Monkeymatic Lassen (Supro 24)

[sluckey]

In your description I interpreted it as a switch between channels and not to blend them, that makes sense then.

This is what I said in the description on my website... "I used a single input jack with a three position toggle switch to select either channel or both channels."

And this is the comment on my schematic... "Input circuit modified to allow either or both channels to be selected."

[xtian]

Question: Let's say you've built according to original, with two jacks and two volume controls. You plug into input #1 and turn Volume1 up, but keep Volume2 at zero. Now, you plug in a jumper cable between channels, but do not adjust the volume controls. Is there a change in tone?

In my experience with this build, and with 5e3 Deluxe, and Marshall 4-input "plexis", there is no difference in tone just by plugging in a jumper cable. That's why, in my custom builds, I always internally jumper the channels permanently, and simply rely on the two volume controls to mix the channels.

[sluckey]

Question: Let's say you've built according to original, with two jacks and two volume controls. You plug into input #1 and turn Volume1 up, but keep Volume2 at zero. Now, you plug in a jumper cable between channels, but do not adjust the volume controls. Is there a change in tone?

That depends. Notice the high inputs go through a .005 cap. Suppose you're plugged into a high jack and you jumper the low jack of that channel into the high jack of the other channel. Now you effectively have a treble bleed network that should have an audible effect on the tone.

I just didn't like the way the original jacks were wired (quite different from a Fender or Marshall hi/lo jack input). That was a big factor in me changing to a single jack and switch. I'm sure my change affected the Jimmy voodoo!

[Mike-t]

Question: Let's say you've built according to original, with two jacks and two volume controls. You plug into input #1 and turn Volume1 up, but keep Volume2 at zero. Now, you plug in a jumper cable between channels, but do not adjust the volume controls. Is there a change in tone?

In my experience with this build, and with 5e3 Deluxe, and Marshall 4-input "plexis", there is no difference in tone just by plugging in a jumper cable. That's why, in my custom builds, I always internally jumper the channels permanently, and simply rely on the two volume controls to mix the channels.

I have the National version of this amp and there definitely is a difference in tone when you jumper the channels and it can be adjusted by tweaking the knobs on either channel. The best sound to me seems to be when you're plugged into the bass input and jumper the treble input of 1 to the treble input of 2.

[xtian]

This weekend I played Friday and Saturday nights. Friday, took my just-built 100w ODS. It was good, though I felt the need to keep pushing the SM57 around, trying to balance the highs with the lows. Then on Saturday, having moved entirely too much gear around, I abandoned the heavy amp and brought my Lassen #2 (documented above in this thread) to the local bar to play four sets. Man, the Lassen was awesome. Since we're mic'd up, I don't have to be loud, and this 10 watt amp with Jensen Falcon speaker sounded great. It's my new best friend.

[xtian]

Well, here I go, with sn #3. In a continuing push for lowest parts count and least expensive iron, I'm using Fender Blues Jr PT and OT from cedist.com, and EL84s instead of 6973s. Also using a solid state recto instead of tube. Component cost will be about as low as it gets for a push-pull amp! It will be very interesting to see how this one compares to #2 (see above)--I have been playing #2 live, and it's a capable little amp when mic'd!
 
[layout updated 1/21/2020]
 

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[Synchu]

Looks great and simple and inspirational!
I’d say - Don’t bother with a board. Do it Valco style - everything soldered to tubes’ sockets

Now do I need a sixteenth (that’s unverified guess) amp?

Niki

[Guy77]

Very cool build idea Aaron! I remember hearing a Supro 24 cranked at a local guitar store. I guy brought it in so he could decide what telecaster to buy so he played several teles through his Supro 24 ( an original amp I think from the 60's).
He was playing Zeppelin songs and nailing Page's tone every time!

Cheers

Guy

[xtian]

Progress. First time using this IEC power inlet with integrated 5x20mm fuse holder. I like it.

 

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[xtian]

All done, and sounding good. Showing 15 watts clean with 315v plates. I thought there was a little too much hum when turned up all the way, but then, the filtering node for the four preamp stages is only 10uF. So I split two stages into their own node with another 10uF, using a 15K dropping resistor. V1a plate voltage dropped only 4% (from 100 to 96v), and the hum dropped more than half, making it quite acceptable. I have updated the layout image in my post of Jan 19, above.

I have both Lassen #2 and #3 in 10" combos with the same speaker, Jensen Jet Falcon. I will do a little A/B testing tomorrow at volume to see if the changes make much of a difference. Changes in #3: Much smaller iron, SS recto, EL84s in power section.
 

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[xtian]

Well, I put the A/B switch in front of Lassen #2 and #3. Aside from the fact that one Falcon speaker is brighter (brand new) than the other (has 20-30 hours on it), I can't tell much difference between the two amps. Simpler, cheaper build WINS.

[statorvane]

Looks very good. Did you roll your own chassis? The lower parts count - I'm betting you could probably shrink wrap that into say a Fender Frontman cabinet or similar SS practice amp.

[xtian]

Looks very good. Did you roll your own chassis? The lower parts count - I'm betting you could probably shrink wrap that into say a Fender Frontman cabinet or similar SS practice amp.

Yes, made my own chassis from raw 0.063" aluminum. And this one goes in a Peavey Back Stage 10" combo cabinet. More photos when the face plate arrives.

[Colossal]

Looks great, man! Another cool design. What 10" speaker will you be using?

[xtian]

Looks great, man! Another cool design. What 10" speaker will you be using?

I'm using Jensen Jet Falcon 10" in these builds. The slightly mid-forward character meets the Tweedy nature of these amps nicely.