[jonathan c]

My ‘tag team’ for ZMF dynamic driver headphones:

[Beyerdynamic A20 (100 ohms), Woo Audio WA3 OTL (Cetron 7236, Genalex / Gold Lion 6922s)]

 

[Wes S]

My ‘tag team’ for ZMF dynamic driver headphones: [Beyerdynamic A20 (100 ohms), Woo Audio WA3 OTL (Cetron 7236, Genalex / Gold Lion 6922s)]

Where is the UltimatE? I have yet to see you rave about it like all the others owners, and just curious how it's going with that one?

 

[jonathan c]

Where is the UltimatE? I have yet to see you rave about it like all the others owners, and just curious how it's going with that one?

It is now at the mountain abode. It is tremendous: quite similar in depth, gravitas of sound to Icon Audio HP8 Signature.

 

[Pharmaboy]

Where is the UltimatE? I have yet to see you rave about it like all the others owners, and just curious how it's going with that one?

Qu'est-ce que c'est "UltimatE?"

 

[Wes S]

Qu'est-ce que c'est "UltimatE?"

It's a custom tube amp built by Eric McChanson, that is getting some serious love and praise. https://www.head-fi.org/threads/eric-mcchanson-headphone-amp.718350/page-471#post-17791976

I am planning to build an Aegis designed by L0rdGwyn soon, or I would be all over a custom build from Eric.

 

[Nuge]

Has anyone heard both the DNA Starlett and the Signature Edition of the Icon Audio HP8?

 

[L0rdGwyn]

Showing off a new 2A3 SET I just finished for Zach. Build details:

- Custom mains and filament transformers from Monolith Magnetics
- Separate B+ and bias supply regulators for each channel to minimize crosstalk
- Rod Coleman filament regulators
- 5687 / 7044 / E182CC input stage, LED biased
- Monolith Magnetics nanocrystalline core interstage transformers
- Fixed bias 2A3 output stage
- Monolith Magnetics nanocrystalline core output transformers with 120ohm, 32ohm, and 8ohm taps
- Besides the power supply, no capacitors in the signal path





More pics, details and measurements here: https://www.head-fi.org/threads/l0rdgwyns-diy-audio.921105/post-17796349

Thanks for checking it out!

 

[mattiastomas]

Showing off a new 2A3 SET I just finished for Zach. Build details:

- Custom mains and filament transformers from Monolith Magnetics
- Separate B+ and bias supply regulators for each channel to minimize crosstalk
- Rod Coleman filament regulators
- 5687 / 7044 / E182CC input stage, LED biased
- Monolith Magnetics nanocrystalline core interstage transformers
- Fixed bias 2A3 output stage
- Monolith Magnetics nanocrystalline core output transformers with 120ohm, 32ohm, and 8ohm taps
- Besides the power supply, no capacitors in the signal path





More pics, details and measurements here: https://www.head-fi.org/threads/l0rdgwyns-diy-audio.921105/post-17796349

Thanks for checking it out!

Wow. That looks badass! Can only imagine how it sounds

 

[Wes S]

Showing off a new 2A3 SET I just finished for Zach. Build details:

- Custom mains and filament transformers from Monolith Magnetics
- Separate B+ and bias supply regulators for each channel to minimize crosstalk
- Rod Coleman filament regulators
- 5687 / 7044 / E182CC input stage, LED biased
- Monolith Magnetics nanocrystalline core interstage transformers
- Fixed bias 2A3 output stage
- Monolith Magnetics nanocrystalline core output transformers with 120ohm, 32ohm, and 8ohm taps
- Besides the power supply, no capacitors in the signal path





More pics, details and measurements here: https://www.head-fi.org/threads/l0rdgwyns-diy-audio.921105/post-17796349

Thanks for checking it out!

Absolutely incredible looking and I can only imagine the sound! Thanks for sharing. Zach is a very lucky guy, but is also so deserving of this special amp.

 

[L0rdGwyn]

Thanks guys. Feels good to get this one done, been working on it off and on for 6 months or so. The amp has excellent clarity, pinpoint imaging, and large staging. The low distortion helps, as does minimizing the number of capacitors in the signal path. It sounds very great. Listening with AC this morning.

 

[L0rdGwyn]

Here's some quick hits tube design knowledge, something that makes an amp like this one, or even Aegis, sound very good.

To bias a single-ended triode output stage, the grid of the tube needs to be made negative relative to the cathode. This can be done two different ways - put the grid at ground potential and make the cathode positive, or put the cathode at ground potential and make the grid negative.

The most common way of doing this, seen in virtually every single commercial SET design, is called cathode bias (aka autobias). In this setup, a resistor is put between the tube's cathode and ground. As current flows through the cathode, through the resistor to ground, a positive voltage develops on the cathode. The grid is then placed at ground potential, and the tube is biased. However, placing a resistor on the cathode of the tube without any other intervention will dramatically increase the output impedance of the stage. For that reason, a cathode bypass capacitor is necessary across the resistor. This preserves the tube's innate output impedance, however the AC music signal now flows through the capacitor. The reason this setup is used in 99% of commercial amps is it is 1) cheap 2) less complicated 3) less prone to failure. Cathode bias output stages can sound very good, it isn't to say that they are bad, but the other biasing method is undoubtedly better sounding.

