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Post by brucew268 on Jul 15, 2021 18:36:59 GMT
A few years ago I built a Pass-design buffer preamp based on matched pairs of JFET's which performed better than my £1200 Classe Audio preamp from 1991. Now with the Neurochrome 686 I've decided to change it from single ended to simple balanced design. That requires a second board, for a total of four channels, and a 4-gang potentiometer. I purchased the parts for the second board a few months ago and was having trouble sourcing a 20K 4-gang pot that wasn't what I considered silly money. But I found a guy on DIYAudio who had implemented the Muse 72320 pot chip. Now I'm finally about ready so thought I'd start a simple build thread. I'm considering whether to change the hookup wire from basic solid core to OCC solid core for the analog signal in/out. Oli, have you done this and have you found any significant difference?
The single ended layout at the moment. |
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Bigman80
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Post by Bigman80 on Jul 15, 2021 19:57:57 GMT
A few years ago I built a Pass-design buffer preamp based on matched pairs of JFET's which performed better than my £1200 Classe Audio preamp from 1991. Now with the Neurochrome 686 I've decided to change it from single ended to simple balanced design. That requires a second board, for a total of four channels, and a 4-gang potentiometer. I purchased the parts for the second board a few months ago and was having trouble sourcing a 20K 4-gang pot that wasn't what I considered silly money. But I found a guy on DIYAudio who had implemented the Muse 72320 pot chip. Now I'm finally about ready so thought I'd start a simple build thread. I'm considering whether to change the hookup wire from basic solid core to OCC solid core for the analog signal in/out. @bigman80 have you done this and have you found any significant difference?
The single ended layout at the moment. It's been a long time since I wired anything with OFC. OCC has been the standard here for a long time. Personally, I think it's absolutely worth doing for two reasons: 1) I think it sounds better. 2) Why have the "I wonder" hanging over you for the sake of a couple of quid? You'll notice a huge difference getting that Alps blue out of the way too. Go for it. |
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Post by brucew268 on Jul 19, 2021 12:37:09 GMT
The original design was Revision 2 of Nelson Pass’s B1 Buffer. I implemented on perfboard and used an external SMPS with the voltage divider he offered. I then replaced the power supply with one based on J Bau’s experiments with LM317 and LT1085, LM337 and controlling for phase.
Here are Pass & JBau’s specs and my layouts on perfboard.
BTW I quickly found that not all perfboard is made equal and rebuilt them on better quality boards.
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Post by brucew268 on Jul 19, 2021 12:38:31 GMT
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Post by brucew268 on Jul 19, 2021 12:47:27 GMT
Case is Modushop Galaxy Maggiorato 3U 330x350
Since I’m converting to balanced, have parts for a second B1rev2 board, and a Muses 72320 implemented by Frank Wilker as 4-gang. The Muses was highly regarded as potentiometer in a couple commercial implementations including Pass Labs, so I’m interested in how it will sound in this setup.
I also decided that the signal out makes much more sense on the left side of the chassis rather than the right, for my room, so I’m flipping the layout at the same time.
Planned back panel layout
Muses 72320 Potentiometer by Frank Wilker |
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Post by misterc on Jul 19, 2021 15:01:55 GMT
I like to see projects like this turn into the finished article Bruce nice work.
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Post by antonio on Jul 19, 2021 22:36:43 GMT
So do I MisterC
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Post by brucew268 on Aug 1, 2021 17:17:12 GMT
After two full days of layout, drilling, and wiring. It's now ready for some basic tests and adjustments... which will probably be tomorrow, but feels good to have gotten this far this weekend.
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Post by brucew268 on Aug 1, 2021 17:19:55 GMT
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Post by brucew268 on Aug 3, 2021 14:49:21 GMT
Got things up and running yesterday. The sound was euphonic but a bit mid-fi, lacking the air and finer HF and LF details I've come to expect. I first tried to tell myself it was just more natural but no it was missing a bit.
