Which impedance would be OK to use?

[cjacek]

Before I start, this is not about spring reverb tanks but rather a question, some help that I need choosing the correct impedance. I am currently trying to find a spring tank replacement for my reverb unit. I wish to experiment with different tanks (type 4 and 9). These usually come in various configurations and impedance numbers. The original tank had an input impedance of 190 and output impedance of 2575. I have attached a spec sheet from my reverb unit. It shows the Input impedance as being 25,000 and the output imp as 1000 or higher. I'm trying to figure out from the spec sheet if I can get away with using slightly different numbers for the input impedance of the replacement tank. For instance, if I understand impedance correct and based on the spec sheet, I should be fine using an input impedance of something much lower, even 10 ohm or even higher, like 600 ohm. The output impedance is no issue as most of the tanks that I'm looking for are close to the original, around 2500. Am I reading the attached specs sheet right? I'd really like to get your views on this. Thanks very much in advance.

 

[miroslav]

Mmmmmm......I think the impedances you are listing (25k and 1k) are for the whole unit.

You need to look at the code (EXAMPLE: 9EB2C1B) on the existing unit to find what I/O impedances it is using, and then check it against this:

Type 9 Options

Type 4 Options

AFA as deviating from the original Accutronics Type 9 impedances....don't go too crazy, as you may not get the right signal input/output level....but it's not going to hurt anything.
I wanted to change the level of signal on my Swart amp....wanted a unit that wasn't so "bold" with the reverb level even at its lower settings....so I used an old Carvin Accutronics long tank, and mounted it outside the cab in an isolated bag (worked out great, and I like it better than the stock reverb flavor).
I did a little basic math (can't for the life of me remember what it all was) and that told me which impedance numbers to shoot for.

Anyway...if you just want to try a Type 4 instead of the 9....I would stick with similar impedances. If you want to experiment with levels and whatnot....then you can go from there.
Bottom line.....you won't be able to tell just from the numbers how it's going to sound....so you just have to get a different tank and see.

 

[cjacek]

The system won't let me rep you again so thanks. I appreciate you taking the time. Yeah, I had hoped the spec sheet from the unit would give an indication of which tank impedance range I could work with. Is there really nothing from the spec sheet that would indicate what range of tank impedance numbers the unit can work with? How would a person know this? I'm just wondering why the manufacturer didn't provide this info in the specs. As I mentioned in my original post, based on the original tank code, it had an input impedance of 190 and output impedance of 2575.

I can definitely contact Accutronics, get them to build me a custom tank but they're not the same company, not made in the USA by the same people anymore and their quality is often questioned. That plus the fact that shipping from overseas is pretty costly. I've been looking at MOD tanks and sometimes I even come upon local old USA Accutronics ones but they're a bit off on impedance. The closest long decay MOD type 4 tank (impedance wise) is input 150 Ohms / output 2250 Ohms. The closest long decay MOD type 9 tank is Input Impedance 10 Ohms, Output Impedance 2575 Ohms. What do you think?

 

[rob aylestone]

You're going about it without any reference to what it will be driven by and returned to? The specs are to help the interfacing to other kit. Historically, these devices were remotely situated, so they'd have been driven by 600 line drivers. The output impedance is designed to allow most typical line level inputs to cope well, so the output impedance needs to be below the input impedance of your mixer returns, which it almost certainly is. Input wise, the usual high impedance mixer output may be a problem with the lower impedance of the reverb input, but if your mixer has balanced proper line drivers at a lower impedance all will be well.

What is your mixer spec, that's the decider for the matching? We don't know how close your old device matched. It obviously worked, but was it near the limit where loading the line alters the sound? In fact it maybe did, and you liked it as part of the sound, so small changes in spec may be critical. The class just puts you in the rough area.

 

[cjacek]

Thanks, I appreciate the reply but my concern isn't about the impedance matching / interfacing between this unit and other equipment but rather finding an appropriate spring tank for the unit itself. (I think that those are two different issues). I had initially thought that the specs indicate this but looks like it's just for the whole unit, only helpful for interfacing with a mixer or what have you..... Now, unless I completely misunderstood what you wrote?