mini reverb circuit design

[makepeace]

Hi guys.

Ok, I've ordered a couple of accutronics mini reverb tanks from CEdist and I need a bit of guidance as to where to start with the design of drive and recovery stages. I've ordered a long and a medium decay and one of each of two input impedances - so 4 in total. They measure about 130 x 40 x 30mm.

The two input impedances available are: 150 and 600ohm; and both have an output impedance of 1500ohm. The recommended drive currents for each input impedance are 6.5 and 3.1mA respectively.

I want to build two circuits: all valve, and all solidstate.

Anyone have any ideas where to start tube/opamp wise for each and topologies? Will a certain input impedance be suited to a particular state?

Oh yeah, I also want to try for as much versatility as possible which one should bear in mind ie: a basic frequency shaping circuit (big muff pi probably, maybe a james), mix control, a pre-gain level control and a post-gain level control.

Hope that someone could shed some light as to some starting points!

Any other ideas would also be welcome!

Thanks!

Jono

[J M Fahey]

Check a couple commercial reverb schematics, whatever Fender/Peavey/Laney/Crate/Marshall use.
Can't go wrong.
Anyway, most of them are based on the generic circuits published by Accutronics themselves in their site.
As of tubed ones, check Ampeg and Traynor, two brands famous for using direct drive reverbs.
Ther must be other examples, but with these you have enough to amuse yourself.
Please post here your experiments, for the benefit of the Community.
And Good Luck !!!

[makepeace]

Thanks for the reply, but not really what I was hoping for. I realize i should have been clearer.. I was hoping for a bit more flesh, some tips, tricks, out of the ordinary solutions (like the 12DW7), the SRPP etc. I don't particularly want to base my designs on a 'big' name design, but rather a more quirky approach. Will make sure to post my flesh if I get this off the ground.

Anyone have any cool ideas? What would you do?

[J M Fahey]

Ok. So you do not actually "add a reverb" to some amplifier but "build something wild".
Fine with me.
How about this?

or this?

or *this*?


Feel free to read:
The Electronic Peasant's Slinky Spring Reverb Page
and
The Electronic Peasant's Thermiomniverb Page
and
SPRINGAtrON 3000 - World's Most Incredible Spring Reverb | Encyclotronica

Good luck.

[makepeace]

Thanks for those interesting links! They look interesting.

But I think you're still missing the drift, or else you're being a troll. What I want to do is in-between your suggestions. I already have my reverb tanks, I'm just looking for some modern, thoughtful, 'diy discovered' starting points as to how to drive and recover them. Like for example using the 12DW7 sections, one as a drive and one as a recovery, or using SRPP, like I mentioned before.

[Enzo]

Oh, let's not call Juan a troll, he is an experienced professional, he is even a manufacturer of amplifiers and speakers in Argentina.


You need to define your projects. Are these to be stand alone reverb units in the tradition of the old Fender reverb units? Or are these to be reverb systems for putting into amps that have no reverb? Or are they to be more like independent FX units like plugged into an FX loop? If going into an amp, they probably won't need power supplies - they run on the existing power of the amp.

To drive the pan, you need a tiny power amp. Solid state drives are usually fed to high Z pan inputs. Tubes can go either way. The Ampeg and Traynor circuits mentioned in Post 2 are using high Z input pans. Alternatively, the circuit Fender used for decades uses a tube driven transformer driving a low Z input pan.


You want input and output level controls? OK, put a pot in either place.

As to quirky and offbeat... reverbs have been around for decades, and methods to drive them were mature designs by 50 years ago. So it is possible to come up with a different circuit from what we usually see, but it probably was already thought of. The common circuits are common because they work. work well, and are reliable. And ultimately all you have is something that feeds your signal to the long springs, and something that picks up the result and returns it to your signal path. It really then doesn't matter a lot what it is. You can get great reverb with tubes or solid state drives. Doing something weird to do the same job, well, if you just want a project, there you go, otherwise, why re-invent the wheel?

