OMEC Digital Amp

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OMEC Digital Amp

Postby Benny Lamb on Thu Sep 30, 2010 5:26 pm

http://cgi.ebay.com/VINTAGE-ORANGE-AMP- ... 2c57c0471c

Not working but interesting. Looks like it belongs on a space ship.
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Re: OMEC Digital Amp

Postby amoun on Thu Sep 30, 2010 8:09 pm

puzzles me why sellers quote no reserve but don't start the auction @ 0.01, he does have a reserve, its $149 :lol:

not sure i would want to pay $149 for a fully working one of those :mrgreen:
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Re: OMEC Digital Amp

Postby Gladmarr on Thu Sep 30, 2010 9:55 pm

Vintage + digital = No Fooking Way!!
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Re: OMEC Digital Amp

Postby christco on Fri Oct 01, 2010 6:21 am

Benny Lamb wrote:Looks like it belongs on a space ship.


Yeah, like the original starship Enterprise, maybe...
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Re: OMEC Digital Amp

Postby bclaire on Sat Oct 16, 2010 8:38 pm

Hi guys- haven't been on here for awhile, but I bought this thing!

It's coming from California, but it was originally sold by a store near me in Boston! I've found a couple of guys who remember it- and maybe one who worked on it. Same guy has a catalog and schematics for the thing!

I was the only bidder so I feel OK about not having to run up bids, but it's going to be interesting. I don't have high hopes for how it'll sound, but whatever. When I visited Orange UK HQ a couple of years ago, Cliff showed me a replacement board for one of the things...!

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Re: OMEC Digital Amp

Postby christco on Sun Oct 17, 2010 12:10 am

So what the hell does the thing do? In what way is it programmable?
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Re: OMEC Digital Amp

Postby bclaire on Sun Oct 17, 2010 1:27 am

Beats me! ha ha ha!

I think basically it stores four different amp settings that you could call up with the footswitch... For 1975, it was pretty innovative.
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Re: OMEC Digital Amp

Postby bclaire on Wed Nov 17, 2010 3:53 pm

So getting this thing repaired is going to be a bit of a challenge. The first guy I brought it to went through it for two hours with me there- said "oh dear" about 16 times along with a "wow... on no." He said it really wasn't designed to be easily repaired. It does have audio going through it albeit very low and broken up. However, something funky is going on with the input jack but to replace it, you'd have to pull all of the boards out! Fortunately, the channel switching is working so maybe it's just audio... but we'll see when I bring it to the next guy.

Pix are here:
http://www.facebook.com/album.php?aid=2 ... a6a549b41a

and here:
http://www.facebook.com/album.php?aid=3 ... 334813e4eb

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Re: OMEC Digital Amp

Postby pjh on Mon Feb 21, 2011 1:06 am

I couldn't resist waking up this old thread. Google brought me here after one of the guys from the original Orange got in touch and triggered a few memories. I designed the Omec amp in 74/75: my first job. Spent a few months as a student fixing amps part-time in the Orange Shop's basement, and then spent about a year with them full-time. The brief was to "design a computerised amp". With some computers costing upwards of a million and needing their own building and air conditioning plant, a few compromises were necessary. Some weird new-fangled things called microprocessors were beginning to appear in the early to mid 70s, but they needed a lot of "support chips" to make a useful system. Smaller single-chip microcontrollers existed for things like calculators, but they were permanently mask-programmed - the tooling costs were huge and they were only affordable if manufacturing quantities were in the hundreds of thousands. So the only sane way to do this job was with SSI and MSI (small and medium scale integration) logic chips. The choice was between TTL (transistor-transistor logic) which was power-hungry but easy to get hold of and well proved, or a new technology from RCA called COS-MOS, which used hardly any power but also had a habit of self-destructing due to static damage. COS-MOS was too risky at the time, but that technology led to today's CMOS microcontrollers, with built in static protection, low power consumption and millions of transistors on a chip - one of those could handle the whole job for a few dollars.

So, the digital amp was really a digitally controlled analogue amp. Real DSP was a couple of decades away. The digital half (the left-hand half of the board Cliff is holding in the pic above) allowed numbers for each parameter (vol, bass, mid, treble, reverb, compression, distortion) to be stored in memory for each of four "channels", and those numbers could be recalled by selecting a channel either from the front panel or the footswitch. The memory controlled the audio circuitry on the right-hand half of the board via analogue switches. Slight snag: TTL is so power-hungry the memory took almost an amp at 5V, so all the settings were forgotten if the power was switched off! A backup battery was added to protect against brief power cuts, but it only lasted for half an hour or so.

An idea before its time, I'm afraid. It was innovative, but there wasn't a knob that went up to 11, it probably didn't sound that good, and I doubt that it was financially viable. Months later the Z80 and 6502 microprocessors appeared and spawned the personal computer industry. The rest, as they say, is history.

