Mpp - Page 111

Joachim Gerhard · 21st March 2010, 01:33 PM

I see no reason why those Fets should not work here.
A simple parallel symmetric buffer whithout the BJTs whould work well too.
John Curl made buffers that way.
I will try my RME Firface 400 card today and try to make some higher resolution distortion measurements.
The RME card should be better then my M-Audio Transit.

Salas · 21st March 2010, 01:38 PM

I guess we all need a small dead bug construction headphones amp to fit in our phono stages as standard. So we can listen to vinyl at night without feeding through preamps, interconnects, stand alone headphones amps. It can be a an integrated phono-phones-preamp even if we steal for current boosted RCA output too. What do you think?

Salas · 21st March 2010, 01:51 PM

Its the 2N54XX are good and linear but they lack current. But have low Ciss, Crss and noise on the other hand. So BJTs are needed to boost. And here is the original from the 90's. JLH used 2N54XX indeed!

Joachim Gerhard · 21st March 2010, 01:53 PM

Yes, good idea. My Self preamp has that feature.

Joachim Gerhard · 21st March 2010, 01:55 PM

i knew the JLH buffer for many years but i never tried it until recently. That was a mistake, it works very well indeed.

Salas · 21st March 2010, 02:00 PM

Can the trimmer really null the offset at JLH's output node in your experience from when you implemented it as input stage in your headphones amp? Or it will need cap coupling if a standalone volume buffer for instance?

Joachim Gerhard · 21st March 2010, 02:40 PM

The offset can be nulled and is very stable at + - 0.1mV.
PSU needs stable voltage of cause so after i listened 2 hours on 7AH batteries the offset was 0.3mV on one channel and 0.4mV on the other becaue the batteries did not have equal voltage any more. No problem with the sound though.

Salas · 21st March 2010, 02:44 PM

Now I think if we put BD139,140 directly in the JLH Jfet-BJT compound follower, maybe we can directly drive headphones with just 4 semiconductors and a healthy voltage input for it?

Joachim Gerhard · 21st March 2010, 03:19 PM

That should be posible.
The circuit as is can drive 150 Ohm, so even that circuit could already drive high impedance phones.

jan.didden · 21st March 2010, 03:21 PM

Quote:

Originally Posted by Joachim Gerhard

Good turntables are not expensive any more.
For example Clearaudio and Rega make good packages of turntable, arm and cart. for
1000,- - 2000,-€. Later a better cart. can be added.
There is also a lot of good stuff on the used market.
Errata : Ikoflexer found a small mistake in circuit post 1088.
The LME49713 op amps PSU connection is reversed. Pin 4 should go to - supply and pin 7
should go to + supply of cause.

A Rega P3 + arm went on eBay yesterday for 277 euro....

jd

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21st March 2010, 01:33 PM	#1101
Joachim Gerhard diyAudio Member Join Date: Mar 2009	I see no reason why those Fets should not work here. A simple parallel symmetric buffer whithout the BJTs whould work well too. John Curl made buffers that way. I will try my RME Firface 400 card today and try to make some higher resolution distortion measurements. The RME card should be better then my M-Audio Transit.

21st March 2010, 01:38 PM	#1102
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	I guess we all need a small dead bug construction headphones amp to fit in our phono stages as standard. So we can listen to vinyl at night without feeding through preamps, interconnects, stand alone headphones amps. It can be a an integrated phono-phones-preamp even if we steal for current boosted RCA output too. What do you think?

21st March 2010, 01:53 PM	#1104
Joachim Gerhard diyAudio Member Join Date: Mar 2009	Yes, good idea. My Self preamp has that feature.

21st March 2010, 01:55 PM	#1105
Joachim Gerhard diyAudio Member Join Date: Mar 2009	i knew the JLH buffer for many years but i never tried it until recently. That was a mistake, it works very well indeed.

21st March 2010, 02:00 PM	#1106
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	Can the trimmer really null the offset at JLH's output node in your experience from when you implemented it as input stage in your headphones amp? Or it will need cap coupling if a standalone volume buffer for instance?

21st March 2010, 02:40 PM	#1107
Joachim Gerhard diyAudio Member Join Date: Mar 2009	The offset can be nulled and is very stable at + - 0.1mV. PSU needs stable voltage of cause so after i listened 2 hours on 7AH batteries the offset was 0.3mV on one channel and 0.4mV on the other becaue the batteries did not have equal voltage any more. No problem with the sound though.

21st March 2010, 02:44 PM	#1108
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	Now I think if we put BD139,140 directly in the JLH Jfet-BJT compound follower, maybe we can directly drive headphones with just 4 semiconductors and a healthy voltage input for it?

21st March 2010, 03:19 PM	#1109
Joachim Gerhard diyAudio Member Join Date: Mar 2009	That should be posible. The circuit as is can drive 150 Ohm, so even that circuit could already drive high impedance phones.