Phono 11 modifications

[B Perry]

I recently set about carrying out some modifications to my stock Pre II and Phono II units, the pre II was first with replacement potentiometer, resistors and capacitors in the signal path. The upgrade to the Pre II was a big success so went on to do the same with the Phono II.

The capacitors changed in the Phono II were C10/11 and C18/19, size differences make this upgrade a little tricky but I managed to shoe horn them in. The outcome was not quite as expected, the clarity of the mid range and upper frequencies was very impressive and the sound stage widened. Lower register is less impressive there is a lot less power to the low frequencies.

With a little tube rolling I have improved it but it still lacks the power of bass notes when compared to the un-modified unit, (most of my vinyl has been transferred onto a NAS drive at 24/96 resolution so have a fair comparison). I decided that I would go back to the orange drop capacitors, unfortunately C10 was damaged in the removal so I intended to buy new replacements. This is were I have come up with a problem which I hope some one will be able to advise on. The C10/11 capacitors are marked up 100K and measure 10x8x4 in physical size, the circuit diagram calls for 0.1 micro farads which for orange drops would normally be marked up as 104k and physically nearly double the size. If my reading of the markings on the original capacitors is correct then they were 10 pico farads.

Has anyone with a phono II able to check what they have in the C10/11 position, and can anyone advise as to whether this is were my loss of bass power stems from.

[bob orbell]

Your two capacitors are .1uF and 2.2uF, both 250 volt rated, I think that the lack of bass is with the Pre II, quite frankly, my experience with Pre II was ****, thin and weak, Pre III however, is light years better, but for me, Akido cathode follower, by John Bronski is super. BOB

[B Perry]

The pre II is fine other sources provide an excellent bass response. I have had these for quite a few years the problem is with the Phono II the loss of bass only arose after the capacitor change in the Phono II.

[Richard]

Hello and welcome!

I have some of those orange drops, same size as you say, from my phono builds.

The smaller ones are marked in nF as 100nK250 (= 0.1uF 10% 250V) and the larger in uF as 2U2K250 (= 2.2uF 10% 250V)

If the new caps you have tried are accidentally of a smaller value at either or both these positions it would cause earlier bass roll off so double check their values

[B Perry]

Thank you Richard, my main concern was the value of the C10/11 capacitors, you have confirmed that the originals as supplied in the kit were 0.1 micro farad.

I have used Jantzen Silver Z caps of the right values for the replacements I may change these to either Soniqs or Sprague Orange drops.

[Richard]

Yes, a cap meter is useful to confirm or check values if you do much of this.

Keep in mind that any decent designer will have "voiced" his product to give a good balance for the money available. Change by all means but be prepared to change back or change again if a different cap doesn't really improve things.

WD orange drops are polyester and quite neutral sounding, bland in a good way. Polypropylene tends to be brighter sounding and some I've tried certainly tip the balance towards brightness.

I used SAX 0.1uF and PXX 2.2uF in two Phono3 builds and felt they offered an improvement in clarity and detail without upsetting the tonal balance,
http://www.world-designs.co.uk/capacitors.htm

[Black Stuart]

If you can still get any, try the Russian K73-16 caps for both positions.

The first cap in my Bada hybrid power amp was a 0.1uF changing this one cap transformed it, totally transparent. If they are still available they are ridiculously cheap and surprisingly very small. You will have no problem fitting either value. They are also far better made than any current made western cap. Not to be confused in any way with the Russian PIO or Teflon caps.