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[Big Chris]

Has anyone mucked around with a Hammond Auto Vari 64?

I'm in the midst of MIDI'fying a Roland TR-77 by following details of a similar mod to a Bentley Rhythm Ace on the Circuitbenders site, but I've just picked an Auto Vari this weekend. I'm getting addicted to the sound of these old drum boxes! The little information I can glean on the web suggests the Auto Vari is a product of the Hammond manufacturing division that was setup in Japan in association with Roland. It's rumoured to have internals similar to the TR-77, but I'd dispute that since the internals look radically different (I can post pictures later if anyone's interested).

There appears to be a service manual, but I can't find scans online and it seems to only be available from a couple of place in the US who provide a Xeroxed copy in return for $20 or thereabouts. Unless anyone here has a copy they can scan I'll order a copy and see if I can work out how to trigger the voices on the thing. Unless anyone's already had a go and can offer advice :-)

By the way, the Roland TR-77 seems to have gone through a few revisions during its production life. I have two of them, and they sound very different from each other. The first was manufactured in September 1972 according to the serial number, and the second is from January 1976 (http://www.chriswareham.demon.co.uk/studio/roland_serial_numbers.html).

Chris

[Big Chris]

As promised, here's some pictures of the inside of my Auto Vari. First is a shot of the machine with the bottom panel off:



The pattern matrix and selector boards are the green ones on the left, and the voice board is the brown one on the right. Below is a close up of the voice board - unlike the Roland TR-77 and Bentley Rhythm Ace there's no tuned LC circuits.to be seen:



There are a number of trim pots, most notably one for adjusting the amount of white noise in the sounds that use it, and a pair of pots for high and low frequency adjustment. There are also pots for adjusting the level of the hi-hat, cymbal, sandblock and brush - although the last doesn't seem to have any discernible effect! On the left of the board is a handily labelled connector:



Poking a multimeter between the various instrument connectors and ground while the machine is playing suggests the thing uses ordinary 5v triggers. I'll hopefully confirm that when a copy of the service manual arrives in the post from the US.

[Circuitbenders]

I've got one of these. That list of sounds on the edge of the voice board are the trigger inputs, but if i recall correctly it needs something like +14v triggers. I could have remembered that wrong though. I think the sync pulseson the control board might be +5v but you really need to get a scope on it.

I had it in pieces a while back but found that like with other machines of this era you have to have the thing playing but with no patterns enabled in order to open the VCA that silences the output when nothings playing. Otherwise you can't hear the sounds when you trigger them. Unfortunately on mine this meant that a unusable amount of clicking and popping was then apparent. This seemed to be coming from the clock signal. I ironed out a lot of it by sticking a cap across the power rails of that big chip on the control board, but its still annoyingly loud.
This might have something to do with the fact that mine doesn't have a power supply board. Its just a load of caps etc wired together with point to point wiring. Can you post a decent photo of the power supply board? Preferably both sides if possible.

If i can't iron out the clicking i was planning on pulling out the voice board and housing it in a new case with midi control and some parameter mods.

BTW, one of the pins on the smaller edge connector on the control board is an unused external clock input for testing at the factory. I can't remember how many ppqn it needs but its pretty simple to wire an external clock in.

I've got a digital copy of the schematics and service manual if you want it.

[Gordonjcp]

Why not just pick up the audio before the VCA and dish the control board entirely?

[Circuitbenders]

Thats what i was planning to do mine, as soon as i can find a nice case to stick the voice board into. I'd prefer to not have to do any transplanting, but i couldn't work out how the timing pulses are leaking onto the audio. I had assumed that it was coming from the unregulated power rails somehow, but having replaced the internal transformer etc with a couple of bench PSU's, that doesn't seem to be the case.
I think it might just be some bad design on the control board, or the main IC is dying.

I love the toms on this thing. They have that excellent slightly distorted hollow sound to them that you hear on loads of early techno stuff.

[Big Chris]

I've got a digital copy of the schematics and service manual if you want it.

I'd love to get hold of the schematics and service manual - I've ordered a hard copy from the States, but I've no idea how long it's going to take to get to the UK, so a digital copy would be most handy. By the sounds of it, I'll probably go down the route of transplanting the voice board into a custom wooden case, along with a Engineers @ Work trigger board and regulator circuits to get the right trigger voltages.

I've also ground to a halt on my Roland TR-77 MIDI retrofit, and was wondering if I could commission you to complete it for me. I've got all the parts (MD24 trigger board, components for the trigger inverter circuits and voltage regulator, etc) but lack the tools for things like making a suitable hole on the metal case of the TR. I did send an email via the CB website, but got no reply and thought my useless ISP may have tagged it as spam (it's a mandatory spam filter that I can't switch off, nor can I see what it's tagged as spam).

[redon]

HEY me too! I would like the service manual as well, s'il vouz plait!! thanks. Ah, to what I know the md24  can natively send inveted triggers. any news on the actual trigger voltage required? thanks!
enrico

[Big Chris]

I've now received a copy of the service manual from the States. It looks like the triggers are positive, and go from 0 - 13V for a typical duration of 31ms. The service manual also makes a few things clearer regarding the voice board. It was intended for use in both the standalone unit and built into Hammond's organs themselves. When built in, several voices could be triggered from the keys or pedals of the organ, including the brush sound that is disabled in the standalone machine. The extra connector pins for the cymbal, bass and snare were for triggering from an organ keyboard, and for some reason simply bypass the diodes on the other pins.

I'll post up a picture of the PSU board when I next have the machine open. It differs in my machine from the one in the service manual, but that may be a because UK spec machines differ from US ones.

Chris

[Circuitbenders]

whoops, sorry, i completely forgot about this in the excitement of a graphics card going up in smoke and nearly taking a whole PC with it!

I've uploaded the service manual that i have here http://www.mediafire.com/view/?4f2z3lq34u4b19z if anyone wants a digital copy. There doesn't seem to be a power supply board in that one either. Are you sure yours is actually original chris?

The extra inputs probably bypass the diodes as they won't actually be trigger inputs. Maybe they just switch high or low. Thats just a guess though.

I don't think the width of the trigger pulse will matter that much if you are triggering from an external source. The sounds will probably just trigger on the upward or downward slope of the pulse. Either way, it shouldn't be hard to make the trigger slope the front of the pulse.

With regards to the TR77, i did reply to an email from you before, assuming your name is chris wareham? If the email went missing i suspect it was a combination of your spam filter and the people who own our server neglecting to turn on certain antispam features. I'll email you again once i've sorted out this PC disaster. 

[Big Chris]

Hi Paul!

Yes, that's the right Chris :-) I'd love to get you to do the MIDI conversion of my TR-77 - I like the sounds on it so much that I bought a second one in anticipation of the first one being out of action for a while. The Hammond should be much easier to MIDIfy, thanks to the simpler triggering, so I'm going to try tackling that one myself.

If you could email me on both my addresses, then hopefully your message will make it past the spam filters to one of them:

chris (a) chriswareham (dot) net
chriswareham (a) chriswareham (dot) demon (dot) co (dot) uk

As for the Hammond power supply, it all looks original inside my one, with a much higher quality of soldering and assembly than the Roland. I've just finished reading the autobiography of Taro Kakehashi (the founder of Roland) and I suspect he had no involvement in the design of the Auto Vari, as that came out in 1974 and he'd parted ways with Hammond International at the same time he left Ace in 1972. I'll get around to disassembling the Auto Vari again in the near future and uploading some close ups of the PSU board.

Cheers,

Chris