OR15 presence

[Squirrels]

Thanks Andy, I did a little more EQ'ing and I think I'm where I want to be with it now. Not to say I wouldn't want to revisit a mod or two down the line (after some reading... thanks again Jon). I had a Dark Terror before this but I found it difficult to get a lower gain sound I wanted without having to use a 5751 in V2, which isn't a big deal, but it took a little away from the overall metal-ish nature of that amp. Also I'm not a huge fan of an overly scooped tone. What I love about the OR15 is that it's easier to dial in a lower gain crunch without losing the amount of gain it has, also being able to dial in some mids is a huge plus for me.

I pretty much just play at home these days, so after reading about the depth control I figured it might be a good thing. The OR15 doesn't do a bad job at low volumes, but with an attenuator (50 watt L-Pad) to push the EL84s a bit and to knock off a few decibels, it sounds fantastic. I usually have the amp on the 7 watt setting and the volume set to around 9:00 and let the L-Pad tame the volume. I'm playing through a stock PPC112 by the way.

[Squirrels]

So after reading the OR15 diagram and the thread about the differences between the JR and OR15, if I changed out C13 to a .1uF cap it should get me a little closer to what I'm looking for in low end, or am I still missing the mark here?

[jontheid]

You can try it and it probably won't do anything nasty, but it may well not give the results you are after.

The OR15 uses a 'Marshall' style tonestack - there is good (and free!) modelling software available here:
http://www.duncanamps.com/tsc/" onclick="window.open(this.href);return false;

It is an old program, but works very well in Windows 7 for me.

If you select the 'Marshall' tab and then click on the components to substitute in the OR15 values it will give you the frequency respone of the tonestack, and you can move the sliders to see how the different controls affects the response.

In standard form the OR15 'bass' control gives a boost in the 50Hz - 100Hz range (interestingly the frequency gets lower the higher the control is).

Substituting C13 for a 0.1uF cap moves the boosted frequency lower (extends it all the way down to at least 10Hz) but doesn't boost the 50Hz -100z range any more than with the stock capcitor.

A lot of the frequencies boosted are below the frequency response of your typical guitar speaker. You might just be throwing output power away on frequencies that aren't going to be efficiently transduced by the speaker.

Try it if you like, it is easily reversible, and components are cheap.
Only you can really know what 'your sound' is.

[Squirrels]

As much as I love this amp, I think I should have stuck with my Dark Terror. If I could get a little more of an aggressive tone out of it to go with how easy it is to dial in a great blues tone, I'd be set. The OR15 does sound similar to the Dark Terror with the mids scooped, but it's still lacking something. I really only have room at home and financially for one amp so there is the dilemma. Maybe I should try to trade for a Jim Root or another Dark Terror.

[Randy Bass]

Might as well give the Jim Root #4 a try at this point. The Rockerverbs seem to cover Blues and more aggressive stuff pretty well, so I'd hope the #4 was designed with similar versatility.

[Man1ak]

Well, the Dark Terror, Jim Root Terror and OR15 are the same amp with different tone stacks. That's why I was telling you to try changing the EQ section. It should be more versatile than the Dark Terror due to 3 band eq vs shape control. I read that by changing the slope resistor you can alter the mid response, which in its turn will also impact bass and treble. The Jim Root has a 39K, while the OR15 has a 47K. My understanding is that lower values also lower the bass frequency range.

[Squirrels]

Well, the Dark Terror, Jim Root Terror and OR15 are the same amp with different tone stacks. That's why I was telling you to try changing the EQ section. It should be more versatile than the Dark Terror due to 3 band eq vs shape control. I read that by changing the slope resistor you can alter the mid response, which in its turn will also impact bass and treble. The Jim Root has a 39K, while the OR15 has a 47K. My understanding is that lower values also lower the bass frequency range.

Yeah, swapping the slope resistor to 39k worked really well, it made it a lot more punchy in the lower mids, definitely more metal friendly and still does everything else really well. Thanks for the advice Man1ak, much appreciated.

Based on the link to the earlier thread that you posted about the differences between the OR15 and #4, I picked up 2 1nF capacitors for the treble caps, I didn't put them in (yet) because it sounded great the way it was and judging by the Rockerverb schematic that I saw, the treble cap (only one) was 560pF, any thoughts on that? I didn't get the 2K2 resistor, I didn't want to alter the gain structure. The bass is perfect, I don't think I need any more. I remember when I modded my old Valve Jr. that a few component changes made a huge difference.

I should just start a new thread instead of continuing to take this one further off topic. I guess I got inspired by the Hovercraft Dwarvenaut 20 in wanting to add a depth pot, a FAC would be pretty cool too, but probably unnecessary. I'll post sound clips with the mods when I get some time to turn it up a bit.

EDIT: While the tone fattened up nicely, the high end is now lacking. I'm going to put the 1nF caps in tonight after work. Sounds great for doom/stoner tones but needs some more treble.

[BrooksBlackhawk]

Did anyone figure out how to do the depth/resonance mod? I have a dark terror and would really like some more bloom from the power tubes. The highs are very icepick even with vintage mullard preamp tubes (which helped a lot) I would at least like to shift the preset presence value down. Does the r48 resistor affect this? Any help would be appreciated:)
Here is a dark terror schematic for reference
http://guitar-gear.ru/forum/index.php?a ... h_id=22573" onclick="window.open(this.href);return false;

[Man1ak]

I have a schematic drawn by an amp expert on how to add a presence control. Since the depth control is added on the NFB as well I presume it will not be very far from it. However, I doubt that you will resolve the icepick highs. The depth mod should remove some of the low frequencies from the NFB. It will make it more bass-y, but the highs will be there.

The only way I could sweeten the highs on my OR15 was to change the speakers to American voiced Eminence and use it with modern humbuckers. With PAF or single coils it is too harsh for my taste, even with the Eminence speakers.