[Zachik]

The one part of the circuit that has me a little concerned for inexperienced builders is the output switch, it's kind of a b**** to solder, but I think I'll be able to explain the method.

Output switch?! Does the amp have headphones / speakers output??

 

[Monsterzero]

Output switch?! Does the amp have headphones / speakers output??

output impedance switch

 

[L0rdGwyn]

Agreed; Keenan its around the price of a Bottlehead Mainline and you get a hell of a lot more here than in that kit. I am really floored. Might be later next year, but I want one. Now hopefully we can get some impressions of it.

Happy listening,

jgwtriode

Yeah that's my thinking too, and the major benefit of doing things DIY, you can make a circuit with high quality parts and it is still affordable, something equivalent would cost 4-5x as much commercially. Could I have cut corners and made it cheaper? Sure, I could have used Hammond chokes in the power supply with higher ripple, cheapo output transformers, a lower gain / less linear input tube at the cost of power output and maybe then I could have gone for cheaper anode chokes. Maybe even a lower quality off-the-shelf chassis by giving up my ability to design and customize it, putting a higher burden of the prep work on the builder. I could have avoided the steel Lundahl transformer shields at the cost of aesthetic appeal and perhaps higher magnetic coupling between mains and output transformers. I think using the better parts is worth the cost and in some areas makes the assembly more simple, that is my style, and it shows in the end result in my opinion. Also, being able to order all of the iron from one place is a benefit, sourcing inductors from multiple places could cut costs but the benefit would be partially lost in the extra shipping charges. Using transistors instead of chokes is another way to cut costs, but of course this has its own compromises - the power supply would need to fundamentally change, the propensity for part failure would go up, and building the circuit would be less friendly to new DIYers.

@zach915m has the amp right now, I know he has compared it to his 45 amp and the comparison is very favorable. @Monsterzero will have it next. I need to come up with a name...

Output switch?! Does the amp have headphones / speakers output??

output impedance switch

Yeah, output impedance switch. Low is 32-150ohms, high 150ohms and up.

 

[carlman14]

What a cool circuit! I might have to build one some day if I ever get bored of my pentode amp. You mentioned that you can get 7:1 to 8:1 damping ratio with this topology. As you know, you can also achieve a higher damping ratio by connecting higher impedance headphones to a lower impedance OPT tap... like connecting 32 ohm headphones to a 16 ohm OPT tap. Would you say that your way of achieving a higher damping ratio is any better or worse than what I described? Any pros or cons doing one vs the other?

 

[paradoxper]

Yeah that's my thinking too, and the major benefit of doing things DIY, you can make a circuit with high quality parts and it is still affordable, something equivalent would cost 4-5x as much commercially. Could I have cut corners and made it cheaper? Sure, I could have used Hammond chokes in the power supply with higher ripple, cheapo output transformers, a lower gain / less linear input tube at the cost of power output and maybe then I could have gone for cheaper anode chokes. Maybe even a lower quality off-the-shelf chassis by giving up my ability to design and customize it, putting a higher burden of the prep work on the builder. I could have avoided the steel Lundahl transformer shields at the cost of aesthetic appeal and perhaps higher magnetic coupling between mains and output transformers. I think using the better parts is worth the cost and in some areas makes the assembly more simple, that is my style, and it shows in the end result in my opinion. Also, being able to order all of the iron from one place is a benefit, sourcing inductors from multiple places could cut costs but the benefit would be partially lost in the extra shipping charges. Using transistors instead of chokes is another way to cut costs, but of course this has its own compromises - the power supply would need to fundamentally change, the propensity for part failure would go up, and building the circuit would be less friendly to new DIYers.

@zach915m has the amp right now, I know he has compared it to his 45 amp and the comparison is very favorable. @Monsterzero will have it next. I need to come up with a name...




Yeah, output impedance switch. Low is 32-150ohms, high 150ohms and up.

Na, don't cut corners. DIY should represent return value not making concessions. Great job.

 

[jgwtriode]

Ceridwen,. Celtic goddess of poetry and inspiration. I think that would be an appropriate name. If you want to switch gender; Maponus. Celtic god of music and poetry! Either rolls off the tongue nicely. I love the the mythos of the Tuatha De'Danann!

Happy naming,

jgwtriode

 

[Monsterzero]

Ceridwen,. Celtic goddes of poetry and inspiration. I think that would be an appropriate name. If you want to switch gender,. Maponus. Celtic god of music and poetry! Either rolls of the tongue nicely. I love the the mythos of the Tuaththa De'Danann!

Happy naming,

jgwtriode

Sticking with the Celtic theme, you can name it 'Taranis' the Celtic God of Thunder, which also happens to be my puppy's name He's not your normal everyday 115 lb. 7 month old pup though.

 

[jgwtriode]

Sticking with the Celtic theme, you can name it 'Taranis' the Celtic God of Thunder, which also happens to be my puppy's name He's not your normal everyday 115 lb. 7 month old pup though.

In the immortal words of Scrappy Doo, "Puppy Power!"

jgwtriode

 

[Mr Trev]

I need to come up with a name...

You can always go with a confusing, albeit meaningless, alphabet soup name, ala ChiFi.
Then a couple months down the road, make a small change and re-release it as the "Pro" model

 

[Zachik]

Sticking with the Celtic theme, you can name it 'Taranis' the Celtic God of Thunder, which also happens to be my puppy's name He's not your normal everyday 115 lb. 7 month old pup though.

OMG - that is a big puppy!!!
Immediately brings The Hounds of Baskerville to my mind...

