[clayman0403]

Hi guys,
 
I'm just building a Morgan Jones OTL clone. Does it makes sense to integrate a switchable buffer circuit like for example
lt1010 for impedance matching to drive low impedance headphones? My favorite headphone at the moment is unfortunately a 32 Ohm one with a sensitivity of 98db / 1mW. The modified MJ puts out 10mW max. into 32 Ohms. I can only hope it will be loud enough.
Or would this destroy the sweet tube sound?
Pls do not answer: Then you can build a soha or other hybrids. The Soha II is already in the pipeline
 
Thanks

 

[nikongod]

Quote:

Hi guys,
 
I'm just building a Morgan Jones OTL clone. Does it makes sense to integrate a switchable buffer circuit like for example
lt1010 for impedance matching to drive low impedance headphones? My favorite headphone at the moment is unfortunately a 32 Ohm one with a sensitivity of 98db / 1mW. The modified MJ puts out 10mW max. into 32 Ohms. I can only hope it will be loud enough.
Or would this destroy the sweet tube sound?
Pls do not answer: Then you can build a soha or other hybrids. The Soha II is already in the pipeline
 
Thanks

 
I like the MJ & its cousins, within their limits. 
 
Depending how "tuby" you want the amp to sound you may like just running the low impedance headphones straight off of the MJ. 
 
If that is too tuby the best way to do what you are describing with SS parts is build the MJ with RCA outputs (as well as headphone outputs) **AND** build a very simple buffer in its own little box. It could be the chip you pointed out or a simple mosfet buffer like the Szekeres buffer as shown on headwize (my preference towards the szekeres). This has the advantage of being modular so you don't need to commit any "case space" or money to this part of the project before you know exactly what you want to do.
 
Be sure to include protection diodes with whatever SS parts you use - the turn-on thump from the MJ may screw up the SS bits otherwise. 
 
Another idea (that I personally prefer) is to add small parafeed transformers to the output of the MJ clone. Not really what you asked for, but a VERY fun tangent to go off on. 
 
Personal favorite option of all is skip the MJ and just build a simple 1 or 2-stage SET amp with a multi-tapped output transformer, but this may be way too far out. 

 

[clayman0403]

Thank you Nikongod. Good that you say: Try it out and not only forget it. Chu Moy uses a kind of transformer for his Grados, but I didn't really understand what he meant with:
 
"[size=x-small]Instead, he experimented with a small impedance matching transformer (1.5K/60-60 from Antique Electronic Supply) for higher power transfer to his Grados."[/size]
 
[size=x-small]Do you know [size=x-small]what it is?[/size][/size]
 
edit: Got it now, it was practically a parafeed transformer. How do I calculate the right cap and input impedance for the parafeed transformers?

 

[nikongod]

They are just little transformers. If you can find 600:32ohm transformers that would be awesome. 
Radio shack makes a (very cheap) 1K:8ohm transformer that is worth at least the $2.50 or so that they cost. 
There are also ways to use 70V speaker transformers or toroidal power transformers. I was talking about it with Kramer a few weeks ago, look thrugh my posts for stuff on the darkvoice. 
 
On that note, I dont know if you wanted to point-to-point the MJ or had some other plan but this should help you out:
http://www.head-fi.org/t/221733/modifying-the-xiang-sheng-708b-56k
is basically a MJ clone, with a nicer power supply and SLIGHTLY different tubes. 
The hard part is finding one used. When I last looked they were way too expensive new, and hard to find used... but search hard if a PCB and (basically) no casework appeals to you. 

 

[clayman0403]

Hi Nikongod,
 
I'll build Bruce Benders 6n1p OTL. I have layouted the schematic in eagle already to make my own pcb. The power supplies will be in point to point.
Can you please send me a link to the Radio Shack transformer? Is parafeed possible with a resistor load for the anode? I have only found a combination of anode choke, cap and parafeed transformer.
 
Regards