2370 Spring Spring Crunchy Spring Spring

KOSMO MODULES
41

So, I finished my spring reverb today and plugged it into the tank from my old Doepfer A-199. I got a very similar sound (of course, no big surprise there) but I can already tell from my little 20 min jam session that having all the reverb parameters on voltage control is going to be a pretty sweet upgrade.

But it’s gotten me to thinking… I have two nice reverb modules and one nice tank. I should come up with something really crazy to plug into the other module.

My first thought was to solder two different cables together and plug the safety valve module, or possibly another guitar pedal like one of my boss hm-2s (I collect them) into the tank connectors. It might be interesting to have a drive/distortion effect with 2370s CV controls. Has anyone ever tried that before?

42

The amplification needs for a tank and a module or pedal are very different. Depending on what you’re looking for, of course, I don’t think you’ll find it this way.

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43

At this point, I think the only thing I’m looking for is something completely off the wall to plug into my extra module, since I already have “good” reverb covered.

44

Some testing trial observations on my shop bench with various Tanks:

First some useful Info on tanks.

Accutronics reverb tank numbering system

The type 4 is 17" long and uses 2 long springs, each of which consists of two springs joined in the middle. Thus, Accutronics considers this model a 4-spring unit. This type was the original style selected by Leo Fender.
The type 8 is 9" long and uses 3 springs. This type is most famous for its use by Marshall™ . The type 9 is 17" long and uses 3 long springs, each of which consists of two springs joined in the middle. Analogously, Accutronics considers this unit a 6-spring device.

All Accutronics part numbers consist of 7 characters as described below.

1st character: type 4, 8, or 9

2nd character: Input impedance @ 1kHz

Type A B C D E F
4 8 ohms 150 ohms 200 ohms 250 ohms 600 ohms 1475 ohms
8-9 10 ohms 190 ohms 240 ohms 310 ohms 800 ohms 1925 ohms

3rd character: Output impedance @ 1 kHz

Type A B C
4 500 ohms 2250 ohms 10000 ohms
8-9 600 ohms 2575 ohms 12000 ohms

Next: What I found through actual plug and play

High impedance input tanks require less signal amplitude to drive them. The feedback feature tends to be almost uncontrollable with these Type E or F input tanks.
RV-1 is the tuning attenuator that can be adjusted to fit the tank but I had to set this almost all the way to minimum with the High Impedance tanks

Low impedance Input tanks respond the best with the feedback loop

A or B input tanks (low inpedance) are my clear favorites as far as sound and control of the feedback are concerned.
I can get a very clean spacious reverb or something quite strange.

Output B Type works best with this Module
I used an A Type output but heard some distortion at even low levels

9AB3—, 4BB3— are good candidates - I had to adjust RV-1 for each

the 8EB3— and 8FB3— tanks I have were too wild… I even damaged U2-A, B using these tanks

2 spring tanks or 3 spring tanks are great with this module

8 Likes
45

Thanks for that informative post. I guess I won the spring tank lottery with my 9AB3 tank.

How do you adjust rv1? Is it just by ear? I have not touched it.

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Turning RV-1 Clockwise Decreases the effect of feedback (lowers the gain), counter-clockwise Increases it.
I set the feedback Pot at a position I would expect the Feedback to really kick in like at 1:30 o’clock (tone pot is interactive) and set RV-1 accordingly.

2 Likes
47

Thanks for that! I kind of had my doubts about the statement that the driver would work with “any tank”. I have a 4EB2C1B, so this one’s not for me. I’ll probably use the Music Thing circuit which is said to work with Type E.

I’m also curious about the fifth character in the code: Per Music Thing, “The fifth code (C) describes the connections, and is important. It must be C = Input Insulated / Output Grounded.” Is it important for this module as well?

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48

Probably bitten of more than I can chew with this one, I have no idea about matching tanks :wink:

Just bought something of e-bay with no real thought a “Belton S2AB2C1B” but I ca’t find any info on it.

