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The diyAudio First Watt M2x
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Old 2nd December 2019, 11:37 PM   #2641
Mazeppa is offline Mazeppa  United States
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The diyAudio First Watt M2x
Quote:
Originally Posted by RafaPolit View Post
You have made me laugh we the "characteristics" that rabid audiophiles require! Really I'd call that a desease!
+1
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Old 5th December 2019, 11:05 PM   #2642
TungstenAudio is online now TungstenAudio  United States
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My F6 is finally up and running. And sounding way better than it has a right to after such a short break-in period.
Why am I posting this here in the M2x thread? Because I created a challenge for myself by extending the design parameters of the amp to the point that it needed a different input buffer. Based on experience with my M2x, I chose to use a variation of the Diamond buffer, basically a tweaked Austin input stage. In order to run safely at +/– 26.4 V, I designed the output stage around a pair of Toshiba TTC004B and TTA004B bipolar drivers. Their TO-126 package is somewhat more thermally efficient than the E-line package of the ZTX parts used in Austin. I added 10 Ohm base resistors and used 10 Ohm emitter resistors on those devices, and haven't found it necessary to add heat sinks.

Remarkably enough, it all fits on a Vero board that is the same size as the Austin PCB. Eliminating the M3 mounting hole pads frees up some space. The keen observers may notice a couple other changes as well. Once I've taken a couple more pictures and possibly made some measurements, I will post a proper write-up in the appropriate F6 thread. But for now I want to thank MJ and 6L6 for making the M2x, and this extension of the F6 possible.
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File Type: jpg F6 Channel Mods.jpg (387.5 KB, 271 views)
File Type: jpg Diamond buffer vero.jpg (313.5 KB, 270 views)

Last edited by TungstenAudio; 5th December 2019 at 11:09 PM.
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Old 6th December 2019, 09:27 AM   #2643
Stanislav is offline Stanislav  Australia
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Quote:
Originally Posted by TungstenAudio View Post
My F6 is finally up and running.
Beautiful job!
Well done.

Always interested in assemblies on strip board, that's how I do 95% of my projects.

Looking forward to your unbiased comparison of F6 and ACA Premium.
(I know it's not fair but still...)
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Old 6th December 2019, 02:03 PM   #2644
Mark Johnson is offline Mark Johnson  United States
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The diyAudio First Watt M2x
Socketed the first stage BJTs (2 x (EF + CS)) but not the second? Possibly because the second stage's TO-126 package pins are fatter than socket holes and, unmodified, are on a pitch of 0.085" rather than 0.100" like the stripboard and socket?

The LM4040 ICs are also housed in three-lead transistor packages, but unsocketed.

Omitting the pole-zero compensator might change the response to fast risetime square waves, using those Toshiba devices. Either for the better or the worse. NP and I went back and forth on this question a couple times in early 2018.

_
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File Type: png sockets.png (26.8 KB, 210 views)

Last edited by Mark Johnson; 6th December 2019 at 02:15 PM.
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Old 6th December 2019, 03:23 PM   #2645
TungstenAudio is online now TungstenAudio  United States
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Hi Mark. Yes, the socketed devices are as you have depicted in your schematic. When I installed the LM4040 ICs, I removed the unused leg and soldered them directly into the board. The TO-126 packages don't socket well into veroboard, so those were also soldered directly.

It is somewhat obvious that the photo and the vero layout drawing don't match each other. The photo was of the first implementation, an incorrect one that caused four resistors to be sacrificed in the name of science during the first channel board smoke test. The vero layout drawing shows the boards as currently built, where it was necessary to use insulated wire for the two power jumpers. It would be possible to un-cross those wires in a new layout, but that would require a different set of trace breaks. I decided I liked the look of the crossed wires, as they reminded me of the important power connections.

I did a little online research about diamond buffers before choosing to go with this one. I did run across some versions that used small value capacitors between the base pins of the output transistors to counteract a minority-carrier anomaly which showed up in high slew-rate square waves. (I believe whoop-de-do is the technical term.) Yours is the only one I've seen so far with an RC network. I simply reverted to an earlier practice of mine to install base resistors in front of drivers to control linearity and bandwidth. The 10 Ohm value is a placeholder for now, until I determine if another is more appropriate.

Last edited by TungstenAudio; 6th December 2019 at 03:26 PM.
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Old 6th December 2019, 11:08 PM   #2646
unixdeveloper is offline unixdeveloper  United States
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Question on the transformer:
Mark has mentioned that he used a 300VA transformer with dual 18v secondaries.

Question is: I have couple of 300VA transformers with dual 22v secondaries and can I use them on M2X. They are the Antek AS-3222 transformers. If not then I would order a 300VA with 18v secondaries from Antek.

Thanks!
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Old 6th December 2019, 11:16 PM   #2647
darrr is offline darrr  Poland
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If you use a classic power supply, the transformer is too large. I saw here on forum an alternative power supply project (SLB?). 2x22v will probably be good for that
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Old 7th December 2019, 12:01 AM   #2648
unixdeveloper is offline unixdeveloper  United States
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Quote:
Originally Posted by darrr View Post
If you use a classic power supply, the transformer is too large. I saw here on forum an alternative power supply project (SLB?). 2x22v will probably be good for that
I also saw the SLB power supply, will give it a try. Its limited to 3+ amps (or atleast tested with load).

I am going to be mounting this in a 4U deluxe chassis, so that I can try out different amps.
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Old 7th December 2019, 12:39 AM   #2649
Mark Johnson is offline Mark Johnson  United States
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I would suspect that 18VAC secondaries are a good match to 3U height full depth heatsinks.

While 4U height full depth heatsinks are a good match to 18 * (4/3) = 24VAC secondaries.

what about the square root? Not applicable here since the bias current is constant. P=V*I = V*constant
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Old 7th December 2019, 01:35 AM   #2650
TungstenAudio is online now TungstenAudio  United States
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I’m using a pair of Antek AS-3222 transformers with SLB power supplies in my F6. I used a different set of transistors in the CFP, which reduced the dropout voltage from 3 Volts to 2.1 Volts. The output voltage of each supply is +/– 26.4 Volts while providing 1.4 Amps to the channel board. The nature of of the SLB as a “ripple eater” makes the final output voltage somewhat difficult to pin down. A single SLB powering a typical M2x might end up at 25 Volts. This is at the upper limit of some of the canonical input stages that come with the M2x PCB set.
That’s a long way of saying it would be easier to build a more conventional supply using a transformer with 18V secondaries. Unless you’re willing to modify the input stages and/or the SLB so they are compatible with each other.
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