MyRefC build guide

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Nice - where are the Obligato's? Or have I not been paying attention and you've answered that already:confused:

Obbligatos are not there...

two reasons:

1 - When I test components I run the MyRef DC coupled, it's easier to ear subtle changes. :cool:

2 - My cap of choice for coupling the MyRef, since last year, is the Mundorf MCAP Zn, Obbligato Copper is second best so I've already ordered a pair of Zn for my new Myref :D

Even for this GB the 1.2uF Zn was my best recomendation but cost was an issue so an Obbligato 1.0 uF was selected (quite half price).

Then the Obbligato became 2.2uF and cost quite the same of the Zn... :spin:

Everyone has its own priorities... :D
 
Dario, have you done any work on substitutes for C4? I placed mine in the C17-C18 holes and there is probably room for a MKP10 to replace the MKP4. At some point I need to take the amp out of service to paint the front panel and plan to do a few upgrades then.

Along the same lines, I have lots of small polystyrene film and foil caps in small values (MIAL and Philips types) and could put them in for C10 and C34. Worth the bother, you think? Or is silver mica likely to be better?
 
Dario, have you done any work on substitutes for C4? I placed mine in the C17-C18 holes and there is probably room for a MKP10 to replace the MKP4. At some point I need to take the amp out of service to paint the front panel and plan to do a few upgrades then.

Hi Bill,

not yet.

It can be for the Week End :smash:

Along the same lines, I have lots of small polystyrene film and foil caps in small values (MIAL and Philips types) and could put them in for C10 and C34. Worth the bother, you think? Or is silver mica likely to be better?

It could be but only if you try you can say for sure, I suggest you to mount some sockets so you can swap them back and forth. :rolleyes:

It's so easy to lift pads desoldering... and polystirene caps are so sensitive to heat!
 
C9 it's a Blackgate Standard like the one in the kit but rated for 16V.

there's people using 6.3V Oscons too in C9...:D

Ceramics are the ones included in the GB kit.
I hardly think so. Or you got some different that mines. AFAIK, other builders received these yellow ones, like me:
http://www.tme.eu/katalog_pics/8/6/4/8644941372206f5419e575ba0512d62b/c317c100j1g5ta.jpg

Mines are kemet gold. Doesn't really matter, just for curiosity.
I can see that, as you said, you have substituted one of them for a film one.
Nice build, BTW.

Regards,
regi
 
Just an update. After delays doing other things (SWMBO influences my activities) I now have both modules working and running-in as I type. First tested with light bulb in series and then powered up and what did I hear? Relays clicking in and then silence. I like silence. No hums, buzzes or clicks. I have around 9mV DC on both of their outputs. It's jury rigged on a piece of MDF at the moment and connected to cheap bookshelf speakers but it's sounding good already. Now I need a case.

Cheers
Geoff
 
Geoff, nice job. Glad to hear it went smoothly.

Online Components raises its head again.... these folks really get to me. When they shipped me 4 of the 100 LM318 I ordered from them 5 weeks or some ridiculous amount of time after my original order with them I got upset and emailed them to not bother with the other 96. I ordered elsewhere and shipped to you all. Now they have shipped me the other 96 and of course charged my card. Idiots.
Uriah
 
Geoff, nice job. Glad to hear it went smoothly.

Online Components raises its head again.... these folks really get to me. When they shipped me 4 of the 100 LM318 I ordered from them 5 weeks or some ridiculous amount of time after my original order with them I got upset and emailed them to not bother with the other 96. I ordered elsewhere and shipped to you all. Now they have shipped me the other 96 and of course charged my card. Idiots.
Uriah

Uriah, dispute the charge with your CC provider.
 
C9 it's a Blackgate Standard like the one in the kit but rated for 16V.

there's people using 6.3V Oscons too in C9...:D

Polymers are also usable at C9 - I've used a Nippon-Chemicon PS 180uF/16V polymer in the M7/Symasym, and will be using them here too.

