DIY Amps for NX-Oticas

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Jon L

Re: DIY Amps for NX-Oticas
« Reply #20 on: 22 Nov 2020, 04:48 pm »
The series resistor and all signal path resistors are Vishay Z-foils.

Like those Vishay Z-foil resistors, except for the price :thumb:

Early B.

Re: DIY Amps for NX-Oticas
« Reply #21 on: 22 Nov 2020, 06:12 pm »
@Jaytor , Any build threads on your projects ?
I'd  love to see the work in progress !!

Yeah, please tell us more about this preamp.

Jaytor

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Re: DIY Amps for NX-Oticas
« Reply #22 on: 22 Nov 2020, 07:08 pm »
I didn't create a build thread, but would be happy to answer any questions.

I used a ModuShop Slimline 2U chassis, 280mm deep with aluminum covers and 10mm front panel. I bought this through the DIYAudio Store. I created drawings using photoshop for the front and rear panels. I wanted something more than just a flat front panel, so I specified a 500mm radius rabbet that is 3mm deep and extends 8mm down from the top and bottom. 

I also specified a rabbet around the control holes so that I could inset the knobs into the front panel. I've got another set of knobs on order that are simpler design and have a sand-blasted look so I think they might look better against the brushed aluminum front panel. It's really hard finding knobs that don't have an indicator line. Since I'm using rotary encoders that don't have a stop, I wanted plain faced knobs.

There is also a rabbet around the cutout in the center of the panel for the OLED display. I found a company (Angel City Lasercraft) on Etsy that made the red acrylic panel that fit perfectly into the opening.

The transformers are from Antek - 100VA 18V, and 50VA 9V (for the 5.2V supply for the attenuator logic). The AMB Labs o11 supply I used for the digital logic is overkill since I only need 1A, but since I wasn't sure when I spec'ed it exactly what I was going to need.

I wanted to use a relay switched attenuator since I think this allows high quality resistors to be used and excellent tracking between four channels (balanced stereo). Originally, I was not planning to have more than one input since I only currently have one source, but after Khozmo told me about this particular product which I really liked since it had the display and remote control, I decided to take advantage of the built in switching and add all the inputs.

The AMB Labs alpha 24 buffer is essentially an instrumentation amp using modern very-low-noise op-amps and is configured to have both balanaced and single-ended outputs. I have to say I'm very impressed with the sound quality. The only challenge with this board is that the op-amps are surface mount and with my old eyes were a bit challenging to solder. I ordered an extra PCB so I could do a little practicing before building the two I used in the preamp. Fortunately, my wife has a dissecting microscope which made it much easier. At this point, I feel pretty comfortable with soldering these (fairly large) SMD components and wouldn't hesitate to use them again.

I used a little ground-break kit from glass-ware.com to connect the analog ground to the chassis ground. In the past, I've hard-wired my own circuit using a bridge rectifier, but this makes it simpler and cleaner.

I decided to use internal panels (modified chassis side panels from Modushop) that I lined with copper sheet around the analog section. I'm not sure if this really helps, but it can't hurt and looks kind of cool.

The Khozmo attenuator was the most expensive part of the project, and a little under $500 for the fully balanced design with Takman REY shunt resistors and Vishay Z-Foil series resistors. That's including shipping to the US. These are made in Poland. Khozmo was really great to work with and very responsive to questions. Included in the price was the customization of the OLED display (I designed the logo, for what it is), and the remote control with engraved logo.

The chassis was also a bit pricey since I had so much machining and printing. This came to about $450.

All in, it probably cost me somewhere between $1800 and $2000, but the SQ is an obvious improvement over my Parasound  (it took seconds to notice the difference) which retails for $4500, the remote works great, and I love the display. And I've got very hlgh quality in-line hi-pass filtering caps built in on a second balanced output.

AKLegal

Re: DIY Amps for NX-Oticas
« Reply #23 on: 28 Nov 2020, 05:25 pm »
I have found both the Folsom 7293 and the Neurochrome Modulus 186 to be great matches for the Super 7.  I owned the NX-Otica monitors for about 2 years so I think both would be a great match for those as well. 

Choose the Modulus 186 if you want a more detailed sound but with slightly set back mids and a deeper soundstage.  The Folsom has aggressive mids, great detail, maybe a more forward sound with great layering front to back.  Both are as transparent as anything you can get. 

Honestly, I like having both, they compliment each other really well.  The Modulus is like Daniel Craig's James Bond while the Folsom is like Ethan Hunt.  Bond is this https://www.youtube.com/watch?v=K2DUFYqc27w&t=1m51s, Hunt is this https://www.youtube.com/watch?v=Sjn3ELLcy2U&t=1m33s

poseidonsvoice

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Re: DIY Amps for NX-Oticas
« Reply #24 on: 28 Nov 2020, 07:10 pm »
Great builds and descriptions.

