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New Millett Hybrid Maxed Amp
Sep 11, 2012 at 7:54 PM Post #6,421 of 6,727
Quote:
bwshockley said:
Speaking of the walwart power supply, I'm looking into alternatives.  I'm not a big fan of blocky, outlet hogging converters, convenient as they are.  I was looking into a different input source without by passing the the two 2200uf capacitor bank or voltage regulator.  I was wanting something that is pretty much self-contained and found the Mean Well EPS-35-36 (http://www.meanwell.com/search/eps-35/default.htm).  It has an adjustable output voltage of roughly 32 to 39 volts DC at 1A.  I'd simply replace everything forward of the power from CR1A on the board, tune it to roughly 33 volts and continue to use the built in voltage regulator to send 27VDC to the rest of the board.  The EPS-35-36 can be had for around $15 online from what I've been able to find.  They are 3" x 2" x 1".  Not exactly small, but not huge either.  Other than moving the bulk for the walwart to inside the amp case, can anyone see a reason this wouldn't work?
 
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The only way you won't degrade performance with the MOSFET-MAX's onboard linear-regulated power supply is to use one of AMB's Sigma 11 power supplies.  The performance on the MAX/MiniMAX is about 45uV noise.  AMB's is down in the single digits of uV supposedly, but I kind of doubt that you would notice the difference with a tube/tube-hybrid amp (the tubes usually have more noise than that).  In any event, there is no commercial switching power supply that's going to meet those kind of specs.
 
The Meanwell power supply you've sugested has 200mV ripple (noise).  That's absolutely atrocious for audio, IMHO.  It represents over 4000 times more noise than the MAX V1.2 PCB's onboard power supply (200 vs. 0.045).  It may even be audible (ripple hum) in certain situations, but the performance will be degraded well before that - fat, loose bass, and other artifacts.
 
Sep 11, 2012 at 10:19 PM Post #6,422 of 6,727
Quote:
scootsit said:
Wouldn't moving the transformer into the case and that close to the tubes introduce noise?
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It's not a transformer, it's a switching-mode-power-supply. Connect Main AC to one side, get DC on the other.
 
Quote:
bwshockley said:
Speaking of the walwart power supply, I'm looking into alternatives.  I'm not a big fan of blocky, outlet hogging converters, convenient as they are.  I was looking into a different input source without by passing the the two 2200uf capacitor bank or voltage regulator.  I was wanting something that is pretty much self-contained and found the Mean Well EPS-35-36 (http://www.meanwell.com/search/eps-35/default.htm).  It has an adjustable output voltage of roughly 32 to 39 volts DC at 1A.  I'd simply replace everything forward of the power from CR1A on the board, tune it to roughly 33 volts and continue to use the built in voltage regulator to send 27VDC to the rest of the board.  The EPS-35-36 can be had for around $15 online from what I've been able to find.  They are 3" x 2" x 1".  Not exactly small, but not huge either.  Other than moving the bulk for the walwart to inside the amp case, can anyone see a reason this wouldn't work?
 
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The problem I see is electromagnetic interference radiating from the SMPS to the rest of the amplifier. These things are not the cleanest components around. The solution is to place a grounded shield between the SMPS and the rest of the amp. You can easily build one using sheet metal. It doesn't have to be air-tight, but is has to be grounded. Here's a picture as example. You can see the shield isolating the PSU in a corner of the enclosure.
 
Edit: Sorry I did not see tomb's reply... tomb, I think bwshockley wants to replace the wall wart with a SMPS, while keeping the amplifier's on-board linear regulator. The idea is to bypass the diode bridge, but keep everything else. I don't see that as a problem, especially since today's DC wall warts are SMPS anyways.
 
Sep 12, 2012 at 11:02 AM Post #6,423 of 6,727
Quote:
kimlaroux said:
 
It's not a transformer, it's a switching-mode-power-supply. Connect Main AC to one side, get DC on the other.
 
 
The problem I see is electromagnetic interference radiating from the SMPS to the rest of the amplifier. These things are not the cleanest components around. The solution is to place a grounded shield between the SMPS and the rest of the amp. You can easily build one using sheet metal. It doesn't have to be air-tight, but is has to be grounded. Here's a picture as example. You can see the shield isolating the PSU in a corner of the enclosure.
 
Edit: Sorry I did not see tomb's reply... tomb, I think bwshockley wants to replace the wall wart with a SMPS, while keeping the amplifier's on-board linear regulator. The idea is to bypass the diode bridge, but keep everything else. I don't see that as a problem, especially since today's DC wall warts are SMPS anyways.
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Yes, my thought was to not bypass the voltage regulator on the board.  I wouldn't have expected the SMPS to provide cleaner juice than what was there.  I'd only bypass the diode bridge (not needed).  Tom, does this alleviate your concern?
 
