Hi Steve. One of the transistors in the power supply section of this amp is a MPSA42. Is that the same in the article?
The other is a big one with no markings on it. What does the article show this to be?
Does this article also show an SSM2210 input stage?
What exactly does the trimpot adjust? (I was told by the builder never to touch it).
What voltages should be measured where?
Are we definitely talking about the same design? The hybrid in the article looks as if the input stage is the EL34's (Though I can't tell for sure just by looking at it.)
I am not yet at a skill level where I can translate this layout into a schematic. An article would be of immeasurable help to me in understanding the amplifier, as would a diagram. Can I purchase the original article somewhere? (I didn't see it on the website you directed me to).
The other is a big one with no markings on it. What does the article show this to be?
Does this article also show an SSM2210 input stage?
What exactly does the trimpot adjust? (I was told by the builder never to touch it).
What voltages should be measured where?
Are we definitely talking about the same design? The hybrid in the article looks as if the input stage is the EL34's (Though I can't tell for sure just by looking at it.)
I am not yet at a skill level where I can translate this layout into a schematic. An article would be of immeasurable help to me in understanding the amplifier, as would a diagram. Can I purchase the original article somewhere? (I didn't see it on the website you directed me to).
Hi Hihopes,
Yes, we are discussing the same amplifier. The transistors in the power supply regulator are MPSA42 and BDV65C (npn darlington power). The input transistor is 1/2 of a SSM2210. The regulator feeds the input stage only and is shared between the two channels. The trimpot sets the B+ to the input stage. The input stage is a hybrid cascode. The gain is provided by the ssm2210, it's collector drives the cathode of the el34. The el34 grid1 is grounded. The amplifier is an inverting one and shunt feedback is taken from the sources of the output fets back to the base of the ssm2210.
How is your amp constructed? The original was a combination of hardwiring and a bit of veroboard for the regulator and input stage. If you can read and follow a simple schematic you can reverse engineer this thing and learn alot about it in the process! PM me if you wish.
Regards,
Steve.
Yes, we are discussing the same amplifier. The transistors in the power supply regulator are MPSA42 and BDV65C (npn darlington power). The input transistor is 1/2 of a SSM2210. The regulator feeds the input stage only and is shared between the two channels. The trimpot sets the B+ to the input stage. The input stage is a hybrid cascode. The gain is provided by the ssm2210, it's collector drives the cathode of the el34. The el34 grid1 is grounded. The amplifier is an inverting one and shunt feedback is taken from the sources of the output fets back to the base of the ssm2210.
How is your amp constructed? The original was a combination of hardwiring and a bit of veroboard for the regulator and input stage. If you can read and follow a simple schematic you can reverse engineer this thing and learn alot about it in the process! PM me if you wish.
Regards,
Steve.
This does sound like my amp and it is constructed the way you describe it. the signal is taken from the anodes of the tubes to the gates of the n channel mosfets, but the regulator also has power going to the gates of the p-channel mosfets by the look of it (via resistors). All the gates are sitting between 41 and 44 volts. Should they match exactly?
Your description is accurate. Each fet will have a low value resistor (220r)soldered to its gate pin. This is the gate stopper and is so-called because it helps to stop unwanted oscillations of the fets. Check the continuity of these resistors. Are the gate voltages measured with respect to ground? Trace the gate leads back to the veroboard. They should go to opposite ends of a 150r resistor. Measure the voltage across the resistor, this is the bias voltage. The design is a simple 2 stage amp, all voltage gain is in the first stage (ssm2210 el34 cascode) and the output fets (source followers) provide current gain. About 15 years ago out of curiosity I built one channel on a bread board and played around with the design. At the time I was designing and building conventional amps and never went further with it.
Cheers,
Steve.
Cheers,
Steve.
Did you ever sort your moscode out. I have designed my own boards for this project and use a different power supply. I also modified the circuit at the input.
This is the best sounding amp that I have ever heard.
Moscode amplifier - The Book Worm
Mac
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