Been buying from this place before. Good store but seems they don’t have 1943/5200 trannies.
I saw Digikey and Mouser has. Will be ordering from there i think.
Thx anyway
where Q320 IS LISTED, Q329 is ment. Typo , misprint or scanerror.
Uneven numbers are the left channel.
Elaborate (left ch, top2btm, "//" is parallel):
Q325 - (Q329 - Q337//Q341)//(Q333 - Q345//Q349): 3 junctions
(Q351//Q347 - Q335)//(Q343//Q339 - Q331) - Q327: 3 junctions
3+3=6
Total bias voltage is some ≥ 4Vdc expected. (Calculation of bias net needed.)
Regulated +/-82Vdc is for front stages, neglectable.
I am wrong! The Pd 54W total is ok, but not the classcalc.
Say every branch 50mA, 4 branches per channel. Yields 200mAdc
Swing can be from +200 mA to -200 mA, 400mA toptop total.
Iac is approx 1/3 of toptop value (sinuswave for simplicity), 133 mA.
PclassA = Iexp2 * Zload -> Zload = 8Ω to start with.
(0.133)exp2 * 8 = 0.14W
You can do the bridge mode (twice the toptop value) calculation yourself.
But in the end it proofs to yank up the idle to a max permitted value to prevent nasty switching of bjt's. (Despite more or less succesfull solutions.)
I'd prefer for this reason only classA amps (Iset ≥ 1A); think Hiraga or Pass.
As a rule of thumb, as long as I can keep my hand on the central heating, it's fine. I do not know the NAD designer nor the claim 'n proof.
Good. It is a solid design, Krell-like. If I had to live with an AB-amp, such was the topology.
I'm currently & still developping a class A amp around these 5200-1943 bjt's in an alternative bridged Hiraga with 4-5A idle per side, some 25WA@8. Pdiss is 300W -- not very green...
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Quoting myself is not customary, but I'm wrong again...
I haven't done these calc's lately, so after posting I didn't sleep well until I woke up screaming what I'm quoting now (not customary either).
Vset TP301-303 = 8mV +/- 2mV; Re = 0.22Ω
Iidle = 8mV/0.22= 36mA
4 branches yields 144mA, say 0.15A
Top value before other side switches off (lineair Vbe curve for simplicity) is 0.3A. AC current is (sinus for simplicity) 0.7 * 0.3 = 0.21A
Pa = Iexp2 * ZL (8Ω) = (0.21)exp2 * 8 = 0.35W
This is the same for bridge mode, because it only counts when bjt's switch of running in B mode. In bridge there is a larger voltage swing, but bjt-switching-off is at the same currents.
To prevent to much consecutive posts as were it wirings on social platforms, the bias calc is as follows:
Q323: 2 * Vbe = 1.3V approx, continuous value
Q321: (680+220+100)/(220+100)*Vbe = 1000/320*0.7 = 2.2V min
Q321: (680+220)/(220)*Vbe = 900/220*0.7 = 2.9V max
Total Vbias range Q323 + Q321 = 3.5 -- 4.2 Vdc (expected was 4V)
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Regulators for lower current sections (preamp, regulated VAS, etc) often get put on heat sinks that are barely good enough for the dissipation, and get run that hot 24/7. Hence, all the discolