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Old 17th July 2010, 04:01 PM   #431
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Quote:
Originally Posted by Bill_P View Post
Note that Wima has discontinued the MKS2XL series and absorbed values up to 10uF into the MKS2 series. Mouser has a very limited stock of MKS2XL in some values.
I saw, as you already noted values up to 10uF are now parts of the MKS2 series.

Those caps probably will never enter the extra PCBs BOM for their scarce availability from Mouser but if confirmed as much better sounding they could be sourced elsewhere.

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Originally Posted by Bill_P View Post
I don't see how changing C1, C2, C6, and C11 would hurt stability. For C6 and C11 the lower capacitance value would be less effective in filtering mains frequency ripple but the op amp PSRR probably takes care of that.
Good to know

Thanks Bill
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Old 17th July 2010, 04:15 PM   #432
lucylu is offline lucylu  England
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Originally Posted by ClaveFremen View Post
Hello everyone.

it wasn't possible to reach a complete agreement with AndrewT but he agreed to see how things will be going in the next days.

The first thing I want to clarify is which components I consider definitive (and so recommended) and which experimental (and so only if you want to experiment).

Definitive and recommended, with Mouser codes:

C12 Wima FKP2 220pF 100V (505-FKP2220/100/2.5)
C10 CDE CD10 22pF (598-CD10ED220JO3F)
C34 CDE CD10 10pF 300V (598-CD10CD100JO3F)

What to expect:

Even less harshness, wider and deeper soundstage, tighter bass.
The most rewarding is C12, I consider that cap mandatory.
The SMs, which are a fine tuning, must be CD10 because CD15 are too big, particularly in C34 (see photo)


Experimental:

All carbon/MK132 shunts (R10,R11,R13)
MKS2XL film Caps in place of elcos (C1,C2 = 10 uF - C6,C11 = 4.7 uF)
C7 Wima FKP2 10nF 100V
C5 Wima MKP10 LS7.5 10nF 630V
LM318 Metal Can

How experiments are going:

The MKS2XLs seems a BIG improvement and so far they don't seems to hurt stability, any suggestion on tests to make?
The FKP2 in C7 will probably be confirmed, it opens-up sound and bass is even deeper. The temperature of the LM318 with 10nF or 100nF remains identical, could this be a good indication of stability?
The LM318 Metal probably can be avoided not such an improvement and it seems it lacks some detail.
The MKP10 in C5 seems a nice improvement but in someway it lacks bass...
All resistors test are very hard, differences, if any, are tiny...


From time to time I'll inform you, like in the preceding paragraph, but please don't take such reports as a recommendation unless I mark clearly a component as definitive and recommended, as these reports simply describes the path to the final choice and thus can change from report to report.

Obviously any feedback from people that actually tries the alternate components is useful and welcome

Please, help me keep the thread on track!

Attached a nice photo and an updated BOM for PCB only buyers.
Hello I enjoy reading your posts on upgrades its very interesting your enthusiam spills over.I am trying to keep my kit till the winter months but i have come close to starting many times normally after reading your posts.Please dont be put off by others thank you john
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Old 17th July 2010, 06:08 PM   #433
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Hello I enjoy reading your posts on upgrades its very interesting your enthusiam spills over....
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Old 18th July 2010, 01:54 AM   #434
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Dario, that was very nice of you to share credit with me for this "ultimate" BOM a few pages back. You are a true gentleman. We are learning a lot together, and I hope Andrew will tolerate our excitement by understanding that we really are trying to help new builders by recommending possible improvements.

On a completely different note: has anyone else noticed that the Russ White schematic shows 24v as the output to the relay/muting circuit? Yet Bill P has calculated, and I have measured in a working amp, 16.7v there because of the size of R14. I cannot find Mauro's original Page 2 of his schematic. Is there a value given that is different? Bill P, have you built a working amp with the smaller R14, yielding higher voltage? Does the relay mute circuit still work okay? Perhaps the voltage was lowered there to obtain a faster drop out of the relay at power off. Do you hear any noises when shutting off the amp with higher relay voltage? Some of these value changes were made on the fly, and perhaps the schematic should show 16v, or perhaps somebody miscalculated and R14 really is too big.

I would like to know if anyone can offer suggestions about how I might optimize these amps for use in a bi-amped system. Is there anything I can do differently to build an amp for bass and an amp for mid/treble?

Peace,
Tom E
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Old 18th July 2010, 02:00 AM   #435
udailey is offline udailey  United States
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I wonder if this relay voltage/ resistor thing has anything to do with the LM318's that didnt click over the relay...
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Old 18th July 2010, 02:07 AM   #436
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Originally Posted by madisonears View Post
Dario, that was very nice of you to share credit with me for this "ultimate" BOM a few pages back. You are a true gentleman. We are learning a lot together, and I hope Andrew will tolerate our excitement by understanding that we really are trying to help new builders by recommending possible improvements.
It is simply the truth... all resistors in the BOM came from your recommendations...the BG in C9 also...C7 also etc.

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Originally Posted by madisonears View Post
I cannot find Mauro's original Page 2 of his schematic.
The page is only present in Rev. A schematic...that you'll find attached.

Quote:
Originally Posted by madisonears View Post
I would like to know if anyone can offer suggestions about how I might optimize these amps for use in a bi-amped system. Is there anything I can do differently to build an amp for bass and an amp for mid/treble?
I guess that the mid/treble section could be DC-Coupled since most crossovers for mid/treble has series capacitors
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Old 18th July 2010, 11:35 AM   #437
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Lazarus, copper transfer heat better, faster, but its resistance to air is more ore less the same than aluminium or other similar materials. But I think you will have enough with two of those copper heatsinks. Put one in each face of the resistor, and that is.

As I said, with an 8 ohm speaker load and about half of the volume of the amp, the output resistor remain almost ambient temperature, maybe less than 5 or 10 degrees above it.
I have although placed two small heatsinks, the standar ones for to-220 devices. Exactly this ones:
http://www.futurlec.com/Pictures/TO220S.jpg
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Old 18th July 2010, 11:41 AM   #438
Bill_P is offline Bill_P  United States
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Originally Posted by madisonears View Post
On a completely different note: has anyone else noticed that the Russ White schematic shows 24v as the output to the relay/muting circuit? Yet Bill P has calculated, and I have measured in a working amp, 16.7v there because of the size of R14. I cannot find Mauro's original Page 2 of his schematic. Is there a value given that is different? Bill P, have you built a working amp with the smaller R14, yielding higher voltage? Does the relay mute circuit still work okay? Perhaps the voltage was lowered there to obtain a faster drop out of the relay at power off. Do you hear any noises when shutting off the amp with higher relay voltage? Some of these value changes were made on the fly, and perhaps the schematic should show 16v, or perhaps somebody miscalculated and R14 really is too big.
My working amp with a 22VAC transformer uses 68 Ohms for R14 and I measured about 24.5 volts across the relay. The relay circuit works fine with no thumps at power off. Spice simulations indicate with R14 = 470 Ohms the drop out time at power off is about 300 milliseconds. With R14 = 68 Ohms it is about 420 milliseconds, not a significant difference in my view.

Andrew and I did some work on trying to improve the drop out time but the circuit doesn't seem to have enough degrees of freedom to maintain its other timing properties while shortening drop out time. It is possible to get a drop out time of less than 8 milliseconds if a separate 555 timer based circuit is added and connected to the transformer secondary.

The LM318 circuit is independent of the relay circuit and could only keep the relay from closing if it caused large DC output from the amp at power on.
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Old 18th July 2010, 03:21 PM   #439
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I sent out a couple emails requesting information on the availability of a current group buy for the Ref-C for those of us who are late to the party. I have not been able to find a "kit" or PCBs for these designs. I am willing to do my own sourcing if that is the path I must take, but I am not seeing a seller of te basic board for the Ref-C. Any help would be appreciated. I am sure there are others looking at this thread who are in the same quandry as I.
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Old 18th July 2010, 04:56 PM   #440
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