Do any of you know if Kondo (Audio Note Japan) uses a regulator on the heater supply for the Ongaku M77 preamp? Looking at pictures on the web, I see a TO-3 package... but it could be a slow start, a capacitance multiplier, a regulator, or something else. In my DIY, I identify products that appeal to my leanings and learn from them, but I haven't been able to crack this nut.
Thanks muchly.
Thanks muchly.
quick google images search is suggesting plain bjt as series reg element
however , taking in account that indirect heated tubes are used , that is hardly issue of esoteric importance
when I'm going overkill , I'm using CCS per heater , voltage or current regulated , depending of tube type
so , no biggie
however , taking in account that indirect heated tubes are used , that is hardly issue of esoteric importance
when I'm going overkill , I'm using CCS per heater , voltage or current regulated , depending of tube type
so , no biggie
Thanks very much Zen Mod. I saw the device on the pictures on Google, but couldn't make out a part number to be sure, nor see how it is used. I know some schematics floated around a few years ago, but I can't find them. My friend and I are well into a build that is highly influenced by the M77, and we are finding that, even with a combined 60+ years of fiddling with this stuff, we are still surprised by some things. I would love to see the schematic of the real McCoy.
https://www.google.rs/search?q=Kond...bUhPHOAhVjDMAKHToGAOYQsAQIJw&biw=1440&bih=738
https://www.google.rs/imgres?imgurl...PHOAhXJKcAKHahvD-MQMwgcKAAwAA&iact=mrc&uact=8
it seems good ole 2N3055 is in case
as I said - not much voodoo in indirect heated tubes heating ....... elevation on proper potential , enough filtering etc.
https://www.google.rs/imgres?imgurl...PHOAhXJKcAKHahvD-MQMwgcKAAwAA&iact=mrc&uact=8
it seems good ole 2N3055 is in case
as I said - not much voodoo in indirect heated tubes heating ....... elevation on proper potential , enough filtering etc.
The Douk schematic is not identical to the actual Kondo, for example a genuine M77 has a rotary selector switch, the Douk uses relays. Not relevant to the discussion other than to illustrate that it is not identical. Also the Douk, which is the schematic in JonSnellElectronic's post, looks to be an inrush current limiter, not a voltage regulator. I appreciate everyone's input, but I am not sure that I am there yet.
tubesandhorns told me he was posting on this topic, I'm his partner in crime on the preamps. tubesandhorns, if I'm hijacking your thread, please feel free to come over and slap the fool out of me. 
After having stared at the Douk board quite a bit, it has a lot of stuff that does not appear in the internal pics of the Kondo M77, namely lots of relays (one is a slow start that shorts out both a series 2k in the B+ as well as the collector to base 500 ohm pot on the 2N3055 circuit, another engages/disengages the phono stage heaters). The relays seem to be the only parts connected to the 7805 regulator.
I haven't been able to find a real Kondo schematic of the M77, but one of the M7 is easy to find with a Google search, and it has the 2N3055 circuit very similar to the Douk schematic. No relays though.
It's my guess that the folks that designed the Douk circuit wanted to include relays to switch signals, provide a slow start, and switch off the phono stage filaments when the stage isn't in use (all not in the original Kondo circuit perhaps), so they added a 7805 on the output of the 2N3055 circuit to power the multiple relays. I found if the input voltage to the circuit isn't stiff enough, the relays switching on the phono stage filaments can cause a race condition that makes the slow start continuously cycle.
IMHO all those relays are engineering band aids. But the phono stage on the board sounds amazing once all the BS is weeded out.
Still looking for a real M77 schematic however....
After having stared at the Douk board quite a bit, it has a lot of stuff that does not appear in the internal pics of the Kondo M77, namely lots of relays (one is a slow start that shorts out both a series 2k in the B+ as well as the collector to base 500 ohm pot on the 2N3055 circuit, another engages/disengages the phono stage heaters). The relays seem to be the only parts connected to the 7805 regulator.
