After 20+ years of searching, I finally found a Vendetta Research MC Phono Section. This is the SCP-2A variant in 4 boxes. I will show modifications / updates in this thread. My plan is to stay true to John Curl's original design while updating caps to get decades more life from this unit.
Current plans include:
I may get a single faceplate fabricated sometime in the future, that's not top priority.
Current plans include:
- Replace all electrolytic caps. This looks like it will cost about $30 + some tax and shipping
- set loading to 100R (same as my PassDIY Pearl 2, Pearl 3, and RS Xono 2019)
I may get a single faceplate fabricated sometime in the future, that's not top priority.
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I recall reading somewhere JC himself suggested to a user to not mess with anything unless absolutely necessary… looking at the components they are all the very best of the day and quite likely could not be improved upon. Did he also say that certain bits were tuned/tweaked to each individual build? I don’t remember, perhaps.
Your idea of taking a very light restoration touch to this almost 40yr old example of the most cutting edge engineering is a sound idea.
Your idea of taking a very light restoration touch to this almost 40yr old example of the most cutting edge engineering is a sound idea.
It looks it might be improved from an EMI perspective - no RF suppression caps on the inputs and a large loop area on the input wiring to pick up magnetic interference. The former is likely to be an issue these days with all the mobile phones around - given this is an MC preamp perhaps 500pF ceramic to ground on the input and output connectors, and a ferrite toroid on the power supply cable might be useful additions?
Quick update. After a few road trips and general business I finally got into the Vendetta. I set the MC loading to 100R (was 46R) and checked the power supply voltages. Everything looked good so I put it into my system without any mods. Long story short - WOW. All of the flowery descriptions I've read about this are true - quiet, black background, 3D, huge soundstage, organic. That confirms the approach I'll take to tweaks when I get to them - new electrolytic caps only.
I started a faceplate layout in FrontPanelExpress. I'm on the fence about getting it fabricated or not. Time will tell.
I started a faceplate layout in FrontPanelExpress. I'm on the fence about getting it fabricated or not. Time will tell.
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I'm looking for a text colour "green with envy" in the palette.
perhaps, with a subject "on the test bench" (so to speak), you can usefully investigate the lessons the Vendetta has for us building other projects... like the Pearls and the BA2018 line stage.
is the separation of power from signal and channel from channel critical?
what of the configuration of grounding and shielding especially in a four box solution? is there provision for ground lift?
one might be tempted to consider experimenting with schemes of local regulation but the performance seems to indicate that remote regulation for this circuit works a treat. (I remember Richard Marsh arguing for an approach that worked the problem from both ends... I.e. regulate but also design circuits that didn't need it as much)
perhaps, with a subject "on the test bench" (so to speak), you can usefully investigate the lessons the Vendetta has for us building other projects... like the Pearls and the BA2018 line stage.
is the separation of power from signal and channel from channel critical?
what of the configuration of grounding and shielding especially in a four box solution? is there provision for ground lift?
one might be tempted to consider experimenting with schemes of local regulation but the performance seems to indicate that remote regulation for this circuit works a treat. (I remember Richard Marsh arguing for an approach that worked the problem from both ends... I.e. regulate but also design circuits that didn't need it as much)
Here are a few initial thoughts.
Vendetta PSUs are transformer, bridge, caps, standard 317/337 setup. I'm not sure about ground lift, that's one I'll look at when I re-cap.
I know when you don't tie the 2 ground posts together on the RIAA boxes it makes a nasty hum at the speakers. A short run of scrap wire fixed that right up.
The PSU umbilical cables are fixed on both sides, and appear to be unshielded. There are no switches, LEDs, or disconnects.
I don't know all of the what is employed in the RIAA boxes for low noise. There appears to be a star ground at the phono ground post. Similar to Pearl 2, 3 and Xono philosophy.
Does it use Cap multiplier(s)? I'm not sure. I do know a key element is hand matched and hand selected low noise JFETs. As I understand it the semis for this preamp are impossible to get now.
My Pearl 2 and Pearl 3 each use a single PSU. I'll likely go for 2x PSU in the P3. Maybe 2x regulated. Will it make a difference - time will tell. I see positive reviews on the P3 thread for going dual.
My RS Xono 2019 PSU is over-the-top crazy using fully dual-mono CLC then CapMX to other box with CLC to Reg. Far more complex than Vendetta, Pearl 2, Pearl 3, etc. Xono also has carefully matched JFETs and RIAA caps.
