I am fixing one of these which includes changing most of the caps, the C609 highlighted in the picture is a 1uF 50v elyt which I was intending to change for a Nichicon gold tune but it turns out I don't have the correct value.
I have a 1uF MKT film cap and larger values 47uF/50v gold tunes but as I am not into details of amp circuits I don't know what C609 is doing or what to consider from a cap point of view?
I have a 1uF MKT film cap and larger values 47uF/50v gold tunes but as I am not into details of amp circuits I don't know what C609 is doing or what to consider from a cap point of view?
I've sort of concluded this cap is part of the signal path and as long as it's not passing more DC (figure of speech) than the associated bias circuit any value that is also not to much of a high pass filter should be good.
In other words it should be happy with values more that 1uF so I will get my 47uF gold tune in there and maybe bypass it with a .1uF 250v film cap, I'll do listening and distortion tests with and without though so we'll see.
In other words it should be happy with values more that 1uF so I will get my 47uF gold tune in there and maybe bypass it with a .1uF 250v film cap, I'll do listening and distortion tests with and without though so we'll see.
I put a 22uF 63v Nichi gold tune as that was the lowest uF and highest voltage I had available and with some of the other changes I made the 1khz THD has gone from 0.03% to 0.0035% which is very nice and frankly a bit unexpected.
However I measured -3dB at 10 Hz which I don't get, did not measure this before the changes so can't say if it's anything I did or was there before.
The input cap has been changed to 2*47uF 100v ELNA Audio BP so that should not be the limiting HP filter (94uF/18kohm)
Looking at the schematic I don't understand what else would be acting as a HP filter, great if anyone can help?
The PS has 86,000uF per channel.
However I measured -3dB at 10 Hz which I don't get, did not measure this before the changes so can't say if it's anything I did or was there before.
The input cap has been changed to 2*47uF 100v ELNA Audio BP so that should not be the limiting HP filter (94uF/18kohm)
Looking at the schematic I don't understand what else would be acting as a HP filter, great if anyone can help?
The PS has 86,000uF per channel.
Look at where the component is - this transistor is the VBE bias transistor. The capacitor across it affects the response time of the thermal compensation. A larger capacitor probably slowed the response down, but I doubt it's very important.
The improvement in THD has probably come from renewing power supply capacitors
The improvement in THD has probably come from renewing power supply capacitors
Just to report back on this incase anyone else gets their soldering iron into one of these.
The amp was a bit thin even though it measured freq wise ok but I felt something was off compared to what it was before. Ordered Nishi gold tune 1uF 50v being the same value as original and the "punch" was back. Don't get how this makes sense but it is what it is so don't change this value.
Generally this is a pretty well designed amp circuit and with help it will really perform, red line is 2nd harmonics, yellow 3rd (all the rest is under the noise floor so did not include them) and brown is the noise floor.
Measurements using REW and focusrite g3 with the source being a Topping D70 directly connected at -6db and amp 200w capable resistive load of 7.5 ohm.
Honestly this outperforms some of my other and a lot more expensive modern amps, I got this used 10 years ago for like 150 EUR and was about to give it to recycling....but with covid I needed something to do.
IMD 19/20khz (the 1khz spike is there with or without this amp so think its the focusrite but not sure how it gets in there)
The amp was a bit thin even though it measured freq wise ok but I felt something was off compared to what it was before. Ordered Nishi gold tune 1uF 50v being the same value as original and the "punch" was back. Don't get how this makes sense but it is what it is so don't change this value.
Generally this is a pretty well designed amp circuit and with help it will really perform, red line is 2nd harmonics, yellow 3rd (all the rest is under the noise floor so did not include them) and brown is the noise floor.
Measurements using REW and focusrite g3 with the source being a Topping D70 directly connected at -6db and amp 200w capable resistive load of 7.5 ohm.
Honestly this outperforms some of my other and a lot more expensive modern amps, I got this used 10 years ago for like 150 EUR and was about to give it to recycling....but with covid I needed something to do.
IMD 19/20khz (the 1khz spike is there with or without this amp so think its the focusrite but not sure how it gets in there)
Another thing, I was planning to use this amp as a fully balanced mono amp to my center speaker BUT when I connect the balanced preamp signal + and - to each amp it gets really hot.
I am bypassing the inbuilt bridge mode circuit by feeding it directly with a balanced signal but that should not make a difference.
Any thoughts as to why it gets hot is welcome.
It did not get hot before when using the inbuilt bridge switch which routed the inverse signal from one amp to the other.
I am bypassing the inbuilt bridge mode circuit by feeding it directly with a balanced signal but that should not make a difference.
Any thoughts as to why it gets hot is welcome.
It did not get hot before when using the inbuilt bridge switch which routed the inverse signal from one amp to the other.