistance can give a clue as to the Z.
My guess is this one I've got is 600 Ohm / 1k Ohm Z.

I've spent a few days A/B testing between the original *MaxiVerb* and This one and although it does not have quite the big slap there is little between the two circuits.
The short tank does sound a tad different but on stage you would not be able to tell.

If you specifically need the country slap-back effect then you will likely need a long tank for that.
With short springs the slap delay is way too short to get that particular effect.

Just like the Maxiverb this one is bright and airy due to plenty of bass roll off which allows a higher output of reverb before it all turns into undefined mud.

With the Dwell full up this is dripping wet reverb reminiscent of the old surf sound which is what the Maxiverb does so well. Not quite the big tank slap of the Maxiverb but I hardly ever use that anyway.

As The Maxiverb (long tank) takes up more space the short tank might be well suited to a smaller chassis and I might even be able to implement it as a floor unit.
Time will tell, still a long way from a working unit but no point in rushing it.

I have no doubt that other chips will work just as well maybe even the tiny LM386 but it's single supply and may not have enough drive and you would likely need an 8 ohm/ 1k Ohm transformer.

I'm Not sure about the NE5532 as they have compensation pins I'm assuming they are not needed here but if anyone knows more about those fine details feel free to comment.  :tu:

Anyone have a background on the 3 spring tank?
OC Electronics, Milton Wi and 2 long patent numbers, on the side reads 756
I assume Wi means Wisconsin?
Phil.

J M Fahey

Cool !!  8)
Eager to listen to some MP3 !!!  :dbtu: :dbtu: :dbtu:

phatt

You know, right as I posted that I somehow knew it would be You that would want to hear it working.
In time, in time.  :-*

Sadly it's all under the bench for a few days until I redesign that Performer 1,000 I fixed a while back.
The owner now wants me to get rid of the massive bass response,, Wish me luck.

Meantime I'm going to try and find some other drive transformers for the reverb testing.
I might even go crazy and drive an 8 Ohm / 1k Ohm tranny with a LM1875. :duh

Heck why not? I hear it is BBQ season.  ;)
Phil.

J M Fahey

#3
Well, you are known to often drive a puny tiny reverb coil from +/-35V rails. :o
If *that*'s not a BBQ, what is? 8|
Is the Performer a single 12"?
If so, it probably has a big heavy 2" VC , thick cone and heavy magnet.
If it's anything like the heavy speaker fit to Stage 100/160 combos or in pairs to Super Twins, it is a "bassy woofy" speaker and not getting any sparkle out of it is not your fault.
Kind of Physics getting in the way.
But cutting some bass at the first or second Preamp stages will help you .
At least Distortions (and "Clean") will be "cleaner", as in "less muddy".
Just for sake of comparison, try that amp with another more "normal" speaker(s).

Roly

@Phatt - I consider the NE5532 to be a bit of serious overkill for most situations.

My personal fave is the LM833 which is cheap, easy, and as close to a perfect amplifier as most of us will ever need.  I changed the preamps in my Twin-50 from BC109C's to LM833's and now you literally can't even tell it's switched on with everything flat tack.  And talk about bandwidth - the first incarnation took off at 455kHz(!) and I had to deliberately roll it off around 35kHz.
If you say theory and practice don't agree you haven't applied enough theory.

phatt

Thanks Roly,
well I don't think my springs will ever reproduce signal at 455kHz  :lmao:
The NE5532 was sitting in my pile of trashed bits and I just wanted to see if my plan would fly.

Most of the reverb circuits found in gear I've seen/heard is not all that good and getting the drive end to move the darn magnet is the tricky bit.

While clearing out the bins of trash I found a few small line trannies I'd forgotten about and got a brain wave. I still have not cleaned out the bin, much to my wife's disgust. lol

Spurring this on also, a local player has heard my way out maxiverb and wishes to buy/swap for it.

