The new "My Ref" Rev C thread

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madisonears

Member
Joined 2007
Dario,

No, that description of sound pulling back behind the speakers referred to all of the sound, as was due to having new caps in the circuit. Since they have burned-in, the sound is once again very full and spacious, emanating from a three dimensional space all around the speakers. Center image is very real.

The coloration that is bothering me took a while to identify. It is subtle, and bothersome only on vocals. I knew something was wrong right away, but it took some serious listening to figure it out. Some might ask why bother if it's that subtle? Well, because I could hear it immediately, and I can hear it easily now. I know it shouldn't be there. Other than this minor defect, everything sounds so good.

I have ordered a smaller MKP cap to try there, 120nF. I figure that's a good compromise between Mauro's designated value of 100nF and Twisted Pear's 220nF value. I'll make a full report after I try it.

The typical recommendation for bypassing an Elco cap is one- tenth to one-hundredth the value. I'm not sure how small you can go before it has no beneficial effects at all. Your trial of 10nF seems awfully small. Does it still give the benefit of smoothing the highs?

I have been comparing Mauro's schematic to the Twisted Pear design and the NS design, and, per your recommendation, I plan now to remove the 220nF bypass caps in the LM3886 power supply, C17 and C18. If that improves the sound, I will consider also removing C19 and C20.

I don't have sockets to use for experimenting, so I must be careful making changes. If I wreck a board, I'll need to start over!

Peace,
Tom E
 
ClaveFremen

ClaveFremen

Member
Joined 2005
inserra.it
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madisonears said:
I have ordered a smaller MKP cap to try there, 120nF. I figure that's a good compromise between Mauro's designated value of 100nF and Twisted Pear's 220nF value. I'll make a full report after I try it.
...
Your trial of 10nF seems awfully small. Does it still give the benefit of smoothing the highs?
...
I plan now to remove the 220nF bypass caps in the LM3886 power supply, C17 and C18. If that improves the sound, I will consider also removing C19 and C20.

I don't have sockets to use for experimenting, so I must be careful making changes. If I wreck a board, I'll need to start over!
Click to expand...

Yes Tom, the 10 nF MKP1837 clear up things and tighten bass but I prefer MKS2 by a large amount.

I was planning to try 10 nF MKS2 and FKP2.

I would suggest you to remove first C19, C20.

C17, C18 removal gives a more subtle improvement.

Those SIL sockets are very cheap.
 
ClaveFremen

ClaveFremen

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Joined 2005
inserra.it
Paid Member
madisonears said:
The typical recommendation for bypassing an Elco cap is one- tenth to one-hundredth the value. I'm not sure how small you can go before it has no beneficial effects at all. Your trial of 10nF seems awfully small. Does it still give the benefit of smoothing the highs?
Click to expand...

I've ordered Wima MKS2s ranging from 10nF to 68nF and FKP2s ranging from 10nF to 33nF but they'll be here only at the end of the next week...

I've at home some 1nf Wima MKP2s and FKP2s buyed as alternatives for C30 and I've tried those on C21 position.

Wow, they do their job even if they're so small! :eek:

Both mitigate well the effect you described and do a wonderfull job cleaning highs :cool:

I particularly love how FKP2s sounds, they're so transparent and natural!

MKP2s are warmer and intriguing but a bit less transparent and I can't still decide between them...

When other values arrives I'll adjust the recipe ;)
 
sandbasser

sandbasser

Member
Joined 2008
Lost a shoulder washer + questions

Do I feel silly... Somehow, I managed to lose one of the small plastic shoulder washers from my kit. Can anybody spare one??? I'll pay a reasonable amount for the part, postage and your trouble. Please email me.

I've been following the discussion of Cap swapping with great interest. I'm going to try my hand at it starting with C9, C13 & C21. Thanks and kudos to Dario for his many thought-provoking posts.

I'd also like someone to recommend a replacement part for C4 & C5, the ones in the kit require too much tweeking of the leads for me.

Thanks,
 
ClaveFremen

ClaveFremen

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Re: Lost a shoulder washer + questions

sandbasser said:
Somehow, I managed to lose one of the small plastic shoulder washers from my kit.
...
Thanks and kudos to Dario for his many thought-provoking posts.
...
I'd also like someone to recommend a replacement part for C4 & C5, the ones in the kit require too much tweeking of the leads for me.
Click to expand...

You're welcome ;)

For C4, C5 you could use the one I've used:

An externally hosted image should be here but it was not working when we last tested it.


