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Old 10th July 2019, 05:48 PM   #2321
Blk Dynamite is offline Blk Dynamite  United States
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Quote:
Originally Posted by Nelson Pass View Post
If the fuse value is adequately small to protect a single transformer of the two, then
you should be fine. Generally audio power transformers are run at a fraction of their
rating.

Gotcha, thank you!!
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Old 11th July 2019, 04:20 AM   #2322
joshua43214 is offline joshua43214
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Quote:
Originally Posted by Nelson Pass View Post
If the fuse value is adequately small to protect a single transformer of the two, then
you should be fine. Generally audio power transformers are run at a fraction of their
rating.
I do this in my pre-amp. It has three transformers, but the fuse is just slightly over the rating for the smallest of them.

My comment was specific to using a 4A fuse with a pair of 235VA transformers, or some other situation where the fuse rating is twice (or more) the current rating of the transformer. In the unlikely event that a mouse chewed through the wires to transformer A, died of electrocution, and its corpse shorted out transformer B just enough to cause it to overheat and set them amp on fire, the smaller fuse will blow while the larger fuse will cause a real mess.
Seriously though, it is not hard to think up a realistic scenario where a 4A fuse on a pair of 235VA transformers could be a real issue.

-Josh

P.S. just wanted to say a personal thanks to Mr. Pass for making the M2 available.
I recently visited PS audio, and listened to their BHK system with the legendary IRS 5 speakers. As amazing as that system sounds (it will make a grown man cry), it did not make my system sound bad, if anything, I felt mine did a few things better. The M2 and B1 are truly worthy.
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Old 11th July 2019, 06:18 AM   #2323
MEPER is online now MEPER  Denmark
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It is quite normal to build in thermal fuse in primary windings of transformers. Especially the larger ones.
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Old 12th July 2019, 04:29 PM   #2324
MEPER is online now MEPER  Denmark
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I made my first distortion measurements on M2X mono block using REW software. I made a "quick and dirty" adapter from banana speaker out to RCA connector and a voltage divider (10:1). Measurements is with 5.3V RMS out in a 6.8 ohm resistor so 4.1 W which is relative high output. The measurement shows 2nd harmonic dominans which is different from FW M2 which is 3rd harmonic. Input board is standard Tucson. I think distortion is on par with FW M2? ..I am a little disappointed with the relative large 50 Hz noise but I can see that some is from external pickup of the adapter I made. If I try to screen with mu-metal etc. I can get it some dB down also if I put my hand on the chassis it drops a few dB. I have no earth connection in the outlet so this could also reduce it if I get earth wire installed. The 100 Hz noise is relative low so it seems PSU filtration is ok and Edcor pickup is minimal?
Will see if other mono block shows same result. It is my intention to make a small adapter box in metal with chassis mount female banana and RCA connectors to reduce noise pickup so what I measure is from amp and not from environment. Warm up was about 1/2 hour.
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Old 12th July 2019, 05:05 PM   #2325
ItsAllInMyHead is offline ItsAllInMyHead
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I’ve had quite a bit of time with the M2x now.

I’m not qualified to post a “review”. However, FWIW, I am extremely happy with the results. It could be new toy syndrome, but who cares? Of the amps I currently have, I find myself listening to it most often.

I had a few others come for extended listening sessions. Everyone seems to enjoy it quite a bit. I did a few very casual A/Bs with some listeners blind. It's a great amp.

If you want to avoid bias on daughter cards… skip the following. I try not to read others’ opinions before I form my own. Unless changes are pronounced, I find that my opinions differ from others’ anyway. It could be my lousy ears, the rest of the components in my chain, my (lack of) taste in music, or my room. Pick an excuse.

For those that are interested…

DAUGHTER CARDS - MORE THOUGHTS

It’s may seem odd to those that have listened to all the daughter cards, but for now the Norwood is my “daily driver”. I’ll be basing most comparisons in the future off of the Norwood.

