I have a Cello Duet-350 power amplifier. It is about 10 years old. It now generates its own gratuitous, random, static-sounding noise. Input level has no effect on the level of this noise. It is not objectionable with listening to Eric Clapton, but it is quite annoying when listening to Chopin Nocturnes. I have disassembled it as far as I could without resorting to a soldering iron; disconnected, cleaned and reconnected every removable contact I could find. I can find no parts inside that are obviously scorched. Does anyone, please, have any ideas about what I might try?
Try some diagnostics to narrow down where it might be coming from.
First use scope to look at output - what does the unwanted signal look like - spikes? Bursts of oscillation? Bursts of white noise? Steps?
Now try looking at few points in the circuit to see if you can see the same thing.
Try the power supply rails, the input terminals (it may be being picked up in the cabling), the inputs to the JFET pair, the output of the VAS and anywhere else you can get an easy measurement.
This should at least give some evidence to build a theory from.
First use scope to look at output - what does the unwanted signal look like - spikes? Bursts of oscillation? Bursts of white noise? Steps?
Now try looking at few points in the circuit to see if you can see the same thing.
Try the power supply rails, the input terminals (it may be being picked up in the cabling), the inputs to the JFET pair, the output of the VAS and anywhere else you can get an easy measurement.
This should at least give some evidence to build a theory from.
Hi Lumanauw,
pag. 2 of the linked .pdf shows the output stage.
From the owner manual available at:
http://www.matthew-james.net/images/PDF_Manuals/encore-amplifier-owners-manual.pdf
it turns out that the Encore Amplifier is just a scaled down version of the Performance Amplifier (see pag. 4, "audio circuitry").
I might be wrong but the +/-Drive_2 signals on pag. 2 are not used in the Encore Amplifier. The only missing piece of information, beside the power supply section, is the EPB-1 board, a small board mounted across the output connector pins.
I'd be interested to hear some of the solid state gurus commenting the feedback scheme and the asymmetric input impedance of the balanced connection (330K on the + side, 5K on the -side according to the manual).
Regards
Giorgio
pag. 2 of the linked .pdf shows the output stage.
From the owner manual available at:
http://www.matthew-james.net/images/PDF_Manuals/encore-amplifier-owners-manual.pdf
it turns out that the Encore Amplifier is just a scaled down version of the Performance Amplifier (see pag. 4, "audio circuitry").
I might be wrong but the +/-Drive_2 signals on pag. 2 are not used in the Encore Amplifier. The only missing piece of information, beside the power supply section, is the EPB-1 board, a small board mounted across the output connector pins.
I'd be interested to hear some of the solid state gurus commenting the feedback scheme and the asymmetric input impedance of the balanced connection (330K on the + side, 5K on the -side according to the manual).
Regards
Giorgio
I stand corrected, the EPB-1 board has four connections to the amplifier main board, so the +/-Drive_2 signal might be two of those. See pictures at:
http://www.fotop.net/TheFabFour/CelloEncoreAmplifier
Questions are:
- what about the fourth wire? Ground?
- EPB-1 theory of operation?
Regards
http://www.fotop.net/TheFabFour/CelloEncoreAmplifier
Questions are:
- what about the fourth wire? Ground?
- EPB-1 theory of operation?
Regards
Page 2 on Jacco's link is not the output stage. It seems the drafter also given up like I did. Only drawing the front end.
The output stage is massive. Maybe 40-50 transistors are there, and I remember the RE degeneration is not 0.22ohm, more likely 1ohm. (+) and (-)DRIVE2 is the connection to the output board.
This output board is bigger than the driver board, and there's 2 (1 pair) of output boards for each channel.
The output stage is massive. Maybe 40-50 transistors are there, and I remember the RE degeneration is not 0.22ohm, more likely 1ohm. (+) and (-)DRIVE2 is the connection to the output board.
This output board is bigger than the driver board, and there's 2 (1 pair) of output boards for each channel.
David,
there are several Encore versions.
You are talking about the big 4-case Performance amp, the posted pdf is of the little dual monaural one from ~'88, hit the market about a year after the intro of the Performance 4-block.
Audio Palette+Performance <=> Encore pre+power amp.
(the one in the link seems to have been manufactured in the second half of 1990)
iirc, the Encore-150 is the bridged version of the little one(lowered rail voltages).
there are several Encore versions.
You are talking about the big 4-case Performance amp, the posted pdf is of the little dual monaural one from ~'88, hit the market about a year after the intro of the Performance 4-block.
Audio Palette+Performance <=> Encore pre+power amp.
(the one in the link seems to have been manufactured in the second half of 1990)
iirc, the Encore-150 is the bridged version of the little one(lowered rail voltages).
Thank you QSerraTico_Tico.
The static comes from the right channel only. (input cables disconnedcted from pre-amplifier.)
This amplifier is a "Duet-350", a two-channel, single chassis, stereo power amplifier with single torroidal power transformer, four large power-supply capacitors (about 37,000mfd each) with rated output of 350 watts per channel. It is neither the very expensive, four-chassis "Performance Amplifier" nor the relatively lower-powered "Encore."
see: http://hso.keskipiste.com/hso_images/7duet350open.jpg
The static comes from the right channel only. (input cables disconnedcted from pre-amplifier.)
This amplifier is a "Duet-350", a two-channel, single chassis, stereo power amplifier with single torroidal power transformer, four large power-supply capacitors (about 37,000mfd each) with rated output of 350 watts per channel. It is neither the very expensive, four-chassis "Performance Amplifier" nor the relatively lower-powered "Encore."
see: http://hso.keskipiste.com/hso_images/7duet350open.jpg
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