Currently listening to a 6U10 or 6ac10's-Mosfet hybrid headphone amp.
6u10 is an input gain stage and SRPP second stage with a Mosfet follow output. I did allow for feedback from the output to the input of the SRPP stage. The output is cap coupled.
I was looking for a simple, inexpensive amp that could use what stuff I had on hand.
The tubes will be visible though a window in the front of the amp, the idea is to use 304 mirror finish to make a divider to reflect the light forward and hide the circuitry. I used foil glued to cardboard for a mock up...
6u10 is an input gain stage and SRPP second stage with a Mosfet follow output. I did allow for feedback from the output to the input of the SRPP stage. The output is cap coupled.
I was looking for a simple, inexpensive amp that could use what stuff I had on hand.
The tubes will be visible though a window in the front of the amp, the idea is to use 304 mirror finish to make a divider to reflect the light forward and hide the circuitry. I used foil glued to cardboard for a mock up...
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Looking to stay away from transformers unless its for power...
Also Looking to stay away from SS components as well...
Mosfet having the same trans-conductance, "voltage in, current out" as a tube and in a Class A follower application has the advantage of low output impedance over a tube....
I tried other ideas, came back to this one. The 6U10 is not the most ideal low voltage tube, but the results are impressive. Other ideas included 5 watt tube PP and SE circuits, but the transformers are very expen$ive for the bandwidth.
You might try a SRPP with a set of GU50's or KT88's
I tried other ideas, came back to this one. The 6U10 is not the most ideal low voltage tube, but the results are impressive. Other ideas included 5 watt tube PP and SE circuits, but the transformers are very expen$ive for the bandwidth.
You might try a SRPP with a set of GU50's or KT88's
But there are improved tube regulated power supplies
I would personally prefer 4P1L output tube with nice transformer, powered by MOSFET voltage regulator. Can't think of anything better for headphones.
Please define "high current".
First of all, what power do you need to feed into your headphones below the level that damages them or/and ears of the user?
It is the starting point.
Gross overkill.. A pair of 5842 in a white cathode follower configuration driven by the gain stage of your choice will drive a 24 ohm pair of headphones effectively. (Note that this requires an output capacitor which may have safety implications if it fails.) Triode connected D3A or 7788 would provide even lower output impedance. (These are all high GM tubes) If you really need balanced input you could use a 12AX7A in a long tailed pair with either a large value tail resistor to a high voltage negative supply or a 6AU6 as current source in the tail again with a high voltage negative supply.
I'd agree, an OPT would allow for a much simpler, likely better performing and safer output option without the need for a potentially leaky electrolytic output cap connected to a source of fairly high voltage.
Engineering always involves compromises and choices. An OPT without coupling capacitor is required to pass dc current which reduces its inductance and hence its LF response. Fortunately for a headphones amplifier a capacitively coupled output transformer presents an impedance of 5 to 10K to the output tube so there is no need to use a leaky electrolytic coupling capacitor - 10uF of metallised polyester or similar is sufficient.
Cheers
Ian
Thanks for the input.
I'm trying not to stray from the original parameters of the MK VI head amp.
Looks like a good design and its just a matter of figuring out the schematic and then its the easy part of building it.
Specs are :
Fully Balanced Architecture
SEPP (Single-ended Push Pull) OCL (Output CapacitorLess) in Class-A
Inputs:
Balanced: 2x 3-pin XLR
Single-ended: 2x RCA
Outputs:
Balanced: 4-Pin XLR
Balanced Pre-Amp: 2x 3-pin XLR
Single-ended: 1/4" (6.35mm) TRS Stereo jack
Input Impedance: 50K ohms
Pre-Amplifier Output Impedance: 600 ohms
THD+N:
0.02% (2Vrms @ 1000Hz)
0.06% (10Vrms @ 1000Hz)
0.3% (20Vrms @ 1000Hz)
Signal-to-Noise: 92 dB
User Selectable Gain Settings: Low (All Headphones) and High (suitable for AKG K1000)
Power Output: 5W per channel in 120 ohms
I'm trying not to stray from the original parameters of the MK VI head amp.
Looks like a good design and its just a matter of figuring out the schematic and then its the easy part of building it.
Specs are :
Fully Balanced Architecture
SEPP (Single-ended Push Pull) OCL (Output CapacitorLess) in Class-A
Inputs:
Balanced: 2x 3-pin XLR
Single-ended: 2x RCA
Outputs:
Balanced: 4-Pin XLR
Balanced Pre-Amp: 2x 3-pin XLR
Single-ended: 1/4" (6.35mm) TRS Stereo jack
Input Impedance: 50K ohms
Pre-Amplifier Output Impedance: 600 ohms
THD+N:
0.02% (2Vrms @ 1000Hz)
0.06% (10Vrms @ 1000Hz)
0.3% (20Vrms @ 1000Hz)
Signal-to-Noise: 92 dB
User Selectable Gain Settings: Low (All Headphones) and High (suitable for AKG K1000)
Power Output: 5W per channel in 120 ohms
Most of these designs use 6DJ8 or 6GM8 tubes, not familiar with the MK VI. The specs provide little useful in terms of the internal circuit topology. Have you considered just purchasing a used one, by the time it is all said and done you will not have saved much.
The archives at headfi seem to have disappeared, there used to be a wealth of designs tube and solid state, might still be, but I don't have time to look.. Might find something on the tubecad site as well that would interest you.
The archives at headfi seem to have disappeared, there used to be a wealth of designs tube and solid state, might still be, but I don't have time to look.. Might find something on the tubecad site as well that would interest you.
The parafeed is a viable option and keeps the capacitor away from the headphone feed which is my biggest concern. I do prefer a conventional transformer, but to each their own..
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