Calling Geekmacdaddy, over Trex psshht.

[Turmoil]

GMD,

Do you find the presence control on your Trex usefull? I don't have one wired in yet, but the amp has plenty of presence as it is. Do you think I need more?

Tim

[Plexi]

The presence circuit is also part of the feedback circuit..which helps knock down some of the gain. Without it..its a pretty wild animal The presence should work fine. If not wanting a presence control..you could also maybe try a resonance control..

Richie

[Turmoil]

The presence circuit is also part of the feedback circuit..which helps knock down some of the gain. Without it..its a pretty wild animal The presence should work fine. If not wanting a presence control..you could also maybe try a resonance control..

Richie

Hey Plexi,

I'm using negative feedback as is in Mark Huss' schemo here:

http://mhuss.com/18watt/schematics/18wTRex.pdf

Could you give me an example of a resonance control?

Thanks,
Tim

[geekmacdaddy]

Listen to Plexi. He designed it. The presence/feedback is needed for the wreck side.....

[Plexi]

ok.. i see, your useing the feedback switch.. that is really like having a preset presence,set between about 2 or 3,if you had a control or pot you could vary the presence..
Marks scematic does not have the .1uf cap across the 1.5k resistor..this cap would add the more highs.

Here is what the resonance control does.. or explained by Peavey below...

And also below that is RA's term..also called a depth control in some amps..but don't get the trem depth control mixed up with this one...
Just look up the 5150 or other amps that use them.

"""The 5150's resonance control is the most happening feature on the amp; it beefs up the sound by boosting power amp gain in the low frequencies and is intended to offset any low-end speaker cabinet roll-off. It worked quite well with a variety of enclosures""""

"""Resonance - a control on a guitar amplifier that boosts the lower frequencies at or below the normal bass control range for added low-end, also called "depth" or other names. This control is usually a shelving type of equalizer, and is normally implemented as a highpass filter inside the global negative feedback loop. By decreasing the amount of low frequencies that are fed back, the low frequencies at the output of the amplifier are boosted. Resonance is also the term given to an electronic circuit that contains both capacitive and inductive elements - there is a "resonant" point where the capacitive reactance equals the inductive reactance. Depending upon whether the elements are in series or parallel, this will result in a maximum voltage and maximum impedance across the elements (parallel resonance) or maximum current and minimum impedance through the elements (series resonance). If the circuit has resistance, either across the parallel resonant circuit or in series with the series resonant circuit, the maximum peak will be limited, and the bandwidth of the resonance will be broader. The relative "sharpness" of the resonant circuit is called the "Q", or "quality" factor. See the definition of "Q" for more details. """



Richie

[Turmoil]

Okay, in goes the presence control

Thanks for the explanation Plexi, I'll try to dig up a 5150 schem and study it.

Tim

[populartsl]

Richie

I take it that the .1uf cap is placed in parallel with the 1.5k resistor on the feedback switch.

Ben

[Plexi]

yes that is correct.

[populartsl]

Thanks

Ben

[Turmoil]

Plexi,

Please confirm that the values in this layouthttp://www.18watt.com/files/t-rex_18_layout_772.pdf are correct for presence control.

I notice it is wired reverse in GMD's photo of it hehttp://www.18watt.com/modules.php?name=Forums& ... &start=0re:

Parts needed are:
25KL pot
100k Resistor
4.7K Resistor
0.1 uf Cap

Thanks for the help

Tim

[Plexi]

neither of those open for me to look at..

[populartsl]

Links wrong

Try this

Please confirm that the values in this layout

http://www.18watt.com/files/t-rex_18_layout_772.pdf are correct for presence control.

I notice it is wired reverse in GMD's photo of it here

http://www.18watt.com/modules.php?name= ... &start=0re:

Ben

[Plexi]

I made corrections to the layout Gabi had.. the .022 that has the 150k resistor attached to it,should be .0022
The inputs should be wired like standard Marshall or fender.. you can put the resistors on the jack..and only have one wire to run to the tube for each channel.
Also the resistors going into the PI should be 220k,those in the layout look more like 22k

Richie

[Turmoil]

Links wrong

Try this

Please confirm that the values in this layout

http://www.18watt.com/files/t-rex_18_layout_772.pdf are correct for presence control.

I notice it is wired reverse in GMD's photo of it here

http://www.18watt.com/modules.php?name= ... &start=0re:

Ben

Yeah those ones Thanks Ben.