My buddy and I both built the Modulus 686 and our own versions of the Orchard Audio Starkrimson. He owns a full fledged NXOtica system with 4 separate subs and a treated room. Loves both amps but for slightly different reasons. We don’t see a reason to purchase commercial amplifiers as our DIY builds seem to trounce them! We have also eliminated our preamps (I used to use my own build of the TAPX with 4 silver autoformers), and go dac direct (Matrix Audio X-Sabre Pro MQA).

I use the AMB linestages in my MOFO and also have Wayne Colburns 2018 preamp for kicks.

Great to see DIY going strong. I will be happy to share pictures if there is interest.

Best,
Anand.

AKLegal

Re: DIY Amps for NX-Oticas
« Reply #25 on: 28 Nov 2020, 08:00 pm »
Great builds and descriptions.

My buddy and I both built the Modulus 686 and our own versions of the Orchard Audio Starkrimson. He owns a full fledged NXOtica system with 4 separate subs and a treated room. Loves both amps but for slightly different reasons. We don’t see a reason to purchase commercial amplifiers as our DIY builds seem to trounce them! We have also eliminated our preamps (I used to use my own build of the TAPX with 4 silver autoformers), and go dac direct (Matrix Audio X-Sabre Pro MQA).

I use the AMB linestages in my MOFO and also have Wayne Colburns 2018 preamp for kicks.

Great to see DIY going strong. I will be happy to share pictures if there is interest.

Best,
Anand.

I am DIY amp all the way from now on for the reason you mentioned.  The fun I have building them is just a added benefit.

I was considering building a AMB preamp but I have heard that they have issues with DC bias over time.  Have you run into that issue?

Tyson

Re: DIY Amps for NX-Oticas
« Reply #26 on: 28 Nov 2020, 08:32 pm »
Great builds and descriptions.

My buddy and I both built the Modulus 686 and our own versions of the Orchard Audio Starkrimson. He owns a full fledged NXOtica system with 4 separate subs and a treated room. Loves both amps but for slightly different reasons. We don’t see a reason to purchase commercial amplifiers as our DIY builds seem to trounce them! We have also eliminated our preamps (I used to use my own build of the TAPX with 4 silver autoformers), and go dac direct (Matrix Audio X-Sabre Pro MQA).

I use the AMB linestages in my MOFO and also have Wayne Colburns 2018 preamp for kicks.

Great to see DIY going strong. I will be happy to share pictures if there is interest.

Best,
Anand.

Oh, there's interest!  Please show :thumb:

Jaytor

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Re: DIY Amps for NX-Oticas
« Reply #27 on: 28 Nov 2020, 08:56 pm »
@AKLegal - I would like to build the Folsom amp at some point. I was actually planning to build one this past spring, but ended up building the F5 Turbo instead. I've got most of the parts (and circuit boards) collected for the Folsom, although I'll need to get another chassis and power supply.

As I mentioned, I'm building a Purifi class D amp right now. I started a build thread on DIYAudio. This is another pair of monoblocks, each with a large linear power supply (1500VA). I'm leaving enough room in the chassis to experiment with input buffers, and I plan to build a few different designs to see how it affects the sound. But eventually, I'll get back to building the Folsom chipamp.

Regarding the AMB preamp, I'm using the alpha 24 board which is op-amp based. It is DC coupled, so any input offset will show up on the outputs, but with the inputs grounded, it is very close to 0 offset. This board was perfect for me since I wanted balanced inputs, and both balanced and single ended outputs (the single ended for the servo subs). I am actually currently using my hi-pass output which is AC coupled through Miflex KPCU caps since I don't want to send the lowest couple of octaves to my NX-Oticas, so offset doesn't matter anyway for the balanced outputs.

But I suspect the AMB alpha-20 (which is a discrete design) may be more prone to offset since it uses a trim pot to compensate for differences in the JFETs. Since these are N and P channel devices, they will never have exactly the same transfer function and may drift a bit over time (and temperature).

@poseidonsvoice - I saw photos of your Orchid and Mod-286 builds on DIYAudio - very nice! But I don't think I saw photos of the Mod-686. Are these posted on DIYAudio?

poseidonsvoice

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Re: DIY Amps for NX-Oticas
« Reply #28 on: Yesterday at 12:33 am »
@AKLegal - Yes, what Jaytor said. The AMB Alpha 24 is a very flexible opamp based preamp that is dc coupled using some of the finer opamps out there, fully biased in class A. DC Offset isn't an issue either.
 
