FISHER TUBE SPRING REVERB MODS

Just got a Fisher K10 Space expaner reverb. made famous by various reggae legends. Sounds amazing but there are a few issues when using as an effect with a line level mixer.
The unit is completely unbalanced.
The output seems to be quite low going into my mixer - I have to crank the line input.
Doing this brings up a very audible hum and hiss from the output.
Is there any mods that anyone recommends to improve these aspects.
Possibly an output transformer? figure alot of my problems are to do with impedance issues. How can I get more juice on the outputs while keeping the noise levels low

schematic is on http://www.triodeel.com/k10.gif

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Even assuming that your Fisher is in good working order, you definitely have an "impedance issue" with going into the 10K-20K line input of a typical mixer. Such a load impedance is too low for the Fisher. A stepdown transformer isn't really a good solution because you'll never find one with high enough primary impedance without sacrificing bandwidth. An active buffer (say, a simple unity-gain JFET-input opamp setup) would be the way to go.

what primary and secondary impedances would I need for a step down transformer?

Try a high-quality 1:10 mike transformer, backwards, into a mike input.

Or get a vacuum tube Fisher or Scott power amp, feed its inputs, load the speaker screws with 10 ohms 10 watts, and take that into your studio line input.

Adapting the super-cheap short-cable Fisher interface to any kind of studio interface isn't a mod, it is a major redesign. Dave and I have been down similar roads before: this is not easy to do well.

will a Neve 31267 do for a transformer?

How about use the PSU of the Fisher and add another valve stage to drive a mixer input at the right impedance.

Its a super cheap effect but its so good. I have a plate aswell but I love the Fisher.

to reduce hum you can first use good cables between the spring tank and the unit.(if you have originals fisher rca cables note they are unshielded).
then there is a small hole on the unit to adjust hum with a screw driver
but take care ! power supply is very crude! i suggest you open the unit to do it. then you can recap it too.. or disassemble the unit and use the parts to re build it in a bigger rack so you can change the psu.
audioforge

I have an Orban 111b spring reverb, and the manual suggests loading the outputs with 600ohm resistors if it is being connected to modern "high impeadence" inputs.
....oh,....and it's hissssy too........the specs admit it...around -65db s/n .

=FB=

has anyone got a spec sheet for a Fisher reverb?
any valve amp designer feel like sharing an output stage for the reverb?

here s the specif. from owner manual
minimum input voltage required:0.2v
maximum input voltage:5v
input impedence:250k ohms
output voltage 0.2v to 5v
output impedence : 2k ohms
gain:unity. hum level :80db below 2.5v
power consumption:16W
do you need somethings else?
audioforge

i have several spring reverbs. the quietest ones have pultec mb1 style pick up amps with 2.5k - 68k input tranformers. these match with the reverb pickups real nice. i use single ended el84 spkr driver stages set for low gain low distortion with a simple tone control . i usually use a surgical eq (orban 4 band parametric) on the output to pull the beauty out. gets a tremendous bottom end and sparkling top.

My new project is a stereo one using twin accutronic units. will post photo when possible.

I saw a fisher reverb on Ebay that had been heavily modified
it had an additional gain stage and balanced outputs.
any suggestions for where to find an output stage that would suffice
thanks for any help

For anyone interested thanks to Ekadek's help I have completed a successful mod on my Fisher reverb to make it compatible with line level mixer etc. I dispensed with the Fisher output stage and swapped it for a Pultec MB1 as the output stage of the spring reverb. It is balanced, has loads of gain and is hum and hiss free. Nice fat sound. It is a great improvement and is well worth doing. I only tapped power from the fisher unit - everything else is intact so the Fisher does not lose its resale value.

Alot of people hate spring reverb! I think they are amazing.

A friend of mine gave me a Sansui consumer spring reverb (Sansui RA-500) a few weeks ago. RCA in and out... It does have some fun retro lights tho.

http://www.classicaudio.com/value/san/RA500.html

Any hope for this unit or is it just junk (or a free enclosure)?

jt

thanx for the feedback mr tardishead. twas a might touch and go there for a while. ive never 'fixed' something over the interweb before and i was genuinely concerned for your sanity. all in all a fine satisfy ing experience.

man thats the coolest funky light show I have ever seen on a piece of gear. If you dont use it do you fancy selling it? Those lights will dazzle my punters in my studio. and me.

cant have enough flashing lights.

I presume this reverb is meant to go with a HIFI preamp kind of setup?
The output will probably not drive 600r line level very well. but I could be wrong

The lights are fun indeed, although the picture makes it seem a bit cooler than real life - its a fixed light going through a colored film, and then it has a diffusion grating over the light. When you adjust the reverb amount it alters the grating to 'diffuse' the lights more or less...

Its a back burner project but I'm going to open it up sometime and see what I can do...

jt

I love anything with a spring in it. I want to make a spring reverb using garage door springs.

[quote author="Butterylicious"]I love anything with a spring in it. I want to make a spring reverb using garage door springs.[/quote]

I would LOVE to see that :shock:

The more I think about it... your nuts.:green:

I also like spring reverbs & have a Master Room XL-210, 2 ch, w/ hi-mid-low EQ, input & Blend control... very cool. Anyone heard of it?

Kevin

Completely nuts, with only a pair of bolts and not a 1 lock washer. Maybe this
would work as a reverb. It's already got a piezo pickup on it in, now how to get signal onto the chasis.

I can't believe it :shock:

I want some of that shit your smoking :green:

Kevin