Did you get the amp going? I doubt that I have any schematics or hardware after all this time, but might be able to rake up a few more memories...
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Re: OMEC Digital Amp

Postby Gladmarr on Mon Feb 21, 2011 6:00 am

Wow! That's an awesome story, and knowing from personal experience how taxing it can be to make complex digital circuitry from individual TTL logic chips, I take back my original poo-poo-ing of the amp. You're probably right, it probably sounds awful, and it was probably waaaay ahead of its time in terms of useability. I would've liked to have been there at some point when new ground was being broken in electronics, even if the result was something as boring as Pong....
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Re: OMEC Digital Amp

Postby amoun on Mon Feb 21, 2011 6:59 am

awesome story 8)
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Re: OMEC Digital Amp

Postby bclaire on Tue Feb 22, 2011 12:33 am

pjh wrote:I couldn't resist waking up this old thread. Google brought me here after one of the guys from the original Orange got in touch and triggered a few memories. I designed the Omec amp in 74/75: my first job. Spent a few months as a student fixing amps part-time in the Orange Shop's basement, and then spent about a year with them full-time. The brief was to "design a computerised amp". With some computers costing upwards of a million and needing their own building and air conditioning plant, a few compromises were necessary. Some weird new-fangled things called microprocessors were beginning to appear in the early to mid 70s, but they needed a lot of "support chips" to make a useful system. Smaller single-chip microcontrollers existed for things like calculators, but they were permanently mask-programmed - the tooling costs were huge and they were only affordable if manufacturing quantities were in the hundreds of thousands. So the only sane way to do this job was with SSI and MSI (small and medium scale integration) logic chips. The choice was between TTL (transistor-transistor logic) which was power-hungry but easy to get hold of and well proved, or a new technology from RCA called COS-MOS, which used hardly any power but also had a habit of self-destructing due to static damage. COS-MOS was too risky at the time, but that technology led to today's CMOS microcontrollers, with built in static protection, low power consumption and millions of transistors on a chip - one of those could handle the whole job for a few dollars.

So, the digital amp was really a digitally controlled analogue amp. Real DSP was a couple of decades away. The digital half (the left-hand half of the board Cliff is holding in the pic above) allowed numbers for each parameter (vol, bass, mid, treble, reverb, compression, distortion) to be stored in memory for each of four "channels", and those numbers could be recalled by selecting a channel either from the front panel or the footswitch. The memory controlled the audio circuitry on the right-hand half of the board via analogue switches. Slight snag: TTL is so power-hungry the memory took almost an amp at 5V, so all the settings were forgotten if the power was switched off! A backup battery was added to protect against brief power cuts, but it only lasted for half an hour or so.

An idea before its time, I'm afraid. It was innovative, but there wasn't a knob that went up to 11, it probably didn't sound that good, and I doubt that it was financially viable. Months later the Z80 and 6502 microprocessors appeared and spawned the personal computer industry. The rest, as they say, is history.

Did you get the amp going? I doubt that I have any schematics or hardware after all this time, but might be able to rake up a few more memories...



Wow... amazing. I had hoped to hear from you somehow.

Well, I tried all of my tried-and-true amp techs and finally brought it to a repair shop that deals with a lot of studio and high-end gear- both design and repair. I have the schematics... but he looked at it and reported that the output section in particular looked like it had had three attempted repairs, plus the front digital end needed attention, and he wasn't sure I should be throwing that much money at it when he wasn't sure he could totally get it right. He said the same thing regarding "it probably won't sound good..." He also said the output section reminded him of a 70's Kenwood design!

So, the plan now is, I'm sending it to the UK for repair. Orange has that last replacement board so that's easy- and the output section should be repairable hopefully.

I'll reply back when I hear something else...

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Re: OMEC Digital Amp

Postby pjh on Tue Feb 22, 2011 7:00 am

He also said the output section reminded him of a 70's Kenwood design!


Interesting. Well I'm not guilty there! I did the rest, but the power amp board was shared with an earlier product designed by someone else: the denim and leather covered "Jimmy Bean". (Cruelly renamed by some the "Jimmy Has-been"). Though to be fair there aren't that many ways to design a transistor power amp, and all designs of the time shared many features. The only innovative and successful power amp technology of that era that I can think of was Quad's "current-dumping" design.

Good news that you have the schematics. With them it will be fixable as all the components, or pin-compatible equivalents, should still be available. (I think. Without a glance at the schematics to refresh my memory I can't be sure, but I've always tried to avoid using non-standard components likely to go obsolete.)

Hmm, I'm pretty sure it used quite a few LM381 low-noise pre-amps. That device is discontinued, but some stockists (including an eBay vendor) still have some - now might be a good time to stock up!
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Re: OMEC Digital Amp

Postby pjh on Tue Feb 22, 2011 1:07 pm

And here is the patent:

http://www.google.com/patents/about?id=FXIsAAAAEBAJ

(How did we survive before google?)
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Re: OMEC Digital Amp

Postby pckpat on Tue Feb 22, 2011 10:51 pm

so,pjh-whattaya up to these days? :wink: (classified?) :P
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