I suspect the magic of the Vendetta is the unobtanium hand matched actives (and other bits) and the circuit design itself. The power supplies appear to be pretty vanilla regulated units (good), but dual mono (great) and in separate boxes (good? great?).
Vendetta PSUs are transformer, bridge, caps, standard 317/337 setup. I'm not sure about ground lift, that's one I'll look at when I re-cap.
I know when you don't tie the 2 ground posts together on the RIAA boxes it makes a nasty hum at the speakers. A short run of scrap wire fixed that right up.
The PSU umbilical cables are fixed on both sides, and appear to be unshielded. There are no switches, LEDs, or disconnects.
I don't know all of the what is employed in the RIAA boxes for low noise. There appears to be a star ground at the phono ground post. Similar to Pearl 2, 3 and Xono philosophy.
Does it use Cap multiplier(s)? I'm not sure. I do know a key element is hand matched and hand selected low noise JFETs. As I understand it the semis for this preamp are impossible to get now.
My Pearl 2 and Pearl 3 each use a single PSU. I'll likely go for 2x PSU in the P3. Maybe 2x regulated. Will it make a difference - time will tell. I see positive reviews on the P3 thread for going dual.
My RS Xono 2019 PSU is over-the-top crazy using fully dual-mono CLC then CapMX to other box with CLC to Reg. Far more complex than Vendetta, Pearl 2, Pearl 3, etc. Xono also has carefully matched JFETs and RIAA caps.
I suspect the magic of the Vendetta is the unobtanium hand matched actives (and other bits) and the circuit design itself. The power supplies appear to be pretty vanilla regulated units (good), but dual mono (great) and in separate boxes (good? great?).
Congratulations on a super-rare and super-desirable find!
Although it's economically unwise to modify a museum piece in any way, you might give some thought to replacing the rectifier diodes with soft recovery devices, and perhaps adding transformer snubbers in the power supply cabinets.
Although it's economically unwise to modify a museum piece in any way, you might give some thought to replacing the rectifier diodes with soft recovery devices, and perhaps adding transformer snubbers in the power supply cabinets.
Solder them to the legs of the diodes. Then the day before you decide to sell, un-solder them. Here is a similar, but not identical, power supply with easily un-soldered snubbing components. Vertical diodes with exposed flywires.
I have a Vendetta SCP-2C and also rst Xono2019. Have you compaired these two? Which one you like more and why?
I'll restate the obvious here, but to make it easier for future readers of this thread:
SCP-2a schematic
If you search around a bit, you can also find explanations from Mr. Curl himself about the upgrades he made over time. One of them was to change the diodes in the power supply to versions with softer recovery characteristics.
If it was my preamp, I'd leave it alone, except for some cosmetic clean-up and to replace defective parts. If you want to experiment, start from scratch. You can't find the same JFETs that John used now, at least not easily, but there are some JFETs around that will get close. If you parallel them, maybe better in some ways. That is what JC himself did for more recent phono stage design efforts of his. Try your own regulators. Try your own raw DC supplies. Choose your own components. See if you can outdo one of the masters of the art. That's not being sarcastic, either. You might be able to do as well or better with some more modern components. You can get fancy PCBs made from Rogers material at JLC for a reasonable price. Use the SCP-2a as your reference. Worst case is that you can't match the original design. Best case is that you do as well or better and can sell the Vendetta preamp to some other lucky soul.
SCP-2a schematic
If you search around a bit, you can also find explanations from Mr. Curl himself about the upgrades he made over time. One of them was to change the diodes in the power supply to versions with softer recovery characteristics.
If it was my preamp, I'd leave it alone, except for some cosmetic clean-up and to replace defective parts. If you want to experiment, start from scratch. You can't find the same JFETs that John used now, at least not easily, but there are some JFETs around that will get close. If you parallel them, maybe better in some ways. That is what JC himself did for more recent phono stage design efforts of his. Try your own regulators. Try your own raw DC supplies. Choose your own components. See if you can outdo one of the masters of the art. That's not being sarcastic, either. You might be able to do as well or better with some more modern components. You can get fancy PCBs made from Rogers material at JLC for a reasonable price. Use the SCP-2a as your reference. Worst case is that you can't match the original design. Best case is that you do as well or better and can sell the Vendetta preamp to some other lucky soul.