Hammond T-522 Mods-modman's Sonic Electronic Adventures

24/01/11 10:59 AMHammond T-522 mods -- part I « :-: modman's sonic electronic adventures :-:

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Saturday, July 22, 2006

Hammond T-522 mods -- part I

After some tinkering with guitar wiring and stompboxes, I stumbled upon a webpage that revived my longlived

interest in Hammond organs:

http://www.keyboardpartner.de/hammond/t-modifications.htm

It's the homepage of a German Hammond tech who really understand the internet and has hence attracted

international attention. He seems to be giving this information in order to boost his ebay store and that is rightly so.

But first a word about Hammond organs.

The novelty of the Hammond organ at the time of its conception in 1935, was it tone generator system. Instead of a

wind-based tone system, like in church organs, tone are created by wheels spinning in an electrical field. Invention of

the electrical guitar is not far off here. This church background is something to keep in the back of our heads all the

time, because no matter how many jazz cats, rockers, funk and soul playas or country slickers immortalized this organ

with a lot of great music, the fact that Hammond Company lived so long became so great is because they sold

hunderd thousands of organs to people playing religious music all over the world. Thank you lord, for having thy Hand

in the Hammond...

By the time the Hammond was picked up by the jazz in the early fifties it had already achieved its definite

configuration with reverb and tube amp built in, with external leslie. It grawled, honked, hit and screamed. That's

good, btw. If you don't understand how a Hammond organ should sound, dig this. I know you will.

That honky sound and hard percussive sounds are of course absent in organ with pipes, so Hammond tried hard to

elimenate all that honky fatness from their organs. Up until 1975 however, they kept on producing tonewheel organs.

The very last models are very interesting from a modders point of view, as they have (almost) every component to

make it into something interesting:

-built-in leslie speaker

-tonewheels

-reverb

-percussion

-chorus and vibrato

but: transistor-based amp. This is probably the reason why they sell cheap, that is sometimes... I paid my T-522

124.4 EUR, but I see them advertised for anything from 450 EUR to 1300 EUR (even 1700 EUR one time...

outrageous!).

Well, out with that T-beast, then:



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The guy I bought I from had acquired it from a lady who had died. He had had it serviced for the last time 4 years

ago. It has a noticeable heavy hum and the previous owner told me that it was solved when it was serviced but came

back. The only thing that didn't work was the cassette tape recorder, the least of my worries. The previous owners

had been so careful and even kept the original serial tag:



register

Finally assembled november 1974, every piece of this organ must be about my age. It was meant to be mine. The T-

5xx has a rhythm unit mounted under the cover, so if you removed the top, you also have to remove the unit. This is

a drag because you have to unplug it and with the RU unplugged, lower manual and pedals don't work.

1. BACK TAKEN OFF

2. RHYTHM UNIT UNPLUGGED



3. GROUND CONNECTION CASE REMOVED



4. PCB SHIELD

Can be removed by loosening the 5 screws on top

Now the different pcbs are revealed and ready to be worked on:



5. RESTORING KEY CLICK

In order to make the tones more flute-like the eletrical attack click was considered a fault in later years. This click

was filtered out by putting capacitors on the drawbars. A first step is removing just some of them from the upper

manual bus amplifier board. We will remove all of them later, but this is a fast way to put your toe in the water.

Removing all of these caps will required other mods elsewhere, but we'll get there.

5.1. On Lower Manual Bus Amp

Second row of caps from the top; one mylar and 3

Removed:

5.2. On Upper Manual Bus Amp



After these mods, that phat attack organ sound start to give way, but it tastes like more. Lets remove all the click

filter caps and proceed with the

6. REMOVING BASS ROLL OFF

Another dreadful 'improvement' was the use of capacitors to roll off bass gradually with every tonebars. Console

organs like B3s, C2s and A100 don't have this filtering and allow for bass cross talk even on the higher drawbars. We

are not going to remove the lower row of mylar caps, but replace them with very high value polarized 10uF (yellow in

picture) instead of the original <1uF mylars. The adjacent original electrolytes will be replaced by 47uF (black,

standing up)

These values are used for both lower and upper manual bus amps:

6.1. On Lower Manual Bus Amp



6.2. On Upper Manual Bus Amp



7. RECOVERY/INTERMEDIATE PREAMP BOARD CHANGES

Removing filtering and opening up the bass response. I also replaced all electrolytes as they are bound to dry out

after some years.

