Hi, seems everyone wants to talk about the 834, but this is a M7 thread, so here's my 2:
I built the kit a year ago, its a nice kit with everything on the same board but I think there's a flaw in the heater supply section; it imparts a nasty buzz that makes the preamp unlistenable. I don't have a scope so I can't be sure but I think it's a 120Hz buzz. I've been so happy with my 834 that I put the M7 on a shelf and come back to it every 6 months or so, but still haven't gotten any improvement. Now that I'm reminded again, I think the next move is to take the sockets off the board and re-wire the heater pins so I can wire them above the board and just use AC. It's a cathode follower so I think I'll need to elevate that voltage, maybe I can just steal it off the cathode of v3, maybe I need a voltage divider off the b+, can't remember if the board has an easy place to get b+...
I built the kit a year ago, its a nice kit with everything on the same board but I think there's a flaw in the heater supply section; it imparts a nasty buzz that makes the preamp unlistenable. I don't have a scope so I can't be sure but I think it's a 120Hz buzz. I've been so happy with my 834 that I put the M7 on a shelf and come back to it every 6 months or so, but still haven't gotten any improvement. Now that I'm reminded again, I think the next move is to take the sockets off the board and re-wire the heater pins so I can wire them above the board and just use AC. It's a cathode follower so I think I'll need to elevate that voltage, maybe I can just steal it off the cathode of v3, maybe I need a voltage divider off the b+, can't remember if the board has an easy place to get b+...
Hi, I've posted the schematic for the M7 clone in the first post, it might help you. The filaments are already elevated with a tap off B+. Good luck (you're gonna need it lol)
That's an interesting thought. One option, recommended by Bob Cordell, is to use that cap with a series'd 75R across the inputs, as a proper RC load for the "transmission line" of the signal wiring from the turntable.
Another potential motorboating issue is the feedback pole formed by C21/C22 with R24/R26. There're better ways to do the job.
All good fortune,
Chris
Another potential motorboating issue is the feedback pole formed by C21/C22 with R24/R26. There're better ways to do the job.
All good fortune,
Chris
I personally precision hand match resistors in all my builds because I am super OCD (really) and frankly, it's not hard with modern components as most are really close anyway, especially same batch/bag o' parts. However, 20% is normal tube variance... maybe even less than normal. And when you look at circuits for tubes that can go... 33k to 220k plate load R, you have to take in, does the exact value matter? And look at when does it matter. And small wattage, modern resistors with a 20% variance sounds very skeptical to me, if as I said, it came from anything close to a reputable seller. Because those parts in the days of computers in the 21st century... just don't really happen. I guess it's a fair warning to all... you could argue, it's still easier to swap a few parts than acquire and build the whole thing. Me, I would (and did) build the whole thing. But I want people who feel more comfortable buying a complete unit and maybe (if at all) swapping a few parts to feel OK too. Also, since this is a eq network, gain stage variances are probably not that important, in the eq section, they could have big influence as Stephe is pointing out. If you order one complete and it doesn't work as it should, return it. Ebay (and most) protect the buyers first and foremost.
Many of these parts can't be checked without removing them from the circuit, and I don't know how much experience you have returning things to China, their mail service is almost a diode. Fast out, can take 1-2 months returning. IMHO populating the board is probably the easiest part of this build and if someone is going to fab a chassis etc. I highly recommend spending the 30-45 minutes to solder up the board.
Guys not defending the buy it built, cause I didn't. I have been building my own stuff since the 80s. Which some like to say in my age is, you remember the 30s before the war? Same time difference now, it is just 2022. And the return to china off ebay is, your $ is back likely before you even send it back. Again this is many times I have explicitly quoted "having a good and trustworthy seller."
"But I want people who feel more comfortable buying a complete unit and maybe (if at all) swapping a few parts to feel OK too."
So how exactly do you determine which of the dozen people selling this kit from china is a "Good and trustworthy seller" and that they check the component values before soldering up the board?
And again, have you ever shipped anything back to china? In most cases the ebay system won't generate a pre-paid return label to china, it's VERY expensive to ship anything back to china (I shipped 2 defective tubes and it was like $40) and you have to trust the seller will refund the shipping (they refunded like $20 of mine after 2 months waiting). You also have to deal with all the customs forms and generally is a PITA. You basically buy stuff from china on ebay assuming you will throw it away if it's bad.
Like I posted, if someone doesn't have the soldering skills to populate this board, how are they going to be able to solder up all the jacks and other fabrication work this requires.
