You'd have to be prepared to make your own umbilical cable so that you could have a tightly twisted pair for the heater AC, then put a screen around it. Maybe even a screen around the other wires as well. Then another over the top of everything to hold it all together. Making cables isn't nearly as hard as it sounds and it ensures that you get exactly what you want.
I've just finished a 12B4 line stage and this is how I did it:
- balanced differential pair of 12B4 with Morgan Jones CCS under the pair giving 6ma per tube. HT of 259Vdc, 170v on plate, 10K plate resistors.
- LL1540 output transformer in parafeed, with a 2.2uF parafeed across the centre pins of the primary.
- termination of secondary via 10k series resistors to a shunt stepped attenuator of 20k
This sounds pretty good to me. The LL1540 is small and cheap, and I was surprised to find it working so well.
- balanced differential pair of 12B4 with Morgan Jones CCS under the pair giving 6ma per tube. HT of 259Vdc, 170v on plate, 10K plate resistors.
- LL1540 output transformer in parafeed, with a 2.2uF parafeed across the centre pins of the primary.
- termination of secondary via 10k series resistors to a shunt stepped attenuator of 20k
This sounds pretty good to me. The LL1540 is small and cheap, and I was surprised to find it working so well.
Battery biased 12b4
I was very much enjoying the muscle this line stage added to my phono amp. But I couldn't leave it alone long...
Twelve AAA batteries (YIKES!) on each side have been added to bias the 12B4A's to 15.6V. The batteries are housed in a "container" separate from the innards of the line stage and have yet to explode.
Switching from unbypassed cathode resister to battery bias has had this effect (to my ear)
1. Gain, little effect. Maybe 5 1/2 vs 4 1/2 gain?
2. High frequency. A little more of the tingly stuff, not real noticeable. But a bit more clearness. It's not that the highs sound more extended, but a bit more clear on the extreme. Maybe the Zout of the unbypassed valve vs the battery bias doesn't compromise the roll off of the output transformer to my 45 yr old ears.
3. Detail, yes detail. Vocals, mumbling vocals, early R.E.M. style with instruments all around are identifiable and clear. This is a subtle but noticeable difference.
4. It just sounds a bit more dynamic.
And something weird. I put on Flaming Lips Yoshimi Battles the Pink Robots (limited edition translucent pink/orange LP version). When "Do You Realize??" came on, the beginning vocal was disembodied sounding like it was about 3 ft left of the left speaker. That was weird!
I think I'll listen some more.
Maybe install a voltage gauge to monitor the bias voltage. And a switch to discharge the batteries from time to time. And some long interconnects so I can move my mono-blocks next to my speakers.
Dan
I was very much enjoying the muscle this line stage added to my phono amp. But I couldn't leave it alone long...
Twelve AAA batteries (YIKES!) on each side have been added to bias the 12B4A's to 15.6V. The batteries are housed in a "container" separate from the innards of the line stage and have yet to explode.
Switching from unbypassed cathode resister to battery bias has had this effect (to my ear)
1. Gain, little effect. Maybe 5 1/2 vs 4 1/2 gain?
2. High frequency. A little more of the tingly stuff, not real noticeable. But a bit more clearness. It's not that the highs sound more extended, but a bit more clear on the extreme. Maybe the Zout of the unbypassed valve vs the battery bias doesn't compromise the roll off of the output transformer to my 45 yr old ears.
3. Detail, yes detail. Vocals, mumbling vocals, early R.E.M. style with instruments all around are identifiable and clear. This is a subtle but noticeable difference.
4. It just sounds a bit more dynamic.
And something weird. I put on Flaming Lips Yoshimi Battles the Pink Robots (limited edition translucent pink/orange LP version). When "Do You Realize??" came on, the beginning vocal was disembodied sounding like it was about 3 ft left of the left speaker. That was weird!
I think I'll listen some more.
Maybe install a voltage gauge to monitor the bias voltage. And a switch to discharge the batteries from time to time. And some long interconnects so I can move my mono-blocks next to my speakers.
Dan
Re: Re: Battery biased 12b4
It's a bit off topic but those effects are part of the metric I use to determine if circuit changes are in the right direction. Common effects in pop production (Q-sound for example) are based on what's called the Head Related Transfer Function, mimicking the acoustic shadowing of head and ears to create the impression sound come from beyond, before and above the speakers. Roger Water's "Amused to Death" is a classic in this regard, on my system there are sections in which almost all sound is located outside the boundary of the speakers. 'Girl' on Beck's "Guerolito" is another good example. Beck's voice is razor sharp dead centre while the piano is well behind and outside the speaker boundaries. I suspect THX and Dolby surround also employs these techniques as some movies literally fill the room corner-to-corner with sound. The thunder peals and bird calls during the opening sequence of the director cut of “Donny Darko” are a great example.
Sheldon said:
It's a bit off topic but those effects are part of the metric I use to determine if circuit changes are in the right direction. Common effects in pop production (Q-sound for example) are based on what's called the Head Related Transfer Function, mimicking the acoustic shadowing of head and ears to create the impression sound come from beyond, before and above the speakers. Roger Water's "Amused to Death" is a classic in this regard, on my system there are sections in which almost all sound is located outside the boundary of the speakers. 'Girl' on Beck's "Guerolito" is another good example. Beck's voice is razor sharp dead centre while the piano is well behind and outside the speaker boundaries. I suspect THX and Dolby surround also employs these techniques as some movies literally fill the room corner-to-corner with sound. The thunder peals and bird calls during the opening sequence of the director cut of “Donny Darko” are a great example.
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