OR80/120 and OTR circuit discussion and documentation thread

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OR80/120 and OTR circuit discussion and documentation thread

Postby fiveightandten on Sun Jul 23, 2017 2:33 am

Intro:
It's been a while since the old school tech nerds had a discussion. I'm curious as to what circuit deviations of OR-120/OR-80 amps are out there and not accounted for in the available schematics.

I've put together a spreadsheet of the different circuits, and only listed the pertinent components that differ between the different iterations. See the attached spreadsheet.

Requested action from you:
If you have a 70's amp and can poke around and verify component values, it would be great to get a list of serial numbers (and/or build dates) and reference how consistent they are with these schematics. Sent me the info, or download the spreadsheet and update it with your info.

If you have a 90's amp...see if it's consistent with mine. I believe they are all the same, but it would be interesting to know.

Referenced schematics and amp:
1) "Orange Graphic MKII" Dated 1972
http://www.orangefieldguide.com/OFG_SCH ... hem_72.gif

2) "Orange Graphic MKII" Dated January 10th, 1974
http://www.orangefieldguide.com/OFG_SCH ... hem_74.gif

3) "Orange Graphic MKII", no printed date. Referenced as "post 74" in online sources
http://www.orangefieldguide.com/OFG_SCH ... post74.jpg

4) 1990s reference amp - Overdrive 80, S/N 941. Believed to be 1996 build date.

5) "Orange OTR120 amp" dated September 23rd, 1998.
http://www.orangefieldguide.com/OFG_SCH ... rschem.gif

Discussion:
I have messed around with these different circuit iterations over the years. There is a definite difference in sound. It's a little involved to discuss the differences in an opening post, but if anyone is curious to talk about that stuff, I'm game for sure.

Tone stack
The '72 and '74 have the same tone stack. The post '74, 90's reissue, and OTR are all unique. Though the component values are very similar. The differences are really in the treble circuit and how that reacts. It's a notable difference if you roll the treble knob over halfway.

V2A and Phase inverter
The '72 circuit is unique, and they changed things after that. The '74, post '74 and 90's reissue are all the same (direct coupled). The OTR is basically a modified '72 style. The plate and cathode resistors are different (that amp runs different voltage droppers, which is likely related to these changes).

Presence circuit
Again, the '72 is unique in that is has an inductor in series with the cap. The The '74, post '74 and 90's reissue are all the same. The OTR is unique to itself in that the feedback loop resistor value is higher than all the others (pot and cap are the same).

Filtering and B+ rail
For filtering, the 70's amps are all the same. The 90's reissue has more filtering in the late (pre-amp) stages. The OTR has the extra filtering found in the 90's reissue, but it also has different value voltage dropping resistors.

Overall
The 70's amps have some notable differences between each other. The 90's reissue amp is nearly identical to the post 74 schematic, but with one cap different in the tone stack, and with higher filtering in at the end of the B+ rail. The OTR takes aspects of most of these circuits, but seems to pay homage to the '72 and deviate where Ade wanted to add his own flavor. The OTR is the one circuit I haven't played around with, so I can't offer any insight on how those changes sound when implemented in a given amp.

Image

Spreadsheet:
https://drive.google.com/open?id=0B8fGe ... Hg1T0ZKczQ
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Re: OR80/120 and OTR circuit discussion and documentation th

Postby LD50 on Sun Jul 23, 2017 9:27 am

If it will help I am happy to take lots of pics of my relatively common or garden pics and text OR120 bought from a forum member earlier this year (how I get the pics out now that Photobucket has pressed the self destruct button I have not decided). It is serial 10507 and features typical of late 72/early 73. No inductor.
I thought that the only ones with mid lift inductor were pics only and pcb mounted preamp tubes. I had a rather road worn one of these that I tidied up for someone and it did sound very good, particularly rich and interesting clean/funky sounds with single coils.
All bleeding stops.......eventually.
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Re: OR80/120 and OTR circuit discussion and documentation th

Postby fiveightandten on Sun Jul 23, 2017 7:10 pm

LD50 wrote:If it will help I am happy to take lots of pics of my relatively common or garden pics and text OR120 bought from a forum member earlier this year (how I get the pics out now that Photobucket has pressed the self destruct button I have not decided). It is serial 10507 and features typical of late 72/early 73. No inductor.
I thought that the only ones with mid lift inductor were pics only and pcb mounted preamp tubes. I had a rather road worn one of these that I tidied up for someone and it did sound very good, particularly rich and interesting clean/funky sounds with single coils.

Thanks. Pics are always good, but not necessary. What I think would be good info is for capable individuals to trace their amp out with a meter and/or component markings and see what they have in there.

I'd like to:
1) Know if there are other circuit variations outside of the online schematics.
2) Get a list of amp serial numbers and/or date codes and face panel design that match each of the known circuit versions.

Years ago, I had a friend who had an OR-80 with laydown transformers and PCB mounted pre-tubes. It was a pics and text amp. I also recall the bias was non-adjustable (no bias pot). It was running very cold, something like 8W per tube and had cheap Sovtek EL-34s in it. It's still the best sounding Orange I've heard. He bought it from Vic, here, IIRC. I don't recall what circuit version it was, or if it had an inductor in the presence circuit. It was, as you mention, particularly rich, and very stout.

I've owned 3 of them, and worked on and played many. That one sounded the best, for sure. My old 90's OR-80 (modded to 120 and '72 schematic specs) was a close 2nd. I stupidly sold it years ago. There's something to that '72 circuit, I'm sure. But I can't say whether or not that's what was in that pics/text OR-80 with laydowns.
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Re: OR80/120 and OTR circuit discussion and documentation th

Postby jp0971 on Sat Jul 29, 2017 1:46 pm

fiveightandten wrote:Years ago, I had a friend who had an OR-80 with laydown transformers and PCB mounted pre-tubes. It was a pics and text amp. I also recall the bias was non-adjustable (no bias pot). It was running very cold, something like 8W per tube and had cheap Sovtek EL-34s in it. It's still the best sounding Orange I've heard. He bought it from Vic, here, IIRC. I don't recall what circuit version it was, or if it had an inductor in the presence circuit. It was, as you mention, particularly rich, and very stout


I have an amp exactly like you describe, but it's an OR120. I think it's a '73. I gather it's just some kind of transitional model - pix and text faceplate, but the everything else '72 spec. There isn't an inductor, and the bias was non adjustable (I've since had a trim pot installed). It does sound different from the other OR series amps I've owned, in that it has more headroom mainly.

I can only really offer pictures though, but I suppose I can identify the components too.
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