Phono II mods : Dynamicap Silver Mica & tubes

[Rupert]

Hi All

Just a quick post on my latest tube rolling and cap replacing efforts in Phono II. Thought I'd better post before Phono II becomes Phono III!

First off a bit of tube rolling. Tried some EH 12AX7E, JJ/Tesla ECC83s and Sovtek 12AX7-LPS in place of the Chelmer valves. Liked the Sovteks but still wasn't quite there so threw one of the NOS Mullards I'd tried some months earlier and abandoned (too polite and soft) into the mix. Finally settled on a Mullard in the 1st valve position followed by two of the new Sovteks. A nice sounding combination. For good measure fitted a Harma 6922 to PRE II, £22 from Watford valves, not the cheapest around, but sounds good. Tried a Phillips Jan 6922 here but ridiculously microphonic.

With everything sounding decidedly better I moved on to the caps. Followed some of the thoughts posted here and tried a mix of Dynamicap and Silver Mica.

First in were the Dynamicaps, ordered from Percy Audio (great service by the way, arrived in three days from states, declared as a gift, no duty).
Fitted them in the 0.1uf and 2.2uf positions in place of the orange drops.
Wow! Very nice indeed, sounded good from the get go. Won't be trying anything else here. A big thumbs up. Nice natural presentation, didn't push the sound in any particular direction, just let more of the music through. They are described as warm sounding, but didn't think they sounded any warmer than the orange drops.

Next to try was a silver mica in the high freq eq section, the 8.2nf cap I believe. Wasn't sure I could here much difference so fitted a switch along with the old cap so I could switch back and forwards between the two. I could hear a subtle difference , the silver mica perhaps a little sweeter in the treble but nothing amazing, but decided to fit the silver mica permanently.

Finally I tried a silver mica in the low freq eq section, the 220pf cap. Decided I would fit a switch straight off so I could compare the difference with the old cap. Very unimpressed. I could be kind and suggest it sounded warmer or smoother. Frankly it just sounded muddy, the upper bass somewhat overblown. The stock cap sounded far more natural. It might work in your system etc., but certainly not in mine, and I've left the old cap in. Now I'm doubting the Silver mica in the HF section and might try something else here when I have time.

Any ideas on some alternatives to the Silver mica, more Dynamicap perhaps or something else? I don't know whether caps have the same effect in a filter position, when they are not necessarily directly in the signal path, rather than a coupling position. Out of interest, what type of cap are the blue cylindrical ones WAD used as standard in the small cap (8.2nf and 220pf) positions in Phono II?

Anyway, those are my findings so far.

Rupert

Rupert

I was interested in reading your about your PhonoII mods. I'm just starting to build up a new PhonoII PCB and was planning to use the Auricaps that I used as the 0.1 and 2.2 µF coupling caps on my old board but I've read good things about Dynamicaps now in a couple of places and might give these a go. Is there a UK supplier? I looked in Partsconnexion and note that they don't list a 2.2 µF but do have a 2.0 µF is this what you used?

BTW - when I ordered capacitors (Auricaps) before from Partsconnexion I checked with UK Customs and Excise and found that capacitors are zero rated on import duty! and didn't get charged any VAT. Service from Partsconnexion was also very swift.

When I fitted the Auricaps to my original board I ended up damaging some of the pcb foil when I tried to enlarge the board holes to take the thicker cap leads. This is one reason I wanted to build-up a new board.... This time I'm planning on fitting pins at any point I might want to switch out componets....

I was also planning on fitting silver micas so was interested in your comments about the results with these. I like the idea of fitting a switch to be able to check the impact - I guess it was just a simple minature toggle switch? Incidentally do you (or anyone else) know what the WAD stock cap types were? Mine are blue axial but no indication material used....

Steve

[John Caswell]

Hi guys,
I think that you will find that if you put a switch in to change between the two types it will add so much extra capacity that you will not get sensible answers. This area of the cct is very sensitive to capacitor type and stray capacity.

John aka Dr John

[Rupert]

Hi John

Thanks for that comment. I didn't realise a switch would have significant capacitance. This might explain why the Silver mica I tried, which is generally thought to be a good mod here, sounds muddy and disappointing. I'll try hard wiring it.

"cct", is that another of those three letter abbreviations you promised us you weren't going to use.

Steve, I did use a 2.0uf cap, I enquired here and this value is not critical. Someone suggested the supplied blue caps are polystyrene but I don't know if this is true. Suggest switch may not be such a good idea!!

Rupert

[John Caswell]

Oops yet again!
cct = circuit

John aka Dr John

[Rupert]

Ok, just for the record, I removed the switch and can hear a difference, it does sound better. You were right John. The difference is not vast though. I do think the switch allowed something of a comparison to be made between the two caps, but obviously I wouldn't now leave it as a permanent thing.

Anyhow, after removing switch I was a bit more convinced by Silver Mica in LF section. Still thought it a bit thick and heavy sounding.

I then tried changing some resistors. First a tantalum for the first resistor R15/16. Blimey! Any thoughts that resistors have a negligable effect blown away. This brought a cleaner, leaner and more detailed presentation that balanced out the thicker heavier sound of the Silver mica rather nicely. I like this alot. Then tried a tant for the last resistor R35/36 but perhaps a bit too much of a good thing. Swapped for a kiwame, but that pushed the sound towards the soft end of the spectrum more than I liked. The first resistor definately seems to have a bigger effect than the last though.

Anyway sticking with the one tant for now and the Silver mica that I didn't like at first! Getting the combination right is important, a rather obvious statement I know. Sorry for being such a Johnny come lately, and stating what most of you found out long ago, but Phono II sounds way better with some tweaking, almost a different phono in fact. Perhaps I should say thanks for the tips.

Going to try some other resistors, to see what happens, as they clearly have quite an effect in Phono, and they are relatively cheap, well most of them anyway. Could do with a little more upper treble without loosing too much warmth or bass though. Any suggestions?

Rupert

Rupert,
Thanks for your ongoing details - very useful and clear reading!

Re upper treble, have you tried the 3.18us modification?

I also found that using 5751 tubes in the Phono added 'sparkle', but you may find them a little less warm than your current choices.