[mkrawcz]

We currently have approved to make the next batch of 29 chip amps. But the same shortages affecting the world has put a but of a damper on its roll out.

But as soon as we have stock inbound, we'll definitely have more info about them available. 

When I was gathering parts for this latest build, most places where out of stock on the LM3886 chip until September 2022!

[Jaytor]

I finally finished the preamp I mentioned on page 6 of this thread. After my first DIY turned out really well (easily besting my previous commercial preamp), I decided to see what I could do to improve on it. I started this project in January, but a couple of the PC boards I decided to use were not available until the next group buy. By the time I got them, I had other projects in the works. But it's now done which means I can focus on the 300B monoblock build I'm working on (https://forums.stevehoffman.tv/threads/ank-300b-interstage-monoblocks.1112018/#post-27958720).

My new preamp is a two chassis design - the second chassis containing the transformer and first stage power supplies. The main output boards and the shunt regulators were designed by DIYAudio.com contributor "Salas", so I gave him top billing on my enclosure graphics.








An umbilical cable from the power supply has separate positive and negative power connections for each of the two required DC voltages and for each channel - a total of four +/- connections with grounds. An additional +5 volt regulated connection provides power for the switched attenuator logic.

The main chassis has eight Salas SSLV1.3 Ultrabib shunt regulators to generate the +/- 12V and +/- 17V needed for different analog boards. These are the boards that have the red heatsinks in the image above.

A Khozmo relay switched selector and shunt attenuator is used for input selection and volume control. Two 2-channel boards are sandwiched to provide fully balanced input selection and attenuation. These boards connect to an OLED display with a rotary encoder to select and display current input and volume. Pushing the volume knob rotates through the inputs.

The selected input is buffered by an AMB A24 buffer board before driving the switch attenuator. This allows me to use a lower impedance attenuator while providing a very high (500K ohm) preamp input impedance. The output of the attenuator drives two output stages. The first is another AMB A24 with AC coupled input. This drives both a balanced output and single ended output and will be used to drive my subwoofer amps. The second is a DC coupled Salas DCG3. I'm using a two channel DCG3 board configured as a fully balanced buffer for each output channel. The DCG3 uses a differential FET input stage feeding a fairly high-bias single-ended class A output stage. Cascoded stages and current sources keep distortion very low with second order being the dominant type. DC offset is minimized with a DC servo.

I've used a lot of premium parts in this build including Vishay Z-foil and Audio Note silver tantulum resistors, carefully hand-matched transistors, silver PTFE hookup wire, etc. Hopefully, all this will translate to excellent sound.



The power supply chassis contains a custom 400VA Toroidy transformer controlled by a Neurochrome soft-start board. This transformer has separate secondaries for each of four linear CRC power supplies, each with ~27,000uF of filter caps. A separate regulated power supply provides the 5V power for the Khozmo.

I don't have this installed in my main system yet. I've just been testing it in my workshop to make sure everything is working (amazingly, everything worked on first power-up  ). I have to do some juggling in my audio rack to accommodate the two chassis design, so I'm hoping to get it installed this weekend.

[AKLegal]

Fantastic!

[corndog71]

Wow!  Impressive build!

[subsonic1050]

All these builds are absolutely amazing.  What kind of education/experience do you have which helped you to build and design these? Id love to build an amp myself - just no idea where to start. Any suggestions for a great DIY amp build?

[Jaytor]

Thanks folks.

All these builds are absolutely amazing.  What kind of education/experience do you have which helped you to build and design these? Id love to build an amp myself - just no idea where to start. Any suggestions for a great DIY amp build?

I studied electronics in college in the late '70s, mostly because I was already into audio while in high school. But I fell in love with computers and digital electronics in college, so never did any analog circuit design for my job. I built a few DIY amps in the late '70s and early 80's, but family and career got in the way and never did any more after that.

