Belton reverb unit

[Leevi]

Does anyone have experience in this box? What kind of delay it is?
Do you think it works with tubes?
/Leevi

http://www.tubesandmore.com/scripts/foxweb.dll/moreinfo@d:/dfs/elevclients/cemirror/ELEVATOR.FXP?item=P-RBTDR-1H-L

[jerrydyer]

I saw that so I called and they emailed me an application page but its a little beyond me. You still need to create a buffer circuit as if it were a spring tank so, aside from space, no other benefits.

[JB]

I've been looking at it too.  Relatively high input impedance and low output impedance which is good.  Unity gain with max input of a volt so right sort of level to sit in a pre-amp.  No transformer needed (space, cost), (hopefully) not susceptible to hum and mechanical damage.

I think with a minimum of additional circuitry (5V supply and maybe an input buffer) it could be knitted into a pre-amp okay.

Of course, it has to sound good!

There is a comparison on a site I found of one of these in a pedal plugged into an old Deluxe Reverb and they switch between the two reverbs.  Sounds okay but would like to hear some more.

JB

[jerrydyer]

can you keep me updated if you try it?

[JB]

Sure.  I don't have one to play with yet though.  Funds and time permitting I'll have a go.


JB.

[jerrydyer]

yep...I have so many unbuilt things right now. I have this cool board someone gave me its a one watt amp board.  Hot rodded champ runs off a reverb trannie ... keeps getting thrown on the back burner.

[PRR]

60-100mA!! What a pig!!

> Relatively high input impedance

10K input is annoyingly low for a tube amp.

3 inches and <$19 is attractively cheap/compact.

> emailed me an application page but its a little beyond me.

This file?  http://www.uk-electronic.de/PDF/BTDR-1.pdf 

That says nothing more than what AES extracted for the item-page, except the order-codes for models AES is not offering.

Typical Fender reverb: 8V into 470K at 12AT7 grid
Belton: 1V into 10K; could be 8V into 80K, still a lowish impedance to hang from the preamp

The full Fender path 12AT7-RT-tank-12AX7 is very nearly unity gain (a bit less).
Belton is unity gain before adding 70K input build-out.

I think you want a cathode-follower or FET in front, and in many cases a little gain at high voltage (12AU7) in back. And a non-trivial 5V supply.

Small Bear also stocks the module, and has "a pedal schematic from the designer of the module, Brian Neunaber." 
  http://www.smallbearelec.com/Projects/ReverbPedalSchematic.pdf
 
He takes a small loss from guitar to module, via a chip which allows for a nice high impedance to the guitar. The plan could be simpler (CMOS just to drive an LED?), but the difference would be less than a buck.

[jerrydyer]

doesnt add up I guess . I would just rather deal with the additional circuitry and find a space for a real tank. Its just that Im almost out of space now and the people who have bought from me, only negative comment seems to be, "I wish it had reverb"  I use a good tube driven loop but I agree that a real tank reverb still feels better than any digital unit they might put in there.

[PRR]

> designer of the module, Brian Neunaber

Neunaber has patents.

http://www.google.com/patents?q=Brian+Neunaber

Apparatus and method of limiting power applied to a loudspeaker
US Pat. 6940981 - Filed Sep 16, 2003 - QSC Audio Products, Inc.
[APPLICATION] Apparatus and method of limiting power applied to a loudspeaker
US Pat. 11087427 - Filed Mar 23, 2005

This seems to be an application relating to reverb:
  http://www.google.com/patents?id=OUmzAAAAEBAJ&dq=12/215,084
A good in-depth summary of digital reverb techniques. The "Claims" are zzzzzzz...., skip to "Background".

It is, or could be, built with several "Princeton Technologies Corp. PT2399" chips:
  http://www.synthdiy.com/files/2007/PT2399.pdf
  --- but I'm sure you are better off buying the Belton module, unless you are incredibly adept at reverb programming.
  
me> could be 8V into 80K
  
No; reading the patent-app, it appears that it "wants" a low-Z source, under 10K. So 70K build-out is no good. Cathode/Source Follower with attenuation in front will be fine.  

[Leevi]

Does the Belton box work like a spring reverb or like a digital delay
simulating endless tape echo?
Leevi

[JB]

There's a sound sample of one used in a pedal here:

http://www.leejackson.com/MrSpringgy_pedal.html

And a kit/schematic here:

http://www.generalguitargadgets.com/index.php?option=com_content&task=view&id=243&Itemid=26

Given that this is a solid state reverb module then I think a source follower driving it and maybe fet recovery/gain stage (if it needs one) wouldn't be out of place if using within a tube amp.