Using a 12DW7 instead of a 12AT7 or 12AX7 is really nothing new. A 12DW7 is just another dual triode, it happens the two sides have different gains. In the Fender stand alone reverb, there is a small power tube driving the transformer, contrast that to the 12AT7 with both sides paralleled as is common in their combo amps. The old one used a 6K6, and the modern reissue of the same circuit uses a 6V6. An EL84 would work as well. Note that something like a 6V6 has WAAAYYY more capacity than this little reverb pan needs, but we can use it, just like a 400 horsepower drag racer doesn't HAVE to make the 1/4 in 4 seconds. The little 12AT7 is more than enough. There are other tubes, like the 6CG7/6FQ7, another dual triode, but it can dissipate 5 watts or more. And for that matter the little 6C4 is a power triode tube you might be able to use.

The ampeg version requires no transformer, the Fender circuit does (both tube drives), but the transformer is not all that expensive, so for a project, take your pick. Peavey drives and recovers a reverb pan with a single dual op amp, usually a 4558. It works well and reliably and has been their basic circuit since the 1980s. Others make a small push pull transistor stage for the purpose. Even PV does that on a few models.

To me the challenge of a reverb is configuring it into a system, rather than trying to invent a drive circuit that doesn't look like all the others. All I need to do is shake the springs with my signal. I;ll steal an old circuit in a heartbeat. I recently had a customer build his own litle reverb to add to his home built amplifier. MY contribution was to help him interface it to his amp.


I'd start with a block diagram of each unit you plan to make.

[makepeace]

Thanks for the great reply Enzo. I was not intending offence to J M off the bat, unless it was due to him; it was rather difficult to judge based on his posts - the second especially as it contextually alien to my first post - which is why I gave two options.

Anyway, and I'm sorry again for not being clearer: The plan is to build an analogue compact 'stompbox' reverb type of thing - relatively small enclosure, probably 150 x 100 x 40mm or so.

Thanks for the ideas re tubes and such, particularly the 6C4. Looks interesting, will do some research, and will take your advice re the block diagram. Have never really used that approach before, such an obviously good idea!

[J M Fahey]

Dear makepeace, post #2 is the full answer.
Which was detailed more in Enzo's post (thanks Enzo, as usual )
But if apparently you needed something **very** different (from the tone of your answer), well, so be it.
Back to the project: please define your goals: you seem to be bent on using a 12DW7 (you mentioned it twice in 2 different posts), maybe you have a spare one and want to use it? Fine with me.
BUT you also mention using it in a stompbox .
It baffles me, high voltage tubes and their supplies are not exactly easy to fit there.
And then, you add the size constraint: 150mm max. dimension ... not even the raw tank fits in there !!!
Even if it did, the power transformer hum on the pickup coil will drive you crazy.
Smallest practical size is about what the Fender stand alone units are: a (not so small) cabinet similar to a tube amp head.
The smallest stompbox type reverb project available is Craig Anderton's Stage Center Reverb.
Great project, has been revamped for more modern ICs, since the original one is somewhat hard to find.
Chek it. Even better , build one and test your tanks,,even if later you design something else.
Stage Center Reverb
And, as I said earlier, good luck !!!

PD: if you want to build a *killer* Reverb project, I can post a link to Phatt's design.
Probably the deepest reverb in the World and I'm not kidding.

[loudthud]

The Sunn Beta Lead uses CMOS gates to drive the reverb pan. Not sure what the pan input impedance is though.

[Alexander]

Mr Fahey- please post the 'Phatt's lnk'-- I'm in the middle of a super-deep reverb project myself and am intriqued by your comment!

Thanks,
Alexander

[J M Fahey]

Phatt is an SSGuitar Forum member.
I suggest you register and follow one of his many Reverb discussions there.
*One* of them is
Can i replace reverb tank in Prince Boogie Copy with an Accutronics tank?
It's incredible how much he knows about the subject and the good *results* he's had.
I tried to link the schematic here but it's posted in a way that only members can see it, so.....
That post also shows his links to various sites which discuss all aspects of reverb design.
He really did his homework
And he's no shy, he slams his reverb tank with discrete transistors fed from +/- 35V rails !!!!
Go there and enjoy.
also:
Fender Frontman 65R reverb tank question

Mosfet Spring Reverb Driver

By the way, PHATT is Phil Abbott from Nambour, Australia and a *great* no nonsense experimenter.
It took him 10 years to perfect his huge reverb ... which is still under development, of course.

