NAD! Early 70s Orange OR120 [Orange OR120 vs. Matamp GT120 vs. Matamp Series 3000]

[FleshOnGear]

Yep that schem is one we made (my son,James, is now an embedded systems design engineer). The feedback is local early in preamp and no power stage NFB. That also applies to the ORST. However the OR100 of similar preamp etc does have NFB.
The boost on the 2000 and ORST works like a distortion knob!

It also looks like the drive switch controls what frequencies get boosted by the boost knob. The Series 3000 replaces the drive switch with a pot. My guess is that they’re using it to blend between two capacitors, rather than having a few caps on a rotary switch. I’m not sure that’s preferable, but I imagine I’d end up putting Drive and Boost on their max settings, anyway.

I’m starting to think I’m going to sell my SV20H and recent OR100 to fund a Series 3000. Hopefully it sounds half as good as the clip above.

 

[neikeel]

All my ORST clones sold pretty quickly. I may have a chassis and faceplate left some where but all the fancy pots and knobs have gone. I used chunky Partridge transformers. The 2000 is very useable in modern context, still benefits from a little attenuation to get into old school use sweet spot. I do wonder what a 3000 sounds like. I'm keeping my 2020!

 

[FleshOnGear]

All my ORST clones sold pretty quickly. I may have a chassis and faceplate left some where but all the fancy pots and knobs have gone. I used chunky Partridge transformers. The 2000 is very useable in modern context, still benefits from a little attenuation to get into old school use sweet spot. I do wonder what a 3000 sounds like. I'm keeping my 2020!

There’s one guy that has put clips of a 3000 on YouTube, but he doesn’t show off its range of tones. He has a particular medium-gain smooth lead tone he uses, and that’s all he demonstrates. It’s not especially enlightening or gratifying.

 

[FleshOnGear]

I made a deal on an early 70’s pics and text OR120, with laydown transformers. I’m probably going to pick it up this weekend. Can’t wait to see how she sounds!

 

[FleshOnGear]

I drove 11 hours round trip today to pick up this beauty. Just got done trying her out through my cabinets, and she sounds monstrous. Definitely not dethroning my 1987, but she has such a different sound. Note decay has a little bit of a staticky sound, so she doesn’t clean up as nicely as the Marshall, but the full throated fuzz texture is really cool.

She’s really clean for a fifty year old amp. One slightly rusty spot on the chassis in the back, one nick in the tolex on the front, and just a bit dirty. The guy I bought it from said it was recently recapped, which is nice - one less thing to worry about. Once I get some time with her, I’ll open her up and get some gut shots.

 

[solarburn]

View attachment 132765
I drove 11 hours round trip today to pick up this beauty. Just got done trying her out through my cabinets, and she sounds monstrous. Definitely not dethroning my 1987, but she has such a different sound. Note decay has a little bit of a staticky sound, so she doesn’t clean up as nicely as the Marshall, but the full throated fuzz texture is really cool.

She’s really clean for a fifty year old amp. One slightly rusty spot on the chassis in the back, one nick in the tolex on the front, and just a bit dirty. The guy I bought it from said it was recently recapped, which is nice - one less thing to worry about. Once I get some time with her, I’ll open her up and get some gut shots.

Is that a 120 or what model is it?

 

[FleshOnGear]

Is that a 120 or what model is it?

Yes, an OR120.

 

[solarburn]

Yes, an OR120.

Well Congratz man!!!

 

[neikeel]

HNAD
They are very different to a Marshall. Assuming all in good order should have very low noise floor and no fizz or crackle.
The FAC is very useful too.

 

[FleshOnGear]

@neikeel, I have a question about the way this amp behaves. It seems the distortion comes on rather suddenly and is a bit fizzy on the edge of breakup. I’ve never played an amp like this before, so I don’t know how normal that is.

My theory is that this breakup is happening at the stage that drives the cathodyne PI. I’m guessing that this amp’s driver stage has the 390k anode resistor DC coupled to the PI. I would think that the very high anode resistor and low cathode resistance would bias that stage only a fraction of a volt below saturation, and leave no room for a graceful excursion beyond that point.

In your experience, does the older driver stage wiring avoid this problem and sound smoother? I.e., using a 100k anode resistor and coupling the driver to a self-biasing PI via a capacitor?

I could be barking up the wrong tree. I haven’t looked at the wiring yet, so it might have the older wiring. Just curious what you think.

 

[FleshOnGear]

Yeah, never mind! This amp has the older version of the driver/PI wiring, so my hypothesis was incorrect. Thanks for indulging me.

This thing has had a bit of a rough go in life. Original transformers, as far as I can tell, but it looks like a lot of “techs” have mucked around in here. There’s just a lot of top-of-board soldering that’s been done. A PPMIV has been added, and it’s not the Lar-Mar variety - it has a 1Meg dual pot with two pairs of coupling caps, whatever that’s called. Oh, well, it sounds good and everything seems to work properly.

