I've got a Musical Fidelity X-P100 preamp on the bench. This is basically the first series Nu-Vista preamp with the nuvistas replaced by some sort of FET. Everything else (including the PCBs) is the same.
Now this one has been Hot-Rodded. Big time. All the audio caps have been replaced by much fancier ones; the larger transistors have been given bolts-as-heatsinks and there's a range of additional, deleted and replaced components here and there. The digital stuff seems unmolested (but I have no remote so can't test).
Naturally, it's not working: the mute really is doing it's thing (tick), the audio makes it through the input selector, volume control and primary pre-amp stage (tick, tick, tick) but then is lost somewhere in the morass of extra transistors hidden under the power supply board (which sits on top of the main PCB). I'm presuming they form some sort of output buffer. (There's also the phono stage stashed under the power supply board - I'm ignoring it for the moment.)
Clearly, someone somewhere put some effort into understanding the circuit and why various bits should be upgraded, replaced or removed. But I can't find even a stock schematic, nevermind a thread in a forum outlining hot to Hot Rod this thing. And, unlike a Ducati, there's no Haynes manual I can order.
Anyone got any ideas or leads?
Thanks!
Now this one has been Hot-Rodded. Big time. All the audio caps have been replaced by much fancier ones; the larger transistors have been given bolts-as-heatsinks and there's a range of additional, deleted and replaced components here and there. The digital stuff seems unmolested (but I have no remote so can't test).
Naturally, it's not working: the mute really is doing it's thing (tick), the audio makes it through the input selector, volume control and primary pre-amp stage (tick, tick, tick) but then is lost somewhere in the morass of extra transistors hidden under the power supply board (which sits on top of the main PCB). I'm presuming they form some sort of output buffer. (There's also the phono stage stashed under the power supply board - I'm ignoring it for the moment.)
Clearly, someone somewhere put some effort into understanding the circuit and why various bits should be upgraded, replaced or removed. But I can't find even a stock schematic, nevermind a thread in a forum outlining hot to Hot Rod this thing. And, unlike a Ducati, there's no Haynes manual I can order.
Anyone got any ideas or leads?
Thanks!
Found this - X-P100 'Guts' | Rock Grotto Lots of photos, but no schematics.
It does highlight that some of the "hot rodding" are bodges that MF applied to get the transistors working (vs NuVistas) Two pairs of diodes and two small capacitors. It also shows that the burn marks are "normal"!
It does highlight that some of the "hot rodding" are bodges that MF applied to get the transistors working (vs NuVistas) Two pairs of diodes and two small capacitors. It also shows that the burn marks are "normal"!
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"Curiouser and curiouser!"
Seems like the previous owner only got half way through the works. There's one missing capacitor (C36) and the output stages have been partially disabled.
For reference, the pre-amp signal chain is: phono stage (which I've not looked at); input selection; tape/monitor ; preamp (nuvistor/fet); volume; output amp; mute; then to the outputs sockets.
The output amplifier (so far) looks like a conventional, if discrete (and likely class A) op-amp. If so, then the output emitter resistors have been removed (R59-61, depending on channel), unsurprisingly resulting in a complete lack of output.
The other interesting thing is that, after all the hoo-hah and effort put into the preamp, the outputs appear to be DC blocked by an electrolytic capacitor - a NP 22uf / 63V unit (C1 /C101) 🤦♂️
And there's three of them in each channel of the phono preamp 🤦♂️ 🤦♂️ 🤦♂️
Very strange indeed.
Seems like the previous owner only got half way through the works. There's one missing capacitor (C36) and the output stages have been partially disabled.
For reference, the pre-amp signal chain is: phono stage (which I've not looked at); input selection; tape/monitor ; preamp (nuvistor/fet); volume; output amp; mute; then to the outputs sockets.
The output amplifier (so far) looks like a conventional, if discrete (and likely class A) op-amp. If so, then the output emitter resistors have been removed (R59-61, depending on channel), unsurprisingly resulting in a complete lack of output.
The other interesting thing is that, after all the hoo-hah and effort put into the preamp, the outputs appear to be DC blocked by an electrolytic capacitor - a NP 22uf / 63V unit (C1 /C101) 🤦♂️
And there's three of them in each channel of the phono preamp 🤦♂️ 🤦♂️ 🤦♂️
Very strange indeed.
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