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Mesa/Boogie, hiss versus tone?

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3/18/2000 8:52 AM

Mesa/Boogie, hiss versus tone?

Hi

In one of my Formula preamp's Lead channels there's
a .001 uF disc-cap which comes from the grid of one if
the tubes and runs directly to ground (don't have a
schematic of the Formula).
I know this is done to reduce hiss somewhat, but what
i'd like to hear opinions about is,what effect does this
have for the tone of the amp (dynamics maybe?)
Since the Formula is a recording amp they could have
chosen to sacrifice some tone for lesser noise.
Should i get rid of these caps,or would it be neccesary
to keep one in there?
There's also one placed in the lead channel of the DC-2
just before V2A (I do have a schematic of this one).
As far as i know most amps don't have this or placed!
Let me know what you guy's think.

Andy

3/18/2000 4:53 PM
Ken Gilbert	boogies are high gain, small physical size amps. if you take that cap off, you will indeed increase the treble response, but you ALSO might introduce some oscillations. if you don't have a scope they can be hard to identify. kg

3/18/2000 4:55 PM

Andy, a .001uF cap is not there to kill hiss. Is there to kill top end and upper midrange which otherwise would take your head off.

I would say a 1-space Boogie preamp is NOT the place to experiment with taking caps out. The Boogie midrange sound is a result of there being caps to ground all over the place to smooth out the distortion sound, period. So if you liek the Boogie tone signature, I would leave that Formula alone...

Gil

3/18/2000 8:10 PM
Andy	Hi Gil You're probably right the main printboard of the Formula looks very fragile and it's even difficult to see where certain leads are going. Not to mention moding it there somewhere. Just wanted to see what you guy's would say about this. On the other hand the tubeboard seems like the savest way for mods (if you want to!) Thanks. Andy

3/18/2000 9:48 PM

Andy:

On the other hand the tubeboard seems like the safest way for mods...

I always figured that with practically any PCB amp it should be possible to replace the cathode resistors and caps with different values because you can always find pin #3 or #8, take the existing components out of the circuit (remove a jumper- not bad/cut a trace- ouch!) and run a new Rk and Ck (possibly with a switch to select different values) to an *appropriate* ground point. But there certainly are exceptions to that, with everything but the kitchen sink hooked up to the cathode circuit...

And if the plate resistors are mounted on the tube board they should be fairly easy to identify, too. Once you get further away from the tube sockets you need to follow the traces very meticulously and hope for the best! (And if you find a double-sided PCB I suggest that you don't even mess with it- other than maybe cutting out a resistor and soldering a new one to the old leads.)

Steve Ahola

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