Hi all!
This is one of my last valve project. An OTL headphone amp with a 6N1P in ground cathode for input stage and a 6N6P in SRPP for the output stage.
I've found that the best working point for this tubes are 10 ma for the 6N1P and 22 ma for the 6N6P. The circuit is a classic and in the next post I'll send to you. With my Sennheiser HD590 and AKG K271 Mk2 works really fine, what a sound!!! I have a slight and impercectible hum but I soon resolve it with a choke in the PSU, now I have a CRC cell but it's bettere a CLC; next step.
The case is a bit ugly but I have used some recycled waste from my factory (rivets... like a Douglas DC3... could be a new trend???)
I bought a lot of russian valves on ebay, different factories and years and works really fine, great sound and incredible price, I'm working with them in my next project: a RIAA-LINE preamplifier.
ciao
This is one of my last valve project. An OTL headphone amp with a 6N1P in ground cathode for input stage and a 6N6P in SRPP for the output stage.
I've found that the best working point for this tubes are 10 ma for the 6N1P and 22 ma for the 6N6P. The circuit is a classic and in the next post I'll send to you. With my Sennheiser HD590 and AKG K271 Mk2 works really fine, what a sound!!! I have a slight and impercectible hum but I soon resolve it with a choke in the PSU, now I have a CRC cell but it's bettere a CLC; next step.
The case is a bit ugly but I have used some recycled waste from my factory (rivets... like a Douglas DC3... could be a new trend???)
I bought a lot of russian valves on ebay, different factories and years and works really fine, great sound and incredible price, I'm working with them in my next project: a RIAA-LINE preamplifier.
ciao
Attachments
Here the schematic
Hi all!
This is one of my last valve project. An OTL headphone amp with a 6N1P in ground cathode for input stage and a 6N6P in SRPP for the output stage.
I've found that the best working point for this tubes are 10 ma for the 6N1P and 22 ma for the 6N6P. The circuit is a classic and in the next post I'll send to you. With my Sennheiser HD590 and AKG K271 Mk2 works really fine, what a sound!!! I have a slight and impercectible hum but I soon resolve it with a choke in the PSU, now I have a CRC cell but it's bettere a CLC; next step.
The case is a bit ugly but I have used some recycled waste from my factory (rivets... like a Douglas DC3... could be a new trend???)
I bought a lot of russian valves on ebay, different factories and years and works really fine, great sound and incredible price, I'm working with them in my next project: a RIAA-LINE preamplifier.
ciao
Attachments
Capacitors K42 is not the best, K40 would be better.
Assessing the impact of coupling capacitors in the audio amplifier.
http://www.magictubes.ru/ves/kondens.htm
Assessing the impact of coupling capacitors in the audio amplifier.
http://www.magictubes.ru/ves/kondens.htm
This circuit is very similar to P. Milletts SRPP design which uses the ECC99. I think this design just uses the Russian equivalent tube.
The P. Millett design runs the tubes at 20mA with a 300 ohm Rk. This design has 150 ohms Rk so the cathode current will be even higher. I am concerned this may exceed the dissipation spec of the tubes used.
The P. Pillet design uses an output transformer to better match the output to the headphones impedance. This circuit has no output transformer so its drive capabilities will be severely limited except for high impedance headphones.
Cheers
Ian
The P. Millett design runs the tubes at 20mA with a 300 ohm Rk. This design has 150 ohms Rk so the cathode current will be even higher. I am concerned this may exceed the dissipation spec of the tubes used.
The P. Pillet design uses an output transformer to better match the output to the headphones impedance. This circuit has no output transformer so its drive capabilities will be severely limited except for high impedance headphones.
Cheers
Ian
Thank'd for the answar Ian.
No problem with running the tube to hot. I will make it inside the safety limit. 6n6p runs fine with 100-150V@20-25mA.
Another matter is the drive capability for my 300 OHM cans. I do not know how to calculate if the curcuit is up to it. Any help is most welcomed.
But back to my Q. Why the 220nF cap on the input, and the 1Meg?
Theo
No problem with running the tube to hot. I will make it inside the safety limit. 6n6p runs fine with 100-150V@20-25mA.
Another matter is the drive capability for my 300 OHM cans. I do not know how to calculate if the curcuit is up to it. Any help is most welcomed.
But back to my Q. Why the 220nF cap on the input, and the 1Meg?
Theo
Drive capability can be calculated from the phones spec. The HD650 are quoted at 102dB SPL for 1V rms input. That's pretty loud but to allow for transient I normally aim for a peak drive capability to 117dB SPL which implies we need another 15ddB of signal or about 5.6V rms. Into 300 ohms, 5.6V rms give a peak current of 26mA. If you run the tubes at 25mA quiescent this is not going to happen.
I have run a simulation of an ECC99 SRPP running at 220V with the Rk values shown in the schematic and this predicts a plate current of 17mA and a plate dissipation of just under 2W a plate which should be OK.
At 3V rms into 300 ohms the simulation predicts a THD of about 0.8%. This should give a peak sound level of 112dB SPL.
At 1V rms the distortion falls to about 0.25%.
To be honest, you don't really need the first tube as the SRPP on its own will have about 20dB gain.
Cheers
Ian
I have run a simulation of an ECC99 SRPP running at 220V with the Rk values shown in the schematic and this predicts a plate current of 17mA and a plate dissipation of just under 2W a plate which should be OK.
At 3V rms into 300 ohms the simulation predicts a THD of about 0.8%. This should give a peak sound level of 112dB SPL.
At 1V rms the distortion falls to about 0.25%.
To be honest, you don't really need the first tube as the SRPP on its own will have about 20dB gain.
Cheers
Ian
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