When I was a kid I had a book written by Michael Palin & Terry Jones post Python but before Palin did Ripping Yarns. It was called Bert Fegg’s nasty book for boys & girls.
In it, amongst many funny pieces, was an item called Build your own 747. It described how the keen amateur constructor could readily build a full scale working 747 from some wood, chicken wire, curtains by mail order etc. I’m sure they were satirising the DIY & Hobby books of the 50’s & 60’s when making stuff for yourself was the only realistic option. With that spirit of grandiose ambition, I decided to try & do the same with the Kondo M77 Pre-amp, ‘kits’ of which have begun appearing on ebay. I say kits. DoukMall supply a pcb and a mains transformer but no valves or case or instructions. I bought a flatpack, ostensibly similar looking (non copper) case from another Asian ebayer, SepStore & I was good to go. You can buy the pcb fully populated & supposedly tested if you want but I bought a lower cost version without all the power supply & signal coupling capacitors as I had, or could readily get, all of the values
The items arrived just after Christmas, The pcb is actually quite a nice thing (despite being 'Desgined by Nobsound) & came with all the components located but not soldered in place. I suspect that whoever did it may have addressed the propensity for the M77 to eat its 6x4 rectifier with annoying regularity. They’ve also incorporated relays (not quite sure why yet) and the provision to run the phono stage alone and take an output directly from it. The layout also includes the provision to include a choke in the psu as the real thing does so I found something of roughly an appropriate size in my junk box. But I’m sure there’ll be a Hammond item you could use.
I spent a short while this afternoon drilling a few holes in the base plate to take the transformer and the stand offs that will support the pcb. This is a view from the right side. The rear of this pre is to the right of the picture.
I think the schematic for this pre got out when some Asian owner traced the circuit and put it online a year or two ago. Having studied some pictures of the real thing I think some of the values as this is supplied might be close but not quite correct so where I can I’ll use what I think they should be.
I had the opportunity to listen to the real thing on some Vox Olympians up at Definitive on Friday & it’s still a fine & very enjoyable item. I think that much of its sound comes from the wholesale use of Tantalum film resistors and their inhouse made silver foil capacitors along with silver wire used throughout. It would be quite easy to splurge several hundreds of pounds on trying to replicate that even if the effects of hard wiring & the copper chassis are disregarded but that isn’t the point of doing this. The other issue is the availability & price of 6072 (12AY7) valves. I have 4 GE ones here and I may just buy 4 more of the supposedly adequate EH items and use them in the less critical positions.
Anyhow I’ll keep a little blog of this as it comes along. I’m intrigued to see what it actually does end up sounding like.