JB

[PRR]

> work like a spring reverb or like a digital delay simulating endless tape echo?

No.

> I think a source follower driving it and maybe fet recovery

Yeah, or tubes.

If you put this into a classic Big Fender which already has reverb, you can save two half-bottles.

Fender Twin Reverb
2 units 12AT7 as reverb driver
1 unit 12AX7 as reverb recovery
1 unit 12AX7 as reverb mixer

You change the "driver" to a buffer, and any triode will do.

You do not need the reverb recovery stage; Belton output is already this big.

Therefore you throw away the 12AT7, re-rig the reverb output recovery as reverb input buffer.

This works because the Fender Twin Reverb's reverb mixer stage has some gain for the reverb path.

[Leevi]

Thank you for the circuit PRR. I would like to ask would the following circuit work?

http://i218.photobucket.com/albums/cc183/kz14100/BeltonReverbUnit.jpg

/Leevi

[PRR]

Obvious:

What happens when the right hand pot is turned full down? (Nothing comes out, wet or dry.)

The apparently complete power supply has no provision for +5V 100mA to power the Belton.

Not obvious:

Where does this go? Inside the amp? In line with guitar?

Subtle:

A reverb spring has loss of 1000:1, so it needs 2 or 3 amplifier stages.

The Belton is unity-gain (0dB); why do you have two high-gain amplifiers?

The Belton input overload is 1.5V. With lefthand pot full-up, and V1 gain near 40, input overload is near 37mV. Guitar outputs can exceed 0.5V, but almost never 1.5V. Why is there gain before the Belton?

Actually the full-up gain won't be 40, because the Belton input impedance is 10K. If the unloaded gain of V1 is 60 with output impedance of 120K, then with the Belton loading it will be more like 3. So the gain may be appropriate... except the loading also loads-down the dry path, which probably should not vary much while the reverb knobs are turned.

The internal mixing inside the Belton may depend on a low source impedance, (<<10K).

If reverb is defeated (how), then the dry/direct path has anything from large gain to no output at all, depending on reverb pot settings; consistent unity would be expected.

Decode the suggested implementation:
http://www.smallbearelec.com/Projects/ReverbPedalSchematic.pdf

First opamp is unity gain, shows a high impedance to guitar and low impedance to internal circuits.

Next opamp has gain of 2 for high frequencies and gain of 0.67 for low frequencies, and shows a low output impedance to the Belton.

Through Belton.

The last opamp is a mixer. The topology is odd. The direct path has gain of 0.8 (not unity, but close). The reverb path gain is adjusted in the pot; at full up (down as drawn) it seems to have gain of 0.25. Traditionally I have assumed that BIG REVERB needed gain equal to the dry path; indeed my software reverb can be turned up to reverb 200+% of dry signal. I only use it to sweeten orchestra/choir, no SURF, but even then I may run over 40% reverb gain. Maybe the Belton sound is so "thick" that it does not have to come back as big as the dry signal to be "big"? Alternatively, maybe the Belton's flaws become apparent if returned too large.

I do not know the module; but I think that plan can guide your thinking.

I'm also not sure what tubes bring to the game, if the max signal in/out of the Belton is only 1.5V, 1/40th of what a tube can do, or ~~0.1% THD. The Belton's basic operation eliminates the power tube driver, driver transformer, and coil-slap of a spring-tank; no place to put the little tube quirks which make classic tube reverb delightful. Oh, you could use 12AT7/6F6 and transformer to drive Belton (it's roughly the right voltage!); but then you may as well use a spring.

What JB said: "I think a source follower driving it and maybe fet recovery". Get some cheezy 12VDC supply to feed the JFET drains, regulate 5V for the Belton. If the designer's plan is good, it does not even need gain after the Belton, though it may need a buffer after the dry/wet mixer..... ah, maybe not.

[Leevi]

What happens when the right hand pot is turned full down? (Nothing comes out, wet or dry.)

Yes that is the idea. The second pot works like a VOL (output level). This circuit has been modified from a standalone
reverb I have been using with a spring reverb where I of course have more amplification stages.

The apparently complete power supply has no provision for +5V 100mA to power the Belton.

Yes it is missing. It has to be built there with a separate trafo/rectifier or use battery which will not last long with a  60mA supply current

t mixer..... ah, maybe not.
Where does this go? Inside the amp? In line with guitar?