Considering that the XLR input/output sockets are new and with a good bit of teflon, and that the Muses potentiometer has a few caps, it may well be that it just needs lots of burn in hours. Well that could be a few weeks! I'll see if any improvement today after 24 hours, and if not, check it weekly.
I do wonder if that cheap and cheerful power supply for the potentiometer is contaminating the circuit common. Well first things first.
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Bigman80
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Post by Bigman80 on Aug 3, 2021 15:11:31 GMT
Got things up and running yesterday. The sound was euphonic but a bit mid-fi, lacking the air and finer HF and LF details I've come to expect. I first tried to tell myself it was just more natural but no it was missing a bit. Considering that the XLR input/output sockets are new and with a good bit of teflon, and that the Muses potentiometer has a few caps, it may well be that it just needs lots of burn in hours. Well that could be a few weeks! I'll see if any improvement today after 24 hours, and if not, check it weekly. I do wonder if that cheap and cheerful power supply for the potentiometer is contaminating the circuit common. Well first things first. Nice and tidy work. Hopefully you get an improvement after some hours |
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Post by firebottle on Aug 3, 2021 16:17:08 GMT
What chip is used on the Muses volume control board?
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Post by brucew268 on Aug 3, 2021 17:07:22 GMT
Nice and tidy work. Hopefully you get an improvement after some hours Thank you Oli.
I am hopeful. I sat down for a listen when I paused for a cuppa just a bit ago. It's definitely sounding better than yesterday and listenable as HiFi music, though I sense it has a bit more to go to match up to others' experiences and will open up a bit more over time.
What chip is used on the Muses volume control board? Muses 72320
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Post by brucew268 on Aug 11, 2021 16:37:35 GMT
Update on the sound:
After 24 hours of burn in, the sound improved a bit but did not seem to continue improving over the next couple of days. The dynamics were anemic, SQ needed to improve, and it didn’t quite seem to be a burn-in issue.
Opening the amp I noticed that the LED on one power supply rail had failed which could be throwing off the balance between the Pos and Neg rails. At the same time, I noted that feeding 4 buffer channels rather than 2 could be limited by less headroom in the PSU. It wasn’t getting warm, but decided to add heatsinks to the regulators anyway.
This fixed the dynamics and helped some of the SQ but something wasn’t right. There was a loss of depth to the sound and bit of glare. That turned out to be a load resistor I had removed thinking it was no longer needed. Replaced that and it now felt the SQ was back in healthy territory, including depth and realistic dimensionality to the instruments.
So, burn in was only part of the issue and that bit seems to have been done in the first day or so.
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Post by brucew268 on Aug 17, 2021 11:09:46 GMT
I thought I'd update the photos to finish this build thread.
This is the internal view with the power supply wiring. Given my fretting over the power supply I've decided to make a new board with a little different layout and all point-to-point wiring. That should improve impedance and flow, and at the same time I'll upgrade to CRCRC setup. First I'll run a couple experiments with more optimal voltage input to the regs and a slightly altered output voltage to see if I can hear the difference. I'll also try a beefed up transformer to see if that extra headroom is hearable. But I won't burden this thread with that.
I did finish setting up the remote capabilities on the weekend and will put that in the next post.
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Post by brucew268 on Aug 17, 2021 11:33:40 GMT
The sensor pins are not centered on the potentiometer board, so either must use flexible leads to position the sensor where wanted or drill the anti-twist pin hole so the potentiometer is mounted slightly turned, positioning the sensor vertically in the centre of the faceplate.
The 3mm infrared acrylic was cut was cut to a 25mm disc by WholesalePOS and appears black, letting no visible light through but passing the infrared signals from a remote.
The shelf for the Infrared disc window is about 2.5mm deep with a forstner bit and pillar drill. I should have used a TCT forstner but found I didn't have one on hand that day so had a go with an untipped bit. It did OK but the circle was a little sloppy and oversized. I then cut the 20mm through hole with a TCT hole saw. All of these are cheap and chearful off the internet for £4-10.
