That is such a great youTube channel. Seeing how he generated his own documentation was amazing. In the past he has custom machined mechanical parts needed for a repair. He just chugs along undaunted by anything. It was fun to see how this case went together. I would have thought there would have been a copper Faraday cage in there, but no.
Of course that circuit is total over kill for a phono preamp as stylus record playback has at best maybe 0.5% distortion at 1 kHz at 5 cm/s and it rises to maybe 5% at 5 kHz. I don't own a record with surface noise low enough to need more than 60 dB dynamic range. So where a preamp designed around four or six $10 - $15 OpAmps per channel and a battery supply would exceed the performance required for any record playback this thing is pure collectable audiophile shoot for the moon over kill work of art. I would expect a sold bit of frame work would be more appropriate at that price point rather than nylon standoffs. I think it also went wide of the mark when he didn't make it out of half inch think milled metal. How was it not supplied with a custom shipping crate?
That case design is interesting as it would be easy to 3D print those corner pieces and I can make or buy rectangular panels out of pretty much anything.
Of course that circuit is total over kill for a phono preamp as stylus record playback has at best maybe 0.5% distortion at 1 kHz at 5 cm/s and it rises to maybe 5% at 5 kHz. I don't own a record with surface noise low enough to need more than 60 dB dynamic range. So where a preamp designed around four or six $10 - $15 OpAmps per channel and a battery supply would exceed the performance required for any record playback this thing is pure collectable audiophile shoot for the moon over kill work of art. I would expect a sold bit of frame work would be more appropriate at that price point rather than nylon standoffs. I think it also went wide of the mark when he didn't make it out of half inch think milled metal. How was it not supplied with a custom shipping crate?
That case design is interesting as it would be easy to 3D print those corner pieces and I can make or buy rectangular panels out of pretty much anything.
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Does anyone know what purpose R6 (750 Ohms) in the line output buffer schematic is serving? IC3 and IC2b are forming a two-stage DC servo amplifier having very high gain at DC. I can’t figure out what is the purpose of R6, though. It seems to be serving as a bypass of IC3, but I don’t know how that would help, seeing as it would forward the output signal into the servo loop. I also note that R6 and R11 have the same values as R10 and R5, all at 0.1%, so form exactly the same divider ratio. Their tight tolerance indicates what must be the importance of their ratios.
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Disregarding the whole price and how it's made, designed, this guy is a bliss to watch/listen 😁 Thanks for the recommendation.
I've done a lot of back to back with paradise and master groove, there's nothing between them at all on sound quality. It's a good photo.
It's just a shame he couldn't be arsed to lay it all out on two boards. What he's done is just assemble a bigger phono with all the bits from the Beat, Groove ÷ Anniversary etc aand then just kept adding more regs.
That's a brilliant repair though. Should have taped the reverse face of the lid before gluing, then the sanding would have been minimal.
It's just a shame he couldn't be arsed to lay it all out on two boards. What he's done is just assemble a bigger phono with all the bits from the Beat, Groove ÷ Anniversary etc aand then just kept adding more regs.
That's a brilliant repair though. Should have taped the reverse face of the lid before gluing, then the sanding would have been minimal.
Great video and thanks for sharing.....subscribed to his channel. Very informative and I leaned a thing or two. He's fun to watch.
That line stage for 25k though. Wow.
That line stage for 25k though. Wow.
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It's actually a phono stage. £25k for a pretty cheesy plastic box.
jeff
There is theoretically a method to that madness. The plastic enclosure supposedly avoids parasitic magnetic effects that would adversely effect the low noise of the circuitry if the enclosure contained more steel parts. If true, and I don‘t immediately doubt that it isn’t, the natural consequence is a light weight enclosure. I imagine that Evans has the instrumented data showing a slight lowering of the noise, whether or not the ear can detect the lowering is another matter.
Would bet that Wayne Colburn's new phono stage, the Pearl 3, blows the MasterGroove away -- and at a cost of $150 plus case and PSU(s)...
Okay, I think I see how it works. Those four resistors determine the AC gain of the closed-loop. Which is equal to the R6,R11 and R10,R5 divider ratios. So, 750/22R = x34 = +30.6dB closed-loop gain.
Attachments
I looked and cannot find a single electrical specification for this preamp. The spec's I found were the case dimensions. It would be interesting to see some quantitative test results for this "magic" box. I looked at several reviews and they were all the usual "talk talk talk" and descriptions of power cords and speaker cables used in the review with some record titles. Useless. The market for this type of device apparently values poetic prose over a single electrical measurement.
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That is a pretty cool way of repairing the damaged through trace by replacing it with a tiny rivet tube. But you would have to have so many sizes and lengths. Still it worked quite nicely, and I may attempt that thinking in the future.
You have to keep in mind that there are different valid reasons why people purchase an audio component. Some find satisfaction primarily in objective metrics (which is intellect based), some in subjective listening experience (which is emotion based), and others in the consumer product aspects (such as, look, cost, pride, reputation, etc.). Of course, most purchase decisions are some combination of these, yet one typically dominates the others. As far as this phono stage, because you didn’t readily find published specification doesn’t necessarily mean they are not excellent. It’s just that the product marketing appears targeted at customers primarily seeking a certain kind of listening experience.
I agree with the intention of the outcome of the sound from a product, but in my view, at such a price point, components were not very special, and the use of much plastic including the cable supports (I use rubber insulated stainless steel types) and just general hardware that I am looking could be of a entirely different level of quality. Again, if it were a Sony, then the product might be believable, but the price would reflect it.
Generally I do agree with the idea that some people buy a unit to look cool, and some buy for completely other reasons, but most generally it is indeed a combination of those.
Generally I do agree with the idea that some people buy a unit to look cool, and some buy for completely other reasons, but most generally it is indeed a combination of those.
Mend it Mark, definitely worth following on YouTube. I guess I have been watching this channel for about 5 years now. He's brilliant at repairing odd stuff, and can make many of the missing bits in his machine shop. (Knobs and other things.) Methodical is an understatement.
I understand you feeling, but you seem to be presuming that the plastic enclosure was a cost cutting decision. It wasn’t.
Yes, I can hardly believe that he traced out all the circuits, identified most components and created a professional service document from that. Wow.
Now if he only x-ray'd the obscured chips and identified them, like a certain KG I know has done, that would be a bonus 
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