Wima MKP4 7.5mm LS (Perfect fit)

This seems ok for replacing the shoulder washer:

Shoulder Washer

Shipping cost to States is not high, 5.25 Euro plus 2 cent per gram, and you could optimize buying from them Elnas and other Wimas... ;)
 
soongsc

soongsc

Member
Joined 2005
As far as I can remember, this looked like an interesting design. Just wondering about a few things.
1. Does this have a DC decoupling cap in series with the signal path?
2. Where can this be bought as a kit in dual mono configuration?
3. If I wanted to feed my own +/-24~36 DC supply, can I just cut out part of the PCB to make it smaller?
 
schro20

schro20

Member
Joined 2008
multires.caltech.edu/
sandbasser

sandbasser

Member
Joined 2008
OK - I'm nearly ready to start casing up my RevCs - I'm going to be using a separate toroid for each amp (mono-block?) and I've got what is probably a dumb question...

I'm considering putting BOTH toroids in one case and BOTH amps in another case. Should I run two umbicals (one power each); OR; one umbilical (with BOTH powers)??? What kind of grounding issues can I expect with either option???

Thanks - and sorry if this seems like a dumb question - this is really my first time with a project this big.
 
troystg

troystg

Member
Joined 2004
Not at all a dumb question.

It is BETTER to run separate umbilicals.

The two cases should be at the same ground potential.

I would suggest (MY SUGGESTION) that you use the Neutric power con plugs or 4 pin Mic plugs. Use a shielded cable for the umbilicals. Connect the shield to chassis on both cases and the chassis to Earth grnd on the Pwr enclosure side.

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=090-542

EDIT: After looking at these I would not use them as they only have 3 conductors and would require a separate wire to Earth ground the chassis's.

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=092-286


Then both chassis will be Earthed properly and you can use a 3 conductor cable to carry each channels ac and pwr grnd.

Remember power ground and Earth ground are NOT the same.
 
M

madisonears

Member
Joined 2007
I agree with the true monoblock approach. There is nothing to be gained in performance by putting both xformers in their own case and both amps in another. In fact, besides the additional expense of connectors and umbilicals, it is possible that such an arrangement will introduce its own set of problems. I have built my monoblocks with the transformer very close to the power supply side of the amp boards, and there is no noise whatsoever.

Peace,
Tom E
 
V

VictoriaGuy

Member
Joined 2008
troystg said:
Not at all a dumb question.

It is BETTER to run separate umbilicals.
Click to expand...
Why?
Is this just because of the more readily available 3/4 conductor connectors (compared to 7-conductor?).
Should each transformer have its own mains cable as well?

Electrically, I don't see why the two transformers couldn't just be put in parallel if you need the VA rating increased. Use a single low voltage AC umbilical and feed both boards?

I agree with Andrew and troystg that if you are going to have 2 cases, keeping the transformers with the amps makes sense- if the cases match .

John
 
troystg

troystg

Member
Joined 2004
VictoriaGuy said:

Why?
Is this just because of the more readily available 3/4 conductor connectors (compared to 7-conductor?).
Should each transformer have its own mains cable as well?

Electrically, I don't see why the two transformers couldn't just be put in parallel if you need the VA rating increased. Use a single low voltage AC umbilical and feed both boards?

I agree with Andrew and troystg that if you are going to have 2 cases, keeping the transformers with the amps makes sense- if the cases match .

John
Click to expand...


No two trafo's are identical. They will vary in voltage and current. You could parallel them but it is not ideal.

A single umbilical cord would have parallel conductors. Channel separation and "power modulation" would be compromised.

The whole point of mono-blocs are complete separation all the way to the primary AC line.

A single AC input, fuse and pwr switch then complete separation there after is best if you are constrained to a single chassis.
 
S

samsagaz

Member
Joined 2004
troystg said:
Not at all a dumb question.

It is BETTER to run separate umbilicals.

The two cases should be at the same ground potential.

I would suggest (MY SUGGESTION) that you use the Neutric power con plugs or 4 pin Mic plugs. Use a shielded cable for the umbilicals. Connect the shield to chassis on both cases and the chassis to Earth grnd on the Pwr enclosure side.

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=090-542

EDIT: After looking at these I would not use them as they only have 3 conductors and would require a separate wire to Earth ground the chassis's.

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=092-286


Then both chassis will be Earthed properly and you can use a 3 conductor cable to carry each channels ac and pwr grnd.

Remember power ground and Earth ground are NOT the same.
Click to expand...





wich other connector brand will be ok to use? i want to see the same product but from another brand or at least with better/worst specs. I would order like 100 of these, i want to use it in all my amps .)
 
troystg

troystg

Member
Joined 2004
sandbasser said:
Sounds like the 'true' monoblock is the way to go.

Thanks for all the replies.
Click to expand...


Is riverside anywhere near Steve at apex.jr?

If so he has some twisted 3 conductor shielded silver plated Tefl*# wire that makes very good pwr cable for low current devices.

If I recall correctly it is 16 or 18/3 with a braided shield. And mono-bloc Rev_C boards are not going to draw that much from the mains..
 
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