I found the Austin and Norwood cards to be the most interesting. I’ve put at least 10 hours or so on each card. The Norwood, Austin, and Tucson (with the TI OpAmp) getting the most attention with much more than 10 hours each. The Norwood probably has over 50 hours on it by now.

I fully expected the Ishikawa (set to “neutral” on the pots and with the Toshiba FETs) and the Mountain View to be my favorites. Expectation bias be darned… They found their way to the bottom on my level of interest. The Ishikawa may be the most neutral. I don’t know, but it lacked some character and detail that I feel I get from the others. The Mountain View truly surprised me. It has (to my ears) an “edge”, which I cannot quite place. It may be my least favorite. I expected the Class A operation to give it the most laid back in presentation. Shows what I know…

Tucson may be my favorite, and I am looking forward to rolling some OpAmps. I got some extra boards from Mark and have socketed the OpAmps on the boards in the initial build.

So why am I so fascinated by Austin and Norwood? Austin is the only one that altered the overall frequencies or my perception of them. It seems to add a bit to the top end without making it harsh. Cymbals sound fantastic and the soundstage seems to open up in all three dimensions. The soundstage aspect is the most fascinating to me. It just seems right. Norwood seems to do everything just that little bit better than all the other cards (except the unique aspects of Austin) without bringing out any particular characteristic. I find myself just wanting to go back to the Norwood. It seems easy to compare against as a very good middle-ground baseline.

It may be that I built a few of them wrong etc. etc. Opinions are fun, but I certainly wouldn't base what to build off mine.

I still recommend building them all, but ... it'd be hard for me personally to recommend spending the money on the Toshiba FETs unless you're just that curious and have the money in the budget.

So... to Mark and Jim - if your one of your goals was to bring an incredible amp to the DIY group and offer some options using modern / cheaper parts than the unobtainium Toshiba FETs. Well-Done and Thank You!

WHAT'S NEXT

Not that I’m hooked on DIY or anything… I can quit any time I want… I really can…

• Make some updates for a common base PSU and chassis for all the future First Watt amps. Possibly duplicate or make changes to have a base for monoblocks.
o Continue to learn what “motor run” caps do and maybe try to implement them.
o Maybe add a set of XLR inputs
o Add a case to the toroid and potentially remount it.
• Measurements I’d like to try.
o Overall noise on the M2x. I think I’m not doing something correctly. I get 0V AC with the inputs shorted. My DMM measures to the microvolt, and I understand that 50mV is common with 20mV being good.
o Measure the distortion characteristics and tune the Tucson. This should be very fun. At the moment, even REW is over my head.
• Swap the caps on the M2x boards to the recommended Nichicons or pick some others and possibly try “bypassing”. That seems to be an interesting discussion. I used some standard Panasonic NPs when the Nichicons were out of stock. I didn’t realize that the “green ones” were highly recommended. It’ll be fun to see what all the fuss is about re: caps.

• Figure out a simple way to bypass the IPS altogether. My pre-amp has a 1Ohm output impedance and plenty of gain.

• Build the SissySIT once the boards arrive and order some Aleph J once boards they are back in stock.

• Research the F4; I think my speakers like some current. I have both a pre-amp with a lot of gain and up to 20V output along with a tube amp. That could be fun to play with in combinations.

Fun stuff!

Last edited by ItsAllInMyHead; 12th July 2019 at 05:09 PM.
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Old 12th July 2019, 05:19 PM   #2326
MEPER is online now MEPER  Denmark
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50 mV AC is not normal......it would be very bad. It is 50 mV DC (DC offset) which is normal and 20 mV DC good…..but with M2X you can get down to 1 mV DC. AC at output shall be much less then 1 mV.….so uV just fine.
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Old 12th July 2019, 05:45 PM   #2327
Mark Johnson is offline Mark Johnson  United States
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The diyAudio First Watt M2x
ItsAllInMyHead, it sounds like you're having plenty of fun, which is after all the end goal of having a hobby. Congratulations!

