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Scored one of this at swap meet. The unit appears NOS with two perfect looking TFK X7, it also comes with schematic. It is an interesting unit.
Follow Ups:
I've found it sounds best in my vintage tube setup with high-output carts that will really wake up the 12ax7s - I especially like the older Stantons/Pickerings - and yes, the TFKs can be spectacular in it.
I replaced the power caps and a couple of resistors that had fallen out of spec, but overall, it's stock and sounds great.
I've linked to one below, showing his modified 'Chrome Cutie', as he called it. He did some fairly extensive upgrades to his, and was very happy with it. If you're interested in modding yours you could try searching the archives, because I recall him going into more detail in some other posts.
You could also try emailing him, but he hasn't posted in over 3.5 years, so I don't even know if he's still around.
I have one that was modified by a fellow known as Lar(tubeactive on Audiokarma). I really like the sound, and the small footprint. Definitely sounds as good to me as the phono sections of my McIntosh C11 and MX110z.
Here's a link to the long AK thread that Lar started about the M65 and modifications he's done.
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You probably already know that but I hate to hear about power transformers burning up.
Look into NPO ceramic capacitors for both coupling caps and EQ. Unlike traditional ceramic caps, the NPOs have zero temperature co-efficient, a dissipation factor very similar to Teflon, small size and very tight tolerances (1-2%). There are leaded versions available.
We've auditioned them and they are quite neutral! They easily keep up with a lot of expensive film caps. Some people won't like that because they are also really inexpensive too.
The dielectric absorption of NPO caps is typically 10X worse than that of dielectrics such as polypropylene and polystyrene. I won't use them for any purpose other than RF. Polypropylene is readily available from sources like Mouser and Digikey, and I think Russian teflons are still being sold on the big auction site.
Edits: 07/02/24 07/02/24
-showing only Teflon and the NPO; and nearly the same, the Teflon being a bit higher and the NPOs being a bit lower. Also the NPO dissipation factor being a straight line with respect to temperature.
I agree the dielectric absorption doesn't look good. But I'm not convinced that's the only thing that is a factor as to why a cap might sound good or not. The ones we tried really sounded quite good.
"the Teflon being a bit higher and the NPOs being a bit lower. "
Ralph, I don't know where you saw that, but there shouldn't be any confusion on this point. Kyocera - whom I trust completely to provide accurate data - publishes the same numbers I posted earlier. When it comes to dielectric absorption, NPO ceramics are simply much worse. The link below includes the Kyocera chart. I would certainly agree that this isn't the only parameter worthy of concern, but it is important as one of the non-linear characteristics that contribute to capacitor distortion.
For my own use, I have switched from all the various mylar and PIO caps to polypropylene for most coupling applications. I would gladly use Teflon, but they're physically too large in many designs. I do use Teflon in smaller values where appropriate. I also realized some time back that the extremely high input impedance of cathode followers allows the use of .01uF or smaller polystyrene caps. These are still available with 630V ratings on the big auction site in many values.
I'm pretty sure at this point I wasn't thinking and had 'dissipation factor' and dielectric absorption confused.
We use mostly Teflon coupling caps in our designs. Recently we ran a casual comparison between the Teflon and NPOs (through-hole with leads). The amps used were fully optioned M-60 Mk3.3s so had Caddock MM series resistors throughout; the only difference was the coupling caps. They were hard to tell apart- I would not want to try to do it blind! So that suggests to me that expectation bias is pretty strong with me in this situation. Since I like the Teflons and also wanted the NPOs to be good, I can't say which way the expectation had me leaning.
I mentioned to Triode Kingdom elsewhere that you had me a bit confused, especially regarding your dielectric absorption numbers for NPO ceramics.
As to your subjective comparisons, that's very telling, although honestly, I probably don't really want to know. It's a bit too close to the Emperor's New Clothes story.
I've been telling people that the spec sheets we've been seeing the last 60 years are exactly that because they do not contain enough information to tell you anything about how something sounds. That's resulted in equipment that that looks good on paper but doesn't sound good at all.
These days we have the ability to draw a straight line between what we can measure and what we hear due to advances in measurement technology. I suspect most manufacturers really don't want to produce a spec sheet that actually tells you how something sounds though!
WRT the NPOs, they are worth a listen. I'm not kidding when I say we couldn't tell them apart from Teflon. Maybe we need to listen harder. But there's also something called the Veblen Effect, in which the more expensive something is, the more people think there is greater value. The Veblen Effect is pointing out that isn't always true!
... that the vast majority of source material nowadays has passed through dozens of opampa, sub-standard SMT capacitors and digital processors before reaching our beloved vacuum tubes. I feel blessed to still have dozens of LPs in good condition that I purchased in the early and mid '70s before everything was totally contaminated. It has recently occurred to me that these are in fact irreplaceable unless I get very lucky at someone's garage sale. All the original master tapes have apparently deteriorated over time, and none of the reissue vinyl or CDs I've heard sound like the older vinyl. Some are only a horrible mimicry, a shadow of their previous selves that I can't even stand to play. It's really a shame.
should own vinyl and a good turntable.
