Quad ESL Cap mods

I have been researching the same options for replacing the electrolytics in my Quad 2905s. FYI the 220uF cap is in series with the input and it does have a 1.5 ohm resistor in parallel with it (which could also use an upgrade to a Mills or something similar). I have read several of the capacitor comparisons including some comments specific to Quad 2905s over on the Audiocircle website. My observation is that for very little extra cost you can get 2-100uF Mundorf MKP 400V. And for a little more again you could get 4-47uF of the same 400V MKPs. With the 2905s any shift toward a heavier balance is not what I want. So with four caps instead of one I have the flexibility to try various values and see if the increased resolution and speed(expected from smaller values with higher voltage ratings) are what I like better. My big decision is whether to spend more on Auricaps which I understand have a slightly nicer midrange and apparently are a step up from the Mundorf MKPs. Their premium price at two to three times the Mundorfs would certainly indicate this. I would definitely appreciate comments from anyone who has compared these two. Another big plus with the Mundorfs is the availabilty of a nice selection of blend/bypass capacitors such as the Supremes or the Silver/oils as someone pointed out. I think its likely combining MKPs with their premium capacitor lines would really improve the sound. I'm not sure if the Auricaps sound would improve being bypassed for extra performance. From reading the Auricap datasheet, its actually discouraged. I would like to know if anyone has had good results doing this also.

I spoke to a moodder and he says F & T MPP caps with a Harmony cap bipass are the best way to go for the price. He feels the F & T MPP caps give a better result than the Mundorf MKP.

He sais the only appropriate cap for this (Quad esl) application is MPP type (Metallised Polypropylene) and of course they have to be of adequate voltage -- because of this, suitable candidates are limited and pricey...

Any comments?

Any experience or comparison of F & T MPP caps?

thanks,
William

The Mundorf is rated at 250V, which should be more than enough.

HI
I have Auricaps and Mundorf PP caps in my tube amps (not the same application, I know). I prefer Mundorf Supreme to Auricaps IMS.
Mundorf caps are metalized polypropilene.
Munforf silver and oil is a significant step forward in transparency as compared to M. Supreme or M. tube cao, but it is only economically feasible as a bypass cap.
Many high-end speaker manufacturers are switching to Mundorf caps for their top model's crossovers: BW 800D, Magico, ZU Definition and some others I forget.
Any cap smaller than 220uF will attenuate deep bass response.

Regarding the paraleel resistor, find out its value and power rating (usually written in the transistor body).
Mills MR12 is widely well regarded as a neutral, non inductive resistor up to 12 Watts per resistor. You can use several in paralell to reach the correct ohmic value and power handling. E. G. ten 80 ohms 12W resistors in paralell will add up to 8 ohms and 120 watts.
Dale makes aluminum-clad non-inductive resistors in 20W and 50W ratings.
DO NOT install the resistor flush with the cap(s), because it will get very hot on music peaks and may damage the caps.
Any PP or MKP cap will certainly sound much better than an electrolytic cap, but if you can avoid the cheapest ones, it will be a wise investment, given the Quad ESL's transparency and midrange naturalness.
Good luck

I hope this helps

I have upgraded the capacitor/resistor with 9-22uF Mudorf Supreme capacitors and a 1.5 ohm Duelund resistor on each 2905 speaker.

Here are my impressions at 100 hours:

Much more coherent, space around instruments sounds more "right". Timbres and brustling sounds from musical instruments are less smeared/obscured. For instance I can now hear Stan Getz taking breaths between notes on "Getz/Gilberto". Glare is reduced to the extent that some recordings which were bordering on unlistenable are back on my playlist. The 60 Hz bump in the low end has been tamed. My big concern that the highs would get edgy or sterile did not happen. Overall changes to the frequency response I would characterize as a slightly less warm/heavy balance which I prefer. The midbass is less round and smeared so a lot of new information is heard in this range. Textures in the mid to upper bass are easily discerned and transients on drums and piano are much more realistic. The low frequency rolloff seems to be about the same but I will probably still try an additional 22uF to evaluate the effects. I also going to try a 4.7uF Mundorf silver/oil on the capacitor bank and will report back on bypassing with other capacitors. Possible suggestions would be appreciated. I will probably also try a 1.35 ohm resistor.

I did make one disturbing discovery during the upgrade. One stock capacitor tested at 216uF and the other was 255uF. This would partly explain why there was such a big improvement in imaging and bass resolution. Both resistors measured 1.6 Ohms. Concerning the cost, I purchased the caps and resistor with a nice 20 percent discount that Partsconnexion was offering, so $1300 was a lot easier to swallow. Would I do it again? At this point, it's a no brainer especially considering how badly matched the stock caps were. I'd say, on the major characteristics I hoped to improve, all were easily met with the exception of the leaner bass which I would rate a draw although its seems to be improving every day with further break-in.

I appreciate all the information from other agon members. I will issue an update after the break-in is complete.