[ruZZ.il]

yes, supposedly wimas have very flat response curves which is ideal for most positions that it's called for. Using caps with non-neutral response in those positions could negatively effects some things. I really cant comment much, just echoing what I've read as a preliminary note. Maybe someone will emphasize the differences..

 

[tomb]

Good advice about the grounding, ruZZ.il.

Except technically speaking, the signal ground is the same as the DC Ground test point on the board.

The Millett, and now the MAX, has always been negatively grounded. In the case of the older revMH Millett Hybrid, which was fed from DC, it was a good practice to use a metal DC power jack where the ground was commonly shared. However, the difference in the MAX is that the rectified-regulated DC power is onboard, so the actual power input jack is 24VAC. In that case, the AC must be isolated from the DC ground of the board and as you correctly point out - is also shared with the enclosure. That's why a plastic power input jack is specified on the MAX's Bill Of Materials (BOM). That AC/DC difference is probably what you were thinking.

 

[tomb]

Quote:

Originally Posted by ruZZ.il /img/forum/go_quote.gif yes, supposedly wimas have very flat response curves which is ideal for most positions that it's called for. Using caps with non-neutral response in those positions could negatively effects some things. I really cant comment much, just echoing what I've read as a preliminary note. Maybe someone will emphasize the differences..

Yes, ruZZ.il is correct.

Also, the big difference for me is that I'm lazy.

There's no more easier part to solder in the board than the Wima caps. The same cannot be said about the K42's. Wimas are cheaper, too. So in those positions where the very slight squeeky-graininess of the Wima has no effect (everywhere but CA8), it's much easier to use them.

 

[John Wilson]

Thank you Russ! JW

 

[ruZZ.il]

hm. I see.. So you're saying the regulator is basically 'standing' on the signal ground, always holding the V+ about ~27v above?
alright

 

[tomb]

Quote:

Originally Posted by ruZZ.il /img/forum/go_quote.gif hm. I see.. So you're saying the regulator is basically 'standing' on the signal ground, always holding the V+ about ~27v above? alright

Yep - and the tubes are adjusted so that their bias is in the middle, allowing the sine wave of the music to swing between those two points. Assuming you set V+ to 27VDC, the zero point of the Left and Right signal sits at 13.5VDC, which is why there are output caps to block that DC from your headphones. When you bias the tubes, you are actually measuring the Left and Right signal voltage and its reference to Ground.

 

[slowpogo]

I'm finalizing the back panel for my Max. Would a small vent in the back be a good idea, or is it basically unnecessary (mine uses BJT with 1" sinks)? The top panel will have pretty good sized vent holes, with metal mesh beneath.

 

[tomb]

Quote:

Originally Posted by slowpogo /img/forum/go_quote.gif I'm finalizing the back panel for my Max. Would a small vent in the back be a good idea, or is it basically unnecessary (mine uses BJT with 1" sinks)? The top panel will have pretty good sized vent holes, with metal mesh beneath.

None of mine have vents in the back. They seem to suffer no ill effects.

 

[jimmyjohn]

Does anyone need a power supply? I sold my MAX to a gentleman in the UK, and he has no use for the power supply. It's a Radio Shack unit:

RadioShack.com - Power & Batteries: Home & office power: AC (Home) adapters: 18/24VAC 1000mA AC-to-AC Adapter

Let me know if you're interested, and we'll work something out.

Jim D.

 

[fault151]

Hey Jim, any idea when you will be posting out the amp? Theres no mad rush, just wondered? Ill have to arrange for someone to be in and sign for it.

Looking forward to listening to it, iv been following the millet thread for ages. Im even in the process of getting a custom box made.



Quote:

Originally Posted by jimmyjohn /img/forum/go_quote.gif Does anyone need a power supply? I sold my MAX to a gentleman in the UK, and he has no use for the power supply. It's a Radio Shack unit: RadioShack.com - Power & Batteries: Home & office power: AC (Home) adapters: 18/24VAC 1000mA AC-to-AC Adapter Let me know if you're interested, and we'll work something out. Jim D.

