arnoldc said:
whoa!
I really don't think that 12B4 is good candidate for that role.........
I have plan to make (even bigger part already in my head) LR based phono section,but I still search locally for several EC8010 and/or 7788....
without them,I don't wanna start breadboarding.....even if I tried few yrs ago just one channel .......just on bench,with drawer parts and PCC88 and PC900........
that's serious beeeeezneeeeeeeeeess ,not just another RCA -right from book phono stage
Just a simple question. I am toying with the idea of building a 12B4 preamp. I have some big light ballast tranformers which I would like to try as plate chokes. I expect them to be good down to at least 400hz. The question is could I put a simple single transistor CCS before the choke (ie +B - CCS - CHOKE - PLATE) to take up the slack.
Shoog
Shoog
"I have doubts that this choke will do the job;
measure inductance,and you'll know .......
besides-mix'n'match of CCS and choke?
why bother?"
Not an ansewr to the question.
The reason to do it is because a choke is generally recognised to sound superior to a CCS(or at least different), and since the choke is doing almost all the work it will contibute almost all its sonic signiture.
Would it work ??
Shoog
measure inductance,and you'll know .......
besides-mix'n'match of CCS and choke?
why bother?"
Not an ansewr to the question.
The reason to do it is because a choke is generally recognised to sound superior to a CCS(or at least different), and since the choke is doing almost all the work it will contibute almost all its sonic signiture.
Would it work ??
Shoog
Shoog said:
choke will be good enough if inductance is big enough,(we talking here in range of tens of H,and I doubt that ballast choke have more than few H).............if you have big enough choke-you don't need additional CCS in series with it.......if you don't have big enough choke,you can put few in series........that's why I wrote-why bother with CCS and choke in series
I'm good now?
Mark wrote:
At any rate it got rid of every last bit of noise form my 12B4 line stage and the stage seems to have improved in many aspects to boot. The S/N has got to be around 90db plus now! The bottom end does seem a tad bit deeper and more refinedl. The midrange is still glorious and the highs seem cleaner and even more refined than they were without it. Needless to say adding this solid state regulator did not change the overall character of the sound, it improved it without doubt!
Hey Mark,
Did you connect the RNT-400 with DC from your PS?
Have you try with 220 VAC?
Venlig hilsen Jan Jensen
At any rate it got rid of every last bit of noise form my 12B4 line stage and the stage seems to have improved in many aspects to boot. The S/N has got to be around 90db plus now! The bottom end does seem a tad bit deeper and more refinedl. The midrange is still glorious and the highs seem cleaner and even more refined than they were without it. Needless to say adding this solid state regulator did not change the overall character of the sound, it improved it without doubt!
Hey Mark,
Did you connect the RNT-400 with DC from your PS?
Have you try with 220 VAC?
Venlig hilsen Jan Jensen
12B4 PS idea?
Your results on the 12B4 sound good enough that I'm going to try it. Another nice feature of the 12B4 is tha the Rp is low enough to use anode choke loads effectively--and I have a boat load of NOS 12B4's.
For the hum issue--what about using a DC 12V CT supply with a filament choke on each leg and braided feeds to the filament. Hum won't be zero coming in to the filament, but with the cancellation it might work. Could add a hum balance pot to improve if necessary. This would satisfy the purist [no silicon in the circuit]
I've got some 18V CT transformers that might do the trick quite nicely.
I like the idea of a 12B4 line stage--only get about 15db of gain, but that's enough to get a good 5V signal out of the loud passages on old Vinyl assuming the phono stage is set up correctly. Couple that with my favaorite driver tube--SN7--and it works great for SE--and keeps the 12SN7 distortion as low as possible by designing for the higher input voltage.
Another thought is that with the nice low output impedance and gain of the 12B4, you could insert a low resistance Stepped Volume Control between the 12B4 and driver tube--and incorporate into a single MonoBlock. I like the idea of using the combination of line stage and drive tube to set the final output gain--instead of specifing that the input sensitivity to the power amp has to be .5V. This simplfies the circuit and should give better performance.
I think I'll go build one and see what it sounds like.
Your results on the 12B4 sound good enough that I'm going to try it. Another nice feature of the 12B4 is tha the Rp is low enough to use anode choke loads effectively--and I have a boat load of NOS 12B4's.
For the hum issue--what about using a DC 12V CT supply with a filament choke on each leg and braided feeds to the filament. Hum won't be zero coming in to the filament, but with the cancellation it might work. Could add a hum balance pot to improve if necessary. This would satisfy the purist [no silicon in the circuit]
I've got some 18V CT transformers that might do the trick quite nicely.
I like the idea of a 12B4 line stage--only get about 15db of gain, but that's enough to get a good 5V signal out of the loud passages on old Vinyl assuming the phono stage is set up correctly. Couple that with my favaorite driver tube--SN7--and it works great for SE--and keeps the 12SN7 distortion as low as possible by designing for the higher input voltage.
Another thought is that with the nice low output impedance and gain of the 12B4, you could insert a low resistance Stepped Volume Control between the 12B4 and driver tube--and incorporate into a single MonoBlock. I like the idea of using the combination of line stage and drive tube to set the final output gain--instead of specifing that the input sensitivity to the power amp has to be .5V. This simplfies the circuit and should give better performance.
I think I'll go build one and see what it sounds like.
Calculate Inductance
You can calculate inductance a number of ways, including the one you mention.
However, the best way to check the inductance of a choke is at the current it will be drawing. To do this set up a simple parallel LC or LRC circuit. Pass the DC Current you intend, and superimpose an AC signal on it using a signal generator. Sweep the SG and note the resonant peak frequency. This allows you to accurately calculate the inductance at the right current.
You can calculate inductance a number of ways, including the one you mention.
However, the best way to check the inductance of a choke is at the current it will be drawing. To do this set up a simple parallel LC or LRC circuit. Pass the DC Current you intend, and superimpose an AC signal on it using a signal generator. Sweep the SG and note the resonant peak frequency. This allows you to accurately calculate the inductance at the right current.