See attached schematic.
1. I see that the output capacitor filter is made up of three capacitors. I've seen a big cap crossed with a small one, by what's the 1.0 part for?
2. Am I correct that C7/C9/C11 forms an RC filter with R43 and R45 (and likewise for the opposite side of the amp)?
3. I've been told output capacitor values don't matter much. If I'm right about #2, I worked out that 1-2 uF changes in total capacitance would have a negligible effect on the output. Again, please check my work?
1. I see that the output capacitor filter is made up of three capacitors. I've seen a big cap crossed with a small one, by what's the 1.0 part for?
2. Am I correct that C7/C9/C11 forms an RC filter with R43 and R45 (and likewise for the opposite side of the amp)?
3. I've been told output capacitor values don't matter much. If I'm right about #2, I worked out that 1-2 uF changes in total capacitance would have a negligible effect on the output. Again, please check my work?
Attachments
I think there are some mistake in the schematics. The anods of second valve are connected togeder, for example. Anyhow, the stereo imagine is alterated and the outputs will not be a clear chanels but some kind of enhanced stereo spatial.
1/ This kind of thing is more 'cosmetic' and imo serves no real purpose. The designer will say the smaller values maintain cap performance at higher frequencies... but this is audio and not RF design.
2/ Partly, but it Is more complex than that because the feedback point take-off which is the junction of R41 and R35 is on the 'output' side of the caps. That means the final output is unaffected by loading (you have to also include the impedance of whatever you dangle off the output sockets) but the signal level before the caps will actually increase at low frequencies as you load the amp more.
The values chosen will be a good compromise.
3/ They don't matter as much as you think because of the feedback being taken from the output. If you reduced the cap value by a factor of ten the output of the amp would essentially be unaffected although what you wouldn't see is the output level increasing before the cap.
If the caps are sized correctly then the above effect will be negligible over the audio band.
2/ Partly, but it Is more complex than that because the feedback point take-off which is the junction of R41 and R35 is on the 'output' side of the caps. That means the final output is unaffected by loading (you have to also include the impedance of whatever you dangle off the output sockets) but the signal level before the caps will actually increase at low frequencies as you load the amp more.
The values chosen will be a good compromise.
3/ They don't matter as much as you think because of the feedback being taken from the output. If you reduced the cap value by a factor of ten the output of the amp would essentially be unaffected although what you wouldn't see is the output level increasing before the cap.
If the caps are sized correctly then the above effect will be negligible over the audio band.
It's a balanced circuit, even though the pins of what I presume to be the XLR connectors are drawn in the wrong order (in reality, XLR pin 1 is not in the centre). The right channel is shown, there is another such circuit for the left channel.
I also don't understand WHY the "Phono" input, which is way lower level and needs RIAA equalization, is treated the same as all others, which are flat and Line level. WTF?
Must be designed for those with an outboard phono preamp or a TT with a built-in preamp.
In this case just a convenient designation on the front panel since it's functionally identical to the other inputs, as you have noticed.
Good eye.
That can't be it; the centre pin of a three-pin 180 degrees DIN connector is pin 2.
A lot of times, that type of coupling is used when they want to lower ESR & insertion loss of the capacitors. Some will use that coupling method with different types of caps to get a certain type of in harmonic distortion character as well.
Nice balanced preamp. Even though the double garter belt buffer circuit is a little overkill,
At the time, the Phonostages that Audio Research sold were all external units. So the XLR marked 'phono' was expected to be attached to a separate product, which was XLR line-level out. Hence the reason there's no EQ or extra gain.
Multi cap is like cooking. Pinch of chilli 0.1. Grind of pepper 1. Spoon full of salt 5uf. IMO caps have different sounds, mix to get ones own sound.
Or mix affordable caps to get a good result?
Or mix affordable caps to get a good result?