A couple years ago I was shopping for new speakers and stumbled across Danny's videos and Ron's review of the NX-Oticas, and this brought back fond memories of my earlier DIY projects, so I decided to take a chance on the NX-Oticas. Needless to say, I very impressed with the results, but I also really enjoyed the process so I started working on more DIY projects. Before building the NX-Oticas, it had literally been 30 years since touching a soldering iron. But I'm having a blast with the DIY builds and as I move toward retirement I think this hobby is going to occupy more and more of my time.

If you are looking for an easy first DIY project, I'd recommend the Amp Camp Amp designed by Nelson Pass. This is a small and inexpensive class A amplifier and is available as a complete kit from the DIYAudioStore.com.

[poseidonsvoice]

Since this thread is turning into a DIY amp/preamp build thread, here's mine that's been an ongoing journey:

The Poseidon's Voice NPXP is an amp that I had aspired to build for quite some time. At it's core it's basically a foundation to experiment with the multitude of Pass inspired designs. The front end is composed of Neurochrome's THAT RX:: Mono circuit along with Neurochrome's Guardian-86 ahead of the speaker output. The main power supply is composed of a Furutech IEC, a massive 800VA custom Toroidy with 4 pairs of 20V secondaries (for ease of wiring) and dual XRK Audio SLB supplies, populated with Mundorf E-lytics.  A soft start is provided by Neurochrome's ISS board and a Bulgin momentary switch is used on the front panel. Neurochrome's THAT RX::Mono circuit is an extremely well designed differential to single ended converter with 0dB gain and operates on a bipolar regulated supply. In my case I decided on Jan Didden's excellent Silent Switcher V3 which when provided a 5V DC to 10V DC supply, pumps out a very clean +/- 15VDC @ 150mA (min) at vanishingly low ripple levels. A Mean Well supply provides the requisite 5V DC with 6A (30W) to spare. The dual SLB supplies provide a rock solid +/- 24VDC at 1-2mV RMS ripple.

The main amp module used in this premier round is the Aleph J. Building this board was fairly easy, thanks to member Dennis Hui who was kind enough to provide me with matched IRFP 240 Mosfets and 2SJ108V JFETs. I had VH Audio's 1uF ODAM capacitors on hand which I pressed into service as the input capacitor. For this build I have elected to use the Aleph J as a single ended input only, even though the input stage is composed of a differential pair and can accommodate XLR sources. At some point, I may experiment with bypassing the THAT::RX Mono module, although I frankly doubt the sonics will improve. The THAT::RX is based on the THAT1200 chip and Tom Christiansen's very elegant implementation/layout (hints of which are available in the THAT 1200 data sheet). In previous amp builds, this module has completely surpassed the sonics as well as measurements of my previous reference (Lundahl amorphous core transformers). The CMRR is maintained over a wide range of source impedance imbalances. Moreover the distortion levels of this module is several orders of magnitude lower than any diy Pass or Pass inspired amp circuit I have seen at typical dac output voltage levels (2V to 5V RMS). Given that the THAT::RX is discontinued, I would encourage folks to look at the Neurochrome Universal Buffer or other competitors like AMB Audio's α24 or XRK's BTSB if a differential input is desired. If you look carefully in the photos, I have drilled holes to mount AMB Audio's α24 which gives me the option of gain settings (from 6dB to 20dB) if needed. On the output, we have Neurochrome's Guardian-86. This is a speaker protection module and my choice here was easy. Many speaker protection modules unfortunately raise the distortion levels of the amp module that they are paired with. The Neurochrome Guardian series has been tested with their own Modulus 686 which is one of the lowest distortion amplifiers I have ever encountered. Given that the Guardian isn't an impediment to the Modulus 686, I was sure they wouldn't be an impediment to any of my Pass experiments.

