[L0rdGwyn]

I have always preferred the 6sn7 over the 6sl7 and I have a few amps that run both. I did more extensive tests with 6sn7's so maybe there are some wonderful 6sl7's out there I have missed along the way.

I'm certain you know this, but the 6SL7 has very different optimal requirements for loading and biasing compared to 6SN7. I think 6SL7s are often misused in audio circuits, either they are under loaded or put in circuits with excessive amount of gain leading to a high noise floor. There are amplifiers out there where the manufacturers say you can use either one. Well if they are using a typical plate resistor for a 6SN7 to load a 6SL7, then the 6SL7 is grossly under loaded and distortion is going to be very high, of course it will sound bad! If used well they have very low distortion, I believe they are actually more linear than a 6SN7, but they needed to be treated kindly with their 44K plate resistance and very high gain, they are wimpy drivers. This circuit requires a high gain input stage, so 6SN7 won't cut it unfortunately.

Here are the traced plate curves from a Tung-Sol 6SU7GTY, doesn't get much more linear than this. Sections were matched in the factory for this model too, seems they weren't lying!

 

[Paladin79]

I'm certain you know this, but the 6SL7 has very different optimal requirements for loading and biasing compared to 6SN7. I think 6SL7s are often misused in audio circuits, either they are under loaded or put in circuits with excessive amount of gain leading to a high noise floor. There are amplifiers out there where the manufacturers say you can use either one. Well if they are using a typical plate resistor for a 6SN7 to load a 6SL7, then the 6SL7 is grossly under loaded and distortion is going to be very high, of course it will sound bad! If used well they have very low distortion, I believe they are actually more linear than a 6SN7, but they needed to be treated kindly with their 44K plate resistance and very high gain, they are wimpy drivers. This circuit requires a high gain input stage, so 6SN7 won't cut it unfortunately.

Here are the traced plate curves from a Tung-Sol 6SU7GTY, doesn't get much more linear than this. Sections were matched in the factory for this model too, seems they weren't lying!

Of course, and I have amps designed for both types of tubes. I recall one of the Schiit amps or pre-amps saying it could use either but the 6sl7 would be noisier lol. I stay away from that. I am currently comparing a bunch of 12AU7's and folks on here whom I have done favors for have been kind enough to send me matched pairs. I only mention that since it seems to work.

 

[L0rdGwyn]

DIY!?? Where do I sign up?? So excited to follow the progress on this project. Have you thought about chassis supply at all? Curious on whether or not it would be feasible to have a standard pre-built chassis available to order.

Yeah no sure thing yet, but I think it might make the most sense, need to talk it over with a few people. If I do it, I would probably release it on diyAudio and then link the post here. That would be the best place for it to be hosted given knowledgeable members there would be able to assist those with less experience. I've reached out to one of my diyAudio moderator pals to get his thoughts on it. Given it is a relatively expensive project, some of the more curmudgeonly members there might poo poo it. Oh well, we'll see what he thinks.

What I would do is release the CAD files for the chassis. Dave at Landfall systems would have the chassis files already, so it could be ordered from him easily, ready to go, just like the one I built. The only part that has me a little concerned is the dexterity required to solder the switch pins to the PCB I made, it's a bit of a pain to do.

I placed a very high priority on ease of building this amplifier. With all of the parts in front of me, I could build one of these in 5-6 hours from scratch.

 

[L0rdGwyn]

I recall one of the Schiit amps or pre-amps saying it could use either but the 6sl7 would be noisier lol.

Exactly! I think this problem is often overlooked in headphone amplifiers. People want tube headphone amplifiers with 10W peak output or something crazy, then complain they can hear a hum. Well yeah, the amp has way too much gain for a headphone! It's going to be noisy.

 

[Paladin79]

Exactly! I think this problem is often overlooked in headphone amplifiers. People want tube headphone amplifiers with 10W peak output or something crazy, then complain they can hear a hum. Well yeah, the amp has way too much gain for a headphone! It's going to be noisy.

LOL I have not checked headphone output level on my PrimaLuna yet but it is hum free, it is of course not strictly a headphone amp and I am running 8 KT88's and 6 12au7's.

 

[Xcalibur255]

Exactly! I think this problem is often overlooked in headphone amplifiers. People want tube headphone amplifiers with 10W peak output or something crazy, then complain they can hear a hum. Well yeah, the amp has way too much gain for a headphone! It's going to be noisy.

I think people widely equate having more power with having superior dynamic qualities. Most people don't realize that the circuit and power supply design of the amplifier mostly determines this and it doesn't need to have a dumptruck load of power to have good dynamic swing.

You can explain, but honestly people don't believe it until they hear a low power amplifier producing a big beautiful sound for themselves.

 

[L0rdGwyn]

I think people widely equate having more power with having superior dynamic qualities. Most people don't realize that the circuit and power supply design of the amplifier mostly determines this and it doesn't need to have a dumptruck load of power to have good dynamic swing.

You can explain, but honestly people don't believe it until they hear a low power amplifier producing a big beautiful sound for themselves.

I think you are exactly right. You can make a lower powered amplifier with those qualities. People equate the ability of an amplifiers "drive" or ability to "power" headphones with a higher degree of dynamics / punch / bass weight and heft. Those qualities I think are often associated with high power amplifiers, but certainly you can get those characteristics in an amplifier that only makes 1-2W.

