[mordy]

I can't speak to how it was set up in Glenn's OTL. I believe one of the other amps you are referring to is a Feliks Audio amp, they list a "preamp safety circuit" in their feature list, likely for the reasons I listed above, to protect against DC transients given that the two outputs are in parallel, the reason both are on at the same time. It isn't something I am interested in incorporating into this amplifier, but sounds like what you have is well-suited for your listening needs.

Thanks. According to my understanding the safety circuit shuts off the amp in the event a tube short circuits in order to prevent damage to the amp and headphones/speakers.
I know that this safety circuit works because at one point I received a defective Chinese adapter that shorted out a power tube and it prevented the amp from blowing up - unfortunately a fate that befell another amp where I tried the same adapter. (Did not understand where the problem was at first.)

 

[bcowen]

I'm excited to get one of these built and get some feedback on it. I am enjoying the sound, I hope others will too. To me, it has excellent transparency, dynamics, and detail retrieval. With the way the circuit has been designed, I also don't think you need very rare / expensive 6J5 / 6AS7G to get very good sound from the amplifier.

I will be using a 40mm RCA fester style bakelite knob. Have to import from Europe unfortunately. Everything has to be the way it has to be...

Your OCD-ness becomes you.

 

[L0rdGwyn]

Your OCD-ness becomes you.

It's a bit of problem, costs me a lot of money LOL.

I placed all final orders for parts today. I paid for overnight shipping from Mouser as there is one last thing to test before I can finalize the chassis order and I want to do that this weekend, $23 well spent I think. So hopefully Saturday the chassis will be checked off the to-do list.

I am listening to the OTL amp right now with MOV L63 and Tung-Sol 5998. I bought a pretty nifty device on US Audio Mart, Matrix Audio X-SPDIF 2 - it's a USB to pretty-much-every-other-digital-output box, including I2S over HDMI. It does its job well, impressive measurements over on Audio Science Review (this is a device where that really does matter).

So now I can run USB into the X-SPDIF 2 box from my laptop and then coaxial SPDIF into my SW1X DAC II, which of course means I lugged the beast into the basement for some listening.



Wasn't a secret, but the DAC in the audio interface I use for testing bottlenecks the crap out of this amplifier, with a proper source, the sound is vivid, reminds you the HD650 was the best headphone in the world at one point.

I also picked up another NOS R2R DAC on US Audio Mart for a song, one that has gotten quite a bit of hype recently, the Border Patrol SE. From what I can tell, it's a pretty simple TDA1543 design, but people like it! I've taken an interest in these DACs since I am designing one very, very slowly...so we will see how it sounds, might mod it.

 

[bcowen]

It's a bit of problem, costs me a lot of money LOL.

I placed all final orders for parts today. I paid for overnight shipping from Mouser as there is one last thing to test before I can finalize the chassis order and I want to do that this weekend, $23 well spent I think. So hopefully Saturday the chassis will be checked off the to-do list.

I am listening to the OTL amp right now with MOV L63 and Tung-Sol 5998. I bought a pretty nifty device on US Audio Mart, Matrix Audio X-SPDIF 2 - it's a USB to pretty-much-every-other-digital-output box, including I2S over HDMI. It does its job well, impressive measurements over on Audio Science Review (this is a device where that really does matter).

So now I can run USB into the X-SPDIF 2 box from my laptop and then coaxial SPDIF into my SW1X DAC II, which of course means I lugged the beast into the basement for some listening.



Wasn't a secret, but the DAC in the audio interface I use for testing bottlenecks the crap out of this amplifier, with a proper source, the sound is vivid, reminds you the HD650 was the best headphone in the world at one point.

I also picked up another NOS R2R DAC on US Audio Mart for a song, one that has gotten quite a bit of hype recently, the Border Patrol SE. From what I can tell, it's a pretty simple TDA1543 design, but people like it! I've taken an interest in these DACs since I am designing one very, very slowly...so we will see how it sounds, might mod it.

Interesting. Wonder how the Matrix compares to the (discontinued) Schiit EITR. The EITR doesn't have anywhere near the conversion options, but makes a significant audible improvement isolating the USB noise and converting to S/PDIF.

 

[L0rdGwyn]

Interesting. Wonder how the Matrix compares to the (discontinued) Schiit EITR. The EITR doesn't have anywhere near the conversion options, but makes a significant audible improvement isolating the USB noise and converting to S/PDIF.

ASR measured both, I think they did well. The Matrix is powered off USB with a crap-ton of filtering / power supply regulation inside. You can use an external power supply, but unless you've got some super low-noise PS laying around, better to run it off USB. It measures well, looks pretty nice, and does it's job! Definitely more expensive than the Eitr on the used market. At some point I'll probably try SPDIF directly into the SW1X vs. USB to SPDIF through the Matrix.