So in summary, the ingredients are:

• Modushop 5U/400 mm deep chassis with UMS heatsinks customized using Front Panel Express.
  #frontpanelexpress #frontpanel
  
• Neurochrome Audio ISS
  
• Toroidy 800VA w/120V primary and a quad pair of 20V secondaries
  
• XRK Audio's Smooth Like Butter supplies (SLB, dual rail)
  
• Meanwell MPM 30-5-ST
• Linear Audio Silent Switcher V3
  
• Neurochrome Audio THAT RX::Mono (pair) [discontinued]
• Neurochrome Audio Guardian-86 (pair)
• DIY Audio Store Aleph J (pair) w/matched pair of 2SJ108V JFETS & quad matched IRFP-240’s mounted on ceramic thermal insulators
  
• Various wires from Neotech, VH Audio, DH Labs and generic mil-spec wiring.
• Cardas XLR input and Cardas Rhodium binding posts
• Furutech FI-10 IEC

Best,
Anand.

[poseidonsvoice]

In my ongoing quest for experimentation, I also built the Aleph J Zen and I am currently listening to the ALPHA 20 which is a Hugh Dean design from AKSA fame. It's actually the Aksa Lender P-Mosfet Hybrid Aleph amplifier (ALPHA). So he takes his Lender preamp topology and marries it to a single ended Class A output stage loaded with Nelson Pass' Aleph CCS. In my subjective listening sessions, I would argue the ALPHA 20 takes the best of the Aleph J and Aleph J Zen and marries them together. A very enjoyable amplifier that fixes the slightly ripe midbass since the damping factor of ALPHA 20 is much better, and yet the top end remains smooth and extended. Moreover, it puts out a little more power into a 4 ohm load (32 watts Class A) which is unusual for a single ended output stage topology, since most SE topologies the output power into a 4  ohm load is 1/2 of what is measured into 8 ohms:







More measurements, info, etc...is available in my diyaudio thread if y'all are interested in scope measurements.

Best,
Anand.

[mkrawcz]

Since this thread is turning into a DIY amp/preamp build thread, here's mine that's been an ongoing journey:

The Poseidon's Voice NPXP is an amp that I had aspired to build for quite some time. At it's core it's basically a foundation to experiment with the multitude of Pass inspired designs. The front end is composed of Neurochrome's THAT RX:: Mono circuit along with Neurochrome's Guardian-86 ahead of the speaker output. The main power supply is composed of a Furutech IEC, a massive 800VA custom Toroidy with 4 pairs of 20V secondaries (for ease of wiring) and dual XRK Audio SLB supplies, populated with Mundorf E-lytics.  A soft start is provided by Neurochrome's ISS board and a Bulgin momentary switch is used on the front panel. Neurochrome's THAT RX::Mono circuit is an extremely well designed differential to single ended converter with 0dB gain and operates on a bipolar regulated supply. In my case I decided on Jan Didden's excellent Silent Switcher V3 which when provided a 5V DC to 10V DC supply, pumps out a very clean +/- 15VDC @ 150mA (min) at vanishingly low ripple levels. A Mean Well supply provides the requisite 5V DC with 6A (30W) to spare. The dual SLB supplies provide a rock solid +/- 24VDC at 1-2mV RMS ripple.

The main amp module used in this premier round is the Aleph J. Building this board was fairly easy, thanks to member Dennis Hui who was kind enough to provide me with matched IRFP 240 Mosfets and 2SJ108V JFETs. I had VH Audio's 1uF ODAM capacitors on hand which I pressed into service as the input capacitor. For this build I have elected to use the Aleph J as a single ended input only, even though the input stage is composed of a differential pair and can accommodate XLR sources. At some point, I may experiment with bypassing the THAT::RX Mono module, although I frankly doubt the sonics will improve. The THAT::RX is based on the THAT1200 chip and Tom Christiansen's very elegant implementation/layout (hints of which are available in the THAT 1200 data sheet). In previous amp builds, this module has completely surpassed the sonics as well as measurements of my previous reference (Lundahl amorphous core transformers). The CMRR is maintained over a wide range of source impedance imbalances. Moreover the distortion levels of this module is several orders of magnitude lower than any diy Pass or Pass inspired amp circuit I have seen at typical dac output voltage levels (2V to 5V RMS). Given that the THAT::RX is discontinued, I would encourage folks to look at the Neurochrome Universal Buffer or other competitors like AMB Audio's α24 or XRK's BTSB if a differential input is desired. If you look carefully in the photos, I have drilled holes to mount AMB Audio's α24 which gives me the option of gain settings (from 6dB to 20dB) if needed. On the output, we have Neurochrome's Guardian-86. This is a speaker protection module and my choice here was easy. Many speaker protection modules unfortunately raise the distortion levels of the amp module that they are paired with. The Neurochrome Guardian series has been tested with their own Modulus 686 which is one of the lowest distortion amplifiers I have ever encountered. Given that the Guardian isn't an impediment to the Modulus 686, I was sure they wouldn't be an impediment to any of my Pass experiments.
Best,
Anand.

