Benson Monarch

[mikeywoll]

My faceplate arrived today, and I had to take out the chassis to install it.

While I was in there... I fixed the signal bleed

Signal was bleeding from the cathode follower of the reverb tube into the plate of the second stage of the pre-amp. I switched the PS order a bit and there is no longer any bleed. I moved the pre-amp tube up a node to join the phase inverter. The reverb tube is now on its own on the 4th node. I kept the filter caps and dropping resistors the same (22uf ->1k -> 47uf -> 4.7k -> 22uf -> 4.7k -> 22uf) after playing around a lot.

I tried the following:
22uf->1k->47uf->10k->22uf->4.7k->22uf - This sounded nice and harmonic but the reverb was noticably quieter and even though the overall feel was great there was less gain when cranked. Pre-amp voltages were about the same as before, PI and cathode follower were low.

22uf->1k->47uf->4.7k->22uf->10k->22uf - this was weirdly both stiff and sterile and lacking reverb. The cathode follower voltages were low and preamp was high. PI was about right.

22uf->1k->47uf->4.7k->22uf->4.7k->22uf - This ended up pretty darn close to the original sound and feel, but with more reverb. This is where I left it. The reverb is not only louder but more pleasant to my ear. There is maybe a little less of the harmonic stuff with the volume low, but there is more gain and punch with it cranked. PI and Reverb tube are right on, voltage wise. The pre-amp is just a few volts higher than before, which I think strikes a great balance between harmonic stuff, feel, and gain.

I didn't try 22uf->1k->47uf->10k->22uf->1k->22uf, which now I wonder if it would have worked? At the time I guessed it would hum.

With the new arrangement, things are still quiet, maybe even a little quieter than before with the reverb cranked. There was definitely not any more hum in any of the 3 variations I tried.

Mike

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[CraigGa]

That's good to know Mike,
I'll file that away for when I start my build.

Craig

[CraigGa]

Ooh I just noticed that your volume goes to 10.5, it's not quite 11 but it'll do

[T Wilcox]

In the pic of the original Monarch gut shot on page 6. The Reverb and preamp share the same node(white wire).
I wonder if that Monarch has volume bleed?

[dorrisant]

Ooh I just noticed that your volume goes to 10.5, it's not quite 11 but it'll do

Do you need one that goes to 11? Take a closer look at my build maybe?!?!

[mikeywoll]

I think I have to walk this back.

There is no signal bleed, but there is a low frequency hum now. I couldn't appreciate it before, but now I'm in a quieter space and it's definitely there. I think, as I've been playing with it set up this way a little longer, I like the feel and tone better with the reverb and pre-amp together. I'm going back and accepting the bleed. Thankfully it's just two little wires to move.

In the pic of the original Monarch gut shot on page 6. The Reverb and preamp share the same node(white wire).
I wonder if that Monarch has volume bleed?

I agree, I think it looks like the pre-amp and reverb share a power supply. Anyone know someone with a monarch reverb?

UPDATE Ahhh, it's like seeing an old friend again. So much better with the original setup. Much more touch sensitive and warm sounding. At least we know 1) it is cross talk in the power supply from the reverb tube to the second stage of the pre-amp 2) We seem to have the best power supply design so far.

Mike

[pullshocks]

In the pic of the original Monarch gut shot on page 6. The Reverb and preamp share the same node(white wire).
I wonder if that Monarch has volume bleed?

In that picture, it looks to me like all 3 12ax7s get their B+ from the white wire that comes out under the tone pot, i.e. from the same node. Which conflicts with what Chris Benson said in his post on page 10 of the thread about the 4 node power supply. I wonder if the amp in the picture is an early version that did not have the 4 node power supply described by Chris. Which in turn makes me wonder if there are other circuit differences.

Whatever the case may be, I'm going to enjoy it as is, bleed through and all.

[CraigGa]

Mike,

I know that the consensus in this thread is that the reverb tank should be *EB but Synchu mentioned that he'd used a *FB to good effect.
This is why I suggested putting 1K in series with the tank to see if the 800 ohm tank is drawing too much current and causing the bleedthrough.

Craig

[mikeywoll]

In the pic of the original Monarch gut shot on page 6. The Reverb and preamp share the same node(white wire).
I wonder if that Monarch has volume bleed?

In that picture, it looks to me like all 3 12ax7s get their B+ from the white wire that comes out under the tone pot, i.e. from the same node. Which conflicts with what Chris Benson said in his post on page 10 of the thread about the 4 node power supply. I wonder if the amp in the picture is an early version that did not have the 4 node power supply described by Chris. Which in turn makes me wonder if there are other circuit differences.

Whatever the case may be, I'm going to enjoy it as is, bleed through and all.