I haven't been able to find a real Kondo schematic of the M77, but one of the M7 is easy to find with a Google search, and it has the 2N3055 circuit very similar to the Douk schematic. No relays though.
It's my guess that the folks that designed the Douk circuit wanted to include relays to switch signals, provide a slow start, and switch off the phono stage filaments when the stage isn't in use (all not in the original Kondo circuit perhaps), so they added a 7805 on the output of the 2N3055 circuit to power the multiple relays. I found if the input voltage to the circuit isn't stiff enough, the relays switching on the phono stage filaments can cause a race condition that makes the slow start continuously cycle.
IMHO all those relays are engineering band aids. But the phono stage on the board sounds amazing once all the BS is weeded out.
Still looking for a real M77 schematic however....
boyz , you're grinding teeth on irrelevant things - filaments and relays and whatnots
what's important , learning and/or cloning/building wise is proper and exact schematic , and study of materials and type of parts used in original Kondo gadget
relays aren't inferior to rotary switch , some other things are way more important than that choice (switching device) , say signal routing and other things on that level field of analysis
what's important , learning and/or cloning/building wise is proper and exact schematic , and study of materials and type of parts used in original Kondo gadget
relays aren't inferior to rotary switch , some other things are way more important than that choice (switching device) , say signal routing and other things on that level field of analysis
Yes and no. There are debates, as you know, regarding sonic impact of heater regulators... so I look to the masters for insight. Lamm and I think ARC use them, but I don't think Kondo does. I am trying to verify and figure out why or why not.
And yes, there are bigger fish to fry, but I intend to fry everything. Like in the movie "The Martian"- you do the math and solve a problem, then solve the next one, and so on.
And yes, there are bigger fish to fry, but I intend to fry everything. Like in the movie "The Martian"- you do the math and solve a problem, then solve the next one, and so on.
maybe you did , maybe didn't read it - The Tube Preamp CookBook by A. Wright
great book , not just from tech. side
btw. the other book is great read , too
The SuperCables CookBook, The TubePreamp CookBook
great book , not just from tech. side
btw. the other book is great read , too
The SuperCables CookBook, The TubePreamp CookBook
I'm in agreement with all you are saying, but what we are trying to do is overcome shortcomings in this particular PCA. In my case I have very limited time to do any sort of clone, but have high sonic expectations. So I wanted a PCA that had a decent topology IMHO (no NFB anywhere except where unavoidable like cathode bypasses and followers, fewest # of active components in signal path) and the M77 PCA was the only thing we found in the ballpark. We know the Douk M77 PCA is in no case a M77 clone, but might be a good starting point to a nice phono preamp/line stage.
We found that the PCA had some good design in it, but a lot of band aids that look to me like an attempt to fix problems the PCA introduced. While the phono pre and line stage block look fairly good in layout, the signal switching is horrible (all signal paths travel on perfectly parallel and unisolated traces around 0.05" apart for almost a foot on the edge of the board to the relays). This is unacceptable IMHO, and certainly not in the Kondo M77.
We also found the heater supply on the same PCA introduced a tremendous amount of 120Hz noise, moving it off the PCA removed the majority, and adding a regulator got rid of the rest. The B+ supply seems very quiet as is. And we suspect the sensitivity to heater supply hum is due not only to the huge currents from the heater bridge/first filter cap on the PCA, but also to the large heater PCB traces weaving through the high gain signal section (probably the low end RIAA boost doesn't help either).
So if anything this project has demonstrated the value of point to point wiring over PCBs; it is much easier to control coupling and leakage paths in some cases. I have been designing high performance PCB's for decades, and strongly believe PCB's have their place, but the layout is critical and the Douk board has some significant shortcomings. But I am very glad we started the project as after the supply issues have been worked out, the phono stage sounds outstanding, much better than I expected. I'm very confident we will meet our sonic goals after we find and fix the PCA shortcomings.
Original M7 Schematic
An externally hosted image should be here but it was not working when we last tested it.
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