[Reverie]

Hey all,

I’ve decided to replace the output capacitors in my 41hz Amp4 kit with Wima Polypropylene ones, specifically MKP2 and FKP3 types (small size- RM5 and RM7.5), with values ranging from 0.1uf to 0.22uf.

However, I’ve checked some of my usual suppliers, but they either don’t stock these, or are sold out. 

Does anyone have any suggestions as to where to look for these?

Of course, I’d be very interested in knowing any as-good or better alternatives. 

Thanks,
Peter.

EDIT: The FKP3 are in fact too large for this application, only MKP2 are suitable.

[markC]

I replaced the Wima's in my preamp with Auricaps and prefered the Auricaps. Sonicap would be another good choice IMO.
I replaced the polyester coupling caps in my CDP with Sonicaps and it was a vast improvement.

[StevenACNJ]

Welborne Labs sells Wima Polypropylene caps.

For those values, I would use Sonicap Gen I. If space is a problem, Sonicap Gen II 200V are pretty small. 

[Gordy]

I've used the Sonicaps for both input and output coupling, love 'em!  They have just a hint of midrange body to them, which I like.  The Sonicaps also have solid core leads, as opposed to the Auricaps multi-strands, which usually makes for an easier install... http://www.soniccraft.com/

[Reverie]

Wow, thanks for all the input people.

I wasn’t expecting quite the same response, so to make it easier to explain what I’m after, I’ll include the recommendations of some people who are responsible for the kit:

According to the chip maker:

‘Co   4 X  0.22 uF 50V    stock cap= 'RM5_5X7'
Output capacitor, which in conjunction with LO, demodulates (filters) the switching waveform into an audio signal. Forms a second order low-pass filter. Use a high quality film capacitor capable of sustaining the ripple current caused by the switching outputs. Electrolytic capacitors should not be used.

Cz  2 X 0.22 uF 100V stock cap= ‘RM7.5_10X6’
Zobel capacitor, which in conjunction with RZ, terminates the output filter at high frequencies. Use a high quality film capacitor capable of sustaining the ripple current caused by the switching outputs.

Cdm 2 X 0.1 uF 100V   stock cap= ‘RM5_5X7’      
Differential mode capacitor.’

And from the Kit maker:

‘IMO the output filter caps are not very influential for the sound. What they do is filter away the switching residual at above 100 kHz. So they are very different from the input caps which form a high pass filter at a few hertz.

For the output caps it is important they have a low loss at high frequency (200kH - 1.5 MHz). The supplied caps are Panasonic polyesters which have worked fine. If you would like an upgrade, you can try to find polypropylenes that fit and have the same voltage rating. Note that unlike the input caps, the leads of the output caps must be as short as possible or they will not be efficient.’

I haven't checked the PCB yet to see if any other sizes can be fitted, but I'm guessing it will be more or less tailorred for those exact sizes.

Hope this helps.

[Gordy]

A switching amp!  The longer leads of the axial type caps could act as antennae for radio noise (note the Noforce amps)  Might be best to use the Wima mkp's for now, you can always experiment with Sonicaps etc. later.  SteveACNJ, JM and I have all used the Sonicaps very successfully in the UcD switching amps but, you never know with different circuits.  I also used Wima's in the UcD's and they worked wonderfully as well, I just had to use 2 in parallel to get the capacitance I needed 

[Occam]

To amplify a bit on what Gordy said about axial leaded caps, they typically, in place, have substantially greater inductance than radial caps. This is quite important in high frequency filtering application. The impedance of the cap is composed of both the capacitive and inductive reactance. Typically, the caps used for these roles are terminated radially for least inductance, as is their actual construction via techniques of stacking, double metalization, etc..... I recall that BelCanto reported substantial improvements on their last Tripath series amps when they used double metalized radial caps (something similar to the Vishay MKP1841, but I'm unsure as to what they specifically used)
Similarly, Auricap is testing (in Beta?) on a purpose developed radial version of their Auricap for the UCD amps.
Epcos, Vishay, Wima, Evox, Illinois Cap all make caps specifically for high frequency filtering appropriate for this application. But the choice from known characteristics really would require actual measurement of the implemented filter characteristics, as well as subjective evaluation if one credits such a worldview.

As to sourcing those Wima caps, a search on those identifiers will generally yield something on Ebay, as will the utility described here -
http://www.audiocircle.com/index.php?topic=14139.0

[Reverie]

Thanks for the explanation. It took me a while, but I think I understand it all now.

I have another question however:

Are there any Vishay (or perhaps other) alternatives that would be considerred better than those Wima offer?

Thanks again.

EDIT: Just had a look round, and I don't think they do anything that small unfortunately.

[mgalusha]

FWIW, the new Mouser catalog came in the mail this week and I see they are now carrying Wima.

[Reverie]

FWIW, the new Mouser catalog came in the mail this week and I see they are now carrying Wima.

Thanks

I'm finding it hard to find a UK retailer with these, so I may have to order from somewhere abroad, perhaps Mouser.

I have a somewhat trivial question that I've been stuck with though - the 100V and 250V models appear to have the same physical dimentions, and only differ in cost. Although more than the circuit's needs, would there be any value in getting the higher voltage?