 

[L0rdGwyn]

What a cool circuit! I might have to build one some day if I ever get bored of my pentode amp. You mentioned that you can get 7:1 to 8:1 damping ratio with this topology. As you know, you can also achieve a higher damping ratio by connecting higher impedance headphones to a lower impedance OPT tap... like connecting 32 ohm headphones to a 16 ohm OPT tap. Would you say that your way of achieving a higher damping ratio is any better or worse than what I described? Any pros or cons doing one vs the other?

Thanks!

Typically a higher turns ratio output transformer is going to be less ideal than a lower turns ratio output transformer in terms of copper losses, leakage inductance, interwinding capacitance, so you are increasing the damping ratio but sacrificing some transformer performance. For using a 32ohm headphone on 16ohm tap, not likely to be a noticeable issue, but using say a 300ohm headphone on a 16ohm tap, I think you would hear a significant difference compared to a dedicated 300ohm tap. Obviously some power is lost doing this as well. A while back I did some subjective comparisons using a speaker transformer for 300ohm dynamic headphones. I used a parallel 8ohm resistor on an 8ohm tap, a parallel 16ohm resistor on an 8ohm tap, then ran the headphones right off the tap without any parallel resistance. The 8ohm resistor on the 8ohm tap in parallel was by far the best, so I try to avoid using high Z headphones on low Z taps if I can.

One advantage of the higher turns ratio transformer is a lower noise output, but if the amplifier is well designed, the noise should be inaudible either way (this amp is dead silent on high Z). In terms of achieving a lower output impedance, between the two I think the cathode follower approach is more effective as you are not having to compromise on transformer performance. It is somewhat similar to using global negative feedback in a class AB push pull amplifier, the output impedance is reduced and bandwidth improve via negative feedback. It just so happens in a cathode follower the negative feedback is happening inside the tube!

That's right folks, all your cathode follower OTLs are technically utilizing negative feedback. Time to throw them in the trash

 

[Monsterzero]

OMG - that is a big puppy!!!
Immediately brings The Hounds of Baskerville to my mind...

lol. We live in the middle of a forest, which is in the middle of nowhere, which is on the very, very edge of a small town that doesnt have a police force.
We do not get many visitors out this way. Taranis is our insurance policy that it remains that way.

 

[Aleh]

Yeah that's my thinking too, and the major benefit of doing things DIY, you can make a circuit with high quality parts and it is still affordable, something equivalent would cost 4-5x as much commercially. Could I have cut corners and made it cheaper? Sure, I could have used Hammond chokes in the power supply with higher ripple, cheapo output transformers, a lower gain / less linear input tube at the cost of power output and maybe then I could have gone for cheaper anode chokes. Maybe even a lower quality off-the-shelf chassis by giving up my ability to design and customize it, putting a higher burden of the prep work on the builder. I could have avoided the steel Lundahl transformer shields at the cost of aesthetic appeal and perhaps higher magnetic coupling between mains and output transformers. I think using the better parts is worth the cost and in some areas makes the assembly more simple, that is my style, and it shows in the end result in my opinion. Also, being able to order all of the iron from one place is a benefit, sourcing inductors from multiple places could cut costs but the benefit would be partially lost in the extra shipping charges. Using transistors instead of chokes is another way to cut costs, but of course this has its own compromises - the power supply would need to fundamentally change, the propensity for part failure would go up, and building the circuit would be less friendly to new DIYers.

Pls don't cut corners. Otherwise you just lose the great benefit of DIY - having the same quality for 3-4x less price.

 

[L0rdGwyn]

Pls don't cut corners. Otherwise you just lose the great benefit of DIY - having the same quality for 3-4x less price.

No I don't plan to, I was more trying to illustrate why cutting those corners isn't worth doing! The design is final at this point.

 

[carlman14]

Thanks!

Typically a higher turns ratio output transformer is going to be less ideal than a lower turns ratio output transformer in terms of copper losses, leakage inductance, interwinding capacitance, so you are increasing the damping ratio but sacrificing some transformer performance. For using a 32ohm headphone on 16ohm tap, not likely to be a noticeable issue, but using say a 300ohm headphone on a 16ohm tap, I think you would hear a significant difference compared to a dedicated 300ohm tap. Obviously some power is lost doing this as well. A while back I did some subjective comparisons using a speaker transformer for 300ohm dynamic headphones. I used a parallel 8ohm resistor on an 8ohm tap, a parallel 16ohm resistor on an 8ohm tap, then ran the headphones right off the tap without any parallel resistance. The 8ohm resistor on the 8ohm tap in parallel was by far the best, so I try to avoid using high Z headphones on low Z taps if I can.

One advantage of the higher turns ratio transformer is a lower noise output, but if the amplifier is well designed, the noise should be inaudible either way (this amp is dead silent on high Z). In terms of achieving a lower output impedance, between the two I think the cathode follower approach is more effective as you are not having to compromise on transformer performance. It is somewhat similar to using global negative feedback in a class AB push pull amplifier, the output impedance is reduced and bandwidth improve via negative feedback. It just so happens in a cathode follower the negative feedback is happening inside the tube!

That's right folks, all your cathode follower OTLs are technically utilizing negative feedback. Time to throw them in the trash

Thanks! Informative as always. I've been using all my headphones from 32-300 ohms on a 32 ohm tap, similar to how I think some of Glenn's SET amps are implemented. Interesting that you found the parallel resistors sounded better. I would have thought that a higher secondary load (and resulting higher primary load) would sound better due to the decreased distortion. I'll have to try out some parallel resistors on the 8 ohm tap and see how that sounds!

Besides loss of power, I wonder if there's a major difference between using parallel resistors with a higher turns transformer and using a lower turns transformer with a higher ohm secondary. I suppose that wraps around to the 3:1 vs 8:1 damping ratios mentioned earlier.