Reverb tank impedance

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codedog
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Reverb tank impedance

Post by codedog »

I'm looking at experimenting with reverb tank replacement and noticed there are some with a huge difference in impedance (10 vs 190 ohms), but for the most part the same specs except for decay length. In a solid state amp how crucial is it to match the impedance? What are the tolerances?

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Re: Reverb tank impedance

Post by bender »

It's pretty crucial in that it affects the frequency response. On the input of tank, that can mean crappy transfer to the springs. On the recovery stage, it can mean a thin/weak reverb return.

My extremely fuzzy understanding is that it's generally OK if the output impedance is less than the input impedance (in the case of a reverb tank, this means that the amplifier send is less than the tank input and the tank output is less than the amplifier recovery input). It's exactly the same for tube or solid-state.

Short version- easiest thing to do is simply get one that has the same input and output impedance as the original.

Another thing worth noting is that reverb tanks can vary wildly, even within exactly the same model number and brand. I have three recent Accutronics 4AB31B tanks and they all sound really different. One is really full with minimal drip, one is drippy and bright, and the other is drippy and smooth. Slightly different decay lengths too. So it might be worth getting one that's exactly the same as the current one, depending on what you're hoping to achieve.

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Re: Reverb tank impedance

Post by Single coil »

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Re: Reverb tank impedance

Post by Optical »

For solid state it doesnt make any difference to the driving circuit. It'll work fine, but the characteristics of the reverb tank will change how it sounds. If the tank load is high and the driver weak, then the reverb will simply sound weak but no harm will be done.

For a tube reverb driver it matters more as there is an impedance matching transformer that works much like a tube amp output transformer - it is more critical to have matched loads to efficient operation in the same way there are speaker impedance taps on a tube amp output transformer to match the speaker load. It'll 'work' but mismatched loads cause more stress on the tube which may shorten it's life.

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Re: Reverb tank impedance

Post by codedog »

Optical wrote:For solid state it doesnt make any difference to the driving circuit. It'll work fine, but the characteristics of the reverb tank will change how it sounds. If the tank load is high and the driver weak, then the reverb will simply sound weak but no harm will be done.
Phew! That's a good start :) When you say "... the tank load..." is that proportional to the impedance figure? Also, how can one determine the "strength" of the driver?

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Re: Reverb tank impedance

Post by Optical »

Yes impedance is the load
Strength of the driver depends on what devices are used. It doesnt matter though, if it's weak there's not much you can do about it except use a smaller/lighter load reverb tank. Just try them out and see

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Re: Reverb tank impedance

Post by codedog »

Optical wrote:Yes impedance is the load
Strength of the driver depends on what devices are used. It doesnt matter though, if it's weak there's not much you can do about it except use a smaller/lighter load reverb tank. Just try them out and see
Ok, let me get it the right way around. If I pick a tank and it sounds weak I should pick another one with lower input impedance figure?

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Re: Reverb tank impedance

Post by Optical »

Just pick one you like the sound of is the short answer. A lower impedance tank might be a step in that direction

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Re: Reverb tank impedance

Post by bender »

Optical wrote:For solid state it doesnt make any difference to the driving circuit. It'll work fine, but the characteristics of the reverb tank will change how it sounds. If the tank load is high and the driver weak, then the reverb will simply sound weak but no harm will be done.

For a tube reverb driver it matters more as there is an impedance matching transformer that works much like a tube amp output transformer - it is more critical to have matched loads to efficient operation in the same way there are speaker impedance taps on a tube amp output transformer to match the speaker load. It'll 'work' but mismatched loads cause more stress on the tube which may shorten it's life.
There are two parts to it though- the input impedance of the tank and the input impedance of the recovery circuit. They will both affect the tone of the reverb.

Reverb tanks aren't that readily available in NZ, so you might as well just try whatever you can get your hands on until you find one you like the sound of.

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Re: Reverb tank impedance

Post by Optical »

The input impedance of a recovery stage will be very very high regardless of whether it's a tube or solid state. That will not going to affect the frequency response no matter the tank the feeds it. I cant speak for any other additional filtering the circuit might contain however... Usually a reverb circuit will contain at least some form of high pass filtering.

I have a large pile of reverb tanks and wouldnt mid selling them in bulk!

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Re: Reverb tank impedance

Post by Kris »

you dont have a accutronics 4EB2C1B in there do you?

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