 

[thomaskuhn]

I finished up the circuit for the VU meter. It worked great when I hooked the inputs to my iPod, so this morning I began installing it in the MAX (I was supposed to be painting the house, and there was hell to pay) Well lo and behold, it does not work. I was wondering if any one could help me out? Below is a simple diagram I made in SPICE.

Please note that the values are correct and the bridge is actually a chip, but I did not find one in the library, so I just drew 4 diodes. My meter is the between the bridge and resistor.

The problem I am having is that when I connect the signal ground to the MAX, it seems to remove my floating ground, so that the input to the op-amp is now 27V, where as when it is hooked to the iPod, the power is properly split +13.5/-13.5. I am sure it has to do with using a floating ground in this setup. Can anyone help me out?

Tom Kuhn

 

[ruZZ.il]

we were just speaking about it, that the signal ground voltage = "Max ground" voltage so it would need a seperate power supply, maybe a battery? or a different type of op amp.. basically, you're shorting that bottom 10k resistor when hooked up to the max like that..
<scratches head>
I have to learn more about op-amps...
can't help too much yet
soon..

 

[soloz2]

Quote:

Originally Posted by ruZZ.il /img/forum/go_quote.gif yes, supposedly wimas have very flat response curves which is ideal for most positions that it's called for. Using caps with non-neutral response in those positions could negatively effects some things. I really cant comment much, just echoing what I've read as a preliminary note. Maybe someone will emphasize the differences..

Quote:

Originally Posted by tomb /img/forum/go_quote.gif Yes, ruZZ.il is correct. Also, the big difference for me is that I'm lazy. There's no more easier part to solder in the board than the Wima caps. The same cannot be said about the K42's. Wimas are cheaper, too. So in those positions where the very slight squeeky-graininess of the Wima has no effect (everywhere but CA8), it's much easier to use them.

Thanks for the info guys. I'm not too worried about what's easier as I find it only takes an extra couple minutes to install a pair of k42's over a pair of Wilmas and I have a box of I think 36 k42's left

So I should just use the Wilmas anyway then.... no biggie

 

[tomb]

Quote:

Originally Posted by ruZZ.il /img/forum/go_quote.gif we were just speaking about it, that the signal ground voltage = "Max ground" voltage so it would need a seperate power supply, maybe a battery? or a different type of op amp.. basically, you're shorting that bottom 10k resistor when hooked up to the max like that.. <scratches head> I have to learn more about op-amps... can't help too much yet soon..

Russ,
You know more about this than I do, but couldn't he just forget the voltage splitter? The tube already splits the voltage. If he just connected the V+ and Gnd to the V+ and V- on the opamp, the signal + would be at 13.5 and the signal Gnd would be the same as Signal -.

That presents a bit of a problem, because the opamp has to burn a diode drop, I believe, because it can't swing rail-to-rail. This is why Runeight installed a set of four 1N4148 switching diodes around the opamp on the SOHA - to insure that the opamp wasn't burned out with a signal that exceeded its maximum voltage differential.

I'm guessing, though.

 

[joneeboi]

I was wondering, as I often do when staring at the insides of my MAX, and I thought about what it would be like to have a 3 channel MAX. How would that work? One way would be to populate a board and a half and use one channel as the GND. Does that make sense electrically or pragmatically? We currently use a huge ground plane, so how does that affect the implementation of a 3rd channel? How would input and output grounds be connected to the board? Wouldn't you just wire the input ground to, say, the left channel and take output ground to be the left output? I don't have any balanced sources nor do I plan on having any in the near future, so pulling a pabbi would be so very nice and useless for me. I don't suppose Team Millett wants to focus on a 3CH design anytime soon.

What do we allegedly have on tap at the moment? MiniMAX, Super MAX, 12AU7/12AX7 (or whatever) MAX? Is a 3rd channel even worth my internet chat breath?