1 Like
49

From Accutronics reverb tank numbering :

1st character: type 4, 8, or 9

2nd character: Input impedance @ 1kHz

Type A B C D E F
4 8 ohms 150 ohms 200 ohms 250 ohms 600 ohms 1475 ohms
8 and 9 10 ohms 190 ohms 240 ohms 310 ohms 800 ohms 1925 ohms

3rd character: Output impedance @ 1 kHz

Type A B C
4 500 ohms 2250 ohms 10000 ohms
8 and 9 600 ohms 2575 ohms 12000 ohms

4th character: Decay time
1 = short (1.2 to 2 sec)
2 = medium (1.75 to 3.0 sec)
3 = long (2.75 to 4 sec)

5th character: Connector arrangement
A = input grounded, output grounded
B = input grounded, output insulated
C = input insulated, output grounded
D = input insulated, output insulated

6th character: Locking device 1 = no lock

7th character: Mounting plane
A = horizontal,open side up
B = horizontal, open side down
C = vertical wall,long axis horizontal, connectors up
D = vertical wall, long axis horizontal, connectors down
E = vertical wall, long axis vertical, input up
F = vertical wall, long axis vertical, output up

Not sure what that “S2” instead of 4, 8, or 9 means but presumably it’s the size/number of springs, and then it’s a very low input impedance, medium output impedance, medium decay time, input insulated and output grounded, no lock, mounted horizontal open side down.

Are these things current or voltage driven? I’m guessing current, since the LMNC circuit uses an op amp mixed with a buffered version of itself via 10R resistors — so looks like it’s trying to pump lots of current into the tank. Conceivably a high impedance tank could benefit from larger resistors and maybe omitting that buffered copy, if anyone feels like doing some circuit hacking.

2 Likes
50

As far as I know the transducers on reverb tanks are current driven.

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51

The C grounding state on the tanks in this case are moot since on the module the ground is common. This is not necessarily the case with tube amps or guitar amps in general.
A lot of that has to do with EMI shielding from transformers and stuff inside the amp.
MOD Tanks have handy solder points in their tanks so you can easily set or break the ground on either jack - this came in handy when I needed a D type grounding for an amp

2 Likes
52

For my purposes I’m letting the LED’s light up just barely and hardly using the feedback (just a touch for that ‘Dwell’ you get from the classic Verbs) - I’m after a pretty pristine and deep reverb sound and actually achieving it well. I am using a 4BB type 2-spring tank

LEDs are a good indication of overdrive I have heard so far.

I can use the effect of more feedback at some point when I want to go there - my tank combo gives me plenty of WHOMP when I let it go nuclear

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53

I dont suppose anyone has a couple of those RCA plugs laying around that they can throw my way?

I’d rather not give bezos the cash

54

I have plenty, but the shipping may be more than buying the 50 pack.

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55

RCA plugs or the 90d sockets?

I have more than I need but again shipping outside the UK may be more than the value.

56

After switching my modular around in the new cases, I am noticing a lot of noise from my spring tank. At this point, I am not sure if it was there before, and I just didn’t notice it, or if something in my new setup is creating some new interference. Anyone have any suggestions on how to fix this? I have tried unplugging and re-plugging several things to see if I could find the culprit, but no luck yet. The only way to get the noise to go away is to unplug the send on the spring tank. I am tempted to grab a different tank to see if it changes.

Update: Pulled the tank out and tried moving it around and there was no change to the noise. It is the return, not the send that I need to unplug to remove the noise, so it must be coming from the tank itself. I tried grounding the tank, but that didn’t make any difference since it is already grounded at the return.

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Does your tank have an open side? If so, you may want to shield that side from electromagnetic interference by attaching it to a metal plate, preferably ferrous metal to block magnetic fields, but a copper plate (e.g. a blank PCB) or even some aluminum foil could be worth trying to block at least the electric fields.

The return input circuit has very high impedance at low frequencies, which could make it more sensitive to interference, you can try adding a 100k or 470k resistor across that input to see if that help without affecting the sound too much.

Reading the whole topic for context, I saw this:

That is probably due to the fact that the LEDs are backwards on the schematic:
image

They should point towards GND as they are driven from +12V:
image

3 Likes
58

How crunch is this spring reverb really?
Has someone put a scope on the send output to see how distorted it is?

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Shielding the open side didn’t do anything, though not a bad idea to add.

I also tried a fancy set of RCA cables, and that didn’t do anything.

Adding the resistor to the return did significantly reduce the noise without much of a noticeable difference to the sound. It is a crunchy spring, after all, so it would take a lot of distortion to make a difference.

1 Like
60

Upon further review, adding the resistor reduces the volume significantly. While it does reduce the noise, it also reduces the entire signal.