[Televator]

Quote:

Originally Posted by J.D.N /img/forum/go_quote.gif If i wanted to build a Millet Max, where would i get a PCB? Do i need to wait for another group buy?

for now there's only the Glassjaraudio kits (member Jrossel sells them through his site, but you have to PM or email him for an order form). These kits offer everything (not just the PCB) and they sound GREAT as they come (one of the "can't miss"-builds on the MAX site). If you are certain you want to go extra boutique you can always ask for a less complete kit.

Besides that, a new group-buy (for MAX or MAX-mini) will come pretty soon, I guess

 

[J.D.N]

Quote:

Originally Posted by Televator /img/forum/go_quote.gif for now there's only the Glassjaraudio kits (member Jrossel sells them through his site, but you have to PM or email him for an order form). These kits offer everything (not just the PCB) and they sound GREAT as they come (one of the "can't miss"-builds on the MAX site). If you are certain you want to go extra boutique you can always ask for a less complete kit. Besides that, a new group-buy (for MAX or MAX-mini) will come pretty soon, I guess

Cheers, i'd love to build a MAX, it really doesnt need to be extra boutique or anything. Just got to weigh up if it's over my head and i should start with a SOHA.

 

[Televator]

I went for a Max as it deals with low voltages only, so I could ruin the amp but not much more if I screwed up good ... but I built a JRossel-kit successfully after having only built a Cmoy (well two) and an alien DAC before...

Just follow the instructions on Tombs MAX-site (they are very precise and easy to follow) and double (no triple) check every part before mounting (correct part, orientation, ...)

For me, the MAX kit was even easier than a cmoy in certain ways as it comes in one complete package and it is very well documented and supported (here in this thread

)

 

[tomb]

A friend has shared with me some data and calculations about the Millett's car radio tubes. It seems that there's not a bean's worth of difference in the performance values between a 12AE6A and a 12AU7A (GE, 1954/56) when the 12AU7A is run at reduced voltage - say 50V or so.

I'll try to get the tube curves and operating points worked up for comparison and post it when I get a chance.

EDIT: Now, keep in mind, that I've always loved the tube-rolling that's possible in the SOHA. but my bias is well-known and documented in this thread.

P.S. Great work Televator! That's a cool-looking MAX!

 

[tomb]

Quote:

Originally Posted by tobias_svensk /img/forum/go_quote.gif Thanks man Remember to always turn your trimmers ALL the way and test... I had like all my adjustment on the last 10-20% of the turns. My PSU heatsink is madly hot but I guess 25.5VAC in under load is a bit on the steep side. Sadly I have to sleep now but tomorrow I will compare it to my QRV-04 (OPA627 + BUF634) Cheers

Congrats! You may find that the sinks will get cooler with run in. Colin and I have been comparing notes on that lately and it seems to be the case with most of our builds.

 

[tomb]

Quote:

Originally Posted by slowpogo /img/forum/go_quote.gif There are genuine Vitamin Q caps on ebay, in .18 and .27uf values. The recommended value for the film bypasses is .22uf, but would either of these Vitamin Q's still work?

Yes. Either of them would probably work very well. The problem with Vitamin Q's are their size. Now, if you are putting the MAX board on the bottom slot of the Hammond, that gives you plenty of room to tombstone even 0.47uf Sprague Vitamin Q's. If you are trying to keep things under 1" and put the board in the Hammond's 3rd slot from bottom (~center for the volume shaft), then the K42's are the choice.

EDIT: This is assuming low-voltage VitQ's (150-250V, I think) from that e-bay seller in LA. If you get up into the several-hundred volt range, then they get gigantic. Something around 1-1/4" to 1-1/2" long may be OK. You only have about 1-1/8" height clearance in the 3rd slot and about 1-1/2" in the bottom slot - but I haven't checked the bottom slot clearance as much, so I maybe off on that.

 

[SmartBomb]

Quote:

Originally Posted by tomb /img/forum/go_quote.gif Congrats! You may find that the sinks will get cooler with run in. Colin have been comparing notes on that lately and it seems to be the case with most of our builds.

I can confirm that both of my MAX builds got noticeably cooler after running in for 48 hours.

 

[rhester]

Got my power supply tonite and hooked it up. All mV were adjusted correctly and have a nice little glow from the tubes. Just waiting on my K42Ys to come in and some good hook up wire. Used BGs as the boutiques so I plan to let it burn in a good while before any critical listening.

This forum was invaluable for all the pointers and tips (and tomb specifically).

This proves that even us Mechanical Engineers can build things right.

 

[ruZZ.il]

Quote:

Originally Posted by tobias_svensk /img/forum/go_quote.gif .. My PSU heatsink is madly hot but I guess 25.5VAC in under load is a bit on the steep side...

Firstly, congrats!

