DIY Accutronics Spring Reverb Problem

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Matt C.
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DIY Accutronics Spring Reverb Problem

Post by Matt C. » Thu Feb 11, 2010 8:20 pm

So, as was being discussed in the "Let's Talk About Spring Reverb" thread, i ordered an Accutronics spring reverb tank (http://www.accutronicsreverb.com/Type9.htm) and tried hooking it up to my mixer as an effect insert, without any extra electronics in between (from channel1 effect send to input on the tank, from tank output to channel1 effects receive). turns out, it is way way too quiet. i thought this simple setup might be too good to be true, but other people seem to have success with it, so i'm a bit confused. i tried to get a model with the proper input and output impedances, but maybe i goofed up? i'm not sure what else could be the issue.

here are the relevant specs:
mixer output impedance: 100 ohms (nominal load 10k ohms)
reverb tank input impedance: 10k ohms

reverb tank output impedance: 2575 ohms
mixer input impedance: 220k ohms

is this a case of impedance mismatching, or am i missing something? i figured getting a reverb tank with a lower input impedance (like 240 ohms) might run the risk of damaging the mixer (the manual specifies a minimum load impedance of 2k ohms). but maybe that sort of guitar amp logic doesn't transfer over to the world of mixers?

any clues as to what i'm doing wrong would be great. thanks.

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Post by The Scum » Thu Feb 11, 2010 10:50 pm

Springs lose some signal level...so you need to be prepared to drive it harder, and follow it with some gain.

Does your mixer have aux FX sends? If so, use one to send to the reverb. Then return the reverb output to a channel, and use the preamp on the channel to boost it back up. You can vary the reverb tone by driving it harder, and also alter it further with the EQ and FX send on the return channel.

Matt C.
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Post by Matt C. » Fri Feb 12, 2010 10:41 am

i just tried the aux out then back into a spare channel. i got it to be a little bit louder this way (with every possible knob turned to 10), but it's still almost inaudible compared to regular music playback. not really usable as an effect.

i guess i'll have to keep testing out other setups (maybe running the aux out signal through a spare outboard preamp turned way up, then into the spring, then back into a spare channel?) i should have known this wouldn't work!

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Post by jv » Fri Feb 12, 2010 11:06 am

Are you sure about the input impedance of the reverb tank? According to that page, the input impedance ranges from 10 ohms to 1925 ohms, depending on which version you have. Maybe yours is actually the 10 ohm version (rather than 10k)? You probably need to drive it with something stronger, like maybe a headphone amp.

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Post by Matt C. » Fri Feb 12, 2010 12:17 pm

i'm pretty sure about the 10k input impedance. i don't know why it's not listed on their site, but i asked before i bought it and they said the models with second digit "G" are 10k ohm input.

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Post by The Scum » Fri Feb 12, 2010 1:29 pm

It could just be that it needs more gain than you've given it.

I've got a Zerotronics reverb that uses Accutronics type 9's, and it takes 50 to 60 dB of makeup gain to be useful in a mix.

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Post by rty5150 » Sat Feb 13, 2010 9:51 am

yeah, i crank my output going to the reverb from my converter and still have to drive it with a preamp to get the level back in at a good level. so ultra hot levels are a must when doing this.


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Post by The Scum » Sat Feb 13, 2010 4:38 pm

If you really looking for DIY stuff, check out the schematics that Accutronics make available, too. Their current-source driver sounds pretty good to my ears.

Matt C.
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Post by Matt C. » Sat Feb 13, 2010 10:34 pm

those schematics look helpful. might be a relatively simple way to dip my toes into the world of electronics building?

i experimented more with the reverb tank today, and finally got it to be loud enough, but it involved sending the mixer aux out through channel one of my RNP, into the reverb tank, then the signal came out of the tank, back through channel 2 of the RNP, and into a channel on the mixer. with a lot of gain added at all stages. not really as simple and practical as i was hoping it would be.

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Post by sean k » Sun Feb 21, 2010 12:58 pm

I've been working on my own tube reverb lately and while doing so I opened up the tank and played it with my fingertips....way loud!!!

So the problem is always one of getting enough drive... and most of that want's to be current.

We look at cathode, emitter and source followers as somewhat useless but they are actually current amplifiers and they are useful in this situation.

A j201, mpf102, 2N5457 or just about any avarage low voltage fet set up as a source follower should give you what you need. Chucking more and more voltage at it won't work as well as you think.

10k outs then a 100k resistor on the input with a 100nano to the gate, drain to 9V, or 12 or 15, doesn't really matter, then a 2.2k -10k resistor to ground on the source and a 10uf cap to the reverb tank. That'll take your adequate line level output voltage and amp up the current with enough juice to properly energise the coil. Start at 10k and work down till it does it without saturating the coil. Not the most elegant solution but it'll get you soldering and on the way to doing fer yerself...
Hello, my names Sean and I'm addicted to being curious!

Matt C.
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Post by Matt C. » Sun Feb 21, 2010 4:02 pm

sean k wrote:10k outs then a 100k resistor on the input with a 100nano to the gate, drain to 9V, or 12 or 15, doesn't really matter, then a 2.2k -10k resistor to ground on the source and a 10uf cap to the reverb tank. That'll take your adequate line level output voltage and amp up the current with enough juice to properly energise the coil. Start at 10k and work down till it does it without saturating the coil. Not the most elegant solution but it'll get you soldering and on the way to doing fer yerself...
more like, once i figure our how to decode this advice you just gave me, then i will be on the way to doing it for myself.

thanks for the info. i think this will become my first real electronics project, but i have a lot to learn before i start.

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Post by airloom » Mon Feb 22, 2010 3:47 am

YO PLAYA
Call me during the day on monday.
I'll be at the studio all day.
We can "look at it."
I love you.

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