I'm looking to get a set of headphones and find that they vary considerably in input impedance.
For instance, Sennheiser Momentum are specified at 18 Ohms, HD-598 specifies 50 Ohm, and HD-600 specifies 300 ohm.
I plan on building a tube based headphone amp, probably with 6Z9P tubes in Mu Stage per the attached schematic.
Aside from the fact that my output transformer will have to match to the headphone impedance, what other considerations are there with regards to impedance.
Does it make any difference if they are 18 ohm or 300 ohm? If so, what?
For instance, Sennheiser Momentum are specified at 18 Ohms, HD-598 specifies 50 Ohm, and HD-600 specifies 300 ohm.
I plan on building a tube based headphone amp, probably with 6Z9P tubes in Mu Stage per the attached schematic.
Aside from the fact that my output transformer will have to match to the headphone impedance, what other considerations are there with regards to impedance.
Does it make any difference if they are 18 ohm or 300 ohm? If so, what?
Attachments
I just posted a thread about needing an output transformer that has 8-16-32-150-300 ohm secondaries. I'm going to have them built buy Edcor unless I can find them, I don't want to re-invent the wheel if i don't have to.
http://www.diyaudio.com/forums/tubes-valves/249061-output-transformer-se-headphone-amp.html
http://www.diyaudio.com/forums/tubes-valves/249061-output-transformer-se-headphone-amp.html
As long as the impedance reflected through the O/P coupling transformer to the tubed O/P stage is correct, operation should be satisfactory.
If the decision to build a tubed setup is not "cast in concrete", I suggest you take a look at Sheldon Stokes SS design. I have 1 of these "puppies" and it sounds GOOD. It has been used with Grado and Sennheiser "cans", to my satisfaction. Like the man said, it doesn't sound like "sand".
I was toying with the idea of winding an interstage transformer myself for another project. I started doing calculations of the requirements for the headphone amp and figure about 198H primary inductance and 25K input impedance.
Going to a 50 Ohm headphone should run around 22.3 : 1 which is in the range of a lot of OPTs. At 25K to 300R the ration drops to around 9.2 : 1, and that is going to be a lot of secondary turns. I figured around 6000 primary turns so the secondary would be 667 turns. Doing a 4:3 interleave it would be three layers of 120 turns per secondary.
When you look at the requirements for the low impedance outputs, they would probably have to be totally separate windings with larger wire.
Going to a 50 Ohm headphone should run around 22.3 : 1 which is in the range of a lot of OPTs. At 25K to 300R the ration drops to around 9.2 : 1, and that is going to be a lot of secondary turns. I figured around 6000 primary turns so the secondary would be 667 turns. Doing a 4:3 interleave it would be three layers of 120 turns per secondary.
When you look at the requirements for the low impedance outputs, they would probably have to be totally separate windings with larger wire.
I hadn't considered that. Thanks.
I was actually considering building a DHT based headphone amp but didn't have models for the tubes so I started the simulation with the 6Z9P. I was surprised how sell the simulations went.
A DHT / DHP Mu Stage headphone amp would be interesting, but the top current source is best with a high Gm pentode/Tetrode and all of the DHPs have low Gm and are not really suitable.
I was actually considering building a DHT based headphone amp but didn't have models for the tubes so I started the simulation with the 6Z9P. I was surprised how sell the simulations went.
A DHT / DHP Mu Stage headphone amp would be interesting, but the top current source is best with a high Gm pentode/Tetrode and all of the DHPs have low Gm and are not really suitable.
This edcor might be of interest. It's a parafeed one specified for the Torpedo
With 300r load, you indeed don't need a transformer. I recently made a µ-follower with a ecl85/6F5P (pentode triode strapped) at the bottom and a mosfet on top. Works beautifully into my senn hd650, low distortion and output impedance, even open-loop. I plan on adding the edcor transformer at its output for 32r duty.
edit: I forgot: if asking Edcor, be careful specifying an acceptable dcr for the secondary.
With 300r load, you indeed don't need a transformer. I recently made a µ-follower with a ecl85/6F5P (pentode triode strapped) at the bottom and a mosfet on top. Works beautifully into my senn hd650, low distortion and output impedance, even open-loop. I plan on adding the edcor transformer at its output for 32r duty.
edit: I forgot: if asking Edcor, be careful specifying an acceptable dcr for the secondary.
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Peerless in the past made autoformers that were apparently good for a headphone amp. Don't know if Magnequest made these or if they were originals. Maybe Mike would make them if enough interest.
Espressivo Headphone Amplifier
John
Espressivo Headphone Amplifier
John
In my 'improved' headphones amp design I use the Sowter 8665 output transformer which has taps that can be configured for headphones from 32 ohms to 600 ohms.
http://www.ianbell.ukfsn.org/EzTubeMixer/docs/headphonesamp/phonesampcctsht1of2.jpeg
I have a couple of spare PCBs for this design, You are welcome to one for the cost of shipping.
Cheers
Ian
http://www.ianbell.ukfsn.org/EzTubeMixer/docs/headphonesamp/phonesampcctsht1of2.jpeg
I have a couple of spare PCBs for this design, You are welcome to one for the cost of shipping.
Cheers
Ian
Thank you Ian, I may take you up on that offer your design looks very interesting, I like. and thanks for tip on Sowter transformers. I could use one that at least has an 18ohm tap for use on 16ohm desk top speakers.
Page 2 just shows the other channel - it's a stereo headphones amp. All the basic documentation including a Bill of Materials is in this directory:
Index of /EzTubeMixer/docs/headphonesamp
The power supply can be quite simple. The tube heaters run from 12.6VAC. For the HT a simple bridge rectifier plus a CRCRC filter will be sufficient. it is a class A circuit so there are no wild fluctuations in HT current as you would get in a class B circuit for example. You also need to elevate the heaters to about 75V above HT 0V to meet the Vhk specs of the ECC99 tubes. The HT supply circuit I use is here:
http://www.ianbell.ukfsn.org/EzTubeMixer/docs/power/HT350cct.png
This is quite easy to build point to point but I also have a PCB for this.
Cheers
Ian
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