 

[Paladin79]

It depends on the transducers of course. I have some low powered amps that work amazingly well with highly efficient speakers, it is the way it used to be in the early days of audio.

 

[carlman14]

I think you are exactly right. You can make a lower powered amplifier with those qualities. People equate the ability of an amplifiers "drive" or ability to "power" headphones with a higher degree of dynamics / punch / bass weight and heft. Those qualities I think are often associated with high power amplifiers, but certainly you can get those characteristics in an amplifier that only makes 1-2W.

This reminds me of the time I saw some of your comments over on the susvara thread. You were trying to show people that they didn't need a 200W speaker amp to drive their headphones. They weren't having any of it haha.

 

[Paladin79]

A gentleman I just visited could run Susvaras with one of the Incubus amps I designed, just over 1 watt output. (I did use more VU meters then.

 

[L0rdGwyn]

This reminds me of the time I saw some of your comments over on the susvara thread. You were trying to show people that they didn't need a 200W speaker amp to drive their headphones. They weren't having any of it haha.

Lol I remember that. I've tried to be better about barging in and being prescriptive about what people should or should not be doing, if it works for them then great! I suspect it is more related to the very low output impedance of these amplifiers given they are designed for more difficult loads (speaker impedances). Lots of people loving Susvara off of tube amps these days, which don't have tons of power on tap and very low output impedances.

 

[whirlwind]

Exactly! I think this problem is often overlooked in headphone amplifiers. People want tube headphone amplifiers with 10W peak output or something crazy, then complain they can hear a hum. Well yeah, the amp has way too much gain for a headphone! It's going to be noisy.

The misconception a lot of people have is they just think or maybe just want more power. (Insert Tim "Toolman" Taylor here)

You don't need more power than you need, they are headphone's and most can be powered properly without crazy watts of power.

I can't even imagine how one's ears would feel if something went wrong when listening to headphones on a speaker amp

 

[Paladin79]

Some time ago I stopped a guy on here from using 16 gauge wire from a 100 watt speaker amp that he wanted to hook to headphones. He wanted to be sure that gauge was enough lol. I told him that hopefully the tiny wire inside the headphones would act as a fuse and save some hearing if he messed up.
I would worry about others in his family even if he was very careful himself.

 

[L0rdGwyn]

So here is my tentative plan...

As I've said, I don't think the version of the pentode headamp that I sent to CanJam is a great fit for commercial production. While I love the simplicity of the circuit and the sound, I think the cost of the Lundahl parts is too much for commercial viability. To make a commercial version of this circuit, I think it needs to use solid state components to replace the chokes in the design. This poses some other design challenges that would need to be worked through.

Since I like the Lundahl iron version and it is relatively easy to build, my plan will be to release that version as a DIY project. Note that it will be an expensive project.

Then, in the meantime, I will work on a transistor-based version of the circuit with the potential of commercial manufacture in the future. That will take some time.

I am just waiting to hear back from Lundahl's US distributor to make sure they will be able to supply DIYers, specifically the small transformer housings were on backorder recently, I want to be sure they are going to be available in the foreseeable future before I go to the trouble of putting together materials to build this amplifier. Likely I will have to build a second one to take photos along the way for the sake of instruction. I will probably sell the original and the second one I build for instruction.

This project will probably be hosted on diyAudio. I am expecting to get a mixed response there given the cost of the design (a lot of DIYers are very budget oriented). Maybe if there are some reviews I can link to, along with some measurements, the curmudgeons will be silenced.

That is what I am thinking for now, hoping to hear back from the Lundahl distributor later today. If so, I will probably feel it is okay to show some pictures of the interior and give an explanation of the circuit.

 

[Paladin79]

So here is my tentative plan...

As I've said, I don't think the version of the pentode headamp that I sent to CanJam is a great fit for commercial production. While I love the simplicity of the circuit and the sound, I think the cost of the Lundahl parts is too much for commercial viability. To make a commercially version of this circuit, I think it needs to use solid state components to replace the chokes in the design. This poses some other design challenges that would need to be worked through.

Since I like the Lundahl iron version and it is relatively easy to build, my plan will be to release that version as a DIY project. Note that it will be an expensive project.

Then, in the meantime, I will work on a transistor-based version of the circuit with the potential of commercial manufacture in the future. That will take some time.

I am just waiting to hear back from Lundahl's US distributor to make sure they will be able to supply DIYers, specifically the small transformer housings were on backorder recently, I want to be sure they are going to be available in the foreseeable future before I go to the trouble of putting together materials to build this amplifier. Likely I will have to build a second one to take photos along the way for the sake of instruction. I will probably sell the original and the second one I build for instruction.

This project will probably be hosted on diyAudio. I am expecting to get a mixed response there given the cost of the design (a lot of DIYers are very budget oriented). Maybe if there are some reviews I can link to, along with some measurements, the curmudgeons will be silenced.

That is what I am thinking for now, hoping to hear back from the Lundahl distributor later today. If so, I will probably feel it is okay to show some pictures of the interior and give an explanation of the circuit.

Are you talking about a headphone amp and if so what do you consider expensive? Sorry I do not read the thread enough to keep up on the amp types.