Pass "DeLite" Amp from BAF

[Jeffreyjuice]

I use the same 130v 300watt bulbs as you and mine do not get brighter or dimmer with volume. Definitely with different drain to ground voltages the brightness changes. I like your build layout. It's sleek and tubey.

What type of transformer are you using? The metal plate holding my 800VA donut in place is nearly as warm as my heat sinks. 58 degrees vs 60ish.

A question about your circuit. Do the tubes in front of the mosfets act as a buffer?

Jeffrey

 

[kodabmx]

Thanks

The brightness imcreases if I drive it into clipping, and returns to normal afterwards (I'm thinking the coupling cap charges up?- I might try transformer coupling instead)

The transformer is a 572VA toroid, mounted inside the chassis rear middle. It's probably as hot as the heatsink. I have a tube amp with Hammond PT that hits 95c in operation so I'm not overly worried about the temperature

The tubes in front are both a gain stage and buffer to drive the MOSFETs. I'm not sure if they are up to it. I hear a HF roll off that is most likely related to CMiller. I might attempt to buffer the tube with a DN2540 MOSFET or something - not sure how yet though but I assume it'll fit into a typical cathode follower circuit (source follower). Either that, or I'll just boost the HF to compensate LOL

 

[kodabmx]

I thought I'd post a picture or two of the amp in it's latest state. I think I'll make it into a source follower though. The Zout is kind of crap.

 

[Nelson Pass]

The brightness increases at clipping because the fet can draw more current than
the bulb can supply, so the DC voltage across the bulb increases.

Yes, the Zout is not a feature unless you are one of the minority who prefers high
output impedance.

 

[Jeffreyjuice]

De-Lite 3.0

Well I'm back to the open/roomy/messy layout and the "De-Lite" is again hum free Now to build a larger family/living room approved chassis. It may just have to rest on the beach a while. Sure it's dangerous but it sounds AMAZING!

@Dennis Hui Aimee Man is now even more soothing.

Jeffrey

 

[Dennis Hui]

Most excellent. Congratulations!

 

[plasnu]

I thought I'd post a picture or two of the amp in it's latest state.

Very nice atmosphere.

 

[Jeffreyjuice]

Messy 3.0 picture

Oops forgot to attach a picture. Hard to believe this mess sounds so great.

 

[Zen Mod]

me likee

in fact, that's super tidy, comparing to amps I'm usually evaluating in my workshop

 

[kodabmx]

Ok I think I'm gonna try this version as a source follower. Anyone see any glaring errors?

If there needs to be more gain, I'll make the cathode follower into a grounded cathode stage.

 

[kodabmx]

I took the output from below instead of above the resistor. I think this will work better?

 

[Nelson Pass]

It might be easier if you just run R11 from ground to V+. Just make sure
the pot can take 0.4W - or get a 100K pot and short across R2.

 

[kodabmx]

Thank you. R11 across R16 doesn't give enough adjustment. The 22k is a 5 turn 2W pot, so in theory if I just connect it to ground instead of the light bulb, I'll get enough adjustment?

Like this?

EDIT: As drawn it's working fine! The 6V6 will be reconfigured into a gain stage...

 

[Nelson Pass]

I like it better with the pot going to V+ instead of the output.
And you can eliminate the 1 ohm resistor...

 

[Zen Mod]

nope

reread and follow literally

see DEFiSIT thread for recipe

edit - Pa was faster

 

[Nelson Pass]

 

[Zen Mod]

 

[kodabmx]

So I reconfigured the 6V6 for gain, and one MOSFET blew (96R from gate to source) even with the 12V zeners back to back... Not sure how this could have happened really I might put a shorting relay in again to short the gate to source while the capacitor charges.

 

[kodabmx]

Ok... I put the relay in to short gate to source while the capacitor charges.

All is working now, and I must say the sound is much improved over the grounded source version. I did however change from 16N20D2 to 6N50D2. Not sure how much of that matters...

I left the bias and 1R in place. I figure the 1R provides some degeneration, lowering distortion.

Also the B+ is 72V... It'd be nice to get it higher, but I can't justify spending 200$ on a transformer to gain a few watts, and the heat sink would need a fan.

 

[Zen Mod]

always spend more on bigger and more sensitive ( not same as efficiency!) speakers, instead on bigger amp hardware ( at least when you're already in big territory)

ok, write something , somewhere, about those EL509/519 amps you have there .......

at least I presume bottles are these