 

[L0rdGwyn]

Well my final test was a success, so I can order the chassis for this OTL amplifier, will do so today after a final check of the layout.

Here are some more random parts going in this amp, NKK power switch and QQQ octal sockets.



For this first one, the prototype so-to-speak, think I am going to do the chassis in this gloss Burgundy red, I think it will look nice with the blue Clarity Caps.

 

[mordy]

Well my final test was a success, so I can order the chassis for this OTL amplifier, will do so today after a final check of the layout.

Here are some more random parts going in this amp, NKK power switch and QQQ octal sockets.



For this first one, the prototype so-to-speak, think I am going to do the chassis in this gloss Burgundy red, I think it will look nice with the blue Clarity Caps.

How many total amps can the transformers handle?

 

[L0rdGwyn]

How many total amps can the transformers handle?

I think you're talking about the heater current - 6A total, 3A per channel, spec'd for a 6AS7G and a single triode input tube, like a 6J5 / 6C5 / 6P5, etc. with some headroom.

 

[L0rdGwyn]

I have the Border Patrol SE in the house. Did a little comparison between it and the SW1X DAC II.



Both NOS R2R designs, the Border Patrol uses the TDA1543, the SW1X DAC II the PCM56. As far as I can tell, the Border Patrol takes the voltage output of the TDA1543, whereas the DAC II takes the current output of the PCM56, uses a transistor active I/V stage and a 5687 tube output gain stage to reach line level (a little higher, actually). I didn't measure it, but output of the Border Patrol is low, below line level for sure, so big swing in the amplifier volume knob between the two DACs. The Border Patrol as a switchable EZ80 tube rectifier - the front switch turns the tube rectifier on and off. The designer recommends leaving the DAC on continuously and using the switch to turn off the tube rectifier for longevity. Looking inside, it appears the switch changes the rectification from a EZ80-diode hybrid full-wave bridge rectifier to a diode full-wave rectifier.

Keeping it short and sweet, I like the Border Patrol, it's a good sounding DAC, very enjoyable, musical, I see why people like it. The DAC II is on another level though when it comes to musicality, detail, and dynamics. The knock on the DAC II is that it has a high noise floor, but overtop of the noise the music is excellent, very tangible, lifelike.

I'll put the Border Patrol on my desk or in the bedroom stereo for now.

 

[Zachik]

How many total amps can the transformers handle?

I think you're talking about the heater current - 6A total, 3A per channel, spec'd for a 6AS7G and a single triode input tube, like a 6J5 / 6C5 / 6P5, etc. with some headroom.

So none of the infamous "mordy's towers"...

 

[Zachik]

Keeping it short and sweet, I like the Border Patrol, it's a good sounding DAC, very enjoyable, musical, I see why people like it. The DAC II is on another level though when it comes to musicality, detail, and dynamics. The knock on the DAC II is that it has a high noise floor, but overtop of the noise the music is excellent, very tangible, lifelike.

I would love to compare one day your designed DAC to my Lampizator Amber 3...
Interestingly, the Lampizator has the same high noise floor "issue" as your DAC II.

 

[L0rdGwyn]

I would love to compare one day your designed DAC to my Lampizator Amber 3...
Interestingly, the Lampizator has the same high noise floor "issue" as your DAC II.

It's a long way off! Projects keep popping up so I am making very little progress on it unfortunately. High-level decisions have been made but I need to dive into the details of the power supply. Whenever it's done though I will bring it along to future Head-Fi meets, maybe ZMFestivus 2022. Slawa at SW1X attributes the high noise floor to the active I/V stage he uses in the DAC II. It isn't audible on my stereo, but with headphones it can be heard in the background.

 

[mordy]

I think you're talking about the heater current - 6A total, 3A per channel, spec'd for a 6AS7G and a single triode input tube, like a 6J5 / 6C5 / 6P5, etc. with some headroom.

So none of the infamous "mordy's towers"...

No tube rolling

 

[L0rdGwyn]

No tube rolling

That's right, this is not an amp for tube rolling, it is optimized for the tubes it was designed for, the 6J5 family. Other 6.3V single triodes and triode-strapped pentodes that bias similarly could also be used, however. At some point I will make a compatibility list.

 

[whirlwind]

No tube rolling

mordy....you already have a killer OTL amp for tube rolling

This amp won't be made to roll lots of power tubes...6336 for example or four 6AS7G or six 6BX/6BL7

Thing is for high impedance cans should sound great and you can still roll many 6J5 tubes for different tones.

For anyone with just high impedance headphones this should be great match.