KGB- DC Coupled Hybrid Balance OTL/OCL HeadAmp

[tubetvr]

Hi,

First I must warn you that I am not a friend of hybrid designs so I can't add so much help with your chosen circuit but I am intrigued why you want to build such a complicated design so I would be intrested to hear your answers to some questions I have.

Why do you use such big tubes as EL 509 to drive headphones?

What is your basic goal? is it to build a headphone amp as such or is to build a hybrid amp? How much output power do you aim for?

I built a much simpler amp that can be seen here http://www.tubetvr.com/headphoneamp.html it gives about 600mV out when loaded with 30 ohm load which is about 12mW and more than enough for most headphones.

Regards hans

[aparatusonitus]

Hi Tubes4e4 & Hans,

Thanks for replay, I really need some feedback from more experience builders around.

I will use PL509 (or PL504, if I can get them) 'couse I allready have 16 pcs of them, and the very same topology will be eventually used for power amp. I will try to build a headamp first to evaluate topology soundwise, it's chiper that way.

Why hybrid? Becouse it's DC coupled balance amp, from input to output, and that is what I like (although one might see a servo opamps as capacitor), and except topology from Kaneda (also hybrid, totem-pole SE output, I think) is the only one I have found out so far.

Headamp should be capable to drive 32 and 300 Ohms headphones simultaneously, so something like 2W in class A

[tubetvr]

Why hybrid? Becouse it's DC coupled balance amp, from input to output,

You don't need to build a hybrid amp to make it DC coupled and balanced if that is what you want, It is more of a challenge to do this using only tubes, it has been done many times before but you need to look up how they built DC coupled instrumentation amps with tubes.

headamp should be capable to drive 32 and 300 Ohms headphones simultaneously, so something like 2W in class A

2W will make your ears fall off!, 10mW is more than enough to seriously risk damage to your hearing with most headphones, 2W would make a good power amplifier for driving high efficiency speakers even in large rooms. My headphone amp can give the same current output regardless of if the load is 30 ohm or 300 ohm so the output power at 300ohm is 10 times higher or ~120mW, please measure at what level you are playing when you think it is too high, you will be surprised how low it is.

Regards Hans

[aparatusonitus]

Hi Hans,

I am aware of the power needed to drive heaphones to ear spliting level, I can only confirm yours findings, but I forget to note that Headzilla will be eventualy used as a speaker/tweeter amp also in biamp system just to evaluate concept soundwise before I go for OTLzilla (speakers are Castle Harlech, benign load, stays over 8 Ohms most of time, no nasty reactance, fairly efficient, quarter-wave + bas reflex technology).

DC coupled instrumentation amps with tubes, newer heard for such, any link before I hit the Google?

Best, a

P.S How about all valve (PCC88) DC coupled (from input to output) balance headamp with Circlotron topology, is it posible?

[tubetvr]

DC coupled instrumentation amps with tubes, newer heard for such, any link before I hit the Google?

I don't know about internet sources but there are of course old tube text books, as an example look up "vacuum tube amplifiers" by Valley & Wallman chapter 11 where the principles of DC coupled tube amplifiers are described, there are also examples of complete circuits.

P.S How about all valve (PCC88) DC coupled (from input to output) balance headamp with Circlotron topology, is it posible?

Should be quite possible, I remember that there where a participant on the forum earlier that had built a DC coupled OTL and I think that was a circlotron variant. My first real OTL was a DC coupled Futterman variant but I never developed it further than a lab prototype.

Although a DC coupled balanced OTL is possible to design maybe you should take a step back and think about what your requirements are? What are the advantages that you think you will get with an all DC coupled design? will it give any noticable difference compared with a simpler design where you use a few coupling capacitors?

The same for why you want to use an all balanced design, what are you trying to achieve and will it give any noticeable difference?

Regards Hans

[aparatusonitus]

Hi Hans,

Originally posted by tubetvr


What are the advantages that you think you will get with an all DC coupled design? will it give any noticable difference compared with a simpler design where you use a few coupling capacitors?

I know I could get a very good sound from an AC coupled amp, but whenever I do that, sound is dependent of copling caps quality and ability to get one here that sounds really good, is variable that I would rather avoid by DC coupling.

Originally posted by tubetvr
The same for why you want to use an all balanced design, what are you trying to achieve and will it give any noticeable difference?

Well, I have very good sounding balance cd player(I meen really balance, like 8 x DACs in dual differential mode), working on a balanced nonos TDA1541 DAC, and just to have a Balance Line Stage (aka Bride of Son of Zen) from Nelson Pass witch could drive HD600 at preety good volume and excelent sound with balaced output. Hope to get even more of that from KGB. Moreover, I want to buid entyre sistem balanced, 'couse I like the sound coming from it more then SE, that is.


Best, a