as far as I can see - they're identical, no different gens
just connect audio GND ( from PSU pcb) to chassis directly
just connect audio GND ( from PSU pcb) to chassis directly
^ to confirm audio GND to chassis directly, I would connect from the black GND right side of diagram below, direct to chassis?
This is also directly connected to the black speaker binding post, yes?
This is also directly connected to the black speaker binding post, yes?
Thanks ZM. It bothered me to no end that two identically constructed amps with matching PCBs behaved differently regarding measuring points to ground such as C* and U-. Close inspection and detection w/ DMM revealed monoblock #1's SIT mount belleville lock washer was just touching one of the wire end eyelets at the drain effectively grounding the device. So even without the audio GND to chassis installed, C* to chassis read normal at ~ 32V. Monoblock #2 did not.
Corrected that mount, added the grounds using the pre-drilled heatsink mounts close by to black speaker binding post. #1 measuring well so far heating back up now.
Corrected that mount, added the grounds using the pre-drilled heatsink mounts close by to black speaker binding post. #1 measuring well so far heating back up now.
First monoblocks test as a pair. Donovan on vinyl Sunshine Superman > Dual 1019 > PSIII phono Pre > IronPre > LSB monoblocks > tiny test JVC fullrange bookshelfs.
Before dropping the needle, no untoward extraneous noise. With signal, what a pleasant sound emerging. Forthcoming through the main system is the next step.
Before dropping the needle, no untoward extraneous noise. With signal, what a pleasant sound emerging. Forthcoming through the main system is the next step.
Now: Sony X77/ES>Monarch DIP>Project DAC Box E > IronPre > > 6-24 crossover > LazySingingBush monoblocks > Altec 420a open baffle. And 6-24 crossover low end to M2x > SLOB 15" beta.
Homage to ZM, Miles Davis Fran Dance. No harshness on the benchmark horn section. With Pat Metheny, these amps do dynamics really well, the quiet sections are wonderful.
I have the Altecs paired with their original console cone tweeters with Solen caps. Dead, dead silent with ear against tweeter.
Good fortune the heat has subsided for a few days, these are going to be great in late Fall, Winter early Spring.
I understand what folks were saying re: low THD and exceptional clarity. Nice amps, thanks very much.
Homage to ZM, Miles Davis Fran Dance. No harshness on the benchmark horn section. With Pat Metheny, these amps do dynamics really well, the quiet sections are wonderful.
I have the Altecs paired with their original console cone tweeters with Solen caps. Dead, dead silent with ear against tweeter.
Good fortune the heat has subsided for a few days, these are going to be great in late Fall, Winter early Spring.
I understand what folks were saying re: low THD and exceptional clarity. Nice amps, thanks very much.
Recalling an earlier Nelson Pass quote: "Heat sinks should stabilize at a temperature at which you can put your hand on the heat sinks for about 5 seconds. This is between 50 and 55 deg C, and is the ideal figure. As mentioned before, you should consider better ventilation or less bias if the heat is much greater."
Running the two Lazy Singing Bush monoblocks, observed the SIT side heatsink on amp #1 warmer than the Mu Follower side, and the inverse on amp #2. Since they are identical that prompted further investigation. I had never done more than the hand test.
I have a filthy old infrared thermometer used for old cars, wiped off the grease and installed a fresh 9V battery. Validated the hand test ~ 50 degree on the cooler sinks and ~ 55 C on the warmer ones. Opened up the amps and measured again w/ DMMs.
#1 stable at 64V rail, 32V C* to GND and 641mV at R4 mu PCB. Good.
#2, C* to GND a bit low at < 31V, adjusted SIT side trim pot to provide 32V. Across R4 measured 619mV, too low and over 3 percent lower than ideal. Maxxed out the mu trim to yield 639-640mV across R4.
Heat sinks on both amps now in the 53 degree C range and more uniform side to side, top covers secured, back to listening mode.
Running the two Lazy Singing Bush monoblocks, observed the SIT side heatsink on amp #1 warmer than the Mu Follower side, and the inverse on amp #2. Since they are identical that prompted further investigation. I had never done more than the hand test.
I have a filthy old infrared thermometer used for old cars, wiped off the grease and installed a fresh 9V battery. Validated the hand test ~ 50 degree on the cooler sinks and ~ 55 C on the warmer ones. Opened up the amps and measured again w/ DMMs.
#1 stable at 64V rail, 32V C* to GND and 641mV at R4 mu PCB. Good.
#2, C* to GND a bit low at < 31V, adjusted SIT side trim pot to provide 32V. Across R4 measured 619mV, too low and over 3 percent lower than ideal. Maxxed out the mu trim to yield 639-640mV across R4.
Heat sinks on both amps now in the 53 degree C range and more uniform side to side, top covers secured, back to listening mode.
^ right now, Boulez conducts Stravinsky, the Cleveland orchestra. Clarity, detail, beautiful amps. In the pic, they're back panel to back panel lower right, one sitting on top of the SissySIT recently completed.
Like you, I also listen to local college radio on an old Sansui TU-517. And old vinyl.
Like you, I also listen to local college radio on an old Sansui TU-517. And old vinyl.
^ you may be right about that. It was a bit of a hack mounting the Altec 420's. Rather than modify the original Speaker Camp lovely cherry baffles which were originally housing the Moths (since sold), I wanted to see how the 15" did up top. I can easily fashion matching plywood plates to cover the helpers and hear the difference. Probably also a good idea to ask gurus on the speaker forum. If the advice is to cover, I could enlarge the baffle mounts to accommodate the Altec's and their cone tweeters. That would mitigate the fulgyness. 😆