Depth or Resonance mod

[Valvehead]

Where can i look at a schematic or diagram of some different add-on mods, known as "Depth control" or "resonance" ? I remember one had a 100k pot and a .02 cap ? something like that ?

[tubeswell]

Don't you usually just find the fixed resistor in the feedback circuit (that is in parallel with a cap - of some teency value) and subtitute that resistor for an Audio taper pot (of - say - twice the resistor value)?

[HTH]

checkout the Peavey 5150 schematic. I've tried this on a high-gain homebrew of mine and it was great for adding that modern rock/metal 'chunk' to the tone.

you could also just put a cap across the feedback resistor for a 'fixed' version of this mod. Marshall did it with the JCM900 models - try a 100pF to 500pF cap.

[Valvehead]

Ok, I'll try that. Isnt the res. control on the 5150 active though?

[tubeswell]

Are we talking VR8 and C12 here? Yep that's active.

Just try subbing different (e.g. wider) ranging audio pots, and different cap values.

[Regis]

I got this mod from the old Ampage.

It works great, but instead of using a 1 meg pot use one much smaller, around 35-50k. I need to fix the page to reflect that.

Regis

[Valvehead]

What happens to the Presence control then, when adding a "depth" into say a Marshall 800 ? Still would function normal ?

[chocopower]

Originally Posted by Valvehead

Where can i look at a schematic or diagram of some different add-on mods, known as "Depth control" or "resonance" ? I remember one had a 100k pot and a .02 cap ? something like that ?

I did it last night.... In my amp (Pro Reverb clon) the .02 cap make just a little effect, but a good effect.
Instead treble distorsion, now i have a bass-crunchier distorsion.

I´m gonna try a .0047uf cap.... (Regis´s web information)

[The Radium King]

your nfb loop is used, to simplify, to keep harmonic distortion out of the power amp. it consists of a feedback resistor and a ground resistor. a cap across the ground resistor will bypass high frequencies, so that you get some high freqency harmonic distortion out of the power amp. this is presence. do the same thing with a cap across the feedback resistor and you bypass bass frequencies and get resonance. change the size of the feedback resistor and you change the amount of presence/resonance; this is depth. you can use potentiometers to control the cutoff frequencies of the presence and resonance effects; these are the presence and resonance controls you typically find on amps. using a potentiometer for resonance control will, given it's location across the feedback resistor, also affect depth, hence the 'resonance/depth' control. so, to answer your question, this control will affect your presence by increasing/lessening its effect. note also that resonance will let the lows out and can cause your speakers to flap around, especially in an open-backed cabinet.

[chocopower]

I had put a 100k pot in my Guyatone GA1050 (like a 45 Watts Twin Reverb) and diferent cap values swichtables with this:

http://electan.com/catalog/product_i...oducts_id=1383

I tried Regis recomedation (.0047uf) but it make just a little effect. In MY AMP work betther caps from .022uf to .1uf

Live one of the swicht´s tip empty for NFB pure cut!!!

It work great!!!

[chunkitup]

I cant tell the values for VR8, C6, C62, C30. If someone can fill in the blanks for me, I would like to try it out. Also, I tried a .0047 across my feedback resistor, similiar to the Meza MKII and I got a nasty oscillation. Why would that be?