[zach915m]

I also measured the output impedances for the three taps:

120ohm tap: 41ohm output Z
32ohm tap: 8.5ohm output Z
8ohm tap: 2.7ohm output Z

 

[AnyDave]

I told my parents to get rid of that picture.

 

[L0rdGwyn]

I came across some interesting headphone transformers for those into DIY, sold by the Audio Feast, made by a Japanese transformer winder named Teramoto. They use Finemet amorphous cores, the same core material used in the Monolith Magnetics nanocrystalline transformers. Multiple primary and secondary taps, 14H primary inductance, rated for 1W at 50Hz. At the time of my posting this, there is a 25% discount code available on their page, making these transformers relatively affordable. Like most Japanese-made transformers, they have a comprehensive datasheet which shows the bandwidth is quite good. I think you could make a really nice headphone amplifier with these output transformers, I'm tempted to buy a pair myself to play with. Could make a nice little spud amplifier (e.g., E55L) or perhaps a two-stage 71A circuit. Lots of options, very flexible transformers.

https://www.theaudiofeast.com/store...et-single-ended-head-phone-output-transformer

 

[heliosphann]

I came across some interesting headphone transformers for those into DIY, sold by the Audio Feast, made by a Japanese transformer winder named Teramoto. They use Finemet amorphous cores, the same core material used in the Monolith Magnetics nanocrystalline transformers. Multiple primary and secondary taps, 14H primary inductance, rated for 1W at 50Hz. At the time of my posting this, there is a 25% discount code available on their page, making these transformers relatively affordable. Like most Japanese-made transformers, they have a comprehensive datasheet which shows the bandwidth is quite good. I think you could make a really nice headphone amplifier with these output transformers, I'm tempted to buy a pair myself to play with. Could make a nice little spud amplifier (e.g., E55L) or perhaps a two-stage 71A circuit. Lots of options, very flexible transformers.

https://www.theaudiofeast.com/store...et-single-ended-head-phone-output-transformer

 

[EagleWings]

For those looking to build an AVC, my advise is to not cheap out on the wires and the RCA connectors. On the cable side, I don’t have any concrete recommendations, as I’m still gathering data and trying out stuff. I went with the Neotech stranded copper to play it safe but I intend on upgrading to something better soon. I am going to look into the VH Audio Pulsar that Keenan has used. But if you have a favorite cable but is not cheap, I’d still encourage you to go for it. For RCA connectors, another good option would be the WBT nextgen connector that Keenan uses in some of his full size amps.

@L0rdGwyn I like what you have done with the layout for the AVC and the amp to keep the signal path as short as possible.

 

[L0rdGwyn]

@L0rdGwyn I like what you have done with the layout for the AVC and the amp to keep the signal path as short as possible.

Thanks. Hard to say how much the Pulsar wire is improving the sound, but I figured I might as well go all in since this is meant to be the end game for me. The goal with using a separate chassis and short wiring was to prevent noise being picked up by the AVC, which worked out well. Unfortunately noise from the mains transformers is too high, so I will be swapping to shielded toroidals. Very eager to rebuild with those, probably not until January or February. Going to bring the AVC along when I deliver Zach's 2A3 amp, so possible I'll build another for him at some point.

 

[AnyDave]

Thanks. Hard to say how much the Pulsar wire is improving the sound, but I figured I might as well go all in since this is meant to be the end game for me. The goal with using a separate chassis and short wiring was to prevent noise being picked up by the AVC, which worked out well. Unfortunately noise from the mains transformers is too high, so I will be swapping to shielded toroidals. Very eager to rebuild with those, probably not until January or February. Going to bring the AVC along when I deliver Zach's 2A3 amp, so possible I'll build another for him at some point.

That's going to be quite the heavy carload.

 

[L0rdGwyn]

That's going to be quite the heavy carload.

Yeah my MPGs are going to suffer lol. I am trying to decide whether or not I should bring one of my tube DACs as well.

 

[AnyDave]

Yeah my MPGs are going to suffer lol. I am trying to decide whether or not I should bring one of my tube DACs as well.

Of course I'd vote yes. I'm assuming that you've designed it?

I still need to spend some time with your Airmid design, but I believe Zach has one of those.

 

[L0rdGwyn]

Of course I'd vote yes. I'm assuming that you've designed it?

I still need to spend some time with your Airmid design, but I believe Zach has one of those.

Yeah I designed it. I have two that I designed. I'd probably bring this one, which is in my two channel system. It's a NOS R2R design, uses two Burr-Brown PCM63 per channel in parallel, which are current output DAC chips. The current output is converted to voltage via a pair of Sowter I/V conversion step-up transformers, which then feed into a 7044 tube output stage. The output is transformer coupled by a pair of Sowter 9705 line output transformers. The tubes are battery biased, so there are no caps in the signal path between the DAC output and the RCA outs. And yeah, both Zach and Kevin have Airmids.

 

[AnyDave]

Yeah I designed it. I have two that I designed. I'd probably bring this one, which is in my two channel system. It's a NOS R2R design, uses two Burr-Brown PCM63 per channel in parallel, which are current output DAC chips. The current output is converted to voltage via a pair of Sowter I/V conversion step-up transformers, which then feed into a 7044 tube output stage. The output is transformer coupled by a pair of Sowter 9705 line output transformers. The tubes are battery biased, so there are no caps in the signal path between the DAC output and the RCA outs. And yeah, both Zach and Kevin have Airmids.

Wow, that's a beast. Do you use an engine hoist to load it into your car?

 

[L0rdGwyn]

Wow, that's a beast. Do you use an engine hoist to load it into your car?

Lol it's actually quite light. Tube circuits always take up a lot of space!

 

[leftside]

Yeah I designed it. I have two that I designed. I'd probably bring this one, which is in my two channel system. It's a NOS R2R design, uses two Burr-Brown PCM63 per channel in parallel, which are current output DAC chips. The current output is converted to voltage via a pair of Sowter I/V conversion step-up transformers, which then feed into a 7044 tube output stage. The output is transformer coupled by a pair of Sowter 9705 line output transformers. The tubes are battery biased, so there are no caps in the signal path between the DAC output and the RCA outs. And yeah, both Zach and Kevin have Airmids.

Piece of art.

@A2029 do you know how to build DACs?!

 

[L0rdGwyn]

Piece of art.

@A2029 do you know how to build DACs?!

Thanks! @A2029 is very sharp, so if he hasn't read into it already, I'm sure he could work it out in short order. NOS R2R designs using these DAC chips are relatively simple as far as DAC designs go. It can get very complex, I'm by no means an expert. Most important is use of a quality digital front end (I used JLSounds I2SoverUSB modules), a low noise power supply (at both high and low frequencies), and the grounding scheme. Lots of ways to tackle the power supply, I used cascaded BJT series regulators. I also used a 1:1 isolation toroid with an interwinding screen wired for balanced output. Texas instruments has some really good white papers on mixed signal grounding.

The thought of upgrading the line output transformers in this DAC has started to creep into my head...maybe early next year.

 

[A2029]

Piece of art.

@A2029 do you know how to build DACs?!

Agreed! So gorgeous outside and internally, and I'm sure it sounds awesome too!

@leftside I've only dabbled a little bit into the digital realm and briefly looked at the datasheets for a few of the most common R2R DAC chips. I have so many new analog amp designs that I've been working on in the shadows for a looong time that doing digital designs sounds like climbing Everest to me right now