Nice work there! I am a fan of the Neurochrome boards. I’ve found that the guardian boards take nothing away from the signal. I just got a universal buffer myself to put in my Folsom amp. That Mod-86 V3 I just built I find to be a significant improvement in sound quality over the Mod-686. It’s pretty much right there with the best amps I’ve ever heard. Sounds a lot like the Folsom amps.

[Jaytor]

Very nice build Anand. I like your idea of a test bed to try different amp circuits. Any favorite yet?

I assume Tom isn't offering the THAT buffer any longer (replaced by the universal buffer?). His designs are very well implemented, and you may have noticed I've used a bunch of his boards in my various DIY builds.

- Jay

[poseidonsvoice]

Very nice build Anand. I like your idea of a test bed to try different amp circuits. Any favorite yet?

I assume Tom isn't offering the THAT buffer any longer (replaced by the universal buffer?). His designs are very well implemented, and you may have noticed I've used a bunch of his boards in my various DIY builds.

- Jay

From my original post:

Given that the THAT::RX is discontinued, I would encourage folks to look at the Neurochrome Universal Buffer or other competitors like AMB Audio's α24 or XRK's BTSB if a differential input is desired. If you look carefully in the photos, I have drilled holes to mount AMB Audio's α24 which gives me the option of gain settings (from 6dB to 20dB) if needed.

Thanks for the compliments.

No favorites just yet as I have a multitude of boards to evaluate/test. Currently I am going through the single ended Class A output stage topologies and should be done in a few weeks. Next I'll move to push pull, such as M2, F6, F5, etc....if you look carefully on diyaudio, you will see various offshoots of NP designs that will fit on the UMS profiled heatsinks. I have a feeling that amongst the SE Class A topologies that I will like the Alpha Nirvana the best (that's next in the queue).

My main amps are Tom's 686, and Leo Ayzenshtat's Starkrimson amplifiers. They are neutral and well anchored imho. These other amp designs are just for fun and experimentation. I've also become more interested in measurements since acquiring a Keysight DSOX 1202G scope along with various other goodies (Jan Didden's Linear Audio AutoRanger, etc...). Measurements in and of themselves are their own sub hobby within this hobby and it's nice to correlate certain sound profiles with certain spectral distortions.

I am currently working on a fully balanced AMB B22 (just for kicks) prior to building AMB B24 monoblock amplifiers. They require quite a bit of matching of discrete semiconductor devices which is fun to do on the bench.  The B22 is a good learning exercise prior to building the big B24.

I've been building Tom Christiansen's work since his inception in 2016. I've pretty much built or bought everything he sells including his HP1/2 headphone amplifiers.

DIY is like a buffet, I like it all! The journey is all the fun 

Best,
Anand.

[Jaytor]

Sorry - should have read your post more carefully. 

This sounds like a great project. I plan to experiment with different buffer designs on my Purifi monoblocks at some point, but haven't had a chance to get back to that.

Assuming my 300B monoblocks work out (my first tube build), I'll probably spend a while on a couple more tube projects before getting back to the Purifi or other solid state amp builds.

I wish Tom still offered his Darn Good 300B design. That looked kind of interesting. Of course, I could replicate by fabricating my own PCBs or doing a point-to-point build, but since I'm already building a 300B SET, I'll probably explore other topologies first.