The other approach is called fixed bias (aka grid bias), which is what has been done in this 2A3 amplifier. In this biasing method, the cathode is put at ground potential and a negative voltage is placed on the grid to bias the tube. Because the cathode is at ground potential (meaning no cathode resistor), you no longer need a bypass capacitor, completely removing a cap from the signal path! But at what cost? A fixed bias design needs a dedicated negative bias supply, which increases the cost and complexity of the amp. The bias point of the tube also needs to be adjusted manually as it ages, so there has to be a means of measuring the tubes bias current (e.g., milliammeters, like on the front of this 2A3 amplifier) and a means of adjusting the bias supply. Also, fixed bias designs are more prone to failure if not designed properly! If the bias supply were to fail for any reason and the grid were grounded or floating, the tube would start to conduct as much current as it possibly can, either destroying itself or other components in the process. For that reason, the B+ supply must also be fused appropriately to protect the amplifier. Now you see why this isn't done in commercial amps, even if it does sound better!

Now a quick note on Aegis. What makes that circuit interesting, and a large reason for its sound, is that it is cathode biased, HOWEVER, it does not require a cathode bypass capacitor. The reason is the output tube is wired as a cathode follower, similar to how tubes are set up in OTL amplifiers. Cathode followers operate at 100% local negative feedback, which gives them a low output impedance and low distortion. This feedback prevents the need for a cathode bypass capacitor, so you get the best of both worlds, a simple design that is cathode biased, without a bypass cap. There are other compromises that need to be made up for elsewhere though, specifically, the output stage only has a voltage gain of 1, so the input stage must have very high voltage gain and low distortion. Instead of a cathode resistor, the tube is biased from the DC resistance of the output transformer plus some added series resistance.

So there you have it, cathode bias vs fixed bias. Fixed bias is better, but more of a pain, so you only see it in boutique amplifiers.

 

[AnyDave]

So there you have it, cathode bias vs fixed bias. Fixed bias is better, but more of a pain, so you only see it in boutique amplifiers.

And guitar amps.

 

[Pharmaboy]

Here's some quick hits tube design knowledge, something that makes an amp like this one, or even Aegis, sound very good.

To bias a single-ended triode output stage, the grid of the tube needs to be made negative relative to the cathode. This can be done two different ways - put the grid at ground potential and make the cathode positive, or put the cathode at ground potential and make the grid negative.

The most common way of doing this, seen in virtually every single commercial SET design, is called cathode bias (aka autobias). In this setup, a resistor is put between the tube's cathode and ground. As current flows through the cathode, through the resistor to ground, a positive voltage develops on the cathode. The grid is then placed at ground potential, and the tube is biased. However, placing a resistor on the cathode of the tube without any other intervention will dramatically increase the output impedance of the stage. For that reason, a cathode bypass capacitor is necessary across the resistor. This preserves the tube's innate output impedance, however the AC music signal now flows through the capacitor. The reason this setup is used in 99% of commercial amps is it is 1) cheap 2) less complicated 3) less prone to failure. Cathode bias output stages can sound very good, it isn't to say that they are bad, but the other biasing method is undoubtedly better sounding.

The other approach is called fixed bias (aka grid bias), which is what has been done in this 2A3 amplifier. In this biasing method, the cathode is put at ground potential and a negative voltage is placed on the grid to bias the tube. Because the cathode is at ground potential (meaning no cathode resistor), you no longer need a bypass capacitor, completely removing a cap from the signal path! But at what cost? A fixed bias design needs a dedicated negative bias supply, which increases the cost and complexity of the amp. The bias point of the tube also needs to be adjusted manually as it ages, so there has to be a means of measuring the tubes bias current (e.g., milliammeters, like on the front of this 2A3 amplifier) and a means of adjusting the bias supply. Also, fixed bias designs are more prone to failure if not designed properly! If the bias supply were to fail for any reason and the grid were grounded or floating, the tube would start to conduct as much current as it possibly can, either destroying itself or other components in the process. For that reason, the B+ supply must also be fused appropriately to protect the amplifier. Now you see why this isn't done in commercial amps, even if it does sound better!

Now a quick note on Aegis. What makes that circuit interesting, and a large reason for its sound, is that it is cathode biased, HOWEVER, it does not require a cathode bypass capacitor. The reason is the output tube is wired as a cathode follower, similar to how tubes are set up in OTL amplifiers. Cathode followers operate at 100% local negative feedback, which gives them a low output impedance and low distortion. This feedback prevents the need for a cathode bypass capacitor, so you get the best of both worlds, a simple design that is cathode biased, without a bypass cap. There are other compromises that need to be made up for elsewhere though, specifically, the output stage only has a voltage gain of 1, so the input stage must have very high voltage gain and low distortion. Instead of a cathode resistor, the tube is biased from the DC resistance of the output transformer plus some added series resistance.