Black Gates should not be bypassed by smaller caps of any kind - it will retard burn-in, apart from being sonically inferior. In particular, high-Q film caps should not be used to bypass a Black Gate - it's recipe for creating peaking/resonances.

A pair of small Black Gates is usable at C1 and C2, instead of the 220 uF/50V FMs. I'd suggest 33uF/50V Black Gate STD here, which I'll use on the second build.
 
OK, I got one board assembled and powered up - it's now playing music. I'm not using the Ultimate BoM, but my own (value-oriented) BoM. I've got to say - it sounds great at first shot, without burn-in, even without the premium components. The entire speaker-protection relay circuit is omitted (I measured only 15 mV output offset, and the turn-on/turn-off pops are barely audible even without the relay).

Here's the value BoM (only relevant changes from the Ultimate BoM are listed):

C1, C2: Nichicon MUSE KZ 100uF/50V
C3, C8: Elna CE W 4700uF/50V (low-profile 30mm x 31mm)
C4, C5: WIMA MKS-3 100nF/250V 7.5mm
C6, C11: Elna RJJ 100uF/35V
C7: WIMA 330nF/50V 5mm (silver text, probably generic MKS)
C9: Nippon Chemicon PS 180uF/16V (polymer)
C10: 22pF/300V Silver-Mica
C12: 330pF ceramic disk, generic (subject to change)
C13: 4.7uF/63V polyester film, generic (subject to change)
C14, C15, C16, C17, C18, C19, C20, C21: (Omitted)
C30: 1.2nF/100V C0G ceramic
C32: 150pF/63V NP0 ceramic
C34: 10pF/500V Silver-Mica

D2, D3, D4: (Omitted)
DR1..DR4: MUR860

R1, R4: 1k/1W, Metal-Oxide, generic
R2: 10k/0.25W, 5% Carbon film, generic
R3: 2 x 0.22R/2W Metal-Oxide, generic (connect in series)
R5, R8: 22.1k/0.25W 1% Metal film, generic (hand-matched to 0.1%)
R6, R9: 47.0k/0.25W 1% Metal film, generic (hand-matche to 0.1%)
R7: 12k/0.25W 1% Metal film
R10: 347R/0.25W 1% Metal film
R11: 3.9R/0.25W 5% Metal film
R12: 2k7/0.5W 10% Allen-Bradley Carbon Composition
R13: 100k/0.25W 5% Carbon film, generic
R14, R15, R16, R19, R20, R21, R22, R23: (Omitted)
R37: 3k3/0.25W 5% Carbon film, generic
R39: 470k/0.25W 1% Metal film, generic
R42: 68R/0.25W 1% Metal film, generic
R43: 22k/0.25W 1% Metal film, generic

Q1, Q2, Q3: (Omitted)
Relay: (Omitted - short the n/o contact to power ground)
ZD1, ZD2: 12V, 1W

IC1: LM318 (TI, CerDIP) - socketed 8-pin DIP
IC2: LM3886TF (Isolated-tab)

If there's any interest, I can put together a component-kit for this value BoM in due course, maybe with minor modifications (Pricing TBD after refining the BoM, will probably be less than $20/ch for all components listed. The RevC bare PCB is not included and can be purchased from Uriah directly).
 
OK, I got one board assembled and powered up - it's now playing music. I'm not using the Ultimate BoM, but my own (value-oriented) BoM. I've got to say - it sounds great at first shot, without burn-in, even without the premium components.

Great.:)

The MyRefC sounds great with standard components but is some key components are changed it could be gorgeous! :cool:

But in your BOM there are some problems...

C3, C8: Elna CE W 4700uF/50V (low-profile 30mm x 31mm)

These are way too little... even cheap Chinese clones of the MYRef used 6800uF ones...

If they're availables in India you could try Kendeill that are cheap but souns great

C4, C5: WIMA MKS-3 100nF/250V 7.5mm

Caps in those position have a great impact on SQ, can't you use 100nF Wima MKP4 or 10nF Wima MKP10?