If your preamp can deliver a 3.5 volt sinewave into a 500 ohm load then your intuition is right: you can run your M2x without any daughter card at all. That's how Nelson Pass designed the original M2, and then at the very end he added his version of Ishikawa so that customers with vacuum tube preamps or "passive preamps" could use and enjoy an M2 as well.

Here is one simple way to do the bypass: #752 in another thread.

One set of experiments which you didn't mention, involves Major Surgery and requires General Anesthesia. You'll have to unplug all the 1/4" Faston connectors and remove the two amplifier boards from the heatsinks. Experiment: Increase the DC bias current in the M2x output stage and listen for improvements / no change at all / degradations to the sound. Do this with both 4 ohm speakers and 8 ohm speakers. You'll have to decide how much extra bias current you want, and then do a few calculations to find out the new component values which result in that new, bigger, current. And this is FUN!

Another member bought himself a couple more Edcor PC600-15K transformers to experiment with, and then he measured their frequency response while varying the output Zobel network (R5 and C1 on the official M2 schematic). You might find that you like the measured numbers better with different R5 and C1 than Nelson Pass selected. And you also might find that you like the sound of the amplifier better, with your Zobel instead of NP's Zobel. If you decide to try this, I suggest you download the white papers by Bill Whitlock on the Jensen Transformers website. They tell how Bill optimizes a transformer loading Zobel.
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Old 12th July 2019, 05:49 PM   #2328
ItsAllInMyHead is offline ItsAllInMyHead
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Quote:
Originally Posted by MEPER View Post
50 mV AC is not normal......it would be very bad. It is 50 mV DC (DC offset) which is normal and 20 mV DC good…..but with M2X you can get down to 1 mV DC. AC at output shall be much less then 1 mV.….so uV just fine.
Thank you for the correction and context. I'm obviously still learning. I got the DC offset to essentially stabilize a 0. It sways up and down with temp, but once the amp is at operating temperature, it's much less than 20mV. Rarely does it go beyond + or - 5 mV.

I just rechecked my notes. I should be more careful with units. The manual for the M2 states 500uV (AC). So, I still should not be getting a zero reading.

I'm clearly doing something incorrectly. My DMM is autoranging and should be able to pick up an AC voltage in that range or lower. It shouldn't be 0. I'll keep at it.

Thanks again!
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Old 12th July 2019, 05:59 PM   #2329
MEPER is online now MEPER  Denmark
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Less AC at output with shorted input is better. 500 uV noise is rather high. 0 VAC at output is much better. 0 VAC is the optimal goal which means "no noise". You should not try to get 500 uV if you have 0 uV. Usally a very good amp has 100 uV or less noise (AC). Probably you have some uV noise…...even your DMM reads 0. I have 100 uV (0.1 mV) resolution on my DMM and my DMM reads 0.0 mV at output which means less than 50 uV noise…..but DMM are not very accurate at these small noise levels…..so it could also be 70uV.....but probably less than 100 uV.
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Old 12th July 2019, 06:03 PM   #2330
ItsAllInMyHead is offline ItsAllInMyHead
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@Mark Johnson -

Thanks as always. Cut and pasted into my notes for future consideration. Until I get another First Watt amp built - I just can't bring myself to perform any major surgeries. I'm easing myself into things...

What's encouraging is that a few short months ago everything in your post would have flown WAAAAAAAY above my head. Now, I understand most of what you wrote, with the exception that I haven't the foggiest clue what a "Zobel" might be or how it may affect things. More fun reading. That may be DIY 201... I'm still trying to test out of 101 with AP credit. The good news is that I do have a stash of unused Edcors. I'll use two for the SissySit, but if there are measurements to do beforehand for either amp, I'll see what I can learn and if I can apply that knowledge.

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