If you are really avid about older recordings where the conductor might have known the composer and the like, the only way to really hear what they sounded like is the LP. By the time the first digital recordings were made in the 80s, the master tapes had lost of lot of their vivacious qualities. Most digiphiles don't know what they are missing on this account!
Expectation bias affects all of us, and I'm no different. Also, I need to correct my previous statement about teflon caps. I actually have used only very few, even in smaller values. The caps I was thinking about (which I use for LTP bypass), are actually Russian polystyrene. In any event, there are so many things that determine the sound quality of an amp, it can be difficult to say how much each component contributes or which positions are the most critical. I've heard some very fine amps that used electrolytics for bypassing. The best we can do is to use component types that we believe are the most transparent and listen carefully. :)
Edits: 07/03/24
View YouTube Video
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Have Fun and Enjoy the Music
"Still Working the Problem"
nada aqui
View YouTube Video
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Have Fun and Enjoy the Music
"Still Working the Problem"
Big fan of the curious McGurk effect.... the interesting line from the video is that the 'eyes override the ears'. A terrifying thought for a medium based on the ears.
dave
"A terrifying thought for a medium based on the ears."
Yes, you have to keep your eyes closed. That is a metaphor. All biases have to be eliminated or you're "listening to the video" with your eyes open. The bottom line is, we can't trust our own ears except in certain, very carefully controlled, conditions.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
It's obviously a script that uses the camera in your computer to determine which image you're viewing and to change the sound. :) Seriously, this is spooky.
As you know, there are a bunch of things that bias what we think we hear and what we think we see. Even when we think we are being "careful"
The human brain is wired to make all kinds of assumptions and to fill in the blanks, jumping to conclusions.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
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Have Fun and Enjoy the Music
"Still Working the Problem"
Below is a link to Conrad Hoffman's site, where he measured a variety of caps, and his also shows a high dielectric absorption with COG/NPO type. I remembered that his ceramics measured poorly, but I'd forgotten that they were the NPO type.
I thought I got lucky finding some 600 V Soviet Teflon caps in picofarad values needed for feedback networks in a pair of push pull tube amps, but then read an old post on the DIY Tube Asylum which said that they need at least 10 VDC on them to 'work'. One cap off the screens will see around 475 VDC, but the one off the 16 ohm tap (hopefully!) won't see any DC. I don't know what to expect if I try them anyway, but I guess I'll find out.
Below, in bold is Hoffman's take on dielectric absorption, speculative, but interesting none the less.
"Dielectric absorption is possibly more disturbing. There is remarkably little published on the matter. It was a significant issue with early analog computers and some related books covered it. There was also a good paper by Bob Pease, published by National Semiconductor, that may be the best write up to date.
I'll speculate that high dielectric absorption is not always serious, since silver-mica capacitors suffer from an excessive amount of it, yet can produce very good sounding RIAA networks. In later measurements of residual distortion, high dielectric absorption doesn't produce high residuals, but I'll still remain suspicious of it until it's proven harmless."
"an old post on the DIY Tube Asylum which said that they need at least 10 VDC on them to 'work'."
I probably have less experience with Teflons than you, but I'm highly skeptical. Was any scientific data presented in support of this claim?
No, there wasn't, not that I saw. But the poster really seemed to know quite a bit about many of the Russian cap types, including details regarding their internal construction. You even left him a "Great info, thanks!" comment. (link below)Here's the statement in question: "Foils are connected to tabs or wires by thicker aluminum strips; these strips are riveted to tabs, but not welded or soldered to foils. For this reason, FT caps may not perform well at very low voltages, and, if used as coupling capacitors at low signal levels, need at least 10V of DC bias."
My curiosity in this matter involves feedback in a tube amplifier circuit, rather than anything directly to do with 'vinyl' (although it does also apply to Teflon RIAA capacitors). So after Independence Day has passed, I'll start a new thread on the subject over on Tube DIY. That way it won't add to off topic clutter here, and may increase the likelihood that other builders may see it.
As always, thanks TK!
Edits: 07/03/24
Thanks for the link. That wasn't a reference to anything inherently wrong with Teflon dielectric for our use. He was referring to the riveted construction. I remember reading that post and thinking it would be wise to avoid those particular caps, regardless of the circuit.
Have a great 4th!
That's really interesting Ralph, thanks. Especially given that the polystyrene supply is drying up, and the price of silver mica continues to climb.
I always thought that ceramics, even the NPO type, were a last resort, except maybe in RF circuits. Thanks again.
for most of my career I've avoided ceramics except for things like power switch bypass.
But the NPOs are a game changer. With characteristics very close to Teflon in some ways and zero temp coefficient, they are better than a good number of boutique caps we've tried- for example anything with paper and oil. I like them better than the custom polystyrenes we've had made for us. Whether they can knock the Teflons out is unknown as yet, but in the comparisons we've run so far I couldn't tell the difference... I don't think my hearing is that bad yet as I can still hear other things we audition with ease.
The modification that the pre went through included a full recap.
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I didn't do, nor do I do, any mods. This was all done by Lar, the fellow who's work on these pre's has been referenced a couple times in this thread. I bought the M65 from him.
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