[runeight]

Kansei, I meant to add that when I was building my prototype I shorted the PS 3 times and had to replace the mosfets 3 times too!!! I discovered just how easy it is create even a very brief short on the regulator when testing. When I tried to think of a way to add protection to the PS I realized it was going to be much more expensive than it was worth.

And then once I stopped fooling around inside the PS, the regulator has been stable. So hopefully, you'll only have to replace the fets once.

 

[rolotube]

Is it possible to use 6N6's safely with regal's mods? There's a comment in the Tweaks section that indicates ECC99's should be used. Is this because the 6N6's draw too much current & may stress the PS?

Any thoughts or experiences would be welcome.

Thanks.

 

[diego]

Will a 270dax overheat if I use it at 120v? If it overheats could I just put a 1.5 ohm resistor in the primary to drop those extra 5v?

Thanks.

 

[holland]

Quote:

Originally Posted by rolotube /img/forum/go_quote.gif Is it possible to use 6N6's safely with regal's mods? There's a comment in the Tweaks section that indicates ECC99's should be used. Is this because the 6N6's draw too much current & may stress the PS? Any thoughts or experiences would be welcome. Thanks.

Yes, though you may have to regulate below 245V. I have mine @ 240V.

 

[runeight]

Quote:

Originally Posted by diego /img/forum/go_quote.gif Will a 270dax overheat if I use it at 120v? If it overheats could I just put a 1.5 ohm resistor in the primary to drop those extra 5v? Thanks.

diego the 270dax should not overheat running at 120V. These transformers are pretty durable.

 

[rolotube]

Quote:

Originally Posted by holland /img/forum/go_quote.gif Yes, though you may have to regulate below 245V. I have mine @ 240V.

Thanks holland. I'll given them a go & check out the voltage.

 

[disco]

Nice chassis Kansei. Next a nice wooden enclosure to finish it?

I'm looking for a schematic of an all tube headphone amplifier and found the Bijou. Being reluctant to reinvent the wheel, I wonder why the headphones are coupled through an outputcapacitor. Is it because of financial reasons the outputtransformer is replaced?

 

[runeight]

disco, the Bijou is what is called an Output Transformerl Less (OTL) amplifier. Transformers tend to limit the output bandwidth of an amp and so, over the years, many designers have sought to eliminate them.

The capacitor in the Bijou is needed because the output point (between the two triodes) is at 125VDC. The capacitor blocks the high DC voltage while passing the AC signal.

 

[disco]

Quote:

Originally Posted by runeight /img/forum/go_quote.gif disco, the Bijou is what is called an Output Transformerl Less (OTL) amplifier. Transformers tend to limit the output bandwidth of an amp and so, over the years, many designers have sought to eliminate them. The capacitor in the Bijou is needed because the output point (between the two triodes) is at 125VDC. The capacitor blocks the high DC voltage while passing the AC signal.

Sorry if I didn't make my point clear

I do own a pair of 4K:300 OT (BW -1dB >30KHz, so no restrictions there) and am looking for a circuit to build. Large output caps do not seem attractive to me...

 

[runeight]

The Bijou will have a much higher frequency response than your transformers. But, there are differences of opinion on how much this matters to the SQ.

And I think you might find that the capacitor is less limiting than the transformer.

But, since you have transformers, there have been quite a few designs posted in various places for making a transformer output headphone amplifier. I wouldn't recomment using the Bijou's futterman topology with a transformer because this type of amp is specifically designed to be OTL, but some of these other designs, IIRC, are pretty nice. I don't have a pointer to any of them at the moment, but I suspect that you've seen many of them already.

 

[disco]

Quote:

Originally Posted by runeight /img/forum/go_quote.gif The Bijou will have a much higher frequency response than your transformers. But, there are differences of opinion on how much this matters to the SQ. And I think you might find that the capacitor is less limiting than the transformer. But, since you have transformers, there have been quite a few designs posted in various places for making a transformer output headphone amplifier. I wouldn't recomment using the Bijou's futterman topology with a transformer because this type of amp is specifically designed to be OTL, but some of these other designs, IIRC, are pretty nice. I don't have a pointer to any of them at the moment, but I suspect that you've seen many of them already.

Using an OT in an OTL would be contradictory, wouldn't it?

The reason for me posting here is to find a circuit. Perhaps other folks are lazy looking for them selves but the only not-OTL design I came across is the one from Simon Busbridge.

That's why I made the remark wrt the OT. Not only do I know that the output capacitor is much more offending to the actual reproduction quality of the amplifier than a good quality OT, it's more a matter of design principle. Financial reasoning would be a valid design choice though.

 

[runeight]

OK. I'm not sure that I can be of any further help except to note that the Bijou was designed as an OTL amplifier just because I had some ideas about doing one with a very simple power supply. There were no financial considerations involved regarding transformer cost vs. capacitor cost.

Perhaps others on this thread can suggest places to find OT amplifiers that might give more selection.

 

[pabbi1]

So far afield, but look at the Raven in my sig, as well as the 307a - both balanced opt designs (though on the 307a, I'm NOT using a phase splitter on input as I have a balanced source). Pete also has a raft of designs on his site, which might be more in line with what you are seeking.

 

[disco]

Yes indeed, Peter has a lot to share

I'm using something similar to his srpp design. Looking for a way to loose the 10uF coupling cap though.
Thanks for the input.

 

[runeight]

Great. Now that you've found something that you're interested in building you should start a new thread around this topic. There might be others who will participate if they see a new thread that is not buried down in the Bijou discussion.