The new "My Ref" Rev C thread

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#661
Bengali said:
I pulled C13 and did DC Couple. Sounds much better. I still get the sharp 'zzzz'. What did you do to get rid of this sharp highs?
Click to expand...

Harshness comes mainly from FMs

Try the baseline mod first, among other effects reduces also harshness.

If what you hear is in the right direction but not enough buy Silmics then.

C21 and C9 as per my mod list helps a lot.

Remember that Silmics needs a quite long burn-in (ca 40-50 hours of use)

Good work! :smash:
 
#663
Bengali said:
what are your thoughts on the sound before the silmics were burned in?

have you tried Nichicon KZ MUSE? I've searched and did not find much talk about them. Seems the Silmics are the current trend.
Click to expand...

Initially Silmics have a wrong tonal balance, they're closed and bass is good but too much; during burn in bass level decrease and highs opens up ending with a nice balanced sound, rich texture and little or no harshness.

Quite all audio electrolytics and most film caps I've tried starts with an overwhelming bass that balance as they burn-in.

KZs tonal balance is very good with a deep bass but I think that they somewhat 'confuse' music, I haven't tried them in C9 position because they're too big (16 mm diameter) but I've tried them in C6,C11
 
#665
Bengali said:
what did you decide on the 150pF. did you stick with the WIMA or the CDE Silver MICA?
Click to expand...

The test of the SM was brief but to me FKP2 sounds a little better and costs 0.24€ Vs 1.07€ each... 😉

Russ White, the PCB designer, use CDE SMs in his MyRef.

It could be that since I've buyed those SMs some day I'll give them a second chance.
 
#669
Re: Heatsink Requirements

bluegti said:
How big a heatsink do these need? Will bolting the chip to the side of a hammond enclosure be enough, or do I need to have a sink with fins? [


Originally posted by AndrewT
Look at the National datasheet and double the recommended dissipation.
If you are working with a two channel heatsink and National say 6C/W is OK, then aim for ~1.5C/W for the two combined chips.
Click to expand...


Is that a "yes" or "no"? 😀

Seriously, I'm a "follow the directions" sort of guy. I looked through the datasheet and don't really understand what I'm looking at. There are two Thermal Resistance values listed, one for JC at 1C/W and one for JA at 43C/W. I'm not sure which of these values to use.

For that matter, I don't really know what to do with the values once I have them. There is probably a formula that can be used to calculate heat dissipation then compare that to the dissipation rate of the heat sink, but I don't know what is the heat dissipation is for a generic aluminum enclosure (similar to a hammond).

What I meant to ask was, will an aluminum enclosure provide enough heat dissipation for a single LM3886 in this design?

If "No" then I have some heat sink that is pretty large that I will use, but it will require some changes to my chassis layout. If "Yes" then I should have amps working by Sunday!

Thanks for your help.
 
#670
Is that a "yes" or "no"?
Click to expand...

depends on how loud you listen and if you drive 4 or 8 ohm load.

I'm using cpu heatsinks and at semi loud volumes, after an 1hour or so, the heatsinks are slightly warm. In this case, the thin hammond chassis will not suffice for heatsinking.

you don't need very large heatsinks at all however.
my previous post has a photo of the cpu heatsinks.
they are about 3" x 3" x 1".

bolting the LM3886 to the heatsink is awkard since the big caps are right in line of sight to the mounting hole.
 
#671
I used a pentium 3 heatsink for each one. This was more than enough. I am not certain but I think I am right that this amp is more efficient than a regular LM3886 chip amp as my little sinks hardly got warm with 8Ohm very efficient speakers. A chip amp on the same speakers got pretty warm with larger sinks. You dont need much sink. Anything 3x3x1 or down to probably a bit smaller will be fine. A computer sink in most cases will do the job. Dont stress this one. Its easy to get it right with whatever you have laying around.
I even tried with a 1.5x1.5x.4 sink. Got real hot but remember these have SPIKE protection and it will turn off before it hurts itself. If it starts to cut out you need a bigger sink. Easy.
Uriah
 
#672
A bit off topic but interesting part II

Some time ago I've reported that thanks to MyRef I've found some faults in my setup and that I've fixed it removing Rubycon ZL, Vishay MKP1837 and Evox-Rifa MMK.

Well, I was still earing something wrong in my setup and I was convinced it was for the ZLs that I've used as opamps PS decoupling in my modded Marantz...

So yesterday I've swapped them first with FCs and after with Silmics.

It was so, ZLs are not good for audio IMHO, they made midgrange 'gray', lifeless.

Both FCs and Silmics are much better but FCs to my ears are definitively harsh...
 

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#674
Elna Silmics

Thanks Madisound for the Elna Silmics. They are in now.

I had Nichicon's in there before, not Panasonics.

Sound is difference is subtle. It does sound warmer
and smoother which in my case works. It sounded pretty thin though, that's with DC couple.

I put back the 1uF K42y's and the sound is much fuller now.
Sounds pretty darn good for a little chip amp 😉
 
#678
Troubleshooting... where do I start

I got all parts soldered and checked joints. Seems ok.

I turned on the amp using "Poor Man's Variac". No bright bulbs so there are no apparent shorts.

The LED lights up.

But... no sound. There is a slight click coming from the board about 2 seconds after I turn the amp on. But no hum, buzz, etc. I checked my preamp, cd player and speakers with another amp and everything works so it must be the amp.

Not sure where to start - I've never had an amp not work the first time. I guess this is a learning experience. Are there voltages I should be checking, etc?

Thanks for your help.
 
#680
Re: Troubleshooting... where do I start

bluegti said:
I got all parts soldered and checked joints. Seems ok.

I turned on the amp using "Poor Man's Variac". No bright bulbs so there are no apparent shorts.

The LED lights up.

But... no sound. There is a slight click coming from the board about 2 seconds after I turn the amp on. But no hum, buzz, etc. I checked my preamp, cd player and speakers with another amp and everything works so it must be the amp.

Not sure where to start - I've never had an amp not work the first time. I guess this is a learning experience. Are there voltages I should be checking, etc?

Thanks for your help.
Click to expand...


Easiest first check is the input signal. Make sure you have a good source <test on a different amp> and then make sure the input + and - are not reversed on the board.

As always, pictures help.

EDIT: also, VR6 or 1.8T engine? Mk IV chassis? I had a 4 dr Mk IV turbo Golf. Loved it until the timing belt went out... :bawling:
 
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