Recent content by mbz

The switch consists of 2 tracks which run most (3/4?) the length of the switch. 4 sliding contacts run on the tracks, the contacts are housed in a plastic hood/holder. This holder is a barrier to any deoxit sprayed from above through holes etc. If the far end of the switch is open, you might get...

Before work begins, a baseline performance measurement would be interesting, ie, THD+N freq resp, FFT While the amp is almost fully discrete I'd be against wholesale transistor replacements for the reason given by Semanon, if transistors are faulty then bo option. Switches (base, mute...) will...

For best performance TR602,3 should be hfe matched, better than +/-5. Don't get bogged down with trying to align all voltages to the schematic, eg. the +/-50 +/-B rails are never 50V. Not sure I follow. TP1,2 is about setting up a 1mA current source to feed the diff pair. If you can adjust...

As per the Getting Started Wiki/link above, depending on what you are measuring/doing

Haven't done any work on quasi-complementary so below would be a guess, happy to be corrected by those that know.

Under "Generators" select the bottom option FreqResponse, see https://github.com/QuantAsylum/QA40x/wiki/Getting-Started This will generate 1 trace for the amps tone settings. Would expect that you would repeat this 10 times for each "turn-over" freq 250Hz and 500Hz and then you would need to...

Haven't been following but looking at the schematic, yamaha has provided some good test points eg, Pin 1 (Preamp left in), 2(Rin) Pin 13(Power amp left in), 14(Rin), schematic has an error lables pin 12 as Rin Tracing at the base of driver transistors along with the wipers ov vol/bass/treble are...

It's just a frequency response with different tone settings. The shape is dependent on amp performance, ie, position of switches. Maybe the QA403 can overlay the 10 seperate traces???

Plots from another amp that only has the one corner frequency, the CA offers a choice of 3, none, 250Hz, 500Hz. The start point of the "divergance" moves depending on if 250/500Hz selected, likewise for treble. The point is to boost the low/high levels to make up in short comings of spkrs, room....

Hard to see 60V anywhere when amp has +46V rails. Note 60V+10V / 2 = 35V, make me think you have a grounding problem, suggest remeasure with black meter probe inserted into any black speaker connector/post. Emitters of output transistors should be at less that 100mV on both channels so 35V on...

I would have thought that a KR-7400 would be worth the effort... With no significant DC offset the relay should kick in, maybe a simple fault in the protection circuit. First up, verify no significant DC offset. Measure dc voltage at midpoint between the emitter resistors Rm41, Rm43(L) and...

Was TR605 "round face to heatsink"? Thinking TR602, consider replacing TR602,603 with a hfe matched pair. Possibly TR604 is in saturation so bs in = bs out pointing to TR602.

Guessing Q14 is breaking down under load. Headphones are an easier load to drive, typically 30-300ohms but speakers 8ohms demand higher current. By the numbers with scope test for distortion at Q12base (ok?) then at Q14b (notok?) Also check for distortion at Q8b and Q10b.

Pinout is ecb, round face to heat sink(I always get that wrong...)

Suggest replace. Odd size for a fusible, if they are supposed to be 1.2ohms then they should read ok in circuit.