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Hoffman Amps Forum image Author Topic: Reverb tank.impedance question  (Read 3394 times)

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Offline Colas LeGrippa

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Reverb tank.impedance question
« on: February 29, 2020, 11:39:27 pm »
I need a reverb tank for a.new build I m working on. The reverb will be external, driven by one of the OPT tap and amplified by a second amp.
There are a couple of different reverb tank input impedance out there,
from 8 to 1,200 ohm. Does the input impedance have to correspond to the input signal source
If so, I 'd have to get an 8 ohm. Would a 600 ohm do the job as well ?
Thanks
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Offline sluckey

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Re: Reverb tank.impedance question
« Reply #1 on: March 01, 2020, 01:05:01 am »

A schematic, layout, and hi-rez pics are very useful for troubleshooting your amp. Don't wait to be asked. JUST DO IT!

Offline glass54

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Re: Reverb tank.impedance question
« Reply #2 on: March 01, 2020, 01:19:07 am »
Hi Colas,
I am attaching a document that may be of interest to you (and others) regarding Reverb tank parameters.
As a matter of interest the Hoffman AB763 project specifies a Rev Transformer p/n 022921 which is a 22k:8R transformer and a 4AB3C1B tank 8R in/2250R out.
You can check the rest from the attached doc.
Kind regards
Mirek
"To measure is to know"

Offline pdf64

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Re: Reverb tank.impedance question
« Reply #3 on: March 01, 2020, 04:27:01 am »
Reverb tank drive coils are an inductive load, to get an even excitation level over the frequency range, need either current drive or, if voltage drive, increasing voltage with frequency.
See https://www.amplifiedparts.com/tech-articles/spring-reverb-tanks-explained-and-compared
If fed from a regular speaker output, from an 8 ohm input tank, a >40 dropper resistor should achieve that.
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Offline Colas LeGrippa

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Re: Reverb tank.impedance question
« Reply #4 on: March 01, 2020, 07:58:51 pm »
Thnx buddies
Don't miss the Woodstock experience : ''FORTY YEARS AFTER'' at Club Soda,  in Montreal, august the 17th and 18th and october the 27th. Fifteen musicians onstage.  AWESOME !
P.S.: call me Alvin.

Offline PRR

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Re: Reverb tank.impedance question
« Reply #5 on: March 01, 2020, 08:21:46 pm »
You want to be in the ballpark.

4 or 10 Ohms are all about the same.

600 Ohms is a different park, 2k yet another.

Offline Colas LeGrippa

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Re: Reverb tank.impedance question
« Reply #6 on: March 02, 2020, 10:39:23 am »
Thank you Seņor PRR, and what do you think about feeding it through a line out or a dropping resistor (8 ohm tap from OPT ) What value should have this resistor if connected to a 50W amplifier ? In other words what max ac voltage can the input transducer can handle ?


Colas
Don't miss the Woodstock experience : ''FORTY YEARS AFTER'' at Club Soda,  in Montreal, august the 17th and 18th and october the 27th. Fifteen musicians onstage.  AWESOME !
P.S.: call me Alvin.

Offline sluckey

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Re: Reverb tank.impedance question
« Reply #7 on: March 02, 2020, 11:52:20 am »
Take a look...

     https://el34world.com/charts/Schematics/files/Ampeg/Ampeg_echotwin.gif

EDIT... I should mention that this is a 4F type tank, ie, input impedance is 1475Ω. It is still driven from the main 8Ω speaker.
« Last Edit: March 02, 2020, 12:36:50 pm by sluckey »
A schematic, layout, and hi-rez pics are very useful for troubleshooting your amp. Don't wait to be asked. JUST DO IT!

Offline shooter

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Re: Reverb tank.impedance question
« Reply #8 on: March 02, 2020, 12:21:39 pm »
 :laugh:
you shoulda linked him to the original schematic  :icon_biggrin:
Went Class C for efficiency

 


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