I picked up a beautiful Sherwood S8900 for 30 bucks, and even though it works I'm going to be replacing the electrolytic caps. After researching (here and elsewhere) there are some lingering questions about replacement as well as issues with the amp I could use some help with:
1. How much higher of a capacitance can the replacement caps be? The larger values might be used simply out of not being able to find the exact ones in the amp. Im talking about power filtering caps here.
2. Can someone help me make sense of the part of the schematic attached? On the "Audio Driver Board" there are 4000uf caps that seem to be in series with the signal out from the board to the speaker terminals on the back of the receiver. On the audio driver board there are two 'voltage in' connections, a couple ground connections, but as for signal connections one from the loudness control and one to the main/remote speaker switch and then to the speaker terminals. It is this part of the circuit that has the 4000uf cap. Is this normal? Am I reading the schematic wrong? Any special considerations (bypassing?) for replacing this cap if it is in the signal path?
1. How much higher of a capacitance can the replacement caps be? The larger values might be used simply out of not being able to find the exact ones in the amp. Im talking about power filtering caps here.
2. Can someone help me make sense of the part of the schematic attached? On the "Audio Driver Board" there are 4000uf caps that seem to be in series with the signal out from the board to the speaker terminals on the back of the receiver. On the audio driver board there are two 'voltage in' connections, a couple ground connections, but as for signal connections one from the loudness control and one to the main/remote speaker switch and then to the speaker terminals. It is this part of the circuit that has the 4000uf cap. Is this normal? Am I reading the schematic wrong? Any special considerations (bypassing?) for replacing this cap if it is in the signal path?
Attachments
The 4000uF cap keeps the 35VDC from going to the speaker.
It is needed. Going below this value will raise the low frequency 3dB point. (less bass)
They are asking for a 50V rated cap...do not go below this rating.
IMO...I would design with a cap rated for more than the supply rail: 70V
In case of drive failure.
But that is just me.
It is needed. Going below this value will raise the low frequency 3dB point. (less bass)
They are asking for a 50V rated cap...do not go below this rating.
IMO...I would design with a cap rated for more than the supply rail: 70V
In case of drive failure.
But that is just me.
Yes, 4700uf would be fine.
By 'bypassing' do you mean bypassing with another size of cap? If so, I would like to hear that answer too. I have sometimes seen the large electrolytic bypassed with a film cap of different capacity and I'm curious what function that serves.
A few general rules for electronics:
Anything with area has capacitance
Anything with length has inductance
If you have capacitance and inductance (pretty well all circuits) you will have a resonance frequency.
So
All capacitors have a complex impedance vs frequency graph.
The simple model has an inductance in series with the capacitance.
At some frequency there will be a series resonance condition and a low impedance point.
Above that the "capacitor" acts like an inductance and impedance rises.
(There is a thread on here somewhere that shows what I am talking about...with pictures...I just can't find it right now.)
Bypassing the large cap with a smaller one creates a path of low impedance that the large cap is not providing at that frequency.
Hope that helps.
Anything with area has capacitance
Anything with length has inductance
If you have capacitance and inductance (pretty well all circuits) you will have a resonance frequency.
So
All capacitors have a complex impedance vs frequency graph.
The simple model has an inductance in series with the capacitance.
At some frequency there will be a series resonance condition and a low impedance point.
Above that the "capacitor" acts like an inductance and impedance rises.
(There is a thread on here somewhere that shows what I am talking about...with pictures...I just can't find it right now.)
Bypassing the large cap with a smaller one creates a path of low impedance that the large cap is not providing at that frequency.
Hope that helps.
It's quite an old receiver so replacing all electrolytics is a good idea but as a newb, could I suggest that you don't try to replace everything at once or in both channels at the same time? If you do something that you later realize was wrong, you may need to retrace your steps or even repair damage, so having an untouched, working channel as a reference, may well save your neck.
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