OR15 signal flow

[Man1ak]

Does anybody know the signal flow in an OR15? I mean, where is the gain knob positioned in relation with the preamp tubes? Is it after the V1, or after the V2 etc? Is the master volume pre or post PI? Is the tone section between V1 and V2, after V2 etc? Even parts of information would be interesting.

[Man1ak]

I have played with tubes to bring the gain down so that I can get clean tones easier. I now run it with a 5751 in v1, 12ay7 in v2 and another 12ay7 in the PI. With a strat it stays clean until 11 o'clock, at 12 o'clock it has a bit of muscle and after it starts to overdrive strongly.

I have switched the preamp tubes with the 12ay7 in v1 and the 5751 in v2, but the gain and drive behavior is the same. Would this mean that the gain knob is before v1? I apologize if I am asking a stupid question.

Some other things that i have noticed so far:
1. If I am using a 12ay7 in v2 and el844 in the output, maxing the master volume will overdrive the output section - not sure which part. The same is not valid if the 5751 is in v2. Is there something special with a 12ay7 that determines this behavior?

2. The fx return does not seem to be affected by the master volume. If I connect another preamp (a processor) to the fx return and connect my guitar to the preamp the MV will not work anymore. Does this mean that the fx return goes in front of the PI? So since the MV does not work anymore does it mean that the PI is post MV?

Appreciate your feedback.

Thanks.

[Man1ak]

After a lot of searching and reading i 've found out some of the information.
1. The tone stack is between the preamp and the fx loop. So i guess it is after the V2.
2. The MV is pre PI - this is why the FX return is not impacted by the MV
3. The PI is (most probably) the Long Tail Pair variety. This would explain why the PI tube makes a diference in the overall tone (and partly volume/gain, but not thwt much). I tried running a 12ay7 in the PI and found that it slimmed down the tone - more buzzy. I also found that I had to increase the gain with one notch to get to the same level as with a 12ax7. I used a JJ 12ax7 in the PI and found the overall tone too dark. I am now using a JAN Philips 5751 and the tone is brighter. So, to my ears, the PI tube in this amp makes a difference in both tone and gain.

The information that I am still missing is the one related to the position of the gain control in the preamp. I am tempted to believe that it is after the V1 - with a single coil I am able to get a reasonably clean and full bodied tone, but with a humbucker or p90 it's a bit crunchy no matter the gain setting.

If any of you guys have similar experience or know more about the structure of this amp, your feedback would be appreciated.

Thanks.

[Man1ak]

I have found a internal shot of the OR15 over at the ilovefuzz.com forum - http://www.ilovefuzz.com/viewtopic.php? ... 5&start=30" onclick="window.open(this.href);return false;. Not sure how useful this can be to you experts out there, but probably better than nothing

[Jondog]

The gain control is most likely a dual gang pot with one half between the first and second gain stages and the other half between the second and third gain stages. This is how it is in the Rockerverb, the Jim Root terror is the same preamp as the Rockerverb and the OR15 shares the same PCB as the Jim Root terror.

[jontheid]

The gut shot shows a dual gain gain pot - I agree with Jondog, this is likely between 1st-2nd and 2nd-3rd gain stages.

The master volume is definitely pre-phase inverter, as it is only a single-gang pot, post-PI MVs necessitate dual gang pots.

I'd bet money that the PI is LTP design.

It strikes me as really strange that the MV doesn't affect the FX return.
Perhaps the MV is pre-fx send, so the lower the MV, the less fx sent so the actual fx amount varies proportionally.

Cheers
Jon

[Man1ak]

@jondog and jontheid: thanks for your feedback and contribution. I guess that the picture us now reasonably clear.

Based on the last information related to the gain control, does it mean that the first gain stage is fixed? So the first triode would impact the rest of the signal the most? The OR15 has obscene amounts of gain, really. With 2 ecc83 and a Les Paul is really not usable after 1 or 2 o'clock. So I constantly trying to figure out a good balance.

I am tempted to try a 12dw7 in V1, maybe even in v2. If the gain control is between 1-2 and 2-3 i guess that it would be good to use it to control the highest gain triodes of the chain. What do you guys think about it? Anybody having experience with these tubes?

@jontheid: this is what i hear as well - the MV controls the amount of signal going to the fx loop, so most probably it is before the fx send. This is actually smart as it makes sure that the fx is not lost with volume increase.

[jontheid]

Why not try a 12AU7 in V1?
Worked well in a dual terror, still plenty of gain.

[Man1ak]

@jontheid: i will try it, I have a JJ ecc82 lying around. I am just thinking that the JJ ECC832 (with a 12au7 type as first triode) in V1 and a JJ ECC823 (reversed version with a 12ax7 as first triode) in V2 could make a lot of sense. I guess you get a clean signal after first stage, then control the next 2 stages with the gain pot and have the final stage clean or clipping, depending on the gain settings. This sounds interesting.

The only problem i have is where to get a reversed ECC823. Eurotubes has them, but international shipping is quite expensive.

[jontheid]

Be careful - 3rd and 4th gain stages may not correspond to 1st and 2nd triodes of V2.
I think you are better off experimenting with standard-type lower gain tubes - it is cheaper too!
I'd just try the ECC82 in V1 first - it might give you just what you are looking for.

[Man1ak]

Thanks for the warning Jontheid. I have checked the RV50 schematic and it seems that stage 3 is actually the first triode of V2. If OR15 has the same preamp, then it would probably follow the same layout. The RV50 schematic is here http://www.orangefieldguide.com/OFG_SCH ... sheet1.jpg" onclick="window.open(this.href);return false; . Maybe one of you guys can confirm my understanding.

[Jondog]

Thanks for the warning Jontheid. I have checked the RV50 schematic and it seems that stage 3 is actually the first triode of V2. If OR15 has the same preamp, then it would probably follow the same layout. The RV50 schematic is here http://www.orangefieldguide.com/OFG_SCH ... sheet1.jpg" onclick="window.open(this.href);return false; . Maybe one of you guys can confirm my understanding.

I wouldn't assume that

[Man1ak]

Well, i guess there is only one way to find out. I will report back here once i test the tubes. I could not find the OR15 schematic, but if anybody has/finds one this is the best place to post it

[GySgtFTL]

Any updates here? I've been thinking of trying a JAN Philips 5751 to see if I could get a slightly cleaner tone but have been "living vicariously" through your trials. Did the last tube-swap help?

thanks

[Man1ak]

@GySgtFTL: no news yet, i am still waiting for the tubes - probably next week i will get them. I have tried a 5751 in V1 and it does loose some gain at the same gain pot position. But still for humbuckers it does
not make a decisive change. For single coils i can get a good reasonably clean tone even with the 12ax7's.