Builders & “modders” Question – Amp(s) vrs the Variac … ?

[R.D.]

O.K., guys let me say right up front, I’m an Axe-Fx user …. That said …, I was very intrigued by a comments made by a few guys after Pete Thorn demo’ed his new Suhr SL-68 a few weeks ago !

John’s “special” switch evidently simulates a Variac @ approx 90v - by dropping the B+ and raising the bias on the tubes ….

Now, I’m not fishing for John’s trade secrets !

But, I am wondering if the same thing can be approximated in the Axe-Fx by manipulating the Advanced & Amp Geek parameters … ?

So …, if you put a REAL Variac on an amp ( and lower the voltage ).

- the B+ drops
- you need to raise the tube bias to compensate

…. what else happens ?

- does the output impedance of the power amp change ( up or down ) ?
- does the amount of negative feedback in the power amp change ( up or down ) ?
- does the power amps interaction with the transformer change ( up or down ) ?
- does the transformer’s interaction with the speaker impedance change ?
- does the lower voltage affect the output frequencies ( low or high ) of the output transformer ?

In case you don’t know the Axe-Fx, all of these questions are driven by the parameters Cliff has exposed to the user for fine tuning the Amp sim(s) ….

THANKS for reading ….

 

[jerrydyer]

there is a guy who has some specs posted, i think its tonelizard or tone lounge. he posted actual readings not just opinion if you can find that youll have your answers but personally, if your going thru all that trouble with you axe, then maybe your actually an amp guy.

It makes me think of the guys who buy a 5150 but want it to be more marshall like or visa versa. "how do I mod my Soldano SLO to be more like a ......................"(add amp name here)

A simulated variac sound on the AXE would be a 2204 2203 type gain structure with maybe a little compression with a quick release so you can hear the squish but then it comes back quick enough to not be able to really tell your using a comp.

 

[R.D.]

Jerry …,

THANKS for the heads-up ! Was that hear on Rig-Talk ? Or another forum ?

I did a quick search for both members and came up empty ….

And BTW – I’ll give you no argument …, I am an Amp guy !

I used to own a number of Amps, the highlights were probably a really nice ’66 Bassman, one of the first Boogie Mk IIC’s that Randall produced ..., a Bray modded 1987x and John Suhr’s OD-100SEPlus …, plus a bunch of others that were much more un-remarkable !

But unfortunately, real life has intruded …. I’m not gigging anymore ( just recording ) and while I tried the Pete Thorn ISO-Cab method, I didn’t have near that level of success …. Plus my 4-year old daughter wouldn’t come into my studio any more when I had the ISO’ed Amp fired up ….

So, hence I went the Axe route …. I’m able to re-produce 95% of the tones I’m hearing in my head.

But like a lot of others, I’m STILL CHASING the last 5% !

Thanks for your advice(s) !

 

[jerrydyer]

most of those lame question were on HCAF

Like how do I make my AXE Ultra sound like a tweed champ.

 

[moltenmetalburn]

if your going thru all that trouble with you axe, then maybe your actually an amp guy

Not sure what your getting at here, the tweaking is the same whether in the axe or the amp. One just takes second to mod the other hours.





Here the link for tone lizard.

http://www.tone-lizard.com/Ultimate_JCM800.htm

 

[R.D.]

molten …,

First of all THANKS for the link, I thought jerry was giving me the name of a forum member ! Oops ….

And BTW – I took his comment to mean if you’re going to all this trouble in the virtual world of the Axe-Fx, wouldn’t it be easier to buy a tube amp instead …, for whatever that’s worth ….

Now I checked out the Tone Lounge site and it’s not exactly what I was expecting …. The author’s position seems to be DON’T use a Variac …, do this instead ….

And while I’m sure that argument has merit ..., it’s not what I was hoping for ….

It does confirm that a Variac @ 90v would lower the B+ and the Bias ( which then has to be manually raised to compensate ). O.K., I got that ….

Next, the Variac also reduces the “heater voltage” ( I don’t think this is an accessible parameter in the Axe ) ….

Then he starts talking about ‘why’ it’s such a bad idea to do it ( capacitor memory, proper filament voltages, etc; etc; ). I’m sure that this is all EXTREMELY important to a REAL tube amp, but not germaine to my experiments in the Axe-Fx …. I don’t have any TUBES that I need to be concerned about prolonging the life of ….

Finally, from his tone, I don't think he 'buys' into the whole .... "Eddie used a Variac" to get his tone either.

He seems to go into a lot of depth of things to do INSTEAD of using a Variac ….

It’s all interesting reading, kinda makes me wish I had a JCM 800 to mod. Or maybe knew about this site before I sent my 1987x out to Dave Bray ? But I think I’m going to struggle to put any of it into practice in the Axe-Fx ….

THANKS anyway !