Tube Amps / Music Electronics
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|7/26/1999 8:12 AM|
||Peavey 5150 schematics redrawn|
A lot of AMPAGERS had been requesting the schematics for the EVH 5150 amp and when I finally received them I found that they were extremely hard to follow since they are drawn for troubleshooting the printed circuit boards. So using the cut'n'paste features of my paint program I redrew the schematics to follow the audio signal path to get a better idea of what is going on.
There are certainly a lot of neat tricks in that design! Like the second stage Ck switch (actually a relay) which reduces the signal going to the third stage with a 220k resistor to ground when you kick in the added 22uF Ck cap (there is a 1uF/50V NP cap always in the V1B cathode circuit). But that is only one of the simpler tricks (take a look at the circuitry around the tone stack and the pre-gain pots...)
The redrawn schematics:
The original Peavey schematics:
P.S. Maybe someone can explain the "Clamp" circuitry using a triggered FET on the signal going to V3B...
|7/26/1999 8:47 AM|
"Maybe someone can explain the "Clamp" circuitry using a triggered FET on the signal going to V3B..."
Perhaps it mutes the output when you switch between channels as it uses a triac with a diferentiator to trigger it. This is only a guess....
|7/26/1999 11:46 AM|
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.
|7/27/1999 1:43 AM|
Thanks for your analysis of the circuit! (Anybody else have something to add?)
"Interesting and kinda strange" seems to sum it up nicely. As for the Clean "channel" running through all 6 gain stages, until I actually traced out all of the jumpers I had just assumed that they were bypassing several of the stages in the Clean mode (as Peavey does in the Classic 30 and 50). But the Clean channel also has something like a "Crunch" mode, too, doesn't it (ref# S1)? Maybe you can post what you remember of the switch and relay options... Also, I assume that VR8 would be the Resonance control- is that correct?
P.S. The "tone stack driver" you mentioned- is that V3B? That stage is after the tone stack but right before the effects loop so I thought it has something to do with that. And the "33k resistor to ground" right before the tone stack: if you think that is weird, Peavey uses a 10kA Post-gain pot on their Classic 30 and 50 amps... That is like a dead short to ground- with the Post pot set to 12! The amp design seems to be one part inspired greatness and two parts Peavey weirdness.
|7/27/1999 7:01 AM|
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.
|7/27/1999 7:52 AM|
"and six stages it the clean channel is a full waste of tubes."
The 'clean' channel is not designed to be clean. That is why it is called Rythm. In fact, it is not very easy to get a real clean sound out of it and it can overdrive more than most OD channels on the market!
Talking about the abundance of gain stages and voltage dividers: as we all know, with a soft clipping occuring on several successive stages it is possible to achieve a higly saturated sound without loosing clarity (less intermodulation occuring during clipping, bass stays tight).
Just play one and you'll see it all make sense. This amp has got quite an unusual tone.
|7/27/1999 11:43 AM|
Please be aware that
you can modify this amp by removing
the two trailing gain stages. Then
you have a circuit close to the
Soldano SLO100. One of the triodes may be
used as cathode follower
It can be heard on recent Deep Purple
releases with Steve Morse. I can't
complain on the distorted tone, but
I'm shure I would complain on hiss.
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