Being it was one of my first success stories with Audio stuff it kinda erks me to sell it,,, but hey I can't keep stuff forever :(

So the challenge is to see if I can find a simpler way to get big drive energy to the driver transducer.
So while the original is still here I'm A/B testing some ideas.
I'm working on the idea that if I can get an output transformer to swing a big enough voltage then it may work.

@ JMF,
      Thanks for the tips on the Performer 1000. I might start another thread on that soon as I'm interested in your observations about speakers and such.
BTW, I did get a 10 watt power chip to drive an OT for reverb drive (Z= 8/1k) and it ran stone cold.
Went fine for about 4 hours but I must have bumped something when the phone rang and my dodgy old BBoard must have popped a wire which melted the chip including the OT.
upon return I burnt me finger on the heat sink trying to establish why it no longer worked. :'(


While working it was very close to the same energy as the Maxiverb,, so maybe the idea has merit.
I'll have to wait for another power chip.

Phil.

J M Fahey

Ugh !!
I don't trust push-in breadboards for anything carrying more than a few mA.
Not their fault, really, they just weren't meant to do that.  :(
For power amp prototyping and such I *still* use the nails_into_some_wood type (usually chipboard leftovers).
They look like baby Alien nests but, who cares?

joecool85

Quote from: J M Fahey on November 27, 2012, 01:48:46 PM
Ugh !!
I don't trust push-in breadboards for anything carrying more than a few mA.
Not their fault, really, they just weren't meant to do that.  :(
For power amp prototyping and such I *still* use the nails_into_some_wood type (usually chipboard leftovers).
They look like baby Alien nests but, who cares?

You don't happen to have a picture of this, do you?  I've never heard of doing this but it sounds like an interesting idea.
Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com

Roly

In my (pre)teens "breadboarding" was still literal, a lump of timber, some wood screws, and something like cup washers.





My experiences of the modern plastic ones have been second-hand, but unfortunate, so I have no time for them - I just lash stuff up, Veroboard or "aero-board" (aka "birdsnest").
If you say theory and practice don't agree you haven't applied enough theory.

J M Fahey

Wow!! That one predates me . my grandfather !!! ;)
Ok joecool, I'll take and post some pictures.
You will see the light ;)

JHow

I love it!  Especially the "insulation is for whussies" approach to wiring.  What is it?  Regenerative receiver?

Roly

Quote from: JHow on November 30, 2012, 10:01:27 PM
I love it!  Especially the "insulation is for whussies" approach to wiring.  What is it?  Regenerative receiver?

It came from Wikipedia under "breadboard".

It's apparently a TRF - Tuned Radio Frequency receiver.  These predated super-regenerative and super-hetrodyne receivers in that they don't self-oscillate or have a down-conversion oscillator.  The TRF generally consists of a tuned amplifier on the signal frequency which feeds a detector then into the audio amplification.

They have rather limited sensitivity, but normally more than enough for receiving local AM broadcast stations, and not having an oscillator are very clean and free of annoying hetrodyne whistles.  They are also therefore well suited to clandestine operation where local oscillator radiation could be a fatal giveaway.  At one time I worked for a radio manufacturer and one of our models was a cheap TRF 'rockerbox' that had surprisingly good performance.
If you say theory and practice don't agree you haven't applied enough theory.

JHow

Oh TRF.  The cub scouts and I put together some ZN414/MK484 TRF receivers a couple of years ago.  Yer basic cub scout radio.  We etched small circuit boards using enamel paint as the resist and just painted simple pads for dead bug style circuit.  Fun stuff.

Roly

Yep, that's a way to go; no-drill dead-bug style works fine, as do a lot of other things for etch resist, nail polish, roofing paint, waterproof marking pen, ... you could quite reasonably do a whole amp like this, say stage by stage modular style.  A cub-safe etchant is vinegar, some salt, and some hydrogen-peroxide.
If you say theory and practice don't agree you haven't applied enough theory.

joecool85

Quote from: Roly on December 02, 2012, 06:26:43 AM
A cub-safe etchant is vinegar, some salt, and some hydrogen-peroxide.

Any experience with this?  If so, I'd love for you to do a thread about it!
Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com