[HAM] hello from Hamtech Cliff in NYC

[CSRote]

Hi folks,

I am reviving an abused 1975 A105 with bad-sounding Percussion. 

 

Can anyone draw a schematic of late model 3-series Percussion tone shaping
circuits?  

Matti Adolfsen addressed this on Hamtech in 1997, but I cannot make enough
sense of the written description below.

The most recent schematic I have found is from the A100 service manual.  

It has some additional components: R63A (820 K) and C35A (0.00015 uF = 150
pF?).

 

I have put this schemo on a web page where you can also download it:
http://hammondorgans.homestead.com/PercussionAmp.html

 

Thank you for any help you can provide.

 

Best,

//Cliff, on digest

 

Date: Sun, 5 Oct 1997 From: Matti Adolfsen
<http://mail.hamtech.org/cgi-bin/wa.exe?A2=ind9710&L=HAMTECH&D=0&I=-3&X=71CE
F566F1524477C4&Y=clifford.rote%40verizon.net&P=51441>
<matti.adolfsen at AOL.LLAKY.FI> Subject: Percussion Differences in AO-28 

Scott Hawthorn wrote: On Fri, 3 Oct 1997, An AO-28-1 has a slightly
different percussion filtering than the AO-28 which amounted to a few R/C
components. One person on this list modified his preamp to an AO-28-1 and
claimed that the percussion sounded more "marimba" like. You can view the
difference in the circuitry at the Hammopnd FAQ website under the schematic
section. I would be *very* interested if someone could write about these
specific differences. If I am the only one here who cannot view graphics
files, then of course this would be a waste of bandwidth. I can think of a
couple of performances by McDuff with percussion only that have a
"marimba-like" quality that I can't get, but always assumed that it was a
technique issue. Technical writers come forth! Scott.

Thanks, Scott, a good question! The general service manual is once again a
good source of information. On page 3-50 there is a schematic of the AO-28
preamp, and this shows the differences between the original and the -1
version.