Moog Music Forum

Hi everyone,

can anybody provide the specs of an original 905 reverb spring, meaning:

- input impedance?
- output impedance?
- input insulation?
- output insulation?
- delay time?

Thanks a lot

Back when Moog started making these, there weren't a lot of choices for springs. I'm assuming that the springs available back then were all about the same as the units being used in most guitar amps.

The typical Fender amp springs back then were usually an 8 ohm input impedance, and a 2.5k ohm output impedance. The output jack was grounded to the chassis, and the input jack was usually isolated from chassis ground, If I'm remembering correctly. Not sure about the delay time.
A transistor driver stage may be more comfortable with a higher input impedance, say around 1.5k or so, but I'm not sure if these types of differences were available back in the mid 60's.

I bought a small MOD three spring setup to try with mine with a somewhat longer decay, and I recently found a small 2 spring pan when cleaning out the garage last weekend that I'll try as well. It might be nice to have a way to switch between them (or maybe even use them in parallel) if they sound different enough!

An interesting article..
https://www.amplifiedparts.com/tech_cor ... d_compared



I had sort of been ignoring how much the spring reverb added to some of Keith Emerson's modular patches, especially live. I'm looking forward to getting that happening (along with a myriad of other possible projects, of course).

synthguy wrote:Back when Moog started making these, there weren't a lot of choices for springs. I'm assuming that the springs available back then were all about the same as the units being used in most guitar amps.

The typical Fender amp springs back then were usually an 8 ohm input impedance, and a 2.5k ohm output impedance. The output jack was grounded to the chassis, and the input jack was usually isolated from chassis ground, If I'm remembering correctly. Not sure about the delay time.
A transistor driver stage may be more comfortable with a higher input impedance, say around 1.5k or so, but I'm not sure if these types of differences were available back in the mid 60's.

I bought a small MOD three spring setup to try with mine with a somewhat longer decay, and I recently found a small 2 spring pan when cleaning out the garage last weekend that I'll try as well. It might be nice to have a way to switch between them (or maybe even use them in parallel) if they sound different enough!

An interesting article..
https://www.amplifiedparts.com/tech_cor ... d_compared



I had sort of been ignoring how much the spring reverb added to some of Keith Emerson's modular patches, especially live. I'm looking forward to getting that happening (along with a myriad of other possible projects, of course).

Ah, this might help starting own experiments, thank you

The smaller than production tank in mine reads 3ohm input and 900ohm output.

Both 'screen' terminals (ground & -6v on mine) are fully isolated.

Would be interesting to know it the production ones are the same...?

Cheers,
Tom

analogmonster wrote:Hi everyone,

can anybody provide the specs of an original 905 reverb spring, meaning:

- input impedance?
- output impedance?
- input insulation?
- output insulation?
- delay time?

Thanks a lot

Yes, when I did my clone you need a:
8 ohm in
2250 ohm out
Grounded input
Insulated output (very important)

An example spec:

1AB2B1B or 8AB2B1B

David