Sounds strange question I know, but I'm sure I read somewhere on here or the DIYforums that someone reported better sonic results when replacing certain capacitors with higher voltage alternatives. Sorry if this is totally wrong  .

[Occam]

I'm finding it hard to find a UK retailer with these, so I may have to order from somewhere abroad, perhaps Mouser.

Hard for you???? Just imagine how hard it is for us when you don't bother to tell us WHERE you would like to source them from and you've not bothered to elucidate in your avatar.

From the 41hz site 'An assembly instruction and schematic is provided by email in PDF format when an order is placed.'

I haven't checked the PCB yet to see if any other sizes can be fitted, but I'm guessing it will be more or less tailorred for those exact sizes.

Hope this helps.

Moderator's hat on
You're guessing and you hope it helps????
No, it doesn't. I realize that you're excited and rar'n to go, but guess based info is simply not enough, especially when a little effort on your part would eliminate those guesses. Nor is the chipmakers suggestions that you did provide necessarily close to the actual implementation of 41hz. Tripath's suggested vallues, leadspacing, etc... in their demo board doesn't necessarily jibe with 41hz's.  Measure the lead spacings, read the provided schematic and/or the actual caps and tell us their actual values.
This will let everyone save time and effort, and you might actually get some useful information.
Hat off

Here are links to (mostly) GB based component suppliers -
http://www.acoustica.org.uk/t/naim/suppliers.html

[Reverie]

Hard for you???? Just imagine how hard it is for us when you don't bother to tell us WHERE you would like to source them from and you've not bothered to elucidate in your avatar.

I apologize for this oversight, I shall now go update my avatar information accordingly.

I haven't checked the PCB yet to see if any other sizes can be fitted, but I'm guessing it will be more or less tailorred for those exact sizes.

Hope this helps.

Moderator's hat on
You're guessing and you hope it helps????
No, it doesn't. I realize that you're excited and rar'n to go, but guess based info is simply not enough, especially when a little effort on your part would eliminate those guesses. Nor is the chipmakers suggestions that you did provide necessarily close to the actual implementation of 41hz. Tripath's suggested vallues, leadspacing, etc... in their demo board doesn't necessarily jibe with 41hz's.  Measure the lead spacings, read the provided schematic and/or the actual caps and tell us their actual values.
This will let everyone save time and effort, and you might actually get some useful information.
Hat off

Both the physical (I double checked myself by measuring) and capacitance sizes of the components I stated are in fact from the 41hz Bill of Materials and only the 'ideal component description' is from the Tripath Chip PDF. I apologize if this was misleading.

I further apologize for not physically applying the stock components to the board and checking for spare space, but on inspection just now, it appears that as I suspected - there is only a small amount of space between them (hence, the PCB is 'more or less tailorred' for caps of this physical size, which I suppose is to be expected). This however is not a problem, as I think the conclusion reached in this thread is that the WIMA MKP2 are very suitable due to their radial design, and conveniently have a size that should not prove a problem. Even if there was more spare space, I do not know any other suitable alternatives due to the lead-spacing restrictions.

Here are links to (mostly) GB based component suppliers -
http://www.acoustica.org.uk/t/naim/suppliers.html

Thank you for the list. I shall now check through some of them.

[Reverie]

Just to note, the only Vishay cap I could find small enough was the MKC1858 (the MKP1840m didn't have a small enough lead spacing). However, the MKC1858 is a 'polycarbonate film'; does anyone know how this compares to the polyproplene?

Thanks

EDIT: Just noticed the 'not for new designs' written on the top of the PDF  .

[Occam]

Reverie,

The Wima MPK2 are suitable for the 5mm lead spacing and the MPK4 for the 7.5mm
http://www.wima.com/EN/mkp2ue.htm
http://www.wima.com/EN/mkp4ue.htm
I've not found these on that list of vendors, but the Wima MKP I believe are available on the Continent. Can someone more familiar with sourcing in Europe please make suggestions?

EvoxRifa makes caps specifically for hf use, the PHE426 in the proper sizes.
http://www.evoxrifa.com/cap_catalog/pulsecap/phe426.pdf
Although RS carries some of the phe426, none are in the values/sizes you need. The other vendors on that list don't seem to have any.

Epcos, Panasonic and Vishay also manufacture appropriate caps, but as you said, it might? be easier to source them from the States.

All things being equal, a higher voltage rating is preferable due to the higher effective dv/dt.

Sorry for being so harsh, I get cranky late at night when I should be sleeping.

[Reverie]

...and the MPK4 for the 7.5mm...

Ah yes, I didn't consider that.

I had planned to just use the MKP2 (PCM5) and adjust the leads to fit a PCM7.5, but considering 'the leads need to be as short as possible' the MKP4 is a much better idea. However, it still seems to me the 0.22uF is only available in PCM10 or PCM15, correct me if I'm reading the size sheet wrong .

...it might be easier to source them from the States...

Perhaps, but as an example,the Mouser people wanted around $35 for postage (to be fair, it was fast), and for an order that came to $10, I found it hard to warrent.

I think I'll try emailing the WIMA Distributor for the UK, see what they have to say about it...

All things being equal, a higher voltage rating is preferable due to the higher effective dv/dt.

Noted.

Sorry for being so harsh, I get cranky late at night when I should be sleeping.

I did worry that I'd done something gravely wrong . No worries .