 

[neikeel]

I prefer the older type but did not have this issue with either of my OR120s or those I have serviced, I suggest you pull the chassis and show me some gut shots, including close ups of that stage. Similarly you might try some tube rolling and check the bias. 50-60% is more than adequate. I have a diagram and pics of how to convert to earlier type on the socket if needed. Just need to know it is set up correctly and has no dodgy mods first.

 

[neikeel]

Our posts crossed.
That version with the pcb mounted preamp tubes actually sounds best of the OR120s (IMO) normally. Someone has added a bias pot (good!) as these didn’t have one as stock. The presence/boost pot has been rewired and I can’t see its bypass cap. Never added a PPIMV to one, personally I go to stock and use an attenuator but you’ve plugged in so can judge.

 

[FleshOnGear]

There’s a good chance that what I’m experiencing is normal, and that I’m making it seem worse than it is. I’m just used to Fender/Marshall style amps.

This thing just behaves differently. A Fender or Marshall will start to distort very softly as you ramp up your volume or gain. You can hit a chord and let it decay, and the clipping will sort dissolve into a clean sound. But this Orange stays clean until you get to a point, then it crunches. It can be controlled dynamically and musically, but it’s not as gradual.

I put an old IEC labeled I63 Mullard, and a Chinese 7025 into it, and it sounds a lot better than the JJs that were in it. Maybe I’ll make some clips tomorrow, and folks can tell me if it sounds normal.

 

[FleshOnGear]

I just want to add that I’m not at all bummed out about how this amp responds. The overdrive it gives is addictively rich and unique. I tend to play around a lot with rolling down the volume on the guitar, and it just doesn’t respond the same as any other amp I’ve played. For that reason, I’m here asking if it’s normal, and if it is normal I’m OK with it. Alright, carry on.

 

[FleshOnGear]

Here’s some noodling at the edge of breakup:

@neikeel, would you please tell me if that sounds normal? Thanks for your time.

And here is some full throttle riffing:

 

[FleshOnGear]

I’m starting to think the output tubes in this thing are biased very cold. If I turn down the PPIMV enough it starts to sound like there’s crossover distortion. Maybe that reduces negative feedback to the point that crossover distortion isn’t being corrected. I will do a proper measurement of the bias this weekend - I’ve just been lazy up to this point.

 

[FleshOnGear]

So I’ve checked out a couple of clips of OR120s on YouTube, and I’ve come to think that there’s something wrong with mine. None of the clips I heard demonstrated an abrupt fuzziness at the edge of breakup. I checked the bias this morning, and it was set pretty warm - about 36mA per tube at 531 volts HT, or 76% of max dissipation. I turned it down to about 62%, but had to leave for an appointment before I could play test it.

Before I left I started looking at the PI voltages, and they seemed suspicious. I didn’t have enough time to map everything out and make sense of what I was reading. I will take more time with it when I get back home.

Btw, all of the voltages are pretty high. Heaters measure 7.1VAC, 12.7% high. The voltage node at the driver stage is 392V. I think I might need to bring down the line voltage for this amp.

 

[FleshOnGear]

Ok, cooling down the power tubes didn’t help. So I focused my attention to the PI.

I noticed that the grid of the PI was sitting at about 34V while the cathode was at about 106V. There was about 70V difference across the grid resistor, which indicated about 70 micro volts of grid current. The voltage across the 1.5K cathode resistor was 1.9V.

I wondered if the very low grid voltage was affecting the sound, so I decided to reduce the grid resistance by piggybacking a 110K resistor across the 1M resistor, bringing the grid resistance down to 100K. This brought the grid voltage up to about 90V, still quite a bit lower than the cathode, but I was concerned about reducing the grid resistance any more. It actually helped the sound tremendously - much more gradual transition to distortion. I’m not sure what this actually did to the signal.

I then tried reducing the cathode resistor to get that 1.9V to 1.5V. I put a 5.6K across the 1.5K resistor, which did the trick. But this did not seem to do anything for the sound.

 

[solarburn]

Ok, cooling down the power tubes didn’t help. So I focused my attention to the PI.

I noticed that the grid of the PI was sitting at about 34V while the cathode was at about 106V. There was about 70V difference across the grid resistor, which indicated about 70 micro volts of grid current. The voltage across the 1.5K cathode resistor was 1.9V.

I wondered if the very low grid voltage was affecting the sound, so I decided to reduce the grid resistance by piggybacking a 110K resistor across the 1M resistor, bringing the grid resistance down to 100K. This brought the grid voltage up to about 90V, still quite a bit lower than the cathode, but I was concerned about reducing the grid resistance any more. It actually helped the sound tremendously - much more gradual transition to distortion. I’m not sure what this actually did to the signal.

I then tried reducing the cathode resistor to get that 1.9V to 1.5V. I put a 5.6K across the 1.5K resistor, which did the trick. But this did not seem to do anything for the sound.

Well that's a positive result for improving the sound to your liking. I sure like the sound of these big OR's.

Very interesting to follow your results.