Hi, this amp has a sensitivity of 150 mV for full power output which is way too much for nowadays sources. With the volume potentiometer at 8 o clock it is darn loud already. I wish to temper the sensitivity to around 300 mV or even 1 V.
My guess is that lowering feedback resistor R361 to 33k is enough. But what to do with R382 and C357 ?
My guess is that lowering feedback resistor R361 to 33k is enough. But what to do with R382 and C357 ?
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Why not just put an attenuator on the input of the amp?
Changing the feedback will have multiple effects. It may make the amplifier oscillate.
Changing the feedback will have multiple effects. It may make the amplifier oscillate.
You could try increasing C357 a little too, but HF stability is hard to predict as it depends to some extent on parasitic components which don't appear in the circuit diagram. You could find you have made a power oscillator! An attenuator at the input would be simpler.
It has a volume potentiometer but if I barely touch it it is very loud. Gain is very high which made me think to change the feedback circuit. I also thought of possible oscillation but my knowledge in this area is lacking to say the least. It occurred to me that the resistors are very high in value too for a power amp feedback circuit. Long ago I was taught that the impedances at both inputs of a differential pair should be equal but I forgot the reason 😉 That would imply that 51 kOhm would be OK. What to do with R382 then ? I should have made more I amps I see now.
Putting an attenuator before the volume potentiometer to have the signal later on amplified a lot again seems counterproductive IMO but I guess it is the safest approach.
Putting an attenuator before the volume potentiometer to have the signal later on amplified a lot again seems counterproductive IMO but I guess it is the safest approach.
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With rail voltage around 40V it seems to be non-ES series SONY amp. It may seem a little strange you have problems with over-sensitivity. I have a bunch of SONY in my possession currently (630 esD, 650esD, F470, F519R), and even with SACD player with 2Vpp output the volume is rather "normal"( up to 11 - 12 with no problems, except the wife 🙂 ). I presume the "problem" you have is in both channels? ;-)
I would not be afraid to lower the value of R361 a little bit, the amps usually are more stable with deeper feedback.
I would not be afraid to lower the value of R361 a little bit, the amps usually are more stable with deeper feedback.
At present one LTP base sees 51k, the other sees 100k in parallel with 100.62k. Near enough the same.
Adding 10dB to the feedback, as you propose, is quite likely to cause oscillation. Maybe not all the time, but with certain signals and certain loads.
Adding 10dB to the feedback, as you propose, is quite likely to cause oscillation. Maybe not all the time, but with certain signals and certain loads.
Yes, it is with both channels. It is not a problem but a feature 😉 I can not set it at 12 o clock or my speakers will catch fire. This type is always like this so it is not abnormal behavior. I just wish I could change this.
It is a semi ES amp as it has ES parts (well there is ES written on the power transformer) and relay controlled inputs but is was not part of the ES series, I will let you guess which one it is.
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Of course, you are right. the LTP bases both see nearly the same value. That is with R382 and with DC but what exactly is the purpose of this resistor ? Obviously a DC path but for what ? I checked some other Sony amps of that time and they have similar schematics ( with higher rail voltages) and the same feedback networks with R361 (51k), C356 and R357 (620 Ohm) but no R382 installed.
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cause it will kill the dynamics and drawn the source completely
alternative to lower the gain of the amp will obviously benefit the amp for the best if done properly
"Kill dynamics"? Do you have access to a special source of music which has never been near any resistors?
"Drown the source"? Only if you use the wrong values.
"Drown the source"? Only if you use the wrong values.
would you like to calculate the input Z of the specific amplifier together with attenuator you suggest ?
roughly i will say less than 5K ...do you think that the pre behind it will be the same happy driving this instead of 50K ?
this will kill the dynamics if casual listening is the target
I didn't suggest any values. It is possible to ensure that the load on the source is no greater than now. There is certainly no need to turn 50K into 5K - that would require quite incompetent design.
Increase the value of R357 to 1.2k or 1.5k it will reduce the input sensitivity to around half. You need not change the capacitor values since the feedback resistor does not change, thus its compensating cap need not change. The value of C356 and the new shunt resistor would extend the low frequency cut off point and you may even experience a better bass response.
Thanks, I knew there had to be a simple and effective solution. I will try that one as I now have two of the same amps (since yesterday) and I can try things out.
BTW I replaced all electrolytic caps in the amp for new Nichicon FW audio grade ones and some for Panasonic FM and I am astonished what a difference it makes in this one.
BTW I replaced all electrolytic caps in the amp for new Nichicon FW audio grade ones and some for Panasonic FM and I am astonished what a difference it makes in this one.
Changing the feedback might require a change in phase correction to maintain stability, however you do it, but try Nica Ras's suggestion. You might be OK.
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