Build your own 747

HiFi
141

Indeed!

142

Interesting to see that someone in China is going full replica!

http://www.ebay.com/itm/Famous-circuit-Tube-preamplifier-Finished-ready-to-use-w-Phono-Amplifier-ZHI/132058141115?_trksid=p2046732.c100040.m2060&_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20140107095009%26meid%3D395760cef4bd44129e12989c0d06a282%26pid%3D100040%26rk%3D1%26rkt%3D4%26sd%3D132058141115

143

Wonder how long before they’re doing the rounds on eBay marked genuine

144

Won’t they need a CE badge :smirk:

145

Yeah, ‘China Export’.

3 Likes
146

:thumbsup:

147

Have this on loan at present,sounding very good in my system.

1 Like
148

I had a nice M77 on loan for a few days recently, it was alright

3 Likes
149

For me, one of the more interesting aspects of the M77 is the use of dual mains transformers which are wired out of phase on the primaries, you can just about make them out here:

The HT and LT windings of the 2 transformers are then wired out of phase on the secondaries, with just one of the 6.3V windings being used for the 6X4 in the hybrid bridge rectifier.

Looks like you could squeeze another mains tx in the box and let us know what happens? :grin:

1 Like
150

I did exchange some emails with Pete regarding Kondo’s use of twin power transformers while contemplating how to build this kit. Still trying to get my head around what the effect of having the pair of them operating out of phase next to one another will be.

As it happens the Nobsound is pretty quiet and it doesn’t seem to be eating its rectifier in the way the M77 seems to but the two transformers ruse might be an interesting thing to try if I build another, more foo-ed up version.

151

There will be some cancellation of any far-field magnetic leakage. But given how big the transformers are the far field will be some way away. It might reduce the extent to which it upsets any other pieces of kit, but I’d be a bit surprised if it had much impact in the device itself. The effect might be more pronounced if they were rotated through 90 degrees about a vertical axis (vertical in real life, not vertical in the pic). Then their cores would be coaxial and the field cancellation stronger.

VB

1 Like
152

It’s like counter rotating platters. It stops the boat spinning.

1 Like
153

fxt

VB

2 Likes
154

I haven’t come up with a plausible, let alone technically robust, explanation but there may be some mileage in it as it appears to be implemented in this Border Patrol preamp

http://imagecdn2.panjo.com/images/sfUCKT2R4zsg.JPG

155

I did wonder whether he’d used two because one wasn’t quite beefy enough (30mA) & Tango weren’t making a single transformer he could actually fit in the case that would do the job!

156

I doubt that’s the issue, all those 12AY7s probably don’t draw more than 10mA in total, making the use of a 3H 250mA choke quite unexpected

157

That’s the most plausible explanation.

Will the arrangement reduce common mode noise?

158

That’s the thought I keep coming back to

159

If it’s common-mode then don’t both ends of the primary flap up and down in synch, so which end is connected to the neutral and which to the live won’t make any difference ? Putting the primaries in antiphase will put the differential mode noise in antiphase too. But this will be cancelled by wiring the secondaries in antiphase so I fear there won’t be any benefits for that noise either. Or have I missed something ?

VB

1 Like
160

Magnetic flux reduction??