[poseidonsvoice]

I wish Tom still offered his Darn Good 300B design. That looked kind of interesting. Of course, I could replicate by fabricating my own PCBs or doing a point-to-point build, but since I'm already building a 300B SET, I'll probably explore other topologies first.

I actually have Tom's DG300B fully built with his Universal Buffer board ahead of it, replacing the input transformers. The power transformers and output transformers are all custom Toroidy. Just need to put in a nice case 

Best,
Anand.

[Jaytor]

I actually have Tom's DG300B fully built with his Universal Buffer board ahead of it, replacing the input transformers. The power transformers and output transformers are all custom Toroidy. Just need to put in a nice case 

Best,
Anand.

Sweet!

[subsonic1050]

I just built a Neurochrome Modulus 86 at the suggestion of mkrawcz - absolutely fantastic!! Thanks for the help mkrawcz - and great suggestion. The amp sounds truly fantastic. I think it may sound better than my $4600 tube amp. I have a Doge 8 tube preamp arriving tomorrow to play with and see what that combination is like.

Tom over at Neurochrome was extremely responsive to questions and very helpful. I don't have the electrical background of a lot of you guys, so having a good build document as well as a resource to ask questions was imperative for my success.

[mkrawcz]

I just built a Neurochrome Modulus 86 at the suggestion of mkrawcz - absolutely fantastic!! Thanks for the help mkrawcz - and great suggestion. The amp sounds truly fantastic. I think it may sound better than my $4600 tube amp. I have a Doge 8 tube preamp arriving tomorrow to play with and see what that combination is like.

Tom over at Neurochrome was extremely responsive to questions and very helpful. I don't have the electrical background of a lot of you guys, so having a good build document as well as a resource to ask questions was imperative for my success.

Nice work! That amp surprised the heck out of me when I first listened. It’s an improvement over the surface mount versions IMO.

[Early B.]

I finally finished the preamp I mentioned on page 6 of this thread....

I don't have this installed in my main system yet. I've just been testing it in my workshop to make sure everything is working (amazingly, everything worked on first power-up  ). I have to do some juggling in my audio rack to accommodate the two chassis design, so I'm hoping to get it installed this weekend.

Report back, please -- how does it sound????

[Jaytor]

Report back, please -- how does it sound????

Jury is still out. I noticed a channel imbalance after installing in my system and brought it back to the bench. When I hooked up the scope to figure out what was causing it, I noticed that I was getting a high frequency oscillation. I tracked this down to the modification I had made to the DCG3 to couple the positive and negative halves by creating a virtual ground in the feedback connection. The circuit did not like this, so I went back to separate ground connections which eliminated the oscillation. I had to order some new resistors to implement this change.

At the same time, I replaced the series resistors in the attenuator. I had asked Khozmo to use shunt resistors set up for a 5K series resistor, but I don't think they did this, and the output level was way to high. A setting of 20 out of 60 was way too loud. So I replaced the 1/2W 5K Audio Note Silver Tantulums with 2W 10K parts. Even with the 10K parts, I'm not able to use much of the range, so I suspect the attenuator was optimized for a 20K series resistor.

The channel imbalance problem was caused by a bad solder connection on the one balanced input I happened to be using. The wire had gone too far through the connection hole, and since it is PTFE insulated wire, the insulation did not melt when I soldered it.

Anyway, I've had it back in my main system for several days. At this point, I'm not sure it's an improvement over my older DIY preamp, but it does seem to be steadily improving, so it could be some of these parts need a reasonable amount of break-in.

BTW - I'm making progress on my 300B monoblocks. Here's a couple of progress shots.

[Early B.]

Thanks for the feedback. It's exciting to hear about the journey -- challenges and triumphs are equally significant. Keep us posted on those monos.   

[Rocket]

Hi Guys,

Thank you for all the updates on your progress building diy amplifiers. It has been a really interesting read.

Cheers Rod