@von Ah I love your choice of test music. You have good taste.
I'm thrilled to hear that everything went together nicely for you. Well done.
When I assemble boards I usually have a trash can sitting next to me to catch the wire leads, SMD tape strips, etc. That way I'm not trying to work in a pile of wire clippings.
Tom
I'm thrilled to hear that everything went together nicely for you. Well done.
When I assemble boards I usually have a trash can sitting next to me to catch the wire leads, SMD tape strips, etc. That way I'm not trying to work in a pile of wire clippings.
Tom
With a single channel (so mono - not stereo) you can use a 2-gang/stereo pot as a balanced volume control. Wire it as shown here, just only build the circuitry for one channel: http://www.dact.com/html/wiring_a_balanced_stereo_passi.html
I doubt it. It might cause a degradation in the common-mode rejection ratio, but I doubt it'd be anything earth shattering. In general I find channel imbalance or gang error receives vastly more coverage than it deserves.
It is true that a good pot like the RK271 is specified to have 2 dB gang error (0-60 dB attenuation), 3 dB (60-70 dB attenuation), unspecified beyond 70 dB attenuation. Anyone can fish this information out of the data sheet for the RK271. But what isn't mentioned in the data sheet is that the gang error is pretty darn low (<0.2 dB, typically in my measurements) except for at 2-3 specific points where the resistance taper changes.
If you were to slowly turn the volume knob while measuring the attenuation of the volume control it would be very unlikely that you'd notice the spots on the pot travel with the higher gang error. Now, if you know where those spots are you can find them, but it takes hardly a touch of the volume control to knock it off those specific spots. For the RK271 you'll find the discontinuities at 60 and 70 dB attenuation. In actual use, you're extremely unlikely to ever notice the channel imbalance. The only time I've ever found the imbalance disturbing was with a high-gain tube headphone amp where the volume control was barely above minimum at ear-splitting levels. Basically once the volume knob is turned past about 8 o'clock you're off the discontinuous parts of the track.
Depends on how you measure quality, I guess. There are higher cost options than the already kinda expensive Alps RK271. The TDK ones seem popular. But are they higher quality or just higher cost?
You can find some TDK data sheets here: https://www.acoustic-dimension.com/tkd/Tokyo-Ko-on-Denpa-TKD-main-page.htm
To my eyes it doesn't look like the TDK pots are any better than the Alps RK271. The data sheets are more detailed and TDK does promise more. For example TDK specs the gang error at more points along the pot travel, but that could also mean that their pots have more segments, thereby, a higher number of discontinuities. Recall that a logarithmic pot (volume taper) is made from several segments of linear resistances and it's at the transitions from one segment to the other that the gang error is the highest. I'm not seeing a strong technical argument for using the TDK pots. There might be a marketing argument...
As far as I read the data sheets the TDK 2CP25xx-series are actually worse than the Alps RK271-series on gang error. The TDK 2CP601-series is on par with the Alps RK271-series. TDK doesn't specify the gang error beyond 42 dB attenuation, so it could be worse than the Alps.
I'm not knocking the TDK pots. I'm sure they're great. I just don't see any technical advantage for them over the Alps RK271 when it comes to gang error.
I agree with your observations around attenuators. The only attenuator I'm willing to accept is an IC-based one, i.e., a volume control chip. The 2-3 dB step size offered by rotary attenuators is too much for me. And the step size is usually extreme (5-10 dB) towards the minimum setting of the volume control.
Tom
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Welcome to club. You'll see why I have a 686. In fact, I've built the Modulus 86, Modulus 286v1 (an early diy SMD that used to be offered by Neurochrome), and Parallel-86 in this series amongst other Neurochrome modules. They are gifts that keep on giving.
Best,
Anand.
Oh... I meant TKD potentiometers, not TDK in Post #5982. Few probably noticed, but precision is important. TDK makes great ceramic capacitors (and many other things). Too many TLAs. 🙂
Tom
Tom
The amp has FAR exceeded my expectations, which were admittedly high based on reading about the Modulus amps for years. It will be my warm weather main amp, for sure. As long as I build an appropriately safe enclosure for it.
That's great to hear. Thank you for sharing.
Meh. Safety-smafety! 😉 Your setup reminded me of of my DeathTrap 500. It was one of the prototypes that led to the DG300B. I built quite a few prototypes like that and you can probably figure out why I started calling them DeathTrap. The number following was the B+ voltage rounded to the nearest 100 V. It's a pretty clear case of "do as I say, not as I do" and "don't try this at home. We're what you call experts". 🙂
You might want to unplug the mains power for the turntable. I don't want to imagine what'd happen if someone turned that on by accident.
Tom
Is it okay to use regular machine screw/washer/lock nut to secure the LM3886 to the heatsink or is a self/tapping screw necessary?
It depends. The LM3886TF and LM3886TF/NOPB come in an insulated (all plastic) package. To mount it you apply some thermal paste on the side that faces the heat sink. Then attach the IC to the heat sink with a machine screw.
The metal-back version of the LM3886 (LM3886T/NOPB) needs a shoulder washer and a thermal pad to keep the metal of the package (connected to V-) from connecting to the (grounded) heat sink.
I'm generally not a fan of using self-tapping screws for mounting semiconductors to a heat sink. Self-tapping screws leave little metal shards and if you get one of those in the wrong place bad things happen. Bad things like blown bond wires to pin 4 of the LM3886 rendering it useless.
Tom
The metal-back version of the LM3886 (LM3886T/NOPB) needs a shoulder washer and a thermal pad to keep the metal of the package (connected to V-) from connecting to the (grounded) heat sink.
I'm generally not a fan of using self-tapping screws for mounting semiconductors to a heat sink. Self-tapping screws leave little metal shards and if you get one of those in the wrong place bad things happen. Bad things like blown bond wires to pin 4 of the LM3886 rendering it useless.
Tom
I was lucky enough to pick up a Neurochrome Modulus-86 (in Quad chassis) from this site. Probably not its intended purpose, but I can report it drives Abyss 1266 Phi TC headphones (47 Ohm, 88 dB/mW) extremely well, sounding especially tremendous playing electronic/EDM/Metal 👍
I built that. It was a fun build and the chassis looks good, has plenty of heatsinking, and is reasonably priced and fits the components well.
I really didn't replace it with anything. At 66 years old I've been "electronic-ing" for more than 50 years. Decades ago, I replaced a solid state amp with a tube amp, didn't look back and I've built many different tube amps since then.
So I decided to try a state of the art solid state amp. The Mod86 is the best solid state amp I have ever heard. However, it doesn't sound (or look) like a tube amp. I realize tube amps have a higher noise floor and more distortion. As an engineer, I keep having to validate my choice of tube amps in spite of data to the contrary. Building this was to be a data point in that validation. It was. My ears and eyes voted tube amps. YMMV.
So I decided to try a state of the art solid state amp. The Mod86 is the best solid state amp I have ever heard. However, it doesn't sound (or look) like a tube amp. I realize tube amps have a higher noise floor and more distortion. As an engineer, I keep having to validate my choice of tube amps in spite of data to the contrary. Building this was to be a data point in that validation. It was. My ears and eyes voted tube amps. YMMV.
I find this aspect of our hobby really interesting. Personally I can enjoy both types of amps; the sheer neutrality and transparency of Tom’s amps makes for a great listening experience, but I also love whatever it is class A amps do (both valve and SS) - allegedly the whole 2nd harmonic dominant profile thing. It ought to be a case of cognitive dissonance, but I find I can enjoy both without it creating any inner
turmoil !