I had two concerns, the first being the EMI and the second heat.  This may not be worth it in the end.  I'd basically section my enclosure in two, isolating both air and EMI for the SMPS.  Ugh.  Maybe I'll build a big ole wireless charging station like the newest Nokia phones.  That's gotta put out a great deal of EMI.  :)
 
Sep 12, 2012 at 12:54 PM Post #6,424 of 6,727
Quote:
bwshockley said:
Yes, my thought was to not bypass the voltage regulator on the board.  I wouldn't have expected the SMPS to provide cleaner juice than what was there.  I'd only bypass the diode bridge (not needed).  Tom, does this alleviate your concern?
 
I had two concerns, the first being the EMI and the second heat.  This may not be worth it in the end.  I'd basically section my enclosure in two, isolating both air and EMI for the SMPS.  Ugh.  Maybe I'll build a big ole wireless charging station like the newest Nokia phones.  That's gotta put out a great deal of EMI.  :)
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bwshockley,
 
To your knowledge what kind of sound sig. are you trying to achieve with the MHM?  I'm interested in getting (YBM) to build me a balanced one and was wondering how they compare to other hybrid or pure tube amps that's out there as far as performance goes.  Any info or links to reviews of the MHM would be helpful.
 
I'm just trying to find out what should I expect from this amp.
 
Thanks
 
Sep 12, 2012 at 8:41 PM Post #6,425 of 6,727
Quote:
bwshockley said:
Yes, my thought was to not bypass the voltage regulator on the board.  I wouldn't have expected the SMPS to provide cleaner juice than what was there.  I'd only bypass the diode bridge (not needed).  Tom, does this alleviate your concern?
 
I had two concerns, the first being the EMI and the second heat.  This may not be worth it in the end.  I'd basically section my enclosure in two, isolating both air and EMI for the SMPS.  Ugh.  Maybe I'll build a big ole wireless charging station like the newest Nokia phones.  That's gotta put out a great deal of EMI.  :)
Click to expand...

Yes - I misunderstood and it does negate my post to a large degree.  If you're wanting to ensure something greater than the typical 27VDC setting for a MAX, I can understand that and perhaps this is a good way to go, especially if you don't want to change the voltage rating on the caps.  You would need something with a dependable voltage control to ensure that it doesn't approach 35VDC, the minimum rating on most of the caps.
 
A couple of things to think about, though:
  • If building the MOSFET-MAX, you could easily substitute with all 50V-rated caps and still meet the 35mm height allowance.  In that scenario, casing up a simple AC transformer might be an easier, cheaper option than fooling with a switching supply.
  • The MAX power supply was tested and tweaked extensively for a 24VAC transformer or simple walwart (nothing more than a cased-up transformer with ready-made connectors).  Switching supplies have been known to throw out a whole lot of high-frequency noise that the MAX power supply may not be designed to filter out. 
 
Sep 12, 2012 at 11:52 PM Post #6,426 of 6,727
Is the only concern the plugpack taking up space ?

I do occasionaly see 24v AC transformers with a short mains lead, then a small plastic housing. Also slimline long ones in plastic or metal ones.

They are pretty ugly though, easiest would be to leave it behind a desk or on the floor floating around. If you wanted to re case them though it should be in theory as easy as chopping off and then re doing the plug. But you still have safety measures to consider. Metal chassis should be grounded or made of another material that is double insulated and it will need strain relief/abrasion protection on the mains cable entry. Not quite as difficult though as wiring it all internally.

Ideally if you go that route, a metal cased transformer should help with shielding and you could more easily bond that to the chassis its going in.

There may be other safety concerns, those are just off the top of my head.

Lastly this is just advice given it may not be safe or legal in your country and should be carried out by someone competent and posessing any qualifications legally required.
 
Sep 13, 2012 at 12:01 PM Post #6,427 of 6,727
Quote:
tomb said:
Yes - I misunderstood and it does negate my post to a large degree.  If you're wanting to ensure something greater than the typical 27VDC setting for a MAX, I can understand that and perhaps this is a good way to go, especially if you don't want to change the voltage rating on the caps.  You would need something with a dependable voltage control to ensure that it doesn't approach 35VDC, the minimum rating on most of the caps.
 
