Hi
1) no matter. Is the volume planned before or after the above
pre stage?. I asked this because this pre will be saturated
if the input signal is greater of about 1Vrms. So I hope the
volume is before.
2) o.k. 4.7k is rather small. you will need low output impedance
and good current capabily.
3) As is ( loaded by 4.7k) the circuit has a gain of 24.5 db,
that is 16.8x but it is at -3db at 40 Hz. The out cap has to be
at least 4u and the bypass cap 300u. This happens
because the output res is too high, greater of 2k, in respect
to the load.
4) a CF is a very simple buffer. It has no gain but is is not
relevant if you utilize, for example, a CD player as source
since you have usually 2Vrms at your disposal.
it looks like the following.
Federico
Attachments
Simple is better. fscarpa's idea is probably more suitable for your application if you're still getting your feet wet with tubes.
I'd probably try the 165V circuit first- you don't really get much benefit to going higher if all you need to swing is 3 or 4 volts (things are a different story when you have to swing 30 or 40V!). And the 6DJ8 will be in less danger. FWIW, I use a 6DJ8-oid in my preamps with a 150 V supply and it works quite well. At under 200V, components will be cheaper and more compact.
Make sure you get a REAL 6DJ8/6922/7308/whatever instead of a relabelled 6ES8.
I'd probably try the 165V circuit first- you don't really get much benefit to going higher if all you need to swing is 3 or 4 volts (things are a different story when you have to swing 30 or 40V!). And the 6DJ8 will be in less danger. FWIW, I use a 6DJ8-oid in my preamps with a 150 V supply and it works quite well. At under 200V, components will be cheaper and more compact.
Make sure you get a REAL 6DJ8/6922/7308/whatever instead of a relabelled 6ES8.
Just a hint:
The plate supply should be delayed until the tubes are heated up. If not, add a diode between the grid and cathode of the cathode follower, diode cathode to the tube cathode. The diode can be 1N4007 or similar.
This will limit the forward bias to 0.7V until the tubes are heated.
I'm using the same topology as fscarpa's myself but with E80CC as gain stage and 6201 as follower. It works well.
The plate supply should be delayed until the tubes are heated up. If not, add a diode between the grid and cathode of the cathode follower, diode cathode to the tube cathode. The diode can be 1N4007 or similar.
This will limit the forward bias to 0.7V until the tubes are heated.
I'm using the same topology as fscarpa's myself but with E80CC as gain stage and 6201 as follower. It works well.
I ran the Circuit you posted through Tube Cad
to see what general properties it had.
Gain = 20, 26 dB
Zin = 284k
Zout = 721 ohm
F -3dB low = 43.2 hz
F -3dB hihh = 227 khz
PSRR = -11.3 dB
Vmax out = -29/+29.2 v
RL=4.7 k
I = 9.7 ma
C Bypass = 141 uF
The Frequency responce with the Coupling cap Shown into the Zen load is 40 HZ. I am basing the load on the article on Zen amp article in tube cad Journal. I found I had to increase the output coupling cap to 3 uF to get a 10 hz responce calculation.
to see what general properties it had.
Gain = 20, 26 dB
Zin = 284k
Zout = 721 ohm
F -3dB low = 43.2 hz
F -3dB hihh = 227 khz
PSRR = -11.3 dB
Vmax out = -29/+29.2 v
RL=4.7 k
I = 9.7 ma
C Bypass = 141 uF
The Frequency responce with the Coupling cap Shown into the Zen load is 40 HZ. I am basing the load on the article on Zen amp article in tube cad Journal. I found I had to increase the output coupling cap to 3 uF to get a 10 hz responce calculation.
Guys
download a free copy of Micro Cap 7 demo at
http://www.spectrum-soft.com/demodown.shtm
you will able to draw circuits as well as to
simulate them ( max 50 components)
very user frendly, recommended.
Tube models on the web or ask in the forum.
Federico
download a free copy of Micro Cap 7 demo at
http://www.spectrum-soft.com/demodown.shtm
you will able to draw circuits as well as to
simulate them ( max 50 components)
very user frendly, recommended.
Tube models on the web or ask in the forum.
Federico
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