tweaking the Peter Millet Hybrid amp?

[flecom]

im trying to get the most out of my Peter Millet Hybrid amp

my frist thought was perhaps stacking buffers... removing the BUF634T's and perhaps making a little stack of 4 or so DIP-8 buffers on a little protoboard and solder that in the space of the 634t....

or another option, maybe make more sence for the effort...

would it be possible to use diamond buffers like glassman's in place of the 634t in the millet hybrid?

also somone suggested that i should change the polarized electrolytic output caps C7 & C16 (currently cerafines) with non-polarized electrolytic caps (black gates perhaps?) would that be possible/improve things?

comments/suggestions/input always appreciated

thanks in advance

 

[slindeman]

Quote:

also somone suggested that i should change the polarized electrolytic output caps C7 & C16 (currently cerafines) with non-polarized electrolytic caps (black gates perhaps?) would that be possible/improve things?

Yes it is possible. It may improve things, I haven't tried it myself. There are 100uF 50V BG N and 680uF 35V BG NX that will fit.

The order I personally would upgrade the Millet amp:

Power supply
Volume potentiometer
Output caps
Output resistors
Buffers
RCA Jacks

This list is based on my experience with various DIY amps, and what changes have affected them the most. I've got one stock Millet amp, and I'm halfway finished with another one that has an upgraded Power supply, an ALPS Blue volume potentiometer, and I'm considering switching to blackgate caps/ riken carbon resistors for the output.

Hope this helps!

 

[flecom]

well i have already upgraded the powersupply to a linear one... and i dont have a volume control since im using my modded sonica as a source (volume control on the pc)

all my resistors are vishay/dale metal film, 1% resistors....

dont have any RCA jacks, sonica is hard wired into the millet...

the buffers and output caps are really what im concentrating on atm since that seems to be my best bet

 

[Voodoochile]

Increasing the size of C1, C9, and C18 is a nice minor tweak, especially if your PSU is not of excellent quality. They do not have to be 100V either, just as Pete (and Scott) have stated. A 1,000uF/50v Muse cap fits well in C1; some 330uF/50v in the other two.

Is your PSU 28 volts, or could it be adjusted to be 28v? The amp sounds especially good running at 28v, with 18 to 19v bias on the tubes. This doesn't really stress the tubes either, since they were spec'd for auto use, which is higher than 12v, typically something like 13.8v.

Also, I'm pretty sure yours already has them, but make sure the wideband jumper is in place for the buffers. You could also remove the output resistor entirely- Pete says it's there mainly to protect the amp in the event of an output short. The buffers have built-in current protection already. Like a PPA, you just be careful not to insert the plug only partway and leave it, even if it is protected.

 

[flecom]

Quote:

Originally Posted by Voodoochile Increasing the size of C1, C9, and C18 is a nice minor tweak, especially if your PSU is not of excellent quality. They do not have to be 100V either, just as Pete (and Scott) have stated. A 1,000uF/50v Muse cap fits well in C1; some 330uF/50v in the other two.

the 1000uF/50v muse cap is 18mm, might be kind-of a tight fit...

C1, C9 and C18 are 16mm caps, could just use the muse 470uF/50v?

any particular reason you would choose the 330uF (also 16mm but shorter) for C9 and C18?

Quote:

Originally Posted by Voodoochile Is your PSU 28 volts, or could it be adjusted to be 28v? The amp sounds especially good running at 28v, with 18 to 19v bias on the tubes. This doesn't really stress the tubes either, since they were spec'd for auto use, which is higher than 12v, typically something like 13.8v.

my psu is 24v, i could make a 28v psu tho, with like an LM317A or whatnot

Quote:

Originally Posted by Voodoochile Also, I'm pretty sure yours already has them, but make sure the wideband jumper is in place for the buffers. You could also remove the output resistor entirely- Pete says it's there mainly to protect the amp in the event of an output short. The buffers have built-in current protection already. Like a PPA, you just be careful not to insert the plug only partway and leave it, even if it is protected.

ya have the buffers in high-badnwith mode...

im guessing that the output resistors are R3 and R7?

i never turn on the amp w/o the headphones plugged in anyway

nobody has any comments about stacking buffers in this thing? i would really like to use the diamond buffers from glassman but im not sure if they would work ok in the millet?

also ive read that removing C4 and C13 should give the amp a "brigher" sound...?

what about C19 and C10? thats another pair of those 100uF 100v caps, any benefit on making those larger uF caps?

 

[flecom]

Quote:

Originally Posted by slindeman There are 100uF 50V BG N and 680uF 35V BG NX that will fit.

youch the cheapest place i found that sells those caps is here...

http://www.kyoto-electro.com/nx.html

and they are $10/$12 a piece respectively, thats pretty fricken expensive for a cap...

i know this has been argued into the ground a billion and a half time, but are the black gates worth it?

is there even another option for a good non-polarized cap?

is the Nichicon Muse ES any good? at around ~$1 for a 470uF 35v its a hell-of-a-lot cheaper than the black gate!

 

[flecom]

Quote:

Originally Posted by Voodoochile with 18 to 19v bias on the tubes.

would that damage C2 and C11 since they are only 16v?

 

[Voodoochile]

No, in fact Pete suggests 19v as his best bias point. I ran mine at 18.5v all along without issue.