While looking at several 6AS7 headphone amps shown on the Net I came across the following circuit which didn't seem to have a link for itself. I found it using Google search. The output stage seems to be a White cascode. It has fewer components than the Aikido headphone amp with 6AS7 in it.
Has anyone used the circuit in the picture ? I couldn't find the original web page from where it was taken.
Thanks.
Has anyone used the circuit in the picture ? I couldn't find the original web page from where it was taken.
Thanks.
Attachments
i´m not a fan of otl.
ok, if you really want tube sound - bottom 6as7 should be feeded with signal instead . (to do a signal amplification)
top 6as7 i would remove; and use ccs or bulb instead.
you have not said, what hp Z do you have.
currently, top tube is just a follower - expect no big sound change at all.
ok, if you really want tube sound - bottom 6as7 should be feeded with signal instead . (to do a signal amplification)
top 6as7 i would remove; and use ccs or bulb instead.
you have not said, what hp Z do you have.
currently, top tube is just a follower - expect no big sound change at all.
This is a White cathode Follower and is feed from the top plate, it is active at signal. Follow the circuit from plate o grid via the 2.2µF cap.
Depending on HP impedance, the 6AS7 can alone. Keep in mind that 6AS7's µ is only 2, then the gain of the 6SN7 perhaps need to be increased, decoupling the cathode resistor.
Last edited:
On a 6AS7 I would not use a 1M grid leak resistor; change both of them to 47k.
This will improve the stability of the tube operating point, improving resolution.
BTW, a white follower would be the best possible way to drive a headphone with a high perveance tube like a 6AS7. It would confer strong drive even down to a 32R headphone.
HD
This will improve the stability of the tube operating point, improving resolution.
BTW, a white follower would be the best possible way to drive a headphone with a high perveance tube like a 6AS7. It would confer strong drive even down to a 32R headphone.
HD
Last edited:
Member
Joined 2009
Paid Member
+1 , this tube can suffer from thermal runaway and the data sheet points out the need for a sensible grid resistor.
PSRR of the White follower is not so good. Search up the Taylor follower, a hybrid improvement to the White follower that purports to address this limitation.
Edit: here ya go Taylor Source Follower
Member
Joined 2009
Paid Member
Thanks for all the replies. My interest in the 6AS7 was because it could drive a 32 ohm headphone configured as a White cascode. I do have headphones ranging from 32 ohms to 600 ohms !
I don't plan to introduce any transistors into the circuit. Yes, the 1 Meg grid resistor appears too big for this tube. The power supply will be a regulated supply so even with the not so great PSRR it should be OK. Actually I do not need much gain at all. Sources will be 1 to 2 V , typically from a DAC.
So I might just add some NFB from the load end to the input. It would be voltage shunt feedback ( old terminology ?) so the input impedance will come down which doesn't really matter to me. Will use a current limited dc heater which should control the inrush current also. I might introduce a delayed plate supply after the heaters are turned on.
I don't plan to introduce any transistors into the circuit. Yes, the 1 Meg grid resistor appears too big for this tube. The power supply will be a regulated supply so even with the not so great PSRR it should be OK. Actually I do not need much gain at all. Sources will be 1 to 2 V , typically from a DAC.
So I might just add some NFB from the load end to the input. It would be voltage shunt feedback ( old terminology ?) so the input impedance will come down which doesn't really matter to me. Will use a current limited dc heater which should control the inrush current also. I might introduce a delayed plate supply after the heaters are turned on.
Hi Ashok,
I read with interest your comments on heart disease - stay well my friend!
You might consider using a much smaller tube, something like a 6BM8 or even a 6BL8. Both have a small triode and a larger pentode. The triode can be excellent for the amplification, say 3-5 times not more, and the pentode makes a wonderful cathode follower, with gain around 0.99 compared to 0.93 for a triode and a very low Zout. The two can be directly connected, and you would need around 300V to light it up.
Ciao,
Hugh
I read with interest your comments on heart disease - stay well my friend!
You might consider using a much smaller tube, something like a 6BM8 or even a 6BL8. Both have a small triode and a larger pentode. The triode can be excellent for the amplification, say 3-5 times not more, and the pentode makes a wonderful cathode follower, with gain around 0.99 compared to 0.93 for a triode and a very low Zout. The two can be directly connected, and you would need around 300V to light it up.
Ciao,
Hugh
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.