Nicely laid out bench. Especially the cabling between pieces of equipment. Neat and clean

@NovaluxStereophonic

8 ай бұрын

Thank you!

Awesome video. Cant wait til this weekend and I will break out my Fluke and see where my 1250 is at present, then set it to 75 and see how she percolates. (my 1250 is totally rebuilt and has new trimpots so its much easier to dial things in)

I'm firmly in the camp of lower bias, because I doubt there's a person on the planet that could hear the difference. And the reduction of heat is so beneficial for the longevity of the unit. I had a Marantz 2325 on my bench, and it ran so stupidly hot when biased per the manual I just had to dial it down. The owner was good with it. You've got a great channel here, and your bench is extremely well thought out!

@NovaluxStereophonic

4 ай бұрын

Thank you Ray! Credit to you for starting a chain of events that eventually led to my acquisition of a VP-7725. Excellent piece of equipment.

@raygianelli3612

4 ай бұрын

@@NovaluxStereophonic LOL. I've probably sold more of those than Panasonic did! 😝

I’ve had numerous units come bk from stereo rehab with bias set to eliminate crossover notch and they are set between 10-27 mv. Heat sinks run upper 70’s F .

Awesome work Ben

I have some info for you , from, the Harmon Kardon Citation 16 service manual. The output stage of the HK is a "Quasi-Complimentary class AB" design, I don't know how much it differs from the SX-1250, but here is some info from the Citation 16 service manual That amp, idles what most would consider as HOT, and the manual says it may be up to 60 Deg C on the heat sinks, BUT, it gives a reason for this. (direct quote) " Most Class AB amplifiers operate in class A until about 0.1 watt of output, and in class B for higher power levels. While class B offers greater efficiency, it also introduces crossover notch distortion which has been identified by some as the cause of harshness and "transistor sound". Psychoacoustic studies have shown that audible crossover distortion is eliminated if the transition from class A to class B is 17dB below full output, or higher. This calls for more extensive class A operation than conventional class AB amplifiers offer. On the Citation 16, the level17dB below full output corresponds to 2.5 watts, therefore, the Citation 16 is biased to operate in class A up to 2 watts." Also quoted , " Because the output stage is driven so far into class A and requires substantial bias current at idling, sustained idling will bring the heat sinks up to about 60 deg C. At one third of full power output, the transistors are the hottest. Sustained output at one third power will increase the heat sink temp to no more than 80 deg C. At Full output, the temp of the heat sink is typically 75 deg C." I have seen some forum comments on biasing a Citation 16, at least one was concerned that the bias was too high because of the heat, but the design of the amp and meeting its spec's depends on the correct setting, and dissipating the heat from the output stage. The bias setting on a Citation 16 calls for "A measurement of 50 mV across a 0.5 ohm emitter resistor", so, 100mA. I own 2 of these fine relics, needing a good going over, and I am sure I will re-grease al of the outputs before putting it back into service, as well as testing the 90 deg C thermal cutoff switches designed into them. Thank you for the time and work on this subject.

@NovaluxStereophonic

Жыл бұрын

The SX-1250 uses a true complimentary output stage but the concept still applies. Thank you for posting this, great info!

@poormanselectronicsbench2021

Жыл бұрын

@@NovaluxStereophonic You are welcome. I covet one of those Panasonic distortion analyzers, but a working version of one is scarcer than hen's teeth, and expensive as all heck if you do find one. I do have a few low end digital scopes that can display a FFT screen though, and I worked out a spreadsheet calculator to calculate THD from the level of the first 5 harmonics relative to the test signal, but I also need a low distortion test signal. I will admit electronics as a hobby is a fun pursuit, but things add up when you start collecting test equipment.

@NovaluxStereophonic

Жыл бұрын

@@poormanselectronicsbench2021 I was extremely lucky to find one. I tried to buy a lower end model from overseas and it arrived not working. When this one came up I jumped on it and drove over 5 hours one way to pick it up. Calibrated in 2020. I suppose this graph was likely made in a similar way to what you describe maybe with a spectrum analyzer back in the day? I was using a Tektronix rig before this that you can see in some of my other videos which served me quite well but the oscillator in the Panasonic is on a different level. I misspoke on the specs. Its actually .0001%

Great info once again! 🔥🔥

Great video! This jives with my findings as well. Subjectively listening though, I "think" the 1250 sounds a bit sweeter (softer?) at the 100mV setting, but there's not much in it.

Really like your videos Ben, very informative. In your opinion how does the quality of sound differ between the SX-1250 and SX-1280 in regards to what seems to be better TDH on the SX-1280. I'm thinking about purchasing either the 1280 or the 1250. I'm leaning more toward the 1250 since the output transistors on the 1280 are no longer manufactured. Thanks! Ron

@NovaluxStereophonic

Жыл бұрын

Sorry, I am not able to answer which one sounds better. Too many variables including room, speakers, source media, personal preference, etc. I would make the decision based on 1. Which one you like the looks of better and 2. Serviceability, SX-1250 is easier to work on an doesn’t have unobtanium parts.

One other thing Ben, do you know anything about the Yamaha A-S 2200 integrated amp and what classification the amplifier is in this unit. Thanks"

@NovaluxStereophonic

Жыл бұрын

I do not have an experience with that model but the vast majority of amplifier designs are class A/B