The AMB Alpha 20 is a different animal altogether.  It is a discrete design, and has a push pull output stage that needs some bias to stay in Class A for most output loads. Only 30mA is required but you can bias it much higher. I use about 50mA. I have found that at higher gains (10X or more) the DC offset can vary a bit, but it isn't too big of a deal. This is common with JFETs which as discrete devices do vary in matching. The closer matched they are, the better, and that is the issue with *any* discrete design. With opamps, the matching is quite exacting, as such DC offset "drift" is very rarely seen. With the Alpha 20 discrete preamp, the small amount of dc offset even at the 10X gain (20dB)  isn't an issue in my setup because the next stage is capacitor coupled (my MOFO stage). If it troubles you, use a very high quality capacitor on the output of the Alpha 20 preamp (sized enough so that it can pass low frequencies, like 10Hz or so) and you should be fine; or else design a DC servo, etc...

Here is my Class D build:

Front panel with push button switch that glows a very subtle blue when on:



Rear panel, which uses Furutech binding posts, IEC and XLR's. The writing in Cyrillic says: Ayzenshtat Class D which pays homage to the designer, Leo Ayzenshtat who is the owner, and proprietor at Orchard Audio.



Here are the innards. It uses Neurochrome Audio's SMPS-86 supplies (dual mono), set to +48V. It has it's own soft start, surge protection, and Pi Filter on the output of the MeanWell power supplies and is also compatible with any AC power grid from about 100V to 240V AC. The audio signal wiring is all Neotech. I purchased the Orchard Audio "BOSC" boards as blank boards and had to order and populate the parts myself, all very small SMD! As such, we had to order an SMD stencil to accurately place the parts on the board. Fun stuff. Nowadays, you can order just the boards, fully built which is much easier for the end user, since it is fully tested as well.







The unit is very light, about 8 lbs, and easily pumps out 100 watts into 8 ohms with astonishingly low distortion figures.  I have comfortably listened to the amps hooked up to my system and achieved SPL levels of 85-95dB at my main listening position of ~ 4 meters. At these SPL levels, I have measured about a minimum of 6watts and max of 20 watts (my impedance varies from 4.8 ohms to 20 ohms from 100Hz on up). Bear in mind that I use a distributed multisub setup for frequencies below ~ 200Hz.

Here is a measurement at 10 watts:

https://www.audiosciencereview.com/forum/index.php?attachments/e215338b-09ca-40e7-8f29-1246f2635a8d-jpeg.83025/

@Jaytor - I will at some point post pictures of my Modulus 686 build which puts out more power and is very amenable to more difficult loads like 3 to 4 ohms. It is a phenomenal amplifier in its own right and the finest Class AB amplifier I have heard.

Best,
Anand.
« Last Edit: Yesterday at 09:11 pm by poseidonsvoice »

AKLegal

Re: DIY Amps for NX-Oticas
« Reply #29 on: Yesterday at 12:38 am »
The Folsom is definitely worth building.  Jeremy says he designed the 7293 to be less responsive to input capacitor changes than the older 7297 was but my 7293 sounds like a completely different amp with a pair of Jantzen silvers as opposed to the Jupiter flat stacks I had in there at the start.  The Jupiters make the 7293 sound a bit closer to the Neurochome 186 without the extreme detail retrieval.  I think if I had the space I would try a pair of MiFlex KPCUs but the 2.2 uf variety are 3 inches by 2.75 inches. 

By the way, Poseidonsvoice and Jaytor, you two make my stuff look super pedestrian.  lol

Folsom 7293







Neurochrome Mod 186 monoblocks








   
« Last Edit: Yesterday at 02:03 am by AKLegal »

Jaytor

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Re: DIY Amps for NX-Oticas
« Reply #30 on: Yesterday at 04:27 pm »
@AKLegal - These look fabulous! Which amp did you build first? I've found that with each project, I learn something new and want to go back and rebuild the early ones.

AKLegal

Re: DIY Amps for NX-Oticas
« Reply #31 on: Yesterday at 09:44 pm »
Thanks for the compliment.  I built the Folsom first.  I originally wanted to make it a pair of monoblocks and I still wish I had but at the time I had concerns about size.  One monoblock would have been almost the same size as the stereo build. After building the Neurochromes in such a small form factor (they disappear on my floor), I don't think I would have minded the larger size.

I have no complaints with the Neurochrome build.  I kind of wish I went all out and built a pair of 686 Monos even though I really don't need the power at all.  The high powered amps I have owned couldn't seem to get out of their own way with high efficiency speakers but I don't that would have been an issue with the 686 given what I have heard of the 186.

Tyson

Re: DIY Amps for NX-Oticas
« Reply #32 on: Yesterday at 10:11 pm »
Anand,
First rate build, as always.  Makes me want to build something just to up my DIY game :D

poseidonsvoice

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Re: DIY Amps for NX-Oticas
« Reply #33 on: Today at 02:55 am »
@Tyson - Thanks! Honestly, at this point of my life I do DIY purely out of boredom and some need for personalization.

Best,
Anand.