So there you have it, cathode bias vs fixed bias. Fixed bias is better, but more of a pain, so you only see it in boutique amplifiers.

Great explanation. I've never understood fixed vs autobias until this post.

My first big tube amp ~1986 (Roger Modjeski/Ram Labs RM-9 / 100 wpc / 8 x EL35s or 8 x KT88s [I tried both]) was fixed bias. And it was no big deal. Every six months or so I sat down with my little screwdriver and flashlight and adjusted the turn-screw until the proper light was lit. Not the end of the world, and not even close to the biggest PITA(s) I faced with that complicated system.

Back then autobias hadn't yet taken over the world. Now it has. Interesting to realize it exacts a sonic penalty...

Your new amp looks astounding, and these posts are TOTL audio info IMHO.

 

[L0rdGwyn]

Great explanation. I've never understood fixed vs autobias until this post.

My first big tube amp ~1986 (Roger Modjeski/Ram Labs RM-9 / 100 wpc / 8 x EL35s or 8 x KT88s [I tried both]) was fixed bias. And it was no big deal. Every six months or so I sat down with my little screwdriver and flashlight and adjusted the turn-screw until the proper light was lit. Not the end of the world, and not even close to the biggest PITA(s) I faced with that complicated system.

Back then autobias hadn't yet taken over the world. Now it has. Interesting to realize it exacts a sonic penalty...

Your new amp looks astounding, and these posts are TOTL audio info IMHO.

Thanks, glad I could help. Yeah fixed bias tube headphone amps are essentially nonexistent on the commercial market, my guess is due to the cost savings of going cathode bias.

I'm building another wild amp over the next two weeks, a personal build, so it's gonna be sorta weird. I'll show some pics here when it's done!

 

[goldwerger]

Here's some quick hits tube design knowledge, something that makes an amp like this one, or even Aegis, sound very good.

To bias a single-ended triode output stage, the grid of the tube needs to be made negative relative to the cathode. This can be done two different ways - put the grid at ground potential and make the cathode positive, or put the cathode at ground potential and make the grid negative.

The most common way of doing this, seen in virtually every single commercial SET design, is called cathode bias (aka autobias). In this setup, a resistor is put between the tube's cathode and ground. As current flows through the cathode, through the resistor to ground, a positive voltage develops on the cathode. The grid is then placed at ground potential, and the tube is biased. However, placing a resistor on the cathode of the tube without any other intervention will dramatically increase the output impedance of the stage. For that reason, a cathode bypass capacitor is necessary across the resistor. This preserves the tube's innate output impedance, however the AC music signal now flows through the capacitor. The reason this setup is used in 99% of commercial amps is it is 1) cheap 2) less complicated 3) less prone to failure. Cathode bias output stages can sound very good, it isn't to say that they are bad, but the other biasing method is undoubtedly better sounding.

The other approach is called fixed bias (aka grid bias), which is what has been done in this 2A3 amplifier. In this biasing method, the cathode is put at ground potential and a negative voltage is placed on the grid to bias the tube. Because the cathode is at ground potential (meaning no cathode resistor), you no longer need a bypass capacitor, completely removing a cap from the signal path! But at what cost? A fixed bias design needs a dedicated negative bias supply, which increases the cost and complexity of the amp. The bias point of the tube also needs to be adjusted manually as it ages, so there has to be a means of measuring the tubes bias current (e.g., milliammeters, like on the front of this 2A3 amplifier) and a means of adjusting the bias supply. Also, fixed bias designs are more prone to failure if not designed properly! If the bias supply were to fail for any reason and the grid were grounded or floating, the tube would start to conduct as much current as it possibly can, either destroying itself or other components in the process. For that reason, the B+ supply must also be fused appropriately to protect the amplifier. Now you see why this isn't done in commercial amps, even if it does sound better!

Now a quick note on Aegis. What makes that circuit interesting, and a large reason for its sound, is that it is cathode biased, HOWEVER, it does not require a cathode bypass capacitor. The reason is the output tube is wired as a cathode follower, similar to how tubes are set up in OTL amplifiers. Cathode followers operate at 100% local negative feedback, which gives them a low output impedance and low distortion. This feedback prevents the need for a cathode bypass capacitor, so you get the best of both worlds, a simple design that is cathode biased, without a bypass cap. There are other compromises that need to be made up for elsewhere though, specifically, the output stage only has a voltage gain of 1, so the input stage must have very high voltage gain and low distortion. Instead of a cathode resistor, the tube is biased from the DC resistance of the output transformer plus some added series resistance.

So there you have it, cathode bias vs fixed bias. Fixed bias is better, but more of a pain, so you only see it in boutique amplifiers.

what a wonderfully informative post, thanks for taking the time! Every time you post stuff like that, I learn so much

you really should, one day, make a career change - your knowledge and talent are criminally under utilized...