6740 Hot Springs Reverb

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6740 Hot Springs Reverb

Post by PAiA-Scott »

Brian Hensley wrote:
> Hello from Nashville,
> I have been interested in your kit for some time but find no references to any "Build Reports" or sound samples or Wav files that may demonstrate some of the differences in the unit as opposed to normal reverb.
> Could you direct me to a web site or provide some information about the kit that will help me with my purchase decision?
> Thanks for all the great material and writing through the years.
> Best regards,
> Brian Hensley

Hello Brian.

Thanks for writing with your questions about the Hot Springs Reverb project kit. It originally appeared in a 1980 Modern Recording magazine article by Craig Anderton and we've offered a kit for it since then. That's a great idea, bringing the scoop for this project into the current format. I'll try to get something together. A build with photos would certainly enhance the assembly pages which are just copies of the article to include our parts list and schematic--not the usual step-by-step, PAiA assembly manual. It is a simple printed-circuit with just a single quad op-amp IC (4136), etc. But building is a matter of referencing the parts list and schematic, followed by modification of the spring tank wiring, and completed with wiring of the printed circuit board to the tanks, connectors, and an external, user supplied dual-dc +and- 9-15v regulated dc power source. There is not a case or cabinet provided, but the image on the front of the assembly pages show Craig's two-channel prototype with the tanks mounted on top of an LMB chassis and the 1/4" input and output connectors mounted on the front.
So, when you order item 6740K you get the assembly pages, a pcb, a handful of parts and wire, and two reverb tanks. The 'heart' of a single channel reverb project for connection with a mixing board. Note too, when ordering from the PAiA site, a 9770R-12 is suggested as the power source. This is fine, but the manual suggests a 15v type. We hadn't considered this when we made the site association, but there is negligible difference between the operation on a 12 vs 15 v supply, and, the 12v supply we offer has more current available than the 15v type. If only being used for the 6740K, the 9770R-15 would be the best choice.

Many wonder about using the 6740K for a guitar set-up. The simplest way to do this is to input the guitar to the mixer with the reverb attached to provided the Wet and Dry mix. The 6740K output signal is 100% reverb, no original signal is in the output for the comparison which is usually mostly Dry with a bit of Wet. The guitar signal can be split two ways and run through one amp/speaker dry and through another amp/speaker after passing through the 6740K. The amp/speaker volumes set the mix. It is best if the guitar is boosted or pre-amped before this split. An effects loop on an amp may boost or buffer the signal to an externally connected device, but if there isn't a control to mix the return signal with the original, then a 6740K patched on this loop will not have original, dry, signal. A simple, but effective guitar-set-up would be to run the guitar to a preamp or boost device and split or Y-cord connect the output from this to the usual guitar amp/speaker and run the other, 6740K signal to a small portable/practice/satellite amp/speaker for the reverb mix.

Hot Springs is different from other reverbs that just run the signal through a single tank. It runs the signal through two tanks connected in-series and out-of-phase in the negative feedback loop of the driving amp for flatter response and a 'balanced' transmission through the springs. The output of the tanks is recovered from the two outputs wired in-series and in-phase for a stronger signal with less spring signal that isn't from the input signal. The reverb effect has been favorably compared to that available from expensive and large plate-type systems.

I am not aware of any places on the internet where you could get the information you're after, but there are a lot of studio owners and musicians that have this kit and many report they are pleased with it. There is likely someone that has posted about it. I'll save this message as a reminder to contact you if I see anything or get anything on our site.

Thank you.

Sincerely, Scott Lee
6740 Hot Springs Reverb.pdf
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Scott Lee