I thought it looked that way as well. All 3 tubes powered via the one white wire. We also have the conversation on page 18/19 with a picture of the head layout power section that has 3 nodes, and is very similar to the schematic Aaron drew... so presumably the PI and pre-amp together.

Looking back at this thread, Chris Benson said "since the production one's don't hum appreciably," in a comment about pi filtering. I think you are right on, there have been changes. In that link I posted with the monarch reverb combo in production, there are clearly 2 power supply wires heading towards the pre-amp. I feel pretty confident (especially after messing with it yesterday) we have the power supply correct. Chris Benson pretty much handed it to us.

Mike,

I know that the consensus in this thread is that the reverb tank should be *EB but Synchu mentioned that he'd used a *FB to good effect.
This is why I suggested putting 1K in series with the tank to see if the 800 ohm tank is drawing too much current and causing the bleedthrough.

Craig

I believe that BobL spoke with someone at Benson and confirmed the correct reverb tank. A couple folks tried the higher Z tank, and I believe have the same issue. It's a small change to try, so I'll probably give it a shot next time I open the amp.

Looking at this another way, the reverb cathode follower is basically a cathodyne phase inverter as we've wired it. Unless there is another power supply node or another change we don't know about, I don't see how there is any way it doesn't bleed over. Either the production monarch reverb plays with the volume off, or we have something wrong with our circuit.

Mike

[mikeywoll]

Am I crazy, or is that a big filter cap hiding near the reverb tube? I don't see the rectifier for the D/C filaments. Maybe that's it there? If not there could be an additional PS node?

EDIT in the picture we have on page 6, there is just the 220k resistor (feeding the grid of the cathode follower) crossing between the two terminal strips there. In this build there is another resistor crossing between. I think this is a dropping resistor for the additional PS node built by that cap on the reverb terminal strip.

Also, the split plate-load does not look like 10K/100K here. Hard to see, but maybe grey, blue, red? 8.7K? Green, blue, red 5.7k? Probably not a significant change?

Source: http://guitaristmarkmarshall.com/anatom ... tory-tour/

benson-wiring-1024x820.jpg

Mike

[CraigGa]

Just to prove that I'm good at something I put the pictures through my Bladerunner device

[mikeywoll]

Just to prove that I'm good at something I put the pictures through my Bladerunner device

Ok, that is just ridiculously cool

[pullshocks]

Just to prove that I'm good at something I put the pictures through my Bladerunner device

I have to confess my ignorance, what is a Bladerunner device?

Thanks, nice to be able to blow the image up...

[mikeywoll]

Just to prove that I'm good at something I put the pictures through my Bladerunner device

I have to confess my ignorance, what is a Bladerunner device?

Thanks, nice to be able to blow the image up...

Thanks to Craig's CSI super computer, I can see a few things and tried a few things....

There is another PS node in the Monarch Reverb. I count 5 nodes... 2 can caps with dropping resistors between the 2 caps there, so 4 nodes assuming the fat, single cap on top of the cans is paralleled with one node (for the screens) and hiding the dropping resistor linking the 2 cans. Based on other builds, I'm guessing the big single cap in the PS is a 20uf-ish cap. The 5th node is on the reverb terminal strip and looks similar to the single cap in the PS (so 20uf-ish)

There has been variation in the split-load plate resistor value. You can tune the amount of gain the second stage of the pre-amp has using this resistor.

Maybe I'm missing it, but I don't see a ground on the reverb pot? Is this part of the issue we have with signal bleed?

I ended up wiring the 5th node in parallel to the 4th node. In other words, the 5th node originates from the node feeding the PI. I used a 4.7k dropping resistor, but I think the one in the picture is 2.2k. This kept the feel and harmonics of the 4 node PS, but improved reverb (more and richer), improved overdrive (more, more compressed and harmonic in a good way), the amp is even quieter, and it drastically reduced the signal bleed with the volume off. I've played a bunch at volume, and to my ear and fingers this is an improvement.

I tried many different variations with the 5th node in series after the 4th (caps from 20uf to 50uf and dropping resistors from 1K to 10K). They all sounded and played well, and some were better with smaller split-load resistor values. I thought the parallel version cleaned up the signal bleed the best, and I liked the reverb and overdrive the best. The change is not drastic (more like a small incremental improvement), and there is still a small amount of signal bleed. The reverb tank does not effect the bleed now, however.

Mike

[CraigGa]

Just to prove that I'm good at something I put the pictures through my Bladerunner device

I have to confess my ignorance, what is a Bladerunner device?

Thanks, nice to be able to blow the image up...

https://youtu.be/D8m_9xNsx9g?t=74

In reality I looked at the web page source code and found the original sized images

Craig