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Aikido transformer coupled output

kacernator

Member
2008-01-09 10:38 pm
Hi,

I have built aikido amplifier with output transformer 10k / 150 ohm. I use it as headphone amplifier.
Would there be any benefits converting output stage to white cathode follower to provide lower output impedance and more current drive? Or it is not need with output transformer?

When I plug 150 ohm headphones bass is good, but with 32 ohm headphones bass is weaker. Would white cathode follower provide more bass with 32 ohm headphones?

Thanks.
 

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Brit01

Member
2008-07-04 10:35 am
I've built a SRPP type headphone amp just with an output cap (at least 200uF or more), and bass is great even with 32ohms.

Try the cap change as mentioned. Or maybe it's an OPT limitation.

Try without the OPT and replace it with 200-400 uF output cap. Bypassed with a small PIO helps.
 

kacernator

Member
2008-01-09 10:38 pm
I've built a SRPP type headphone amp just with an output cap (at least 200uF or more), and bass is great even with 32ohms.

Try the cap change as mentioned. Or maybe it's an OPT limitation.

Try without the OPT and replace it with 200-400 uF output cap. Bypassed with a small PIO helps.

I have OPT mainly to invert phase back to normal, because aikido already inverts phase.
 

45

Member
2008-12-18 2:29 am
UK
Hi,

I have built aikido amplifier with output transformer 10k / 150 ohm. I use it as headphone amplifier.
Would there be any benefits converting output stage to white cathode follower to provide lower output impedance and more current drive? Or it is not need with output transformer?

Thanks.

Be aware of the fact that if you want a White CF with lowest Zout this does not necessarily mean increased current drive. More likely you will find that the highest current output happens for a Zout similar to that of normal CF. So you have to be sure about the extreme case (load, voltage, current..etc) and design the WCF as a consequence.

45
 

Brit01

Member
2008-07-04 10:35 am
Originally Posted by Brit01 View Post
If it inverts the phase, what difference to the headphones would this make?
That'd be just fine and won't make any difference at all...as long as you stand backwards!

If you're using JB's Aikido design then decoupling direct to a set of headphones will be fine. He has this option on his boards.

Can't quite make out what is different about your circuit to require the need to invert the phase with an OPT. Please correct me if I'm wrong.;)
 

kacernator

Member
2008-01-09 10:38 pm
I tried the white cathode follower and didnt like the sound. So I went back to stock aikido. But I have another idea, but I have not enough skill and knowledge to finalize the design. Look at the attached pictures, it is from tubecad.com, article called super-triode meets aikido. Would it be possible to use IRF820 high voltage mosfets to deliver more current? Would it be possible to set desired current manually or is it circuit dependent?
 

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Hi,

I have built aikido amplifier with output transformer 10k / 150 ohm. I use it as headphone amplifier.
Would there be any benefits converting output stage to white cathode follower to provide lower output impedance and more current drive? Or it is not need with output transformer?

When I plug 150 ohm headphones bass is good, but with 32 ohm headphones bass is weaker. Would white cathode follower provide more bass with 32 ohm headphones?

Thanks.

Hello,
Thoughts!
The circuit that you posted looks to be from the tubecad site. Please confirm that you are running with the tube types and resistor values shown. You did not tell us the value of the output capacitor.
There can be a couple of things going on.
With the 150 ohm headphones connected the amplifier sees a 10K load. With the 32 ohm headphones connected the amplifier see about a 2K load. This will result in 2 completely different AC load lines. The amplifier with (if) 6H30’s should be up to swinging the 5 times current of the 32 ohm headphones if not there will be clipping.
If you have a minimum capacitor installed for the 150 ohm headphones it should be 5 times larger for the 32 ohm headphones. This is a likely culprit.
If you want to use multiple headphones an autoformer transformer with multiple taps is an idea to consider.
DT
 

kacernator

Member
2008-01-09 10:38 pm
Yes, the circuit is from tubecad.com. I am using 4x 6SN7. I am aware that with 32 ohm headphones bass will be lower. But I tried changing output cap from 470nF to 1uF and bass got muddier, not well defined, tuneful - this was with either 32 ohm or 150 ohm headphones. I also tried biasing output tubes hotter, but that again didnt sound as good. I am satisifed with the sound as it is, but I am looking for more grunt, drive, or powerfull, if it is possible.

What dou you think about supertriode? - two schematics posted above.
 
Yes, the circuit is from tubecad.com. I am using 4x 6SN7. I am aware that with 32 ohm headphones bass will be lower. But I tried changing output cap from 470nF to 1uF and bass got muddier, not well defined, tuneful - this was with either 32 ohm or 150 ohm headphones. I also tried biasing output tubes hotter, but that again didnt sound as good. I am satisifed with the sound as it is, but I am looking for more grunt, drive, or powerfull, if it is possible.

What dou you think about supertriode? - two schematics posted above.


Hello,
I have not tried the Super Triode you are speaking of. From my view it is worth the effort to try it. One thing I did try was Figure 5 in the attached BUF634 data sheet. JB also discusses the use of the 634. I used a LM4562 Op-Amp rather than the one shown. I was impressed with the results using Sennheiser HD600’s (300 ohm), sounded very solid and tight, no flab. I used 12 volt gel cell batteries for power.
http://focus.ti.com/lit/ds/symlink/buf634.pdf

DT
All just for fun!
 
Can I invert phase with BUF634?

Hello,
You can invert to your heart’s desire in that Op-Amp / buffer amplifier. The Op-Amp can be setup inverting or non-inverting. One thing to add is that I set up the Op-Amp thing with a gain of 2. As it is shown it has a gain of 21. 21 is way too much if you are driving it with an Aikido with a gain of ~ 20.
If you want a tube option consider rolling out the output 6SN7’s in the Aikido and using a pair of NOS 6BX7’s that would be lower output impedance and provide more “grunt” tube power. I have used this capacitor Dayton PMPC-30 30uF 250V Precision Audio Capacitor | Parts-Express.com
as a Aikido output capacitor to feed a headphone transformer as you are doing and liked the results.
DT