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Messages - phatt

#2371
Amplifier Discussion / Re: Peavey Bandit 75 schematic?
January 08, 2009, 05:02:23 AM
Hi JV,
I just simulated some of the Bandits circuit for a friend and the results where as sad as the tone/sound they produce.
You only get about 6/10 Db of boost/cut anywhere in the preamp circuit.  ??? hum?  No wonder my friend is not happy with his Bandit.
There are obviously many models of this rig but I get the impression they are all much the same.
You need at least 20 Db of cut at around 300/500Hz to get a worthwhile tone that resembles a guitar tone.

I built a very simple "Stand Alone Tone Stack" which improves the Amp dramatically, if your into building your own gear I can post it up here. [battery powered if you so wish]

I tend to try and work  "Outside" of Amp circuits as much as possible as modding some of these circuits can end you up in more trouble than the Amp is worth.

Cheers Phil.
#2372
Schematics and Layouts / Re: Peavey's steel amps
December 23, 2008, 07:55:34 AM
Hi again Teemu,
                       Have read the above links, some of which is a bit over my head but yes I do understand the basic principal.
                       
OK here is what I think keeps getting missed with these things.
Most if not all of these Compressor/Limiter circuits work on the basis of turning down the gain at the input "After" the signal has already passed through the Amplifier circuit.

To my mind this is very different to how a power tube stage works when it is at or near full power. "That is my main point."

So far for me at least It has proven to be rather futile trying to get SState power stages to compress in the same way that tube power stages do.
With regard to the "Clean sounds",
The only basic diff between SState powerstage and Tube powerstage  is some bandwidth limiting/colouring [partly valves and AC coupling, partly transformer] 
BUT as they get towards full power the Tube output section develops the magic mojo.
I think it is that part that I'm wishing to recreate/emulate.
[As I'm sure you know, SState power stages just keep on going up untill they run into the rail voltage, sonically not much changes.]

I'm the first to admit that with some modern music I don't know if you even need power tube compression effect as there is so much preamp crunch/fuzz or just plain noise that I doubt if one could hear the difference between tube or SS.
Quite frankly a lot of modern tube amps ALSO have so much preamp gain stages that it becomes almost impossible to attain that magic sweet point of the output tubes compressing and it's just fuzz to my ears.

Vox Valtronic sounded like a good idea until I realised that the gain curve of a triode is vastly different than a pentode. I think that one will ba a passing fad,, but then some rave about it.
Anyway that's my 2 cents worth.   Cheers, Phil Nambour Australia.
#2373
Amplifier Discussion / Re: Reduce power Randall RG80?
December 23, 2008, 03:51:00 AM
Quote from: Fretts on December 22, 2008, 08:18:25 PM
there is feedback off the speaker that is used to modify the impedance/damping of the power amp.  Personally, I can hear it, so I want to get that same effect with less earsplitting volume.

I lack basic familiarity with SS power amp topologies.  This unit uses a pair of 2n6254 power Q's, cascaded apparently, per rail.  It has an elaborate biasing scheme I don't understand very well, but it does not look like there is any quick n dirty way to operate the existing amp to produce less power.  Technically, is the only real way to reduce the rail voltage?  Can I artificially limit the available current by modding the power supply and introducing intentional current limiting there?
Hi Fretts,
              If I follow you correctly, then That Feedback Resistor is likely a very small value [ie less than 1 ohm] Large Wattage wire wound.  You can "Increase" the value of that R and it will turn down the Wattage somewhat.
If it is say .1R, or .22R go up to One ohm and try it. [Make sure you understand the circuit first!!]
The idea is called a "Defined impeadence" setup ,,trying to emulate a non zero imp to sound more like valves,, Yeah works kind of OK but IMO it does not do that much.
Depending on the circuit and more Ïmportantly the speaker used,, turning down the voltage rails won't work well as some poweramp circuits are designed to work at specified voltage. you could stuff up the Amp.

Note also for "daffe"
I personally would take a long look at speakers as use of Big name Drivers with SState Amps is kinda Daffed [no pun intended] if you really understand whats goin on. They are mostly designed for tube Amps remember and I'm sorry but SState Amps are vastly different in the way they work with speakers.
Tube Amps of old had limited bandwidth especially under full output and hence NEED the extra peak at say 2/3khZ but with SState it's a whole different story. 90% of SState Power sections have a dead flat freq response at any volume level,  so you really need to be cutting not boosting those freq otherwise they get painfully harsh at high SPL.
I just fixed the harshness of a Tradsman 60 [tech21] by changing the speaker from the over sensitive "Special design wank" to a much lower SPL driver. [note also lots cheaper]
Now the Amps tone makes sense, It was stupidly harsh and the guy wanted to get rid of it but I think I may have changed his mind :)
Cheers,  Phil Nambour Australia.



