Name:
           ken g
 E-Mail:
 Date/Time:
           7/26/99 11:46 AM
 Subject:
           Re: Peavey 5150 schematics redrawn


    Thanks for the schems, Steve. They are
    interesting, and also kinda strange... Some of the
    design choices PV made are definitely seldom
    seen. Like the tone stack driver... it is made a
    virtual earth inverter stage with a gain of -1,
    since the series input resistor is equal to the
    feedback resistor. Most would have plopped in a
    CF, which would have a gain of <1, but probably
    a slightly lower output impedance.

    What I don't like about the design is the simple
    fact that a) the clean channel's signal goes through
    just as many stages as the distorted channel. This
    is needless, and adds noise.
    b) there's only one tone stack. I can't STAND this
    about amp makers (Soldano's SLO comes
    immediately to mind).
    c) there's a lot of gain added by each stage that
    must be "thrown away" by heavy shunting to
    ground in between stages. To me, this is
    somewhat wasteful--like what is that 33K to
    ground resistor doing there right at the beginning
    of the tone stack? If there was too much gain
    coming off the virtual earth inverter, why not
    make it's gain less than unity? There are plenty of
    examples of this in the schematic.

    Speaking of that section, there looks to be a very
    easy transistion to an active tone control section
    that could be simply plopped in around that V.E.
    inverter.

    That clamp circuit indeed looks like a FET
    controlled mute point, which is CRITICAL once
    you take a look at all the damned relays sprinkled
    around the signal path. It's certainly a
    complicated preamp circuit.

    And what the hell are those 100p grid shunt caps
    doing on the output tubes??? Talk about a tone
    sucker...

    I think the screen resistors could be upped in
    resistance to offer a little better reliability--100R
    is kinda low. Also, those grid leak/bias injection
    resistors seem a bit large at 220K.. there's no
    reason why they couldn't be decreased to 100K
    or so, which would make the outputs happier.
    And a balance/range setup would be preferred
    for biasing.

    I haven't had to work on one of these, but I have
    played out of one for a while, and while it had a
    unique distorted tone, the clean sound was very
    undynamic and uninspiring, and the noise levels
    were rather high in both channels. Other than that,
    as always, Peavey gets you a bang for the buck
    product.

    Again, thanks for the schems, Steve.

    ~KG~ 

Name:
           Santiago
 E-Mail:
           santiago@ate.uniovi.es
 Date/Time:
           7/27/99 7:01 AM
 Subject:
           Re: Peavey 5150 schematics redrawn


    This amp has two channels ("rithm" / "lead"). The rithm channel can be
    either "crunch" or "bright".

    The switching schem is the next:

    K1 and K2 are for the "rithm" / "lead" channels and they are drawn in
    the "rithm" position

    K4 switches between "crunch" and "bright" into the "rithm" channel
    and is drawn in the "crunch" position.

    K3 controls the effects loop.

    VR8 is actually the "resonance" control

    I want to add a comment about the relays. When switching between the
    "lead" and rithm channels V1B grid becomes floating while K2A is
    moving its contacts. I think that this can make a pop and since there are
    many stages after this it would be translated in a BIG POP at the
    output, so here is the need of a clamp circuit. Any comments?

    I havenīt heard the amp myself but in the Harmony - Central database
    there are several reviews about this amp and in the vast majority of
    them the amp fails in the sound subject. In my opinion six stages are
    too many stages even in the lead channel, and six stages it the clean
    channel is a full waste of tubes.