Good evening,
in order to build an OTL to drive the LCD-2 (at the specific request of a friend) I was wondering if it was possible to create a low impedance circuit for headphones with e.g. somenthing like SRPP, WCF, etc. with suitable tubes preceded by the "external" preamp stage.
That is, he would like to use a good solid state preamp he owns. He doesn't want an OT amplifier, only OTL.
Yet my doubts are 2: being the headphones at 70ohm with such a thing it will result in a mediocre damping factor, unless you introduce a decent feedback. And then they are headphones that require no low current.
Moreover, usually tube pre-amplifiers are usually preferable followed by s.s. power amplifiers (there are also examples in the opposite way, but as far as I know they are few in comparison).
All that is a good idea?
in order to build an OTL to drive the LCD-2 (at the specific request of a friend) I was wondering if it was possible to create a low impedance circuit for headphones with e.g. somenthing like SRPP, WCF, etc. with suitable tubes preceded by the "external" preamp stage.
That is, he would like to use a good solid state preamp he owns. He doesn't want an OT amplifier, only OTL.
Yet my doubts are 2: being the headphones at 70ohm with such a thing it will result in a mediocre damping factor, unless you introduce a decent feedback. And then they are headphones that require no low current.
Moreover, usually tube pre-amplifiers are usually preferable followed by s.s. power amplifiers (there are also examples in the opposite way, but as far as I know they are few in comparison).
All that is a good idea?
Only if he gives you all of the money in advance, with the understanding that it may not work very well.
Otherwise I would not get involved.
Otherwise I would not get involved.
Yes, he has not problem for the cash.
Exactly, I would not like to try my hand at something that does not work well then...
Since headphones are a big fad at present, I'm sure you can find some OTL circuits that people have used.
But who knows how well they will work?
But who knows how well they will work?
Bruce Rosenblit from Transcendent Sound offers array of tube otl amplifiers. Select low power kit, built it, use resistors to load the output and drop some signal for headphones. If it can drive speakers, it will drive 70 ohm headphones easily.
And any pre will work.
I used to have his otl long time ago. First used only to power radian tweeters, later hifiman headphones. It works.
If your friend pays for it, why not.
Today i would do it other way around.
Tube pre, solid state buffer.
Cheers.
And any pre will work.
I used to have his otl long time ago. First used only to power radian tweeters, later hifiman headphones. It works.
If your friend pays for it, why not.
Today i would do it other way around.
Tube pre, solid state buffer.
Cheers.
Just make sure that whatever he wants to do, the OTL must have an output DC blocking capacitor.
Even if the amp does not normally come with one. You'll need around 3300uF NP at least.
Even if the amp does not normally come with one. You'll need around 3300uF NP at least.
Those kits from Transcendent Sound seem great, especially the one with 300b...I'll refer to my friend. They aren't cheap but that can be worthy. The only thing... shipping to EU, I guess many days for delivery.
Rayma, yes a high value output capacitor is mandatory for such a low impedance. Possibly using good quality el. caps too,
Rayma, yes a high value output capacitor is mandatory for such a low impedance. Possibly using good quality el. caps too,
Some OTLs do not have an output coupling capacitor, but it is necessary for headphones, to be safe.
The basic simple "OTL headphone amp" is a FAT triode like 6080, working as cathode follower around 100V 100mA. Voltage gain in headphone impedances is very much less than unity, so you DO need a voltage gain stage before.
Google "otl headphone amp schematic images" turns up MANY images. A large chunk are from the defunct HeadWize site. Broskie has a bunch and he tends to label his sketches with 🙁 and 🙂 icons. His 'bad' ideas are usually flawed (and he explains why), but his 'good' ideas are not 100% proven. All tube amps are prone to LARGE DC transients at turn-on (and turn-off).
Google "otl headphone amp schematic images" turns up MANY images. A large chunk are from the defunct HeadWize site. Broskie has a bunch and he tends to label his sketches with 🙁 and 🙂 icons. His 'bad' ideas are usually flawed (and he explains why), but his 'good' ideas are not 100% proven. All tube amps are prone to LARGE DC transients at turn-on (and turn-off).
In effect, I already built a couple of 6AS7 OTL's few years ago and then WCF and some hybrid...
I have in mind those examples from Headwize memorial (thè site) and as for Broskie schematics, never tried one..
I must say there's not so much inspiration sources on thè net - talking about innovative ideas, in thè limit with what can be created with OTL tubes - and good projectists keep their working schemes off hands from DIY builders.
E.g. FUTTERMAN's could be a valid alternative, but a little complicated for my skills.
Another friend suggested me to take a look to MicroZOTL amp (also a version with separated psu)...so yes this one would be perfect, but finally out of budget for his pockets
I have in mind those examples from Headwize memorial (thè site) and as for Broskie schematics, never tried one..
I must say there's not so much inspiration sources on thè net - talking about innovative ideas, in thè limit with what can be created with OTL tubes - and good projectists keep their working schemes off hands from DIY builders.
E.g. FUTTERMAN's could be a valid alternative, but a little complicated for my skills.
Another friend suggested me to take a look to MicroZOTL amp (also a version with separated psu)...so yes this one would be perfect, but finally out of budget for his pockets