Help with Onkyo M-501

[jimmyjazz]

Grabbed a mint Onkyo M-501 the other day for the express purpose of trying to "tweak it up". My brother-in-law is in on the project. He has an extensive background in audio repair, along with a EE degree.

I'm looking for any tips on areas to target first, and where we might get high quality parts in low volume. I'm not against spending a couple hundred dollars more on the thing -- this is just for fun, anyway. Thanks in advance for any help,

jim

[SY]

What aspects are you trying to improve?

[jimmyjazz]

In my naivete . . . everything? (Not power output, but I'd like to see if I can drop the noise floor, increase separation, beef up the power supply, things like that. Believe me, this is a fishing expedition.)

[SY]

Naive boy!

The separation in these units is generally limited by stray capacitive coupling. I'd take a close look at wire routing and grounding to see if there's anything obvious that can be improved- don't be surprised if the separation is already way better than you'll ever need.

Noise will usually be limited by grounding (particularly power supply hum and buzz) and the input transistors (hiss). I'll be surprised if you can actually hear any noise unless the power supply caps are failing, but you can potentially make the test bench results look better. If the input stage uses a tail resistor, changing it to a constant current source will slightly improve power supply noise and possibly reduce distortion.

Component swapping is a suckers game; special wire is even a worse con. It's less glamorous to redo grounding and wire routing, and there's no designer parts to show off, but if you want to squeeze the last bit of performance out of the amp, that's probably your best bet.

[jimmyjazz]

Thanks, I'll definitely take a look at the layout and grounding scheme. If I do mess with components, would bulk capacitance be the place to start? What about the power devices -- are there more modern equivalents that might be better?

I'm not against just giving her a tuneup and buying more years of service.

One function question: I know the 501 is intended to be triggered by a 301 preamp for 2-channel service. Can that be bypassed internally, or is it better to consider conversion to a monoblock and grabbing a 2nd unit? That sounds kinda fun in and of itself.

[SY]

Bulk capacitance can sometimes be useful, but you have to consider the effect on charging and ripple currents- it can sometimes degrade performance. If you're planning on running high power at very low frequencies, there can be a benefit. If it were my amp, I'd replace the power supply electrolytics with newer, lower ESR caps of about the same value (avoiding "audiophile" brands) and high temperature ratings (105°C) for reliability, then look for ways to shorten the wiring path from the caps to the circuitry.

[ostripper]

Nice amp
ONKYO M-501 SM Service Manual free download, schematics, eeprom, repair info for electronics

, worth the effort. "blameless" (lin - IPS/ CM/CCS-VAS) topology
(below 1) with a triple output. 2 -10Kuf /80V PS caps. Most likely 4 pin/ 20mm lead spacing. Mouser has the 4 pin panasonics up to 15k/80V.


Here are the skinny -tall ones 40mm X 80mm
ECE-T1KP153FA Panasonic Electronic Components Aluminum Electrolytic Capacitors - Snap In

the 12.5K's are 35mm X 80mm

ECE-T1KP153FA Panasonic Electronic Components Aluminum Electrolytic Capacitors - Snap In

Re-grease the op's , replace all the small electrolytic's , there are not many in this amp. Nichicon/panasonics are highly recommended.

Semi's are already high Ft modern devices , this amp is essentially the blameless I just built with new parts.
OS

[jimmyjazz]

Thanks! I had already downloaded the service manual. It will mean a lot more to my brother-in-law than me.

I'll have to look up the "Blameless" amp.

[yldouright]

ostripper

Is the 5160 the same circuit? What has changed between this and the 501?

[rhtatro]

I own both M-501 and M-5160, off ebay. The 501 uses discrete output transistors, 4 per channel. The 5160 uses two STK-4048V Sanyo chip amplifiers. Discrete is supposedly better, the chip amps are more cheaply produced. Average listeners are not supposed to tell the difference, I guess.
I am curious to know if the 4048V can be directly swapped with the better 4048XI chips with no mods? Anyone?