Presence Mods?

[kinder5150]

Are there any mods that can be done to the presence knob to give me more headroom, high end clarity? I have the knob maxed and still want more clarity. I have new preamp tubes installed. This amp(RM50LB)has always seemed dark. Thanks!!

 

[eyeball987]

I had 2 RM50's and 2 RM100's. Both of the 50's seemed much darker than the 100's. If I was using only the poweramp (say with a modeler) I liked the 50 better. With the modules, the 100's had more clarity and bite.

With that being said, what speakers are you using?

 

[kinder5150]

The combo has the Super V Eminence. I also run a Nuno NB King cab off of it with Celetion Greenbacks in it. Ohms set at 4. No matter what preamp tubes I put in it, still not as bright as I want it. Thanks.

 

[eyeball987]

I am going to say power tube issue without having any additional information. I have the treble on almost all of my modules at 10:00 or under, mids up over 2:00, and the amps pres just under noon.

Power tubes are EL34's and Scumback M75 speakers (high powered, large dust cap so darker than the regular model). I have mostly Marshally modules which tend to be bright anyway but you should not be having any brightness problems.

 

[JKD]

My experience with the RM50 combo is that is sounded brighter than into a regular closed back 4x12..two reasons, there's some sound dispersion out the back and without the closed back, less low end.

I'm surprised it's that dark.

 

[Jaded Faith]

There was a revision to the Presence/Density board in the amps at one point. I combed through my emails and searched here, but I had no luck digging up the specific details for you.

There were older ones that the knobs had very limited effect up until a rather high setting and then it thinned out the sound a good bit. I had a customer with several of my mods that had lots of problems that didn't exist with the mods here in my rig. We tried them in his buddy's amp and it was exactly like they should be. Working with Randall we hunted down that issue and a new board was installed in his amp. Problem solved.

Just a heads up before you spend a load of money on speakers or tubes. :wink:

 

[eyeball987]

There was a revision to the Presence/Density board in the amps at one point. I combed through my emails and searched here, but I had no luck digging up the specific details for you.

There were older ones that the knobs had very limited effect up until a rather high setting and then it thinned out the sound a good bit. I had a customer with several of my mods that had lots of problems that didn't exist with the mods here in my rig. We tried them in his buddy's amp and it was exactly like they should be. Working with Randall we hunted down that issue and a new board was installed in his amp. Problem solved.

Just a heads up before you spend a load of money on speakers or tubes. :wink:

That could be the reason why the two RM50 combo's I had sounded a little dull and muddy compared to the RM100's I had. Good info to know.

 

[jitterybit]

'Think you just found another gig Rob.

 

[Kapo_Polenton]

Guys , I'm reviving this thread. I just installed new preamp tubes and KT77's (which aren't exactly dark) and my amp is the same way.. only has effect at about 3 pm (6 being max).. I must have one of the earlier lynchbox amps because there is a serious lack of clarity with my amp too. I have greenies and superV's together in a 4 x 12. My JCM800 has the presence at about noon - 1 pm. Clearly it isn't the cab... are there any mods or parts that can be made available to the rest of us for these amps? To my ears, it needs a presence cap or presence board mod. What is the word on these? Mine is a 100 which I run as a 50 with two tubes pulled. I always was dark from the first day I got it. (got it used over a year ago). Any help would be appreciated..

 

[eyeball987]

Guys , I'm reviving this thread. I just installed new preamp tubes and KT77's (which aren't exactly dark) and my amp is the same way.. only has effect at about 3 pm (6 being max).. I must have one of the earlier lynchbox amps because there is a serious lack of clarity with my amp too. I have greenies and superV's together in a 4 x 12. My JCM800 has the presence at about noon - 1 pm. Clearly it isn't the cab... are there any mods or parts that can be made available to the rest of us for these amps? To my ears, it needs a presence cap or presence board mod. What is the word on these? Mine is a 100 which I run as a 50 with two tubes pulled. I always was dark from the first day I got it. (got it used over a year ago). Any help would be appreciated..

Read Jaded Faiths comment above. Maybe contact him also. He has always been helpful to me.

 

[Kapo_Polenton]

Well, shipping this thing back to a non existent company with no customer support is the last thing I want to do... a new board means either a section of a board or a whole new PCB and that could be a disaster.... i 'll pm him thanks..

 

[Kapo_Polenton]

Ok, working with Jaded Faith to hopefully resolve this but also moved this to DIY section as i found some more info that might be helpful and will be cracking my amp open this week to have a look.

 

[bmi]

I just posted this in the Fractal Audio forum.
It will solve your issue with presence.

http://forum.fractalaudio.com/axe-fx-ii-discussion/42204-just-how-good-axe-fx-ii-modeling-2.html

Change c2 with an old silver mica :

 

[Kapo_Polenton]

Interesting.. I read your post on the axe forum. You mentioned you have about 200 of these older caps.. cap type aside, the value to me is what would seem more important. What value did you find in your randall and what value did you replace it with? I also noted that direction of my cabinet was impacting the perceived brightness in my tone so in the end the sweep isn't that bad but it definitely is not usable for me below 2 or 3 pm but I tend to like a bit mroe high end on any amp I play and never have the presence below 1 pm. . How has it improved your situation?

 

[bmi]

You are wrong.
Here, this is the type of cap which is more important.
I can't remember exactly the value but it was the same or almost ie 4700pf.
These caps work perfectly, nothing too much bright or sharp and more you increase the presence more you get clarity and details.
They are perfect with classic modules or modded modules.(by myself)

This is a small mod but very very....very useful.

I can send you one if you want to test it.

 

[Kapo_Polenton]

I'm definitely interested.. I will pm you my address.

How did you find out about this mod or these caps? So you are saying that all you changed was literally one capacitor on the presence board and it made that much of a difference?

 

[bmi]

Yes.
I find it alone. :wink:

 

[bmi]

only has effect at about 3 pm (6 being max)..

I just read your comment again. The first mod gives you clarity but it seems that you want to get a presence which work before 3pm when you turn the knob.
You can improve that by using a reverse log pot.
The presence, in my RM50 head, uses a 25k linear pot. Change it for the same value but reverse log, presence will be effectiv sooner.

Call the "reverse log pot + cap" the bmi presence mod. :wink:

 

[Tbag]

only has effect at about 3 pm (6 being max)..

Call the "reverse log pot + cap" the bmi presence mod. :wink:

lol......

 

[Kapo_Polenton]

Hey, I'll also take clarity! So with the reverse taper , would the presence max out at about the same place? In other words, It won't get any brighter, it will just engage sooner.. I am still perplexed as to why they designed the amp this way but that is just me it seems as there are some people here who apparently play with their presence at noon.