Question concerning the reading of Peavey schematics

[Luke G]

Hello all,

I have a small collection of '70's vintage Peaveys that I enjoy: Artist 240, Artist VT, Deuce 240, Mace 320 Head, and Mace VT. I have acquired most of the schematics from the kind folks over in the tech department (thanks, guys). Anyway, I've been studying them trying to figure out signal path, etc. Not for any repair or modification purposes, just to try to understand how these things work.

Anyway, I'm being relatively successful except for one thing (well, more than one, but one I'm asking about today!): The power amp schematics for the Artist and Deuce (same power amp) have a couple circles in the lower left that are just hanging there. They are connected to the base leg of the phase inverter transistors via a 25/25 capacitor. Can anyone tell me what those connect to, or what that symbol means?

Thanks for the help!

[danman7677]

I was checking the schematic for my Classic VT 212 which i believe is similar. If your referring to a small empty circle at a 25/25 capacitor, on my schematic it is the input jack labelled "power amp input". It is the effects loop return jack back into the power amp. You mentioned two on your drawing, but mine only shows one. Mine also shows a 4.7k resistor (ir13) and a 1k resistor (ir14) to ground just before that capacitor. Hope this helps out!

[Luke G]

Thanks for the reply...I do have two of those small circles, not just one...I have multiple schematics and they appear on all...some are for VT amps, which have an effects loop, but some are for earlier models that don't...I'll have to look more carefully and see how they compare!

Each line coming off those circles branches quite a bit, but they all lead to three places: the base of the phase inverter transistors, the +24V feed labeled "from pre-amp," and also the +300V feed from the power supply that heads to the collector of the same transistors.

I have a feeling this is one of those things that's totally obvious to someone who really knows what he's looking at!

[danman7677]

Im sure that Enzo will check in later this evening and he should have an answer for you.

[Enzo]

On the ARtist power amp, I see a small circle at the cap going to the PI transistor base. But I see arrows for the +300 and From Preamp not circles. Not that it matters much. Those mean a connection to somewhere else. They can't run wire lines off the page. Look on the preamp page lower right, arrow says To Power Amp. And on preamp page lower left, see BIAS WINDING making a small DC supply forming the +39 and +24v supplies. That +24v runs the preamp, and it also goes to the power amp page for use in the PI. See on the power amp page by the transformer bias winding, the violet wire has an arrow that says To Preamp.

So those things all indicate a connection to another page. Or at the very least to another part of the page. They may have several things connected to one point, and rather than draw lines all over the page to hook them together, they just use an arrow or othe symbol to say that it connects there. ANy points in the schematic that have an arrow that says +24v are all connected togther. And so on.

[Luke G]

Thanks again for the added input...

I figured those empty circles connected somewhere, like the arrows do. I have been able to account for all the arrows, and can see how everything connects--except for those pesky circles coming off the PI transistors! I'll keep studying, and hopefully get it figured out!

[Enzo]

I only see the two circles lower left. The one with the cap is the input to the power amp. That is the inoput to the differential transistor stage which is your phase inverter. The one below it is just ground.

That is connected to the output from the preamp on the other page, where it leaves the master volume. On the preamp page it was drawn with an arrow, but on the power amp page it was drawn as a circle. Pretend that circle is an arrow. The two pages were drawn at different times.


There really is no deep meaning to the circles, they just represent the input to the stage, in this case the PI. It is generally apparent from the context where that signal comes from. In the case of a guitar amp here, it has to be from the preamp.

[Enzo]

You wrote about extra arrows. ANy arrow that says +24 goes to the same place as any other. There is not some one to one correspondence. If +24v went to ten places, they would not draw lines to all ten places and gather them together at one arrow, they would draw ten arrows.

On the Artist there are two +24 arrows in the preamp circuit, plus a third over on the power amp page. All three of those connect to the +24v arrow in the lower left corner of the preamp page where the +24v power supply is made. All +24v arrows are connected together, whether two of them or twenty of them.