C7: WIMA 330nF/50V 5mm (silver text, probably generic MKS)

Idem, a Wima MKP2 or a Evox SMR 100nF are way better

C9: Nippon Chemicon PS 180uF/16V (polymer)

I think it would be better to not change values, isn't that cap available as 220uF?

C12: 330pF ceramic disk, generic (subject to change)
C30: 1.2nF/100V C0G ceramic
C32: 150pF/63V NP0 ceramic

Caps in those position have a great impact on SQ, a Wima FKP2 is the best you can buy, IMHO, and it's cheap too.

C13: 4.7uF/63V polyester film, generic (subject to change)

This cap is the MOST important of all... if safe with DC it would be better to omit it

R3: 2 x 0.22R/2W Metal-Oxide, generic (connect in series)

A 5W power resistor costs only 50 cents... and is much safer!

R12: 2k7/0.5W 10% Allen-Bradley Carbon Composition

I imagine you changed this value according to the also changed C12, I wouldn't change those values...

IC1: LM318 (TI, CerDIP) - socketed 8-pin DIP

This is a MAJOR problem, Mauro Penasa stated BOLDLY that it has to be a National Semiconductor LM318 because others have a different compensation networks...

Replacing the caps with Wimas costs less than 3$, will you sacrifice a BIG difference in SQ for so little?

Regarding the power resistor and LM318 (National) you should replace it...

I'm curious about your mixed choice of carbon and metal film, what guided you? :cool:
 
Dario, thanks for your comments as well as the immense amount of work you put into optimizing the component selections for this amazing amp.

But in your BOM there are some problems...
These are way too little... even cheap Chinese clones of the MYRef used 6800uF ones...

These are the only ones that are short enough for the particular case/mounting I'm thinking off. I have 6800/50 Panasonics, but they're taller - we'll see.


C4, C5: WIMA MKS-3 100nF/250V 7.5mm

Caps in those position have a great impact on SQ, can't you use 100nF Wima MKP4 or 10nF Wima MKP10?
...Idem, a Wima MKP2 or a Evox SMR 100nF are way better

Sadly, MKP4s are very hard to find locally. The MKS3s that I used were the only ones with the 7.5mm pitch available here.

I think it would be better to not change values, isn't that cap available as 220uF?

That polymer at 16V maxes out at 180 uF. I have some FMs in 220uF/50V, but those will not be sonically comparable to a Silmic II, leave alone the polymer. I can bypass it with a 47uF below the PCB, but that's not sonically advisable for a polymer.

This cap is the MOST important of all... if safe with DC it would be better to omit it

I'll short it, check the DC offset and proceed accordingly.

A 5W power resistor costs only 50 cents... and is much safer!

I can't find the vertical mounting 5W type in that value locally - so I went with a quick and dirty alternative.

Solving for I(rms): I(rms) = sqrt(4W / 0.44 ohms) = sqrt(9) = 3A => Ipeak = 4.2A => Vpeak into 8 ohms > 32V. My rails are 32V, so this is adequate even at peak power.

This is a MAJOR problem, Mauro Penasa stated BOLDLY that it has to be a National Semiconductor LM318 because others have a different compensation networks...

But the TI CERDIP sounds good enough, in fact great. OK, I'll go and look for the Natsemi ones, which are about half the price locally.

I'm curious about your mixed choice of carbon and metal film, what guided you? :cool:

I kept the metal films for all the accurate ratios, including the Howland and the GNFB loop. The remaining stuff was guided by whatever I had in hand, with carbon films being used in locations where the tolerance is not critical. I kept the Allen Bradley for R12 because I wanted a non-inductive resistor there to avoid having an LC pole with either C12 or C13 - this has caused problems of metallic resonance in past designs. R13 should be metal film, but I only had a carbon film in hand - I'll fix this later, but it appears to have no audible impact.
 
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This is a MAJOR problem, Mauro Penasa stated BOLDLY that it has to be a National Semiconductor LM318 because others have a different compensation networks...

