Based on ciufolli's otl ocl i would like to build a similar amp with 6AS7 for headphones
The openloop Zout will be about Rp/2(u+1) = 46.6Ohm
Here is what i am thinking about
http://s12.postimg.org/3zr9mbnwd/headphone.png
I hope with some gnfb to get a Zout much under 32Ohm
Waiting for some advices, thanks
Out of thread: any spice models for these tube on Proteus?
The openloop Zout will be about Rp/2(u+1) = 46.6Ohm
Here is what i am thinking about
http://s12.postimg.org/3zr9mbnwd/headphone.png
An externally hosted image should be here but it was not working when we last tested it.
I hope with some gnfb to get a Zout much under 32Ohm
Waiting for some advices, thanks
Out of thread: any spice models for these tube on Proteus?
Last edited:
You will not be getting any signal past your -65 and -205 bias supplies.
(I've always found putting tube symbols inverted and having negative supplies on top of the page and positive supplies on the bottom sort of confusing)
🙂
(I've always found putting tube symbols inverted and having negative supplies on top of the page and positive supplies on the bottom sort of confusing)
🙂
Sorry fot the confused pic, i draw another one
-65V at 140Vak is about 50mA
An externally hosted image should be here but it was not working when we last tested it.
-65V at 140Vak is about 50mA
Much better. (IMHO)
Is R3 intended to bootstrap U3?
(You still need some kind of resistor in the bias path from the -65 and -205 supplies.)
Is R3 intended to bootstrap U3?
(You still need some kind of resistor in the bias path from the -65 and -205 supplies.)
This schem is based on Technics variation of Futterman. This circuit provides balanced drive to both tubes by returning the cathode of the phase splitter to the output, this makes the circuit more balanced and both output tubes actually operates as ordinary cathode coupled amplifier. That is what R3 does.
6C33C OTL
Yes grid resistors are needed, removed for simplicity
6C16P is good if paralled, 6AS7 can do the same job alone
Can that schem work correct or need any changes?
My point is to work outputcapacitorless
6C33C OTL
Yes grid resistors are needed, removed for simplicity
6C16P is good if paralled, 6AS7 can do the same job alone
Can that schem work correct or need any changes?
My point is to work outputcapacitorless
Last edited:
Hi,
The circuit you show is also based on the Technics OTL.
When doing away with the output coupling cap you do expose the high impedance coils of the headphones to any DC offset which is risky.
Ciao, 😉
The circuit you show is also based on the Technics OTL.
When doing away with the output coupling cap you do expose the high impedance coils of the headphones to any DC offset which is risky.
Ciao, 😉
Exactly, and that risk is a choice i have accept
I don't know if 6AS7 behaves like 6C33C, that is why i ask if need any changes
Thanks
I don't know if 6AS7 behaves like 6C33C, that is why i ask if need any changes
Thanks
Hi,
O.K. Technically the circuit seems fine.
Do keep in mind that the 6AS7G/6080 is a dual triode and not a twin triode. So, expect wide variations between the two halves.
In fact a pair of 6C19P is easier to select but it's up to you.
For practical reasons I'd add current sense resistors in the cathodes of the output tubes and testpoints so you can check the tubes with a DVM and null DC on the output.
Further, keep in mind that the heaters of the 6AS7Gs need time to warm up.
Either add a switch so you can pre-heat them or add a protective diode between grid and cathode.
If you don't you risk blowing the grids. (I learned this the hard way blowing 20 6080s in one go).
Other than that bass performance really depends on the B+ caps of the output stage (they are in the signal path) and the power xformer which should be rated very generously.
Just out of curiosity, do you have any experience with OTL amps?
Ciao, 😉
O.K. Technically the circuit seems fine.
Do keep in mind that the 6AS7G/6080 is a dual triode and not a twin triode. So, expect wide variations between the two halves.
In fact a pair of 6C19P is easier to select but it's up to you.
For practical reasons I'd add current sense resistors in the cathodes of the output tubes and testpoints so you can check the tubes with a DVM and null DC on the output.
Further, keep in mind that the heaters of the 6AS7Gs need time to warm up.
Either add a switch so you can pre-heat them or add a protective diode between grid and cathode.
If you don't you risk blowing the grids. (I learned this the hard way blowing 20 6080s in one go).
Other than that bass performance really depends on the B+ caps of the output stage (they are in the signal path) and the power xformer which should be rated very generously.
Just out of curiosity, do you have any experience with OTL amps?
Ciao, 😉
I've build the Technics OTL and i know where to pay attention
As you say the cathode resistor for testpoints, the delay of heaters and the xformer with the caps are inevitably
In other hand I have no experience with 6SA7/6080 and i've read a lot of weakness, so i don't want to find out the hard way 😉
Thanks for advise
As you say the cathode resistor for testpoints, the delay of heaters and the xformer with the caps are inevitably
In other hand I have no experience with 6SA7/6080 and i've read a lot of weakness, so i don't want to find out the hard way 😉
Thanks for advise
- Status
- Not open for further replies.