A couple of things to think about, though:
  • If building the MOSFET-MAX, you could easily substitute with all 50V-rated caps and still meet the 35mm height allowance.  In that scenario, casing up a simple AC transformer might be an easier, cheaper option than fooling with a switching supply.
  • The MAX power supply was tested and tweaked extensively for a 24VAC transformer or simple walwart (nothing more than a cased-up transformer with ready-made connectors).  Switching supplies have been known to throw out a whole lot of high-frequency noise that the MAX power supply may not be designed to filter out. 
Click to expand...

 
My reasoning behind the change is simply cosmetic in nature.  I'm not smart enough to go messing around with higher voltages.  I'd still tune the on board regulator to around 27VDC.  On your second note, that may be more of a concern.  I don't want to introduce any additional noise.  I'll stick with the walwart for now.
 
preproman - Your question is beyond my knowledge.  I am just looking for an interesting project that provides an amp for some headphones.  I'm no audiophile and wouldn't have the capability to compare or contrast with other amps.  Sorry, maybe someone else can chime in with an answer?
 
Sep 15, 2012 at 12:51 PM Post #6,428 of 6,727
Well, today was first power on for my MOSFET MAX.  The build was more difficult than my Millet P-P Engineer's Amplifier.  I guess because many of the components are smaller and closer together.  I made two mistakes while building, which I noticed immediately after I did them.  Both mistakes was installing a PNP/NPN transistor backwards.  The first time I thought to myself "Well, that was dumb, the silkscreen is right there to show you the way!"  The second time I just shook my head.  After making the switch TWICE, I was very very careful after that.
 
I turned all the variable resistors full CW, crossed my fingers, and powered on.  LEDs glowed nicely, nothing popped and I quickly checked the MOSFET Bias'.  With them both reading zero, I adjusted the input voltage to 27.0VDC, adjusted each tube to 13.5VDC - going back and forth to let them "warm up" a bit and adjust to themselves.  Then I started adjusting the MOSFET bias.  At first I didn't think I was doing anything, even though I knew it'd be a jump from zero to something, but I unturned the resistor 15 full turns at least before it jumped to about 80mV.  I set each one at 240mV, rechecked my supply voltage and adjusted, checked the tubes again, adjusted, checked the MOSFETs.  Well, you get the idea.  After about 30 minutes everything seemed settled in for now.  Wasn't as hard as I thought it'd be.  I've got a few connectors coming in the next couple days, so that's as far as I get to go for now.  No actual listening!
 
But, I did get some materials for my case ordered.  Mahogany and some Alder wood.  Think I'm going with the Alder for this one.
 
Well, I tried adding some images to my post, but got errors.  I'll try again later.
 
EDIT: Okay, here is a link to what should be an album here on head-fi.
 
http://www.head-fi.org/gallery/album/view/id/691846
 
Sep 15, 2012 at 1:48 PM Post #6,429 of 6,727
Quote:
bwshockley said:
Well, today was first power on for my MOSFET MAX.  The build was more difficult than my Millet P-P Engineer's Amplifier.  I guess because many of the components are smaller and closer together.  I made two mistakes while building, which I noticed immediately after I did them.  Both mistakes was installing a PNP/NPN transistor backwards.  The first time I thought to myself "Well, that was dumb, the silkscreen is right there to show you the way!"  The second time I just shook my head.  After making the switch TWICE, I was very very careful after that.
 
I turned all the variable resistors full CW, crossed my fingers, and powered on.  LEDs glowed nicely, nothing popped and I quickly checked the MOSFET Bias'.  With them both reading zero, I adjusted the input voltage to 27.0VDC, adjusted each tube to 13.5VDC - going back and forth to let them "warm up" a bit and adjust to themselves.  Then I started adjusting the MOSFET bias.  At first I didn't think I was doing anything, even though I knew it'd be a jump from zero to something, but I unturned the resistor 15 full turns at least before it jumped to about 80mV.  I set each one at 240mV, rechecked my supply voltage and adjusted, checked the tubes again, adjusted, checked the MOSFETs.  Well, you get the idea.  After about 30 minutes everything seemed settled in for now.  Wasn't as hard as I thought it'd be.  I've got a few connectors coming in the next couple days, so that's as far as I get to go for now.  No actual listening!
 
But, I did get some materials for my case ordered.  Mahogany and some Alder wood.  Think I'm going with the Alder for this one.
 
Well, I tried adding some images to my post, but got errors.  I'll try again later.
 
