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Old 13th February 2009, 06:51 PM   #1
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Lightbulb Moskido Headphone Amplifier

Hi,

I would like to build moskido headphone amplifier. This time just cap-coupled version, because it is easier and I already have PT, which is capable providing just positive supplies.

I would like to use IRF610/IRF9610 combo, but I dont know how to choose right values of diodes and resistors to bias it at 250mA - 300mA at idle at +15V supply.

Here is the beta schematics:
http://img132.imageshack.us/my.php?i...adphonebv8.png


I already tried SE mosfet buffer, but I do not like SE sound, so thats why I would like to have moskido for headphones.
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Old 13th February 2009, 10:35 PM   #2
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I have changed the biasing method.
Here is the new schematics:
http://img3.imageshack.us/img3/4043/...adphonedc2.png

Any comments are welcome.
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Old 18th February 2009, 11:40 AM   #3
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New updated schematics. I still do not know, if I will get right bias with this scheme, will update after the build.

Schematics: http://img337.imageshack.us/img337/6...adphonedb0.png
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Old 26th February 2009, 09:30 AM   #4
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Hi,

I had the amp running. The last scheamtics works very good, but you must be very carefull with bias pot adjustment, because it is very sensitive, but it is ok.
The amp sounded good, but I went back to SE szekeres headphone amplifier. There were two reasons for that. One is that SE topology inverts back the phase which is already inverted by aikido preamp - lots of headphones cannot be connected to compensate phase shift. Second is PP sounds more true to the source, but closed in. With such a low power amplifier, SE with its very open and very airy sound wins for me.

This amplifier also drives my speakers very well for low listening levels (actualy it can sound quite loud). So when I do not need my 30W moskido I save lot of electricity when listening through this amplifier.

Next project will be DC coupled Szekeres with servo, but I have to find yet somewhere big enough chassis for that.
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Old 10th December 2010, 04:46 PM   #5
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Default New design

Hi,

right now I am using 4x 6SN7 aikido coupled to transformer 10k/150 Ohm as headphone amplifier. It sounds very good, but not much authority on higher volume levels. Changing the output tube to another more with more current capability would help, but I would like to try mosfet buffer instead of transformer - see attached schematics. How do I adjust the current? Or how to modify the schematics to make the current adjustable? I am not skilled enough to make these modifications. I am planning to run output stage at 24V and cca 200mA.

Thank you.
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File Type: png aikido_hybrid_se_16w_power_amplifier_with_feedback.png (19.5 KB, 667 views)
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Old 11th December 2010, 01:48 AM   #6
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Quote:
Originally Posted by kacernator View Post
Hi,

right now I am using 4x 6SN7 aikido coupled to transformer 10k/150 Ohm as headphone amplifier. It sounds very good, but not much authority on higher volume levels. Changing the output tube to another more with more current capability would help, but I would like to try mosfet buffer instead of transformer - see attached schematics. How do I adjust the current? Or how to modify the schematics to make the current adjustable? I am not skilled enough to make these modifications. I am planning to run output stage at 24V and cca 200mA.

Thank you.
Hello,
The original Moskido Headphone Amplifier was an Aikido followed by BB BUF634. I built two. One with just the BUF634. The other with the BUF634 in the feedback look for a 4562 Op-Amp. The 2nd was better. A cheep refrence amplifier.
A Aikido with a 6BQ7 output stage into a Hammond 119DA Para-Feed transformer sounds better. There is much lower output impedance than with the 6SN7 output stage.
DT
All Just for fun!
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Old 11th December 2010, 08:31 AM   #7
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Hi,

thanks for reply. I want to get rid of the any sort of output transformers. With BUF634 I cant invert the phase back (as aikido inverts) and I dont like sound of inverted phase. With 4562 there is negative feedback right? I would like to have non NFB amplifier. So I need inverting unity gain buffer and one is in the attached schematics above. Or if you know some opamp inverting buffer?
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Old 11th December 2010, 03:36 PM   #8
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Hello,
First off, if it does not have negative feedback it is not an Op-Amp.
The LM4562 with the BUF623 in the feedback loop is easily built to be inverting.
If you want to get the transformer out of the tube headphone Aikido try the White Cathode Follower output versions with one of the beefy high ma tubes listed in the user manual. With no transformer in the output you have higher output impedance and that big ugly electrolytic capacitor in its place.
I do not get your aversion to inverting. I believe the signal is dizzy from the many inversions between recording and play back. How do you and the signal which way is up? Your ears will not be able to tell as long as woofer, squawker and tweeter have it the same!
DT
All Just for fun!
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Old 11th December 2010, 05:30 PM   #9
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Well I can hear inverted phase easily. Music sounds weird. Just try swap your speaker leads and you will see. Transformer coupled aikido sounds so far the best, but I cannot get high ma octal output tubes in my country - 6BL7 and 6BX7. ECC99 could be an alternative I know. So for the easiest solution I am looking for inverting buffer with or without output cap.
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Old 17th December 2010, 04:27 PM   #10
qusp is offline qusp  Australia
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Quote:
Originally Posted by kacernator View Post
Well I can hear inverted phase easily. Music sounds weird. Just try swap your speaker leads and you will see. Transformer coupled aikido sounds so far the best, but I cannot get high ma octal output tubes in my country - 6BL7 and 6BX7. ECC99 could be an alternative I know. So for the easiest solution I am looking for inverting buffer with or without output cap.
I believe this may be the answer to your question??
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