Now, what kind of AC converter are you using? You should be able to turn the voltage up a bit, say to 27v. This would mean the regulator has to regulate the voltage to a closer value to its input, so it would dissipate less heat. Generally, a 24vAC output, when rectified, gives about 24*1.4=33.6v, though the rectifiers are diodes, so theres about a 1.5v drop (thats about 0.7v on each diode, and the current goes through 2 each cycle) so, 24*1.4-1.5=32 after the caps, you're left with a rough DC voltage of about (24*1.4-1.5)*0.9=28.9vDC the regulator needs about 2 volts to regulate down to a steady 27, which is just fine (note, the output of a 24vAC regulator is a little more than 24v, so its actually around 30v unregulated DC at this point). now lets say your amp draws half an amp(of current), the regulator would be dissipating 3 volts(30-27) time half an amp, (P=VI), about 1.5 watts of heat. If you're regulating down to 25.5V, thats about (30-25.5) times half an amp, so about 2.25 watts.. thats 50% more heat.. so, I suggest bumping your regulated DC value up a bit, and the regulator should run a little cooler.. hope this helps a bit

edit: I just found this, not sure what it says(I'm running out the door..) but it looks like it should graphically explain most of what's going on..

 

[tobias_svensk]

Firstly, congrats!

Now, what kind of AC converter are you using?/QUOTE]

Hello, well I have a toroid with four windings:
9V-0
24V-0 (3A)
18V-0-18V

The 24VAC winding measures 25.5VAC on MAX's inputterminal when it's running so bumping up the PSU to 28.5-29.0VDC (29 was max?) would be better I guess (running 27.0V now).

Cheers

 

[ruZZ.il]

strange toroidal configuration you have but 25.5vAC is good. I thought you meant your DC was set to 25.5. Anyway, with your toroid, the regulator would probably work sufficiently and coolest at around 28v.. sorry bout my confusion, but I hope you understand what I meant anyway

 

[amphead]

Quote:

Originally Posted by tobias_svensk /img/forum/go_quote.gif Thanks man Remember to always turn your trimmers ALL the way and test... I had like all my adjustment on the last 10-20% of the turns. My PSU heatsink is madly hot but I guess 25.5VAC in under load is a bit on the steep side. Sadly I have to sleep now but tomorrow I will compare it to my QRV-04 (OPA627 + BUF634) Cheers

Tobias congrats! Another Max Lives

About 50% who build the Max for the first time have the exact same experience you had, myself included.

 

[slowpogo]

Quote:

Originally Posted by tomb /img/forum/go_quote.gif Now, if you are putting the MAX board on the bottom slot of the Hammond, that gives you plenty of room to tombstone even 0.47uf Sprague Vitamin Q's.

Should I infer from this that for the boutique film bypass positions, more capacitance is better? Could you hear a difference between .18uf and .47uf versions of the same cap? (Assuming size is no issue)

I will be using the bottom slot, since I have a TKD pot I need to hand-wire anyway...so I will go nuts with the .47uf, if it's advantageous.

 

[tomb]

Quote:

Originally Posted by slowpogo /img/forum/go_quote.gif Should I infer from this that for the boutique film bypass positions, more capacitance is better? Could you hear a difference between .18uf and .47uf versions of the same cap? (Assuming size is no issue) I will be using the bottom slot, since I have a TKD pot I need to hand-wire anyway...so I will go nuts with the .47uf, if it's advantageous.

Generally speaking, the higher values may offer some additional smoothness, but bypassing is a highly variable experiment in each case. There's no guarantee that any combination of sizes works better than another without trying it for sure.

I'm not aware of any downside with the larger bypasses, but there is bound to be a point of diminishing returns. Technically, the film bypasses are only there to make up for the limitations of the electrolytics, which are pretty much required because of the RC filtering efffect. This limitation is mostly in the higher frequencies where more distortion or harsh harmonics are formed in some electrolytics (I believe from what I've read). The guiding principle of the original Millett was that the Wima bypasses allowed regular power caps to work just as well as something boutique and expensive.

All that's to say that improvements are probably slight. Bigger changes may be completely unpredicatable and you may be better off investing in better electrolytics.

EDIT: There are at least two builders who've used 0.47uf Vitamin Q's (there may be more): MrMajestic2 and Colin Toole. Colin's are Philco brand, however, and no larger than 0.22uf K42's. I know he his quite happy with is. I would be recommending them to everyone as with the K42's, but have not found a reliable, steady source for them.

 

[slowpogo]

Thanks tomb, super helpful as always. One more capacitor question...Welborne Labs has Wima MKP10 .22uf at 160v. They are smaller than the 250v on the BOM (still 15mm spacing), and there's the advantage that Welborne will match pairs for $1.

Is there any audible advantage to matching the Wimas, or is it plenty good to just go with the unmatched ones on the BOM?