Spring reverb

[martin manning]

warning: solid-state content

In another thread I mentioned that I was breadboarding the basic driver and recovery amps for a spring reverb rack unit from here: http://sound.whsites.net/articles/reverb, looking to drive a long delay 4AB3C1B spring tank, and experimenting with drive and dwell, and mixing of wet and dry.

That was done, and so I started looking around for preamp circuits and discovered a schematic known as the Tape Op Reverb (Tape Op, May-June 2017), and then a parts and pcb kit produced by the author of the article here: http://hamptone.com/sr1-build/ (the schematic is there, if you want to roll your own). The convenience of the kit was too good to pass up, so I ordered one and I t’s now working quite well using a breadboarded +/-18V regulated power supply, and a 150-ohm long delay tank (equivalent to the classic Fender type above except for the input impedance). There are still some things to explore, like the effect of the two-position input filter at higher volumes, and an optional tone shaping cap that, if useful, could be an array of caps on a rotary switch.

An interesting feature if this circuit is the high-power op amp directly driving the spring unit: the LM1875 is capable of 20W output from 25V rails. That, and the discussion on Rod Elliot’s site about the importance of driving the tank pretty hard, makes me wonder about the shortcomings of the typical paralleled 12AT7 driver, and the improvement from using 6K6 or 6V6 as in the 6G16 reverb unit. Anybody else chased spring reverb sound?

[xtian]

Improvements in spring reverb design are 40 years overdue! Do you have an estimate on how much current the circuit consumes at +/- 25v?

[martin manning]

I haven’t measured total current draw, but the data sheet says power amp idles at 70mA from +/-25V.

[Reeltarded]

We all like such different reverb sounds. I like it huge and long time and band passed really low and short. Radio Shack used to sell a 7 or 8 band graphic with rca connectors and a tail I used on lots of recording DRs and Twins. It had a massive filthy sounding boost and you could moderate the whole contraption at the knob.

I need a stereo spring reverb in my rack.

The Fender stand alone design uses a 6k6, does it not?

[martin manning]

Yes 6K6 in the original Fender unit and 6V6 in the reissue. The four knobs on this unit seem to allow a range of sounds and mix. The optional cap is a high pass for trimming the low end. There is a production stereo unit offered on the Hamptone site, but it’s pricey.

[tubeswell]

warning: solid-state content Anybody else chased spring reverb sound?

I’m always chasing that sound LoL

Surfy bear industries do a transistor powered stand alone reverb in a kit which is quite good. I think it borrows heavily from the white site, or something R.G. Posted once. I have another schematic on my desktop at home with a 60’s transistor driven spring reverb. Will post it when I get home

[strelok]

EL84 might also be a nice choice for driving a spring reverb. Would let you stick to a noval socket if space is an issue, and requires a bit less drive voltage than a 6V6. +/-18v into a 150R load is about 1 watt, assuming the output devices can swing rail to rail. I would think a paralleled 12at7 could manage that, but of course it all depends on the tank used and the turns ratio of the transformer. I think most Fenders ran about 400v on the plates of the reverb driver. Bigger certainly couldn't hurt though.

[tubeswell]

Here it is - Kay Model 710 (from the Jack Darr book)

Edit: silicooti datasheets added for the 2N408 and the 2N2613

[martin manning]

EL84 might also be a nice choice for driving a spring reverb. Would let you stick to a noval socket if space is an issue, and requires a bit less drive voltage than a 6V6. +/-18v into a 150R load is about 1 watt, assuming the output devices can swing rail to rail. I would think a paralleled 12at7 could manage that, but of course it all depends on the tank used and the turns ratio of the transformer. I think most Fenders ran about 400v on the plates of the reverb driver. Bigger certainly couldn't hurt though.

True enough. 12AT7 has 2.5W plate dissipation capability, and with a 300V swing into the usual 23k driver transformer, that would do it. I recall seeing at least one EL84 driven reverb.

[tubeswell]

Using a triode-pentode like a ECL86 is an option for one tube reverb. A ECL86 pentode is rated at 9W plate dissipation and drives a reverb xformer very nicely and an ECL86 triode is a 12AX7 equivalent so picks up the recovery well.

[martin manning]

That’s 6BM8 to us yanks. Looks like a very good option for one tube, using maybe a Champ or some other small SE OT. Fender Vibroking used 6BQ5 or 6V6 for a driver tube.

[norburybrook]

Martin,

I love spring reverb. I really want to build one of sluckly's revibes but the chassis is an issue for someone like me who doesn't have the facility to make his own.

I'm still itching to make one but unless I can get a chassis made I'm stuck.


anyone in the UK/EU able to make a one off chassis?



MC

[martin manning]

This is just about right: https://modulusamplification.com/Amp-Ch ... 30122.aspx

[didit]

Hello -

Did preliminary breadboard a few years ago from this cap coupled constant current design as starting point. Concluded an ECL86/6BM8 makes a better triode/pentode than NOS RF to push the tank.

--http://www.channelroadamps.com/articles/reverb_driver

Different from classic Leo 6G15 or Blackface. Bit more HiFi. Worth trying for the curious. When time allows, I do plan to build into revised ReViBe.

Best .. Ian

[rangdipkin]

For my money, the best reverb results I've ever had used the "classic" fender style parallel driver / single recovery but using a 12BH7 driver tube, a fully bypassed 4k7 cathode resistor and a hammond 1750Ax (7k5 primary) driving a full size short decay tank. It drove the absolute snot out of the tank!