Just thought I would post a quick pic of the reason I am still up tonight. Just having real trouble turning Opeth's Deliverance CD off. Had a bit of trouble with way too much gain and getting the volume knob too high with my KSC75's earlier tonight, and even with my HD580s, I cant even make it a quarter turn on the volume knob. This is with DuMont 12ae6a tubes and the cathode resistors unbypassed.

Way to go, Colin! It was nice to come into work this morning and see this.

So I take it prototyping is done ?

If so, me wants one!

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I sure hope so, but it's not as if we've had a hard time with it, really. I'll be building one from the new board this weekend. Hopefully, that will have a good result, too.

I've been keeping an eye on these for my main rig project. Looks awesome!

what are the differences between this and the 'regular' millet?

w00t! that is SWEET. cetoole...m(_ _)m

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Ooh boy - let's see if I can embarass cetoole again!


The Millett Hybrid Maxed, or Max for short, was designed by Colin Toole (cetoole, otherwise known as Mad Max) to incorporate all of these features and more:

* the basic Millett Hybrid circuit
* onboard, STEPS-quality Power Supply
* onboard, dual Diamond Buffers output stage
* onboard, e12 delay circuit (abbreviated for Millett)

Also:
* extruded TO-220 heat sink footprint for power supply
* extruded TO-220 heat sink footprints for all four output transistors
* options for MOSFETs on the output transistor positions
* CCS has been changed to a feedback transistor pair with selectable resistor sizes for different currents and superior tube regulation
* power resistor option for heater circuit, allowing higher voltage supplies without damage to tube heaters
* 16mm minimum cap diameter pads throughout, 18mm for the PS
(Note: this is spacing for 1000uF-1200uF caps and larger. The Panasonic FM's in cetoole's photo are 1000uF@50V.)
* 15mm lead spacing for film caps, even larger for cathode bypass films
* signal input pads front and rear, 5mm spacing for terminal blocks
* Noble and Alps adjustable pot positions
* onboard Neutrik output jack pads
* tube LED and panel LED pads included
* PS choice of Schottky rectifier diodes or generic axial diode positions, ceramic snubber caps
* board sized for Hammond 1455T1601 case, center post for stability around tubes

The Power Supply allows the use of a simple, cheap 24VAC walwart supply (750ma minimum recommended), but results in STEPS-quality power. Capacitor pads allow use of very large boutique electrolytics and film caps. The CCS is superior to the old current-limiting diode, resulting in improved tube current regulation for superior performance.

The DB's use only one set of complementary output transistors for each channel, but with the board mounted heat sinks, biasing up to 50ma each and beyond is possible, allowing the transistors to operate within their optimum power range, and lowering distortion for a very clean sound.

Finally, for the ultimate in convenience, a small version of Amb's e12 delay circuit is used, resulting in 10-15sec power delay and protective cutoff. No need to unplug your phones upon power on or power off.

There is no other DIY amp design that offers as much of a complete package as the Millett Hybrid Max (IMHO). After populating the board, all that is needed are a knob, jacks, the enclosure, and a 750-1000ma 24VAC walwart.

The sound? Well, it's the best Millett I've ever heard - by a long shot. Initial reports by others are that it competes favorably with many of the best DIY amps.

i cant wait to get my hands on the pcbs :drool:

Is it possible to bypass the PS section so a Sigma22 can be used ? A design such as this calls for more than a LM317.

any guesstimate on when the boards will be available, my new hakko is itching for some work, and i've been looking for an excuse to try out tubes

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Sure, I use an LM338. Seriously, compared to a separate power supply - whether it's the STEPS or one of the SIGMA products, the STEPS-like circuitry on Colin's board is trivial and inexpensive, but it gives nothing away in quality, IMHO. A lot, if not most, of the expense and design of a separate power supply is in the line voltage components, the transformer itself, and the enclosure.

More importantly, you circumvent fully half of the advantage in Colin's board trying to do that. A guiding strategy of this board was to have STEPS quality without any of the worries of line voltage filtering/chokes/inductors or expensive toroids. Even with all that stuff - if you put it the STEPS/SIGMA anywhere in the vicinty of the MAX, you'll have worse sound quality than if you hadn't done anything (This has been tested already.)

It is not a favorable scenario, IMHO.

Any estimate on completed cost for a fully populated board?

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MillettHybridMax.xls
MHMax BOM Web Page

This has piqued my interest. I may be DIY'ing again soon