Hello All,
Just bumped into this ecl82 design and could not figure out the phase splitter design, looks sort of a biased concrtina and the FB does not go to the usual place.
Can anybody explain to me how this design works?
thank you very much.
http://www.fonar.com.pl/a_index.htm
Glass_painter.
PS
Look at this web site, this is a gold mine of info, do not let the fact that it is in Polish stop you, look at the schematics.
Gp
Just bumped into this ecl82 design and could not figure out the phase splitter design, looks sort of a biased concrtina and the FB does not go to the usual place.
Can anybody explain to me how this design works?
thank you very much.
http://www.fonar.com.pl/a_index.htm
Glass_painter.
PS
Look at this web site, this is a gold mine of info, do not let the fact that it is in Polish stop you, look at the schematics.
Gp
Sorry about that, from some reason the first URL directs to the main page and not to the article, lets try again.
http://www.fonar.com.pl/audio/projekty/wzmacniacze/wzm13/wzm.htm
Thanks.
Glass_painter
http://www.fonar.com.pl/audio/projekty/wzmacniacze/wzm13/wzm.htm
Thanks.
Glass_painter
Wow! That is unusual.
It's a concertina sat on top of a common cathode amplifier, so the lower valve thinks its a mu-follower. Very cunning. Distortion will be low due to mu-follower action. Analysing output balance will be much harder. Because the output voltages must be referred to ground, output balance will be a bit problematic, hence the tweak. I would expect it to work well, but (like all series amplifiers) be hungry for HT volts.
It's a concertina sat on top of a common cathode amplifier, so the lower valve thinks its a mu-follower. Very cunning. Distortion will be low due to mu-follower action. Analysing output balance will be much harder. Because the output voltages must be referred to ground, output balance will be a bit problematic, hence the tweak. I would expect it to work well, but (like all series amplifiers) be hungry for HT volts.
It is an interesting circuit - the designer is obviously a fan of cathode followers, as there are two in the pre-amp also - the second one feeding into a 500k volume control, which I would have thought was rather high in value for this circuit
Because of the language the explanation of the amp is not available, but I would be interested to know why an ECC85, a VHF RF/frequency changer tube was chosen for the second pre-amp tube in preference to a designated audio tube, and I cannot see how the first half of the first tube in the pre-amp receives bias, as the cathode is taken straight to chassis and there does not appear to be grid bias.
Because of the language the explanation of the amp is not available, but I would be interested to know why an ECC85, a VHF RF/frequency changer tube was chosen for the second pre-amp tube in preference to a designated audio tube, and I cannot see how the first half of the first tube in the pre-amp receives bias, as the cathode is taken straight to chassis and there does not appear to be grid bias.
The output cathode follower has a strange bias arrangement too. It's direct coupled from the previous valve (which would bias it) but it also has self-bias from its cathode chain. The two will fight one another. Using the cathode follower to drive the Baxandall tone control makes sense as the first stage will be incapable of driving anything. Perhaps the logic of the design is explained by the fact that it was designed in the "flower power" era?
....Certainly an unusual circuit. Two cathode followers in the pre-amp which are hardly going to contribute to gain, the Baxandall tone control system which will hold down the gain of that stage, meaning that the first stage of the first tube will be providing the most gain in the pre-amp! And this tube not properly biased!
I agree with Frank that really a minimum of 3.3Meg is needed to provide bias to avoid distortion in the first stage, although I'd prefer higher values, 4.7 - 10meg preferably. Even then, using grid bias has traditionally not been recommended for hifi amps because of its non-linear amplification. When used with amps such as the Mullard 3-3 it was with the proviso of large amounts of NFB to correct the linearity.
I agree with Frank that really a minimum of 3.3Meg is needed to provide bias to avoid distortion in the first stage, although I'd prefer higher values, 4.7 - 10meg preferably. Even then, using grid bias has traditionally not been recommended for hifi amps because of its non-linear amplification. When used with amps such as the Mullard 3-3 it was with the proviso of large amounts of NFB to correct the linearity.
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