[makepeace]

JM. I am calm. Although, it still seems as though you aren't getting the gist. As stated in the first post, I will be using the 'mini' reverb tank (specs featured in post 1), which will fit perfectly into the enclosure dimensions specified in post 7. Sorry to say, but as I see it post 2 is a very undimensional answer. I know very well that I can glance ideas from schematics of commercially available amps and standalones, but I'm looking for other ideas that might prove more efficient and suitable. Ideas that fellow DIYers have experience with and have gained great results (thanks very much for the links re Phatt, looks very interesting). I don't know how you gleaned that I am bent on using a 12DW7. That was an example I used to genre'fy what I want to implement: something slightly different, but all-together functional, especially in such a compact project. Tubes are not irrelevant in this application at all. I could easily get away with using a small (toroidal) transformer to supply the VA that is required (see EH Black-finger, English Muff'n, LPB 2ube etc), and I could very easily deal with the noise. I would like to try and experiment with both a tube approach and a solid-state one. Compare, and if results are favourable on both sides, investigate each further and come up with some end designs.

[Enzo]

Look into Belton's reverb IC. It is a digital circuit in one little puck with a half dozen leads. Ideal for a pedal reverb. MAybe not your cup of tea, but check it out.


I think when it comes to stealing someone's circuit, consider that getting the most out of a circuit is usually one way of making it cheaper. And amp makers are ALL OVER that approach. So I tend to think their conventional circuits are pretty efficient, all things considered.


If you have or will soon have the little reverb pans, try using them in a regular amp in place of the larger pan. That shoukd give you an idea of what they sounbd like. Tiny reverb pans are a compromise. They are made for cramped spaces, like little practice amps. Frankly they don't have the best sound, the tiny springs don;t have the opportunity to spread the waveforms out. Just as the 16" pans sound better than the little 8" ones, the tinjy ones sound even less cool. However, that is a judgement only you can make. Just before engineering the whole pedal thing, try one in an existing circuit.

If you want tiny, then I'd be staying away from tube/transformer drives. The transformer is bulky when considering pedal space. The high impedance tube drive might be preferred. But really, if I were making a reverb pedal, I;d go solid state. You are not probably planning to overdrive it, so the tubeiness we love about amps is less a factor. And the low voltage requirements for a 4558 IC or even a LM386 or similar to drive it, take up FAR less space and generate boatloads less heat.


ANd just my opinion, but in the interest of the great getting along in the sky, maybe we could get away from discussing how cogent or to the point individual posts are. We read a post, it helps or it doesn't. We get out of it whatever we find of value, and move along to the next.

[makepeace]

I had looked into the belton brick a while back, but I kind of got over it. But yep, you make a very good point in sticking these little tanks in an existing circuit and seeing how they sound. Thanks, I will definitely do that before going too heavy into the design.

I'm not too phased about the need to use a transformer, so I think that I will try out the tube idea if the tanks sound alright. I dissected a EH Black Finger tube compressor and they use these little toroidals that are about 40x40x20mm. That's fine for me (assuming of course that it can deal with the VA).

ANd just my opinion, but in the interest of the great getting along in the sky, maybe we could get away from discussing how cogent or to the point individual posts are. We read a post, it helps or it doesn't. We get out of it whatever we find of value, and move along to the next.

I agree completely, and I'm sorry - but I'm sure that you can understand my frustration. I just feel that people should read the question PROPERLY before answering, and hesitate at least before giving a throwaway answer that's useless to anyone that knows how to use the internet, and then stubbornly purport that theirs is the right answer (when its not, unless it is, to an unasked question), whilst being unnecessarily belligerent. I wouldn't be here if I didn't know how to google. It wouldn't be so bad in itself, but it appears that many people here tend to rather not post if they think the questions have been resolved, unless someone gets called a troll . Oh, and since when is being an experience professional and a troll mutually exclusive?