Original board:



Components to be modded removed:

Board finished and back in place:



You can see the new mylars with resistors in series.

8. PERCUSSION AND DRAWBAR REGISTRATION PRESETS

This mod introduced a B3-like percussion preset and changes the preset registration to some less cerebral settings:

Jimmy 'Groove Holmes' Smith and Errol Garner

Drawbar are just variable resistors the more you pull m out, the less resistance, the more volume. So presets can be

created by a string of resistors to ground:



9. TOUCH SENSITIVE PERCUSSION and NO MORE MULTI-TRIGGERING

This is the truly ingenious part of the mod, swapping out an NPN transistor for a PNP in order to achieve that the

percussion only triggers on the first note like in consoles. Furthermore you can set the percussion level with the

trimpot.



and a small cap 1.8nF for treble bleed when vibrato is on, so we don't lose those precious highs.

10. CHORUS DEPTH

Just decrease the 12k on the Chorus tab to 6.8k. This really is a quick fix, and you could even decrease the value

further, I eventually settled on 4.2k. Adds a nice soft touch, but off course its not like your averages Boss pedal. Still,

Kon Sizzis in his build report, suggests using a inductor coil of 78 Ohm DC resistance and 278 uH. Something to try if



I find one.

WHAT'S NEXT THEN?

I'm glad I spend the hot July nights modding this baby, it almost got compulsive. Couldn't stop and feel helpless now

most is done. The sound quality has improved considerably and it's a joy to play, lots of honk and heaps more click. It

was difficult at time because the off board connections, normally just slid over the pins, were sealed with solder. I took

some time unsoldering with one hand, pulling with pliers in the other hand at the pins. In order to put them back (ie

flow solder with iron one hand) was easier by hand, so you can feel the direction of the pin. If and as long as your

finger can stand the heat, that is.

One thing is; the bass keys, after playing it some time, go realize that bass keys really do make it fat and there just

not there on the T-series.

Some questions remain, though...

Humming amplifier. This is easily remedied had it not been such a pain to recove the power amp board.

Replacing the polarized caps will help for sure, but since I replaced the electrolytes I encountered, the hum has

decreased considerably and is almost gone with 'Soft' on. So will leave that for now.

Rhythm Unit. Really feel like kicking it out, getting an metal plate and fill it up with custom knbs for changing

parameters, would make organ also less tall.

Will a grounded power plug help the hum that's still there?

FUTURE PLANS FOR IMPROVEMENT

Carsten used to sell minitube-based preamp boards for these T-series organs, but is sold out, so his site says. Did



email him today for leftovers, as I already found the tubes I need on ebay. Let's hope...

But maybe maybe we don't really need the tubes for tube sound as it's just about overdriving the signal and putting

that in the leslie. I found a very interesting zener diode-based distortion circuit cooked up by Kon Sizzis

It really is not over yet, but it is for today, I'm busted.

MM

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Bruno December 31, 2010 07:35 PM PST

Hey Modman,I have a T412 w/no service manual and most infoabout this type of modification refers to the T512 orT200. Since I am not a certified tech and attempt tomake some changes to my T412, can I rely on theT512 schematics without running into problems?Thanks...

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Jorn June 28, 2008 12:01 AM PDT

Fantastic page.I am strugling with a buz sound at high volumes. Itcomes from the rythm unitand both keyboards, so i guess it's the power amp.Can hear it in both speakers and the leslie. Any ideas ?

Terence September 6, 2006 10:08 PM PDT

Hi thereGlad to see someone else tackling these beasts. I havea T200 and still am battling with the hum. Idisconnected every input to the main amp and still ithums. All the Caos have been replaced and the onlything still to be done is to change the Zener diode onthe 15volt supply. That will happen tomorrow.Regards and keep me posted on your progress

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