EDIT: Okay, here is a link to what should be a public album on google plus.  We'll see.
 
https://plus.google.com/photos/106773569132196240394/albums/5788450450146009329
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Nice work!  The 2nd paragraph in your post describes exactly how firing up the amp should go.
smily_headphones1.gif

 
Sep 17, 2012 at 12:40 PM Post #6,430 of 6,727
Question on source selection.
 
I've decided to go ahead and add in the skeleton DAC to my board.  I'm now reviewing my options for switching sources.  Of course, I could use a simple SPST attached at "IS".  However I was thinking about using the TRS headphone jack as the switch, such that the circuit at IS is normally closed when no analog input is used, selecting the DAC as the source and likewise, open when an plug is inserted into the jack, selecting the analog as the source.
 
Does anyone have a recommendation for a 3.5mm or 1/4" stereo jack with a built in SPST or even SPDT switch rated at ~27vdc?  Specifically, I'd like something similar to schematic "C" shown here: http://en.wikipedia.org/wiki/TRS_connector#Configurations_and_schematic_symbols Notice the isolation of the switch and the audio connects.
 
Anyone know of another option if my above fears are true? It'd sure be nice to just have the amp automatically switch sources based on either signal or a plug switch.
 
Sep 17, 2012 at 3:46 PM Post #6,431 of 6,727
Quote:
bwshockley said:
Question on source selection.
 
I've decided to go ahead and add in the skeleton DAC to my board.  I'm now reviewing my options for switching sources.  Of course, I could use a simple SPST attached at "IS".  However I was thinking about using the TRS headphone jack as the switch, such that the circuit at IS is normally closed when no analog input is used, selecting the DAC as the source and likewise, open when an plug is inserted into the jack, selecting the analog as the source.
 
Does anyone have a recommendation for a 3.5mm or 1/4" stereo jack with a built in SPST or even SPDT switch rated at ~27vdc?  Specifically, I'd like something similar to schematic "C" shown here: http://en.wikipedia.org/wiki/TRS_connector#Configurations_and_schematic_symbols Notice the isolation of the switch and the audio connects.
 
Anyone know of another option if my above fears are true? It'd sure be nice to just have the amp automatically switch sources based on either signal or a plug switch.
Click to expand...


The Max uses relays. I built one with a switched 1/4" plug on my original Millet hybrid, works great. I didn't use relays though, I just had the three channels going through the plug, then when a plug is inserted, they lift off and make contact with the plug. Also, on my Skeleton DAC, there's a tiny bit of noise, which is absent on the Grub. If you have the option, I'd recommend the Grub over the Skeleton.
 
Sep 17, 2012 at 8:39 PM Post #6,432 of 6,727
Granted, the SkeletonDAC is not as detailed as the GrubDAC, but the GrubDAC is more expensive.  However, I've built several SkeletonDACs and know many other people who've built them, too - there should not be any "noise."  Outside of that, I agree with your recommendation - assuming someone wants to pay the difference in price.
smily_headphones1.gif

 
Sep 17, 2012 at 8:46 PM Post #6,433 of 6,727
Quote:
tomb said:
Granted, the SkeletonDAC is not as detailed as the GrubDAC, but the GrubDAC is more expensive.  However, I've built several SkeletonDACs and know many other people who've built them, too - there should not be any "noise."  Outside of that, I agree with your recommendation - assuming someone wants to pay the difference in price.
smily_headphones1.gif
Click to expand...


I guess noise is the wrong word. When I connect the SkeletonDAC to the Millett with 14x gain and crank it, there was a little bit of digital gunk for lack of a better word.  It was very faint, but sounded sort of like a 56k modem. Granted, it is 100% imperceptible unless you turned the knob to 11, may have been an issue with my build, but that was my experience. The grub may well have done the same thing, it is in a different amp at lower gain...so I probably should have left that content out.
 
Sep 17, 2012 at 10:40 PM Post #6,434 of 6,727
Quote:
tomb said:
Granted, the SkeletonDAC is not as detailed as the GrubDAC, but the GrubDAC is more expensive.  However, I've built several SkeletonDACs and know many other people who've built them, too - there should not be any "noise."  Outside of that, I agree with your recommendation - assuming someone wants to pay the difference in price.
smily_headphones1.gif
Click to expand...


Hey Tom, any chance you have or are getting more GrubDAC kits?  Or even just the PCB?
 
Sep 17, 2012 at 10:59 PM Post #6,435 of 6,727
Quote:
bwshockley said:
Hey Tom, any chance you have or are getting more GrubDAC kits?  Or even just the PCB?
Click to expand...

Kits will be restocked probably by this weekend.  As for the PCB, there's plenty.  They've been in stock and available on the Beezar website for months ... and months.
 
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