Tube Lab

We take a look at the volume pot and a highly resolving stepped attenuator option.
LINK to Mellow Tone Kits Stepped Attenuator Video: • Stepped Attenuator Pro...
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[@CollectingRetro]

Nice video! Don't forget that cable direction is very important for shielded cables! The shield will typically only be connected on one end, thus the arrow on it. Stepped attenuators are a very nice upgrade indeed! A good autoformer volume control is even another step higher, Dave Slagle from Intact Audio makes an incredible DIY unit with hand wound nickel core autoformers. Digital glare is very annoying, but the right DAC is a revelation. A nice NOS DAC using vintage R2R chips is an excellent solution and a tube output stage can be the icing on the cake. Keep up the good work!

[@tubelab194]

Thanks for the comments! One thing I'd point out is that typically quality RCA cables have both ground ends connected to the shield. As a designer of tube gear I'm constantly keeping an eye on my 0v return (ground return path). By connecting both ends of the shield up you're helping to maintain a balanced 0v between equipment. I've never understood why designers mess around with the ground return path. We recently came across a Rega "improved grounding method", which is a total disaster for many Rega owners. Lately we're seeing more and more crazy designs hit the market, 90% of them will be in the bin a year from now. So far our Kit Amps play nicely with most other gear, every once in a while we come across a ground issue and it always relates to a design that ignores standard grounding topology. Cheers!

[@CollectingRetro]

​@@tubelab194 Very interesting! Maybe my cables are less common, they have a 0v return wire, but the shield/screen is only connected on one end. Some standards and better labeling would be nice. Not like they will tell us when it's a snake oil arrow...or maybe they will with the excessive marketing, lol. Grounding is always fun, a friend admitted to having a hum in his system he can hear from the listening position, but it's not too bad...lol. That would drive me crazy!

[@gerihifi]

You guys really rock and I can listen hours over hours to your insights, greatly appreciated!! Love your idea and look forward to get this kit (hopefully I can buy it prebuilt). Need to place my tube orders, christmas coming! Your German fanboy 😅 Also very interested about chinese bad gear (just ordered an Cayin CS-805/300B)..

[@Brighamdoc]

Yes! I would love a remote volume control but it's not a deal breaker for me. All of the MTKs I've built have been amazing. Thanks guys.

[@tubelab194]

Thanks for the vote of confidence! The big question is how would you feel about carefully soldering up 48 matched pairs of resistors? We're looking for a PCB version of a stepped attenuator, but the simplest version electrically will be the one I used in the prototype build.

[@Brighamdoc]

@@tubelab194 I think that would be fun to make. Sounds like a great thing to do on a cold winter night.

[@joenovak6393]

I have used Goldpoint Level Controls, Khozmoa Acoustic and I like the TKD 2CP over the Alps "blue beauty".

[@mfr58]

When I tried using an external volume pot between a DAC and power amp, the sound lost all its "life". There seemed to be an impedance issue from the interconnects on the output of the volume pot. The amp input impedance was only about 50K. I guess your tube amps will be 100k or above, so maybe not a problem.

[@tubelab194]

In modern equipment and well designed older equipment, a power amp will be set with a very high input impedance, traditionally around 470k and these days as high as 2meg! The reason for this is obvious as you've discovered. Unfortunately designers in the past and more so lately have been fooling around with what they call a "low input impedance power amp", which imo is about as stupid a design decision as you could make. But we're seeing more and more of these poorly designed products being sold as "high end" gear.

[@jonshimamoto2710]

Jim, the motorized pot on the left appears to use the same part as the Willsenton R8/R300 and Muzishare X7. I have two R8s and one X7. For some reason all three amp pots are noisy. It generates a scratchy sound when you adjust the volume between 9 and 2 o'clock. I was told either the pot is either poorly made or grounding is bad. Does your R8 exhibit the same problem? If so, do you know what is the real cause of the noise and how to fix it? It is driving me nuts.

[@tubelab194]

No ours has been dead quiet. If the R8 pot is in fact analogue, you could add our soon to be Kit Attenuator to the front end of your r8, and turn the R8 volume pot to max and Bob's Your Uncle. Or just replace it.

[@PetraKann]

Chinese garbage?

[@tubelab194]

Yup, the last quad of Chinese power tubes I brought in, had one die on the tester and a 2nd one within 24hrs. That was the last time I brought in any tubes made in China. On top of that the vast majority of Chinese made tubes I've heard sound terrible. We've always specialized in quality vintage tubes and all of my experience with modern tubes just reinforces my opinion that this was a very good decision!

[@PetraKann]

@@tubelab194 Strange. Harley Davidson make bikes in China, Apple makes iPhones and iPads.....the list is long. All garbage? I don't subscribe to channels that make generalised racist remarks. Very disappointing Sir

[@tubelab194]

@@PetraKann With all due respect I handle thousands of tubes in a year and almost never come across a Chinese made tube that isn't garbage. One thing we do on Tube Lab is tell it the way it is.

[@Yessssz]

@@PetraKannneither of those companies have good reputations for quality. Many Harley people hate the motor company and the decisions they make. Apple does not “just work” like it used to 15 years ago. China is capable of making quality products but businesses want the cheapest products so they can increase their profits and everyday items become semi-disposable.