vc508 noodlings



Well, posting about the VC508 is either beating a dead
horse or continuing the conversation about the group's
amp mascot!  

I had the chasis pivoted open in the workshop today
(aka my livingroom). I was trading out various preamp
tubes and, probably because I'm new at this
amplification thing, I couldn't hear much difference. 
Now, I was only trading out lower gain NOS tubes (and
1 new JJ dw7).  In hindsight, I wish I had plugged in
the GT ax7 that came with it -- that difference may
have been gross enough for even me to detect.  Also,
by the time I wait for the tube to cool, put in the
new one, and let it warm up a little, my brain doesn't
remember what it just heard.

In common with all the tubes seems to be:  there is a
small range on the gain knob (with volume knob high)
from being audible above the natural sound of my
harmonica, to sounding artificially distorted (to my
humble ears), to feeding back.  Which isn't to say it
didn't sound good at that point right before it gets
"artificial," but I was wondering about extending the
range a bit that still worked for my ears.  

So, I tried a couple of pedals on the way in.  (BTW,
I'm using a stock, recent issue CAD jt-30 with volume
control.)  A friend lent me his BOSS EQ pedal.  This
worked very nicely.  I could run the 508 at that sweet
spot and then step on the EQ which had the trebles cut
and the level raised -- the raised level added some
distortion, but the treble cut decreased that sound
I'm calling "artificial."  -- I gather from other
posts that the artificial sound may be the solid state
portion of the gain stage.  I also ran the mic through
a TubeWorks BlueTube (12ax7) which also has 3 band EQ
- -- that pedal did "warm up" the distortion, allowing
the 508's gain to be turned a up a bit more and still
sound good (but then disengaging the pedal was too
trebley and close too feedback). In both cases, it
worked well, but still there was an "artificiality" if
the EQ "level" was too high or the 508 "gain" was to
high, no problem.

The topper:  I'm getting a new speaker for my Pro Jr.,
so I decided to pull the chasis.  Then I thought I
would run the 508 into the 10 inch Pro Jr. speaker. 
Wow!!  It sounded great -- less artificial (trebley?),
louder, fuller  Made me realize that a big part of
what I had been dealing with was the 508's 8 inch
speaker!  Even my newbie ears could hear the
difference.  I'm thinking of getting a "speaker out"
on the 508 to make this kind of thing easy (including
then running it through a matchbox to a PA).

One more:  I used the 508's line out into the
disembodied Pro. Jr chasis (and its speaker).  It also
sounded good.  Perhaps the felt deficiency in using
the 508's line out (gain stage only, not power stage)
doesn't matter as much when you are running it through
a tube amp vs. a PA. 

I never would be trying all this stuff if not for time
spent lurking on harp-l.  Thanks. It was fun and I
feel more "in touch" with my gear.  Just don't send me
a soldering gun!

I know this stuff is extremely elementary to those of
you who routinely post about this kind of thing, but
maybe it will be useful to other newbies/lurkers who
picked up a 508 or are thinking about it. --john k

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