#2374
Amplifier Discussion / Re: Testing Reverb Tanks
December 03, 2008, 05:38:24 PM
Quote from: gbono on December 02, 2008, 03:09:44 PM


Are these good units? Is there a way to bench test these tanks with an signal generator/scope?

THX

That won't tell much what they will sound like tone wise,, if that is what you wish to know?  My option is to build a driver and pu and play with the 3 tanks to see which one works for you.

Likely the tanks will all sound ok,,, be aware it's more to do with the way they are driven that makes them sound good or bad not the fault of the tank at all.

Check the schemo I just posted if your looking for clues on how to go about it.
under "Mosfet Spring Reverb Driver by josh 777.

Have fun with it. Phil, Nambour Australia.
#2375
Schematics and Layouts / Re: Peavey's steel amps
December 02, 2008, 10:07:09 AM
Thankyou Teemu,
                           Alas way past my bed time now so I'll get back when I've done some reading.

I'm interested in the "How" but also looking for comments regarding the colouration [for want of a better word]
Some of these comp circuits seem to come out rather bland and I noticed you mentioned this tonal effect in your book while discussing these things.
catch up soon, Phil.
#2376
Amplifier Discussion / Re: Mosfet Spring Reverb Driver
December 02, 2008, 09:27:38 AM
FWIW,
          I wasted many years [10 in fact] trying to build a decent Rev unit so here is my 2 cents worth.
Build a stand alone unit and be done with it.
Forget current drive you need voltage drive.
[Yes I know all the experts tell us that current drive is best but having built most of the circuits out there,, well they must have missed something.]
Don't  bother with Accutronics circuits [utterly useless]

I doubt that a big drive will kill the transducer unless you pass full bandwidth signal through it.

Rod Elliot [ESP] helped me out a great deal in the end trying to perfect my circuit so search his pages for the reverb drive ideas.

The problem with the booster circuits for opamps is that they need to run off a much higher voltage not the same 15/15 supply.
Rod E will agree with that if you care to ask him.
You really do need a big swing to get it to work as it should.

Anyway to save my babbling on about it,,
here is my "MaxiVerb Stand alone Reverb unit".

No doubt the experts will see flaws in this but still as is this is a killer tank slapping Reverb that will put a lot of other more expensive gear to shame.   [very little noise /hum].
Have fun with it,,, Phil, Nambour Aust.
#2377
Schematics and Layouts / Re: Peavey's steel amps
December 02, 2008, 07:47:03 AM
Hi,
I'm new here but can I ask what U6 and associated components wrapped around the bases of the diff input do?  Yep I see it's a compressor but is U6 a Transconductance unit or similar opamp?

In my limited experience a lot of the comp stuff tends to lack something.
cheers, Phil. [Nambour Australia]
#2378
Quote from: Jack1962 on December 02, 2008, 02:56:13 AM
lmao-check out a Peavey Musician 400 Series B , it comes reall close to tube sound(real close).

                                   Rock On

Ok,, is this similar or same as to the Nashville 400 amp?
I noticed the schematic of that under "Steel amps post".

That Nash 400 is not that much different than the Bandit models,,,
[a higher wattage of course.]
At a glance nothing stands out to me but I may have missed something as I'm not the expert that others are.

A Schematic would be good though?

If it's anything like the bandits with all that "Defined output impeadence" stuff then they where nothing special? That "Saturation" thing was a bit of a joke.

I have a friend who has two of those 112 Bandits and he would gladly swap his two bandits for my ReAmp setup anyday  ;)

Cheers, Phil Nambour Aust.

#2379

Re the subject question,

I have had great success with ""SState pre, into 10watt tube PP power stage driving a resistive load and ReAmplified via a SState power section"". [I call it the "ReAmp system" for short.]
I got the basic idea from the Guytron GT100 and thought it could work just as well with SState output.

As I had exhausted most of the other ways to attain good sound with all SState and this idea was modular and the Tube section is not expensive to make.
I would love to see/hear an all SState amp that does the tricks but until then my hybrid works fine.

But I,m always on the lookout for new ideas.
I did try the Valtronices gear but it was a sad excuse for guitar tone ,, [IMHO]
even some of my own SState Amp build attempts where better than those.

Anyway this is my first post so thankyou Teemu for the book, , a good read.

Cheers all, Phil Nambour Australia.