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Millett "Starving Student" hybrid amp - Page 456

post #6826 of 6828
Originally Posted by vixr View Post

With extreme patience and sheer expertise on the part of GlowGale, my "only one on the planet" single tube MHSS prototype is working beautifully, thank you for your awesome kindness sir. The balance control is the coolest feature I've seen in a long time. Right now I'm waiting on my 10k Alps pot to show up in the mail, and I need to come up with a clever case.


GlowGale this 18yo scotch is for you...



Vixr, I'd like to thank you for all the feedback on the initial design, this gave me an excellent insight into the real world version of this design. Bottom's up!


The secret of the design is of course the floating volume pot, which gives an "airy" feel to the sound. The balance system should work even better if you use a dual gang 25K linear pot instead of trimmers. I'll be looking into some further optimisations to make things less variable on assumptions I made.


The main disadvantage I still see in the design are the output capacitors. Not when you're listening to music, but when you forget to unplug your headphones & fire the thing up. The output capacitors will charge & discharge through the headphones. I understand that this is inherent to a design with output capacitors, and this also happens in the original SSMH. I noticed someone advising to not plug in your headphones during startup & shutdown, but I don't find this safe enough according to Murphy's law. So I'm looking for a simple & elegant solution to make the startup safer with your headphones plugged in.


The simplest way is to reference the headphones to 48V, but this only works if you won't be interconnecting the output to anything else but headphones. So I'm thinking of flipping the voltage the other way around toward -48V. This would only need an extra capacitor at the audio input, and maybe a DPDT power switch instead of a SPST. The main problem would then be that you need a PSU with a very clean output voltage. Another way would be to just implement a simple headphone protection relay circuit like in the MiniMax.


To make things more debug friendly, I also need to have less potentiometers & resistors to fiddle around with because they can confuse beginner builders and I'm too lazy to adjust them. Chassis mount pots also have a rather high price, so I'd rather spend this to a much cheaper addon circuit which does the bulk work for me. This either means running the tube in non optimal conditions, or having some kind of 'automatic' potentiometer setting the right output voltage for you. This should also allow for variations such as wear & tear, replacing the tube and using other tube types like the E88CC without any major retweaking.


Stay tuned,

GlowGale Audio Design

Edited by GlowGale - 10/9/14 at 10:49am
post #6827 of 6828

Fantastic work from both the designer and the prototyper! Congratulations!

post #6828 of 6828

A new run of SSMH PCB kits is close to becoming a reality.  PCB's have been ordered and Hammond Mfg is fabricating the cases.  There will be 50 kits, period.  No substitutions, no modifications, and no extra PCB's or other parts. BOM is the same as it's always been on the SSMH PCB website (with the exception of price).  You'll get two tested 19J6 tubes with each kit, but if they are microphonic or go bad soon after, you may be on your own.  I will have a handful of spares, if any.  However, onesie-twosie's have always been available through reputable tube dealers and on ebay, although a bit expensive (typically $10 ea). I'm still acquiring parts, so I'm not sure of the final kit price, yet - perhaps $30 more than last time.  Remember that the last time we sold these was around 2009!  I will have the BOM corrected within the next week or two, so you'll be able to see.


They may go on-sale on Beezar in mid-November/Thanksgiving, I'm hoping.

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