software

After visiting the website tip on the Gilmour thread here i saw some tips on how to set your amp Eq etc, but my amp don't have some neccesary controls like middle and something called presence, what is presence?

Is there a way of installing controls on an amp that's not there? My amp is a Vox Pathfinder 15R.

I think presence sets the quot;cut throughquot; ouf your guitar... so if you're playing lead it should be higher or something... but actually I don't really know.. never had an amp with such a knob.

I am pretty new to modding amps, but the only additions I have seen possible are merely manipulations of existing circuits... To add a presence quot;knob,quot; you would have to alter the circuit board... And as far as I am aware, Presence knobs are exclusively for tube amps, and tube amp emulators... I'll have to do some more research, as your questions are pretty unique....

Hope this helps some, I'll do some research and get back to you,
Allen

Afaik, the quot;presencequot; area is in the upper mids\treble area.

Atleast on the amps i've tried, it was just a boost\cut frequency knob for that area.

A presence control is generally located in the feedback loop of an amplifier - a bit of the output is fed back into an earlier stage (usually the phase inverter) to help stabilize the amp. The presence knob controls the amount of feedback, and its frequency content. The overall result is to change the overall brightness, but it a wider and more subtle way that a treble control.

Without knowing the design of your particular amp, in order to have a presence control, it must have a feedback loop, and therefore must have a phase inverter stage. Small single-ended amps don't have a PI, so they CAN'T have a presence control. Most 2xEL84 amps (Marshall 18 Watter, small Voxes, Matchless Lightning, are push-pull amps, and therefore have a PI stage, but they were not designed with feedback circuits. Again, no feedback, no presence. To add a presence control, you'd need to add a feedback loop; an interesting experiement that would undoubtedly change the fundamental character of the amp's tone.

Similarly, you could add a mid control to an amp that has only treble and bass, but you'd basically be replacing the existing TB tonestack with a TMB tonestack. Unfortunately, the more involved the tonestack, the gain is lost passing through it. So, by ading a mid control, you would lose overall gain. So, unless am amp is designed to drive the more complex tone circuit, adding tone controls is probably not a good idea.

However, amps can be tweaked to provide slightly different sounds while not altering their basic topology. If you know what you want, it may be possible to get the amp closer without major re-design. For example, my 18 Watter clone (see link in signature) sounds like a Marshall, period. The Marshalls I played long ago were 100-Watt JCM800's with TMB tonestacks, feedback loops, presence controls, preamp gain controls... the works. In contrast, my present amp has one volume and one tone control, and a pair of EL84-ish output tubes. Its topology is NOTHING like the big JCM, yet they sound a helluva lot alike.

Thanks everybody for the information! So you think i should stay away from adding the quot;knobsquot;?


Originally Posted by ThurisarzThanks everybody for the information! So you think i should stay away from adding the quot;knobsquot;?

Yes.
There's not much to be gained by modding a 15W solid state practice amp. The real purpose of a presence control is to add tonal control when the amp's power stage is clipping. Since SS amps are very rarely set up to get power amp distortion, a presence control is not needed.
If you want more control of EQ, I'd suggest getting an EQ pedal rather than modding an amp that's worth little more than an EQ pedal.

Rich S- you're all over it like a lap-dance!!
yes, if you don't have a tube amp, you really can't add a real 'presence' circuit.