Millett "Starving Student" hybrid amp - Page 192

^Punnisher, I made that same assumption. Tomb, thanks for the info, I doubt ill be getting a matched pair, what are the negatives of having a unmatched pair.

Hey Everyone,
I'm having a bit of trouble obtaining these parts:
R16/17 50K, 1/4W Resistor
RLED 2.4K, 2W Metal Oxide Resistor
3MMAJ Neutrik [NMJ6HCD2] 3.5MM, Stereo Audio Jack
SNDOF 20MM M3x0.5, Male-Female Aluminium Hex
TO220 TO-220 Heatsink Kit
HEATS TO-220 Heatsink, Unspecified (Which one?)
PWRS Cisco [PSA-18U] 120/240V Input, 48VDC@0.38A Reg. Pwr. Supply

I need to find these parts in Australia. I haven't got much time (i'm in the middle of holidays atm so I have about a week and a half to get all the parts ordered ) and i'm using Farnell for the majority of my BOM, but I am also using Jaycar for some of the parts that Farnell don't carry.

Any help would be greatly appreciated.
Sorry i'm talking like a lunatic, but i'm in a rush

-CaptHowie

hope that helps
cheers
Fred

Thanks heaps for that Fred. I've changed a few things in my design like removing the LEDs so that will remove those hard to find resistors. I'm using the Jaycar 3.5mm Stereo Chassis jack as you mentioned above as well. With the standoffs and the heatsink and kit, why didn't you need the standoffs and the kit, and how do you insulate the MOSFETS using the case? I'm trying to minimize the price (i'm a student...) and cutting those things off the list would reduce the price, as would using Jaycar's heatsinks (2x$3.00 something for the Jaycar vs. 2x$12.10 for the Farnell one). Removing the heatsink kit would also save some money as the minimum order quantity on Farnell is 10. Any further tips would be greatly appreciated.

Thanks,
-CaptHowie

Oops! Head-Fi stuffed up on me and double posted... sorry!

Heres some pics











I was using a Jaycars ABS box (HB5970) so the heat sinks were insulated from the circuit, the switch has abuilt in LED ( SP0704) which makes life simple, the home made pcb is sitting flat on the case's base, So I didn't need to stand it clear of any metal. The Mosfets have clear heatshrink on them but its hard to see (because its clear). The amp is great well worth building
cheers
Fred

Anybody know the voltage gain of a starving student with 12sr7 or 12sw7 versus the 19j6 tube?

An unmatched pair means the channels will be mis-matched. However, keep in mind that Pete Millett foresaw this to a certain extent, which is one of the reasons he chose to use two tubes with dual triodes tied together - the entire effect is to minimize those differences. That means the chances are less than they might've been, but it's still possible.

In cases such as the Millett MAX/MiniMAX, there is a bias adjustment that allows you to "center" the Left and Right channels (among other things), but even if biased the same - if one tube has a different output than the other, then one of your headphone cans will seem "dead" compared to the other.

In the case of the Starving Student the bias adjustment is fixed, so a true tube mis-match is not correctible even for channel centering. One might say that makes tube matching much more critical than not with the SSMH. For example, the 19J6's I've tested run from 70 to 120 (on a Jackson 658A tube tester). I think most tube vendors state tube matching within 10%. So, it might be safe to assume that differences greater than that are noticeable. 70 to 120 is a variance of 25%, so the potential for mis-match exists.


P.S. Nice work, Fred!

Looks good Fred, the only thing I noticed was WRT the FET's. If my memory is correct, I thought Pete said at one point that it was important to attach the 2k resistors connected to the gate of the mosfet as close as possible to prevent oscillation in the buffers. I may be mixing this up with another design, so folks, please correct me if I'm wrong here.

Anyway, looking at the photos, it looks like you have a wire going from the gate to the board, with the 2k on the board. Again, it's hard to tell from the photos, but that may be a minor change worth making.

But on the other hand, if it's working, maybe it's not worth messing with...

nice build fred the braiding was an excellent touch

Guess I'm a little late to the party...just bought a bunch of parts for this project...only to realize that the tubes are nowhere to be purchased...

A few pages back, there's a post on substitute tubes. It also requires different values for some of the resistors. You can also wait a little and buy boards with tubes.

The gain with the 12sr7 and 12sw7 is around 6.

Yes I've just read about the resisters, however its super stable with no hum/hiss or background noise, it drives my AD700's very nicely, so I think I have got away with it, beginners luck

cheers
fred

Sounds like an ideal recipe for some grados and other low Z cans

zk