Dumble Reverb Pan/Tank Tests - 2AB2C1B, 9AB2C1B, 4AB3C1B, 9AB3C1B

[rccolgan]

I just finished going down the (not so deep) rabbit hole of different reverb tanks for our Dumble clones. Relatively inexpensive way of changing things up. I made a video comparing different tanks two of my amps. The carbon fiber tolex is a John Mayer Sig clone and the turquoise suede is a Dumble SSS #004 clone.

https://youtu.be/nVmGF9nBW9k

Hoping this is informative for tinkerers. Enjoy and let me know if there is any questions!

[10thTx]

Wow! I really appreciate the demo. What totally surprised me was that I much preferred the 2 spring reverb pan over the 3 spring both on the medium and long delay.

Would have not anticipated that at all. With respect, 10thtx

[rccolgan]

Very cool!! I like them all in different ways but that's not easy to switch in the middle of songs! Lol

[GPD]

Gave that a listen...something a lot of amp builders/tweakers ponder...

Having spent a large portion of time studying the various old original pans (Hammond, Gibbs, Accutronics and OC Electronics) as well as the modern Asian made versions Belton, MOD, etc., what I've found is that no two (even of the same brand, vintage and inductors (input/output impedances) perform similarly. We'll leave pot tolerances out of the equation for now.

Simply plugging in a different tank isn't exactly a scientifically viable test due to this reality and leaving the reverb settings untouched. You have to break out your scope and check the signal voltage getting blended with the dry signal. You can pick a level for the sake of a baseline and then you adjust the pot (or pots if you have this type of circuit) so you pick your benchmark and adjust the amp accordingly to whichever pan is installed. BTW, some pans will have such a low signal level that you run out of adjustment level in the pot(s) to get the blend correct. Similarly, some pots are so hot that they actually will cause oscillations in certain circuits.

Then you can try and hear the differences between two spring (actually 4 springs) or three spring (actually 9 springs) variations along with the medium and long decay versions.

I'm not sure why there is such inconsistency with the Reverb pans. It is a problem on old pans just like it is on new pans. It seems to me that winding the inductors consistently should be simple enough to do with machine winders which is what they use. The gauss levels of the magnets? Perhaps this is where the inconsistencies are? But permanent magnets have been around for a long time...so that seems to not make sense either.

Regardless, if you go through the effort of what I described above what you'll find what you like is different than what you though you liked before you studied the output of each pan and made adjustments to accommodate these big variations.

BTW, the last batch of MOD's I purchased were all over the board...not even remotely close to one another. One of them was actually DOA...though a new part. Given this reality I suspect this inconsistency has existed since the beginning of the Hammond spring reverb circuit way back when.

Best Regards,


GPD

[xtian]

what I've found is that no two (even of the same brand, vintage and inductors (input/output impedances) perform similarly.

Same experience here. Both in terms of length of decay and frequency content. Really wide variations between same spec/different brands.

[rccolgan]

Thanks, all, or the feedback and suggestions! I did realize a dip in reverb when going between the 2 (4) and 3 (9) reverbs. I know the impedance is different so yeah.. a more scientific and technical approach would be better.

Interesting about such a swing in reverb between brands as well as even within the same model! I like the MOD brand from the construction and seems closer to a 60's USA Accutronics. They also go the extra mile with the grommets on the sub chassis. Any brands I should try or stay away from?