Monkeymatic ODS

[xtian]

RJ, you know, it was an unusual pleasure to have a drilled chassis and a layout to follow, instead of starting from scratch. I think this one took about 12 hours, as compared to the typical 30-40.

I took liberties with the grounding of the 5v switching system. The layout goes to great lengths to ground the switching system "properly" (to eliminate ground loop hum, I suppose). But why bother? I figured it would be very unlikely for any hum in the switching system to couple to the signal. So I grounded the system at the most convenient points, omitting miles of extra ground wire shown in the layout. Worked perfectly, and no hum.

[RJ Guitars]

This was loosely based on the Brownote D'Lite but with a bigger sized box that allows a little more room to operate. It sorta became my standard size for ODS chassis'... can you give us a look at the front, top, and rear views? I need to complete my regret that I didn't finish it for myself But I am happy for you!

[xtian]

Photos as requested.

430v on plates, biased at 65%, showing 42 watts clean output with a pair of JJ EL34s.

Think the plate voltage is too high? Might whip up a MOSFET B+ reducer.

[amplifiednation]

There's so much room in that chassis!!!! Looks great man. What kind of coax did you use?

[xtian]

Thanks, Taylor. The co-ax is "RHE MIL TYPE RG174A/U", 2.6mm diameter. I think I got it from Apex Jr. The longest run, from the MV to the preamp out jack, is about 18 inches, and measured 60pF.

[jelle]

Your B+ voltage is fine.

[xtian]

Your B+ voltage is fine.

Whew. That's a relief. I was afraid to taste it.

[jelle]

Just so you know...it tastes like about ehhrm.... 48 batteries. Take my word for it.

[Smokebreak]

Great looking build, Aaron. I could take a nap in that chassis! Your preamp voltages are going to be much more important.
I'm looking forward to some clips!

[xtian]

Preamp voltages are 180 to 210 or so, from first triode on up.

I don't see any target voltages on the schematic or layout. Is there a chart?

[Smokebreak]

Tom posted a chart for his build here : https://tubeamparchive.com/viewtopic.ph ... tage+chart

[xtian]

Thanks. My voltages are within 1% of Tom's. Amazing!

Feeling like I want to brighten the overdrive sound. I was sparing with co-ax cable, and I know in general these amps are not known for sparkle. But I may try a bright cap on the master, as I rarely play loud. Any other suggestions?

Also, I'd like to raise the frequency of the Presence control. Raise or lower value of 1uF cap there?

[xtian]

I tacked in an additional 1uF on the Presence control. Frequency shelf is now higher and I like it, but control is now only affective in the last 40 degrees of sweep of the pot. My fault, I guess--I have a 5K pot in there, instead of the 2K on the schematic.

I also tacked in a 47pF bright cap across the MV. Much better.

Trying to decide if the overdrive circuit is too flubby (too much bass). That "Pre-DO network" (the 10M, 0.05uF, 220K group), maybe reduce the value of that coupling cap to tame the flub?

Advice appreciated.

[jelle]

That is one approach, or you can change the value of the V1B output coupler.

Or lower the value of the 220K resistor.

Many approaches more available. OD couplers, cathode bypass caps, etc.

[RJ Guitars]

Aaron you continue do great work on this build. if you succeed in building an amp that has both the Dumble sound and sparkle and keeps it all with a MV control, I may have to go forward and build one of them for myself... because i need another amp!