"Presonance" Control Mod

General discussion area for tube amps.

Moderators: pompeiisneaks, Colossal

User avatar
Reeltarded
Posts: 9926
Joined: Sat Feb 14, 2009 4:38 am
Location: GA USA

Re: "Presonance" Control Mod

Post by Reeltarded »

I added a normal master as well. Tones can't hide in there now! Astonishing!

The pot I used it horken up a little at low settings, so I will change asap.
Signatures have a 255 character limit that I could abuse, but I am not Cecil B. DeMille.
User avatar
Reeltarded
Posts: 9926
Joined: Sat Feb 14, 2009 4:38 am
Location: GA USA

Re: "Presonance" Control Mod

Post by Reeltarded »

So what happens when I change the 100k resistor? I am going to put it on a 4 position switch for any tap and none. I previously liked 27k on the 4 ohm.
Signatures have a 255 character limit that I could abuse, but I am not Cecil B. DeMille.
User avatar
martin manning
Posts: 13080
Joined: Sun Jul 06, 2008 12:43 am
Location: 39°06' N 84°30' W

Re: "Presonance" Control Mod

Post by martin manning »

So you have 3 taps, 4, 8, and 16? And you had a 27K FB resistor from the 4 ohm... what were the tail restor and presence cap values? Switching taps is an easy way to change the FB ratio, a factor of 1.4 per click.
User avatar
Reeltarded
Posts: 9926
Joined: Sat Feb 14, 2009 4:38 am
Location: GA USA

Re: "Presonance" Control Mod

Post by Reeltarded »

Was variable 27 to 100k on 4 ohm tap. .1 or .68 presence caps, with 10k tails. I think the 8 ohm tap might work better for me with this control.

Yeah, 3 taps. Need a 4 stop switch for 3 settings and bypass.

Did I mention this thing is fantastic? It is freaking great!
Signatures have a 255 character limit that I could abuse, but I am not Cecil B. DeMille.
User avatar
martin manning
Posts: 13080
Joined: Sun Jul 06, 2008 12:43 am
Location: 39°06' N 84°30' W

Re: "Presonance" Control Mod

Post by martin manning »

Since the FB resistor is involved in the frequency break points I think using the different taps is a good plan for varying the FB ratio. From where you are now you can double it on the 16 ohm, so see if that is enough. If not, I think you'd want to increase the tail (I think it's 4k7 now?) and then change the caps to match that.

Edit: if you're starting from a typical presence circuit as a baseline, I guess it'd be easier to decrease the FB resistor and then reset the caps based on that and the presence cap you had.
User avatar
Reeltarded
Posts: 9926
Joined: Sat Feb 14, 2009 4:38 am
Location: GA USA

Re: "Presonance" Control Mod

Post by Reeltarded »

MASSIVE! The tap selector is a big yes. The amp gets more forward as you go up the taps with the midrange becoming tremendous but still very sweet and useful. There isn't a harsh setting.

In a rhythm amp (marshall) it works wonders with a standard (off the treble) master volume. On a lead amp, it pairs very well with a Jose type master (.022 and 10k off a 1megA between the cathode and tone stack with series 12v zeners tail to tail across outside lugs). The rhythm amp will knock you down with defined depth, and the lead amp sings with that beautiful midrange I can never live without for a minute.

Life long tone search: OVER.

Honey, I'm home!
Signatures have a 255 character limit that I could abuse, but I am not Cecil B. DeMille.
paddy
Posts: 112
Joined: Thu Feb 02, 2006 7:28 pm
Location: Tasmania, Australia

Re: "Presonance" Control Mod

Post by paddy »

Just installed this mod on my 2 x EL84 Liverpool. At first it worked but
produced quite a noticeable difference in volume across the range. I tried a 10k log pot and also tried it with the original 25k linear. After
some experimentation, I found that the original 25k pot worked a treat when changing the cap C11 to .01uF.

Thanks to everyone involved in the development of this mod. It now has
a permanent home in my amp.

cheers
Paddy
loctal
Posts: 82
Joined: Wed Feb 27, 2008 12:33 am
Location: stumptown

Re: "Presonance" Control Mod

Post by loctal »

This mod looks great.


Would anyone mind posting the values for employing this in an Express? Thanks for your help.
User avatar
martin manning
Posts: 13080
Joined: Sun Jul 06, 2008 12:43 am
Location: 39°06' N 84°30' W

Re: "Presonance" Control Mod

Post by martin manning »

Replace the 5k linear presence pot and 0.1u presence cap in the standard Express with a 4k7 resistor to ground. Use a 10k audio taper pot for the presonance control, and a pair of 0.047 or 0.05u caps. I'm interested to hear how it goes!
loctal
Posts: 82
Joined: Wed Feb 27, 2008 12:33 am
Location: stumptown

Re: "Presonance" Control Mod

Post by loctal »

Thanks Martin, This is the second time that you have answered one of my presence circut questions. I am starting an Express with 7B5 pentodes for output tubes. They are the loctal version of 6K6s and have sounded great in a couple of Rockets that I have built.
Tone Lover
Posts: 256
Joined: Tue Apr 27, 2010 4:39 am
Location: Everett Wa.

Re: "Presonance" Control Mod

Post by Tone Lover »

I think I will try this, you answered my question with the 10k pot.
Thanks Bill
Cliff Schecht
Posts: 2629
Joined: Wed Dec 30, 2009 7:32 am
Location: Austin
Contact:

Re: "Presonance" Control Mod

Post by Cliff Schecht »

I'm looking at using this in my upcoming bass amp build. Thing is, I'm not sure what the presence control on a typical bass amp does bandwidth-wise. Am I going to need to modify the frequency response of this control for use on a bass amp?

Also what values is the LTP expecting? Just use the stock values from whatever amp you are shoving this into right?
Cliff Schecht - Circuit P.I.
User avatar
martin manning
Posts: 13080
Joined: Sun Jul 06, 2008 12:43 am
Location: 39°06' N 84°30' W

Re: "Presonance" Control Mod

Post by martin manning »

Hi Cliff, as described this thing is intended to replace an existing FB network with or without a presence control, replicating the HF cut response and adding the ability to go over to the dark side with a LF cut at the CCW end. I haven't looked at enough bass amps to know what they are typically doing in this area, but if it's similar then there would be no reason not to give it a try.
User avatar
roberto
Posts: 1841
Joined: Tue Nov 27, 2007 4:45 pm
Location: Italy

Re: "Presonance" Control Mod

Post by roberto »

I'd prefer to avoid depth controls on the poweramp of a bass amp.
You need a strong control on lows, and you can obtain this by NFB.
If you reduce NFB on those frequencies, so enhance those frequencies, you'll obtain also a less controlled sound on lows.

If this could be acceptable (or maybe needed) for guitar amps, for my tastes it's not a good way to approach bass amplification.
Cliff Schecht
Posts: 2629
Joined: Wed Dec 30, 2009 7:32 am
Location: Austin
Contact:

Re: "Presonance" Control Mod

Post by Cliff Schecht »

Alright thanks guys!

Next we need to have a discussion about damping factor and what one would be looking for in a bass amp. I'll take this to my bass thread so I don't derail this sticky.
Cliff Schecht - Circuit P.I.
Post Reply