The common-mode impedance is fairly low, but in differential mode, maybe about 1KΩ.
If you try larger cylindrical capacitors, use a C-meter to determine which lead connects to the outer foil, and connect this to the Bottom PCB lead (nearest J2).
Shielding the capacitor, or locating big caps too near to chassis may also degrade performance.
Leads of more than about 20mm, or capacitor bodies longer than 20mm are likely to cause more problems than they solve.
Having said all that, you may be able to find a silvered-mica cap of 150n 50V+, and that might be worth a try. The ac-voltage is so small that mica's soakage-effects won't be a problem, and the dielectic is otherwise as good as it gets.
If you try larger cylindrical capacitors, use a C-meter to determine which lead connects to the outer foil, and connect this to the Bottom PCB lead (nearest J2).
Shielding the capacitor, or locating big caps too near to chassis may also degrade performance.
Leads of more than about 20mm, or capacitor bodies longer than 20mm are likely to cause more problems than they solve.
Having said all that, you may be able to find a silvered-mica cap of 150n 50V+, and that might be worth a try. The ac-voltage is so small that mica's soakage-effects won't be a problem, and the dielectic is otherwise as good as it gets.
C3 is in the control path, but the signal voltage across it is well below 1mV, so I would be surprised if there were any differences with fancy dielectrics./QUOTE]
Surprisingly -or not- the difference is audible.
Good polypropylene capacitors are "better" than stock ones.
I regularly use Amtrans metalized PET capacitors here.
Amtrans AMCO | Hifi Collective
This old sorrow for us.
As you can see, the soldering -via as poppy seed - and fixing is a real pain.
Redesign would be an salvation.
Attachments
check out the 17 pages here:
http://www.diyaudio.com/forums/tubes-valves/38248-new-dht-heater.html
there are a number of posts reporting sound quality changes with parts substitution, mainly the R1 for a Mill NI WW, and your favourite flavour of film cap....for example I really liked an old yellow Hovland or a Dueland
many more disturbances to your contentment field await
C3 is in the control path, but the signal voltage across it is well below 1mV, so I would be surprised if there were any differences with fancy dielectrics./QUOTE]
Surprisingly -or not
Good polypropylene capacitors are "better" than stock ones.
I regularly use Amtrans metalized PET capacitors here.
Amtrans AMCO | Hifi Collective
This old sorrow for us.
As you can see, the soldering -via as poppy seed - and fixing is a real pain.
Redesign would be an salvation.
How about PPS dielectric? It's better for time-constants than MKT, and the 6mm long SMD chip will solder to the back of the PCB easily, and its EMC 'moment' (susceptibility to pickup) is that same as the standard part.
ECHU1H224GX9 PANASONIC ELECTRONIC COMPONENTS, Film Capacitor, 0.22 µF, 50 V, PPS (Polyphenylene Sulphide), ± 2%, ECHU(X) Series | Farnell element14
I haven't compared caps, but use a 0.22uF Hovland Musicap as C3, mainly because Simon (sjs) said he uses fancy caps and resistors (R1) in positions "where they are claimed to make a difference". I have a bunch of the Hovlands, 0.22uF and 0.33uF, so it cost me nothing.
EDIT: I posted this before I read Simon's post!
I have a bunch of the Hovlands, 0.22uF and 0.33uF, so it cost me nothing.EDIT: I posted this before I read Simon's post!
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Although I love the 26, I think I found the best way of getting the most out of the 10/VT-25 with the gyrator load. It overcomes the challenges of its high ra and works like a charm.
The dynamics, detail and powerful bass is outstanding. hard to achieve with a transformer. I previously tried LL1660/40mA in 4.5:1 and couldn't get this results.
I'm a happy bunny, this is my current preamp and is as good (or not even better) than the CX-301a:
Here are the details VT-25 DHT Preamplifer – Bartola Valves
The dynamics, detail and powerful bass is outstanding. hard to achieve with a transformer. I previously tried LL1660/40mA in 4.5:1 and couldn't get this results.
I'm a happy bunny, this is my current preamp and is as good (or not even better) than the CX-301a:
Here are the details VT-25 DHT Preamplifer – Bartola Valves
The alternatives are:
1. Wait for Ale to try the devices out and read it on his blog
2. Swap the components yourself and see of you can hear any differences (or measure them if you have the equipment)
I've done shoot-outs with capacitors, which took me to the Russian teflons years ago. And of course with transformers, plate chokes and the tubes themselves. I've done shootouts with cathode resistors - I could hear differences there in filament bias. You just put a few hours aside, line up the different components and then use a lot of clip leads and do a lot of repetitive listening (or measuring).
Problem is that with surface mount devices it's harder to use clip leads..... I guess the only solution if to make up two or three Gyrators with different parts and then swap them around. Ale can supply his gyrators with gold pins and sockets to make that easier.
1. Wait for Ale to try the devices out and read it on his blog
2. Swap the components yourself and see of you can hear any differences (or measure them if you have the equipment)
I've done shoot-outs with capacitors, which took me to the Russian teflons years ago. And of course with transformers, plate chokes and the tubes themselves. I've done shootouts with cathode resistors - I could hear differences there in filament bias. You just put a few hours aside, line up the different components and then use a lot of clip leads and do a lot of repetitive listening (or measuring).
Problem is that with surface mount devices it's harder to use clip leads..... I guess the only solution if to make up two or three Gyrators with different parts and then swap them around. Ale can supply his gyrators with gold pins and sockets to make that easier.
Are you talking about the IXTP08N100D? There's also the IXTP08N50D, IXTP01N100D. I don't have any of them right now.
I don't know if I want to do a shootout. I'm kind of interested on one level, but my interest in building hifi comes and goes in periods, and I'm a bit interested in other things right now. Weather is getting warmer and I like playing golf and making my own golf clubs. I also want to do some songwriting - I have to balance my passive interest in music with my active interest as a musician in making music.
I don't know if I want to do a shootout. I'm kind of interested on one level, but my interest in building hifi comes and goes in periods, and I'm a bit interested in other things right now. Weather is getting warmer and I like playing golf and making my own golf clubs. I also want to do some songwriting - I have to balance my passive interest in music with my active interest as a musician in making music.
I've built over 26 boards so far and tried multiple combinations. The problem is, I'm more interested in trying DHTs which due to its characteristics (e.g. High ra) weren't best suited for a transformer/choke coupling rather than all the permutation of FETs, etc.
I settled for the IXTP08N100D simply because has a higher Vgs (th) which helps the lower FET and the BSH111BK as lower FET because has great gm and low Crss. They both sound brilliant btw.
Even with a DN2540+2SK170 you can't go wrong.
I settled for the IXTP08N100D simply because has a higher Vgs (th) which helps the lower FET and the BSH111BK as lower FET because has great gm and low Crss. They both sound brilliant btw.
Even with a DN2540+2SK170 you can't go wrong.
Not really. I think they get very close to the DN2540+BF862. The BF862 is very low noise and sounds great. The BSH111BK provides higher bandwidth and slightly stronger bass as the higher gm lowers the output impedance a bit.
I will bring over some of the preamps next time with several boards and we can try a shoutout for fun...
I will bring over some of the preamps next time with several boards and we can try a shoutout for fun...