Standalone reverb to be used before the amp.

Thanks a lot for your deep analysis. I think the box is worth to test since it is not so expensive.
Probably it never reach the sound of a real spring reverb but might give another type of sound.
An advantage is that the box is small and you don't need any reverb transformer and can manage it
with less tubes (at least I believe it will work with tubes as well).

/Leevi

[FYL]

(Resurrecting an old thread)

I've got a few samples of Belton magick bricks and have begun playing with them. The digital reverb is surprisingly good, even in a basic low V rail to rail opamp config, so I've begun toying with an hybrid module (Cf. enclosed schemo - not for general consumption).

A 12AU7 used half as a cathode follower - nice low Z out in order to drive the brick with a <5K Z, half as a gentle amp stage; some glue; a 5V DC supply derived from the 6.3V heaters and that's pretty much it. The basic schemo should include suitable frequency contouring - a coupple of RC filters will do the job and limit bandwith to, say, 100 to 4 KHz or so, that'll be for another day.

[tubenit]

Did anyone come up with a hybrid version of this that they are using and like?  One using a tube and the Belton reverb brick?

If so, would you be willing to share a schematic for it?

I did find this which has a schematic using tubes and a soundclips which sound really nice, IMO.

http://alumni.soe.ucsc.edu/~danman/belton/BeltonCarrier.html

With respect, Tubenit

[FYL]

Did anyone come up with a hybrid version of this that they are using and like?  One using a tube and the Belton reverb brick?

I built the 12AU7 version. It sounded very nice but was too noisy for real world apps with a Q&D 5V power supply. IMO the "carrier" approach should be better, just forget the first half triode.

[tubenit]

FYL,

Thanks for the response. I am presuming you are saying don't use the 12AX7 triode and just implement it with the 12DW7?

Am I understanding you correctly?

With respect, Tubenit

[FYL]

Yes, you don't really need the 1/2 12AX7 used as a gain stage - the brick only needs 1.5V peak! Re. the actual module, you can use a great sounding and cheap 12AU7 because you don't need lots of gain: one half is used as a cathode follower, the other one as a "recovery" stage with 25 dB / x 17.5  of gain and app. 26 V out, more than enough for a reverb stage.

[tubenit]

FYL,

Thanks for the information! I appreciate it.  With respect, Tubenit

[moonbird]

Great thread -- I have been itching to try the belton module but do not have the knowledge to implement. Tubenit -- could you please draw a schematic for the 12au7 "carrier" implementation described above? It would like to avoid buying a 12dw7  -- I got lotza 12au7s. Thanks very much!!

[John]

I know this is an old thread, but resurrecting it. This is how I did the reverb *at this point*. Right now I've got my Webster open with alligator leads going everywhere. The 18K and 300K resistors are the readings taken off my decade boxes.


I think Ed said he's used the Bricks before and likes them. If he'd chime in and give me better ideas to implement, that would be great. In this particular circuit, it works great. Surprisingly, there's no heater hum present even with the CT lifted, perhaps the bridge for the DC supply acts as an artificial? I'm using the older Brick, not the newer smaller one.


I'm going to try a 12aU7 in place of the aX when I find one that's not dodgy since I've read that's what other ones use. But, I like the sound as is too.

[John]

Quick follow up. Took a Mullard au7 and popped in, and sounds fine too. Not sure I don't prefer the ax7 in there though. The more I play it, the more I like it, and this is in my cement walled and floored milk house with a truly crappy 12" speaker.


Next I want to play with the R values- the 56k cathode and 120k plate. Thinking of lowering both of them. I really like the reverb at the end of the preamp just before the power tube.


**updated** I did lower the values, made a tiny tiny bit of difference  in loudness -maybe a decibel, maybe not? - , none in tone (to me). When I removed the reverb circuit, the amp was noticeably louder, but also had more distortion and not in a good way, IMO. With the 'verb in the circuit, there's still plenty of volume but there is a sweeter, smoother "overdriven" tone, not so much the the fuzzy distortion.


In short, I like this a lot and will incorporate it into my next build or re-build.

[Leevi]

I decided to build the reverb I proposed earlier in this thread. The circuit can also be used as a tube preamp
even if the reverb is switched off. The only problem I noticed  is a hum with higher volume which is more wiring issue I think.


So, this is now proven and it works. Don't care of the layout, it's a prototype.


/Leevi