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Old 15th November 2012, 11:50 PM   #731
tuyen is offline tuyen  Australia
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Hello chippers,

Not sure if this is the right thread to ask, but is this myref incarnation meant to be an improvement over the myrefC ultimate BOM version? or just different?

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Old 16th November 2012, 12:20 AM   #732
bcmbob is offline bcmbob  United States
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Jac, you're reading my mind waves. I really appreciate you considering a fix, but the things you mention were checked early in the struggle. I have had a home A/V studio (I produce a few local TV commercials) with multiple computers and a rack of audio boxes for several years. I drove myself crazy back then and understand the loop complications. The switch to digital connections has greatly reduced those glitches.

Sunday I set up the complete system on a table and used short (6 to 12") interconnects. That didn't help. As I write this I'm finishing a little rig that might help the diagnosis. It's a bare SMD pot with solid grounds on one end and loose grounds on the other. There is also a jumper available to check if the L/R grounds need to be common.

Now I have to move everything back to the table and do some poking. Hopefully I'll have something good to report in the morning.

Thanks again....
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Old 16th November 2012, 10:39 AM   #733
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Originally Posted by tuyen View Post
Not sure if this is the right thread to ask, but is this myref incarnation meant to be an improvement over the myrefC ultimate BOM version? or just different?
I would say both, refer to this thread for project goals.
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Old 16th November 2012, 11:32 AM   #734
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I would say both, refer to this thread for project goals.
tuyen,

I would say that Dario is being modest. I can't find the exact post, but bcmbob has built both, loved the ultimate MyRef C, and found the Fremen Edition to be a clear improvement. Bob even put his FE Beta amp up against a $5000 tube amp owned by a friend. He said it didn't match the tube amp everywhere, but he was very pleased with the FE, even without considering costs. Both of those posts are in the Beta build thread, if you can find them.

Jac
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Old 16th November 2012, 01:21 PM   #735
bcmbob is offline bcmbob  United States
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Let me respond by simply showing my path.

Started with the ChipAmp BrianGT. I was amazed that it sounded as good or better than my Carver M-1.0t, Hafler 120 and a $1700 Denon AVR-2807. There was not as much gain as those three, but the price/performance ratio was outstanding.

Next was the Twisted Pear MyRef V1.2. The gain was about the same but it had a more relaxed sound and was a little less forward. At this point (at the risk of offending anyone's music choices) I got the impression the BGTs (and a set of BPA-150s I built) might be great for pop and party music, but the MyRef would do a better job with classical, small chamber and jazz combo offerings. Both amps are great and I would have been happy with either.

Linuxguru introduced the V1.3 which I viewed as a refinement of the TP design. The stock kit was very close to the previous version but seemed a bit more solid and detailed. The addition of his LF0-1 module removed almost all of the upper register graininess/edginess so often reported of the LM3886 chip itself. This is also when I moved from a 120VA transformer to 200VA. That brought the gain (bare pot and/or LDR attenuator) close to a point where no preamp was necessary. Again, I could have stopped right there and been satisfied for years.

When I completed the beta version of Dario's Fremen Edition I had to restrain from stating it was a quantum step beyond anything I had owned. I eventually did post that evaluation. That was the stock BOM with the old 120VAs, but the clarity, stage, sweetness and definition blew me away. Won't go into great detail but better main caps, higher grade resistors and small caps along with two new 300VA toroids created a truly impressive build. This is where I took the FEs to a local audio dealer and a friend with a high dollar tube amp for comparison. The results were very satisfying considering I had ~ $625 invested in the pair and the others cost thousands.

The RC version continued to refine the sound and smooth away that last bit of LM3886 edge on the top. Further testing and selection of components in the signal path continues and a real "Cloud 9" power amp is developing - IMO. With high quality sources and good speakers, the FEs will convince you the performers are in the room, be they a small folk group, large orchestra (with pipe organ) in a cathedral or any style and venue you fancy.

The only thing I haven't heard and most likely will try (for comparison) this spring is the Pass F5 house heater. I suspect someone like madisonears might even talk me out of that.

Any of the amps in this post are super projects for the DIYer. It's just a matter of budget and how much "Hi" you want in your "Hi-Fi"

P.S. Linuxguru is developing a dual chip design that looks very promising and will probably fit well in the top choice LM3886 power amp group.
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Old 16th November 2012, 03:59 PM   #736
tuyen is offline tuyen  Australia
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Cool! Thanks guys

The FE sound like it may still be worth the effort to try later on, even though I have the myrefC ultimate bom + lf-01 coming!

I'm looking for basically the ultimate sounding low powered (10-20watt is enough) ss amp possible. diy by design so as to save $$$. This My_Ref FE seems like one to put on top of the list. I have been using a modded TA2020 chip amp.
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Old 19th November 2012, 12:24 PM   #737
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Exclamation Hummmmm?

Bob,

You may already be doing a useful experiment for all of us who have yet to "box" our FEs. If I remember correctly, you were having a bit of a hum from your FE RC but none from the FE Beta. I also recall that you have 300VA shielded torroidal transformers for one and conventional, non-shielded torroids for another.

I was curious if, either boxed or boarded, transformer shielding made any difference? Have you already run the experiment of using both the RC and the Beta with the same transformer and box setup? Or both transformers with the RC? If so, is there any correlation to hum and transformer or board?

I note that Dario uses the R-Core transformers which are likely to be better for radiation.

Has anyone else built their RC into a box and been clean for hum? If so, can you detail your ground layout? Actually, the amp that Dario built for his brother may be a clue. Does that one have conventional torroids and no hum?

As for me, I am still no hum and on a board, but I am working on the box, rereading Douglas Self, and thinking about ground loops.

Jac
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Old 19th November 2012, 01:34 PM   #738
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I note that Dario uses the R-Core transformers which are likely to be better for radiation.
Yes they radiate less but I don't think Bob's problem is related to the type of transformer.

Quote:
Originally Posted by lehmanhill View Post
Actually, the amp that Dario built for his brother may be a clue. Does that one have conventional torroids and no hum?
My brother's amp uses the same R-Cores as mine, both works with no hum, attached to AV receivers, DCB1 and simple pot.

Jac, can you measure voltage between PGND and safety ground?
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Old 19th November 2012, 05:05 PM   #739
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Jac, can you measure voltage between PGND and safety ground?
Dario,

Just for clarification, I do not have any hum and I have the FEs mounted on a wooden board. That means, no connection between safety ground and PGND. But it was still interesting to measure, so...... with the amps on and connected to the DAC + bare pot, I measured 0.4 mV DC, then switched to the AC channel and measured about 10.4 mV AC. This was the same for both channels and stayed the same with music playing or not.

At this point, I am just researching and trying to understand proper grounding techniques. If my math is correct, 10.4 mV is only about 20 dB below a typical input signal, so connecting PGND to safety earth might be expected to generate a hum.

If we don't connect the FE amp to safety ground, but the chassis is properly grounded, then safety should be served as long as the box stays closed. I'm not sure this is true with Class 1 transformers. I need a better understanding.

It looks like the FE and other MyRefs refer to ground through the shield of the input signal via R11, so the DAC or other source provides the reference to ground. That assumes isolated single end connectors at the chassis.

If you follow Andrew's suggestion, then the input shield connects to chassis ground and, if you have a high quality star ground near that point for the safety ground, then you should minimize the hum risk and reference earth within the amp. This approach is recommended by Douglas Self. In neither case would PGND be connected, although it might be interesting to see what happens if you ran a wire from PGND to the star ground.

As I say above, I am just trying to better understand what is happening so that I can build a boxed version that stays quiet for hum.

Jac
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Old 19th November 2012, 06:01 PM   #740
bcmbob is offline bcmbob  United States
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Jac,

Dario Is trying to help with some unexpected voltages on my builds - possibly leakage or some defective parts. This is what I'm getting:

Neg probe to PGND
Pos probe to safety/earth Gnd.

RC Build
Left AC= 45.9V-----Right AC= 27V
Left DC= +200mV --Right = +158mV (these readings keep going up - stoped at 300)

Beta Build
Left AC= 88V ------Right AC = 88V
Left DC= -58mV ----Right DC = -47mV

These are both on boards. Both play music perfectly if correct source is used. I don't think it is a no-metal-chassis problem.

?????????
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