I just downloaded the TI LM318 datasheet and compared the equivalent schematic with that in the Natsemi datasheet. They are identical in every respect, including all internal passives (except for the input latchup-protection diode network which does not come into use in normal linear operation).

In particular, the internal compensation networks and compensation pins are identical in the NatSemi and TI parts.

In short, you should be able to safely substitute the TI part for the NatSemi part, and vice versa, in the MyRef.

I can confirm that the audible sonics of the MyRef with the TI part are impeccable. Just to be certain, I'll also substitute the NatSemi part after I get hold of one to check if there's any audible difference.
 
Dario, thanks for your comments as well as the immense amount of work you put into optimizing the component selections for this amazing amp.

You're welcome! :)

These are the only ones that are short enough for the particular case/mounting I'm thinking off. I have 6800/50 Panasonics, but they're taller - we'll see.

I would change the case height then, 4700uF are not enough, IMHO

Sadly, MKP4s are very hard to find locally. The MKS3s that I used were the only ones with the 7.5mm pitch available here.

7.5mm pitch are best but you can adapt also 5mm and 10mm

And the FKP2s, hard to find too?

If so I would use Silver Mica that I suppose in India should be easy and not so costly to buy ;)

In some positions I've tried SMs and FKP2 and preferred the latter but SMs were near...

That polymer at 16V maxes out at 180 uF. I have some FMs in 220uF/50V, but those will not be sonically comparable to a Silmic II, leave alone the polymer. I can bypass it with a 47uF below the PCB, but that's not sonically advisable for a polymer.

Change manifacturer, there are a lot of polymer caps at 220uF! :D

6.3V rated ones are good too.;)

I can't find the vertical mounting 5W type in that value locally - so I went with a quick and dirty alternative.

Use a normal 5W ceramic power resistor and bend leads... or a Mills if available cheaply...

See the attached photo (it's the not yet finished cheapo version for surround channels...)

I kept the Allen Bradley for R12 because I wanted a non-inductive resistor there to avoid having an LC pole with either C12 or C13 - this has caused problems of metallic resonance in past designs. R13 should be metal film, but I only had a carbon film in hand - I'll fix this later, but it appears to have no audible impact.

Interesting, why don't simply use a carbon film? Their inductance should be pretty low.

Regarding R13 it's better a carbon film (and so for R11 and R10, IMHO), so it's good like you did.

If you look at the photo you'll find that in those positions I've used normal carbon film resistors too... ;)

I just downloaded the TI LM318 datasheet and compared the equivalent schematic with that in the Natsemi datasheet.
...
In short, you should be able to safely substitute the TI part for the NatSemi part, and vice versa, in the MyRef.

I've just reported what the author of the circuit recommend for the opamp.

It could be that the TI counterpart is (apart simplified schematic) identical, it could be not.

Mauro stated that he tried other manifacturers other than NatSemi and only the latter worked correctly.

Other than that I don't know what to tell about it.

Good listening! ;)
 

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Black Gates should not be bypassed by smaller caps of any kind - it will retard burn-in, apart from being sonically inferior. In particular, high-Q film caps should not be used to bypass a Black Gate - it's recipe for creating peaking/resonances.

We have seen a number of posts suggesting that C21 (bypass for C9, Black Gate) would be better omitted. As C21 needs to be mounted under the board, it would be useful to know one way or the other. Has anyone compared this BoM with and without C21? Unfortunately I have already built this as supplied and getting C21 off as an experiment (and then possibly putting it back) will be difficult.

Cheers
Geoff
 
Has anyone compared this BoM with and without C21? Unfortunately I have already built this as supplied and getting C21 off as an experiment (and then possibly putting it back) will be difficult.

Hi Geoff,

I suppose to confirm it in the next week or two but so far I'm using my MyRef without C21.

I can confirm that C21 is necessary if C9 is a Silmic or a Panny FM.

I would suggest you to wait that this last fine tuning is done and then, if you want, make all mods together.
 
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