To give a cleaner appearance a black acrylic paint pen (uni Pasco) was used on the side and edge of the shelf the disc sits in. The paint is better than a permanent marker, since it's paint and is passable since those surfaces won't be touched once installed. Then glued in place with epoxy.
From the maker, the potentiometer remote works with a Sky remote or my Sony TV, which is convenient until one realises every time the TV volume is adjusted, the preamp volume is also adjusted if powerd on. That could make for a nasty surprise when I start listening to music!
But programming the potentiometer to read a different remote was very easy and worked on the first pass. I bought the same remote that HFC is currently sourcing for their remote kits and it has a nice feel to it, if too many buttons. I thought I'd use the acrylic paint pen to black out the unneeded buttons but the white lettering is some sort of vinyl that the paint won't stick to. So I guess I'm stuck with extra buttons. The remote fits the hand well and works great. Since the potentiometer electronically controls the volume, not physically, using the remote does not turn the knob which makes the volume marker a bit useless.
When I sourced this from Frank Wilker in Dec 2020 he was just prototyping a version with a beautiful display, but it was not ready for others yet and that required too big a window for me to DIY without a router anyway. He now has that finished and is selling.
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Bigman80
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Post by Bigman80 on Aug 17, 2021 12:50:11 GMT
That's some fine work there, Bruce.
Very impressive 👍
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Deleted
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Post by Deleted on Aug 19, 2021 4:54:37 GMT
Nice work, Warren.
A word about the power supply unit:
The Volume Control does not require a high-quality power supply. The Muses chip works similarly to a resistor network. Only when the Muses chip is switched to gain mode is a higher-quality power supply required.
For those who want to be on the safe side: a power supply in almost battery quality is already available.
A word about sounding:
The polymer capacitors need a break-in period. The sound will improve considerably in the next listening sessions. Especially in the first hours, it is extreme. The capacitors can also be removed. However, this can lead to unpleasant cracking or popping noises when switching the pot on or off.
By the way, I have never had a buyer who did not notice a noticeable improvement in sound after replacing his old pot with the Muses chip.
I am currently testing the replacement of the polymer capacitors with film capacitors.
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Deleted
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Post by Deleted on Aug 19, 2021 5:02:49 GMT
A word about the Display: The potentiometer is now available with 2 displays 1.5 Oled and 2.4 TFT. I hope it is allowed to post links. If you like, you can get an overview here: www.audio-perfect.de/muses_oled.en.htmlThere is now also an input module with 4 inputs. A Muses chip also works on it. This is located on the input board. |
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Bigman80
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Post by Bigman80 on Aug 19, 2021 6:59:32 GMT
A word about the Display: The potentiometer is now available with 2 displays 1.5 Oled and 2.4 TFT. I hope it is allowed to post links. If you like, you can get an overview here: www.audio-perfect.de/muses_oled.en.htmlThere is now also an input module with 4 inputs. A Muses chip also works on it. This is located on the input board. Hi @frankie You are more than welcome to post links, articles or anything else related to the work you do. Feel free to introduce yourself and tell us about your system, future products etc. Oliver. |
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Bigman80
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AA Founding Member & Bigbottle Audio Creator
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Post by Bigman80 on Aug 19, 2021 7:01:57 GMT
Nice work, Warren. A word about the power supply unit: The Volume Control does not require a high-quality power supply. The Muses chip works similarly to a resistor network. Only when the Muses chip is switched to gain mode is a higher-quality power supply required. For those who want to be on the safe side: a power supply in almost battery quality is already available. A word about sounding: The polymer capacitors need a break-in period. The sound will improve considerably in the next listening sessions. Especially in the first hours, it is extreme. The capacitors can also be removed. However, this can lead to unpleasant cracking or popping noises when switching the pot on or off. By the way, I have never had a buyer who did not notice a noticeable improvement in sound after replacing his old pot with the Muses chip. I am currently testing the replacement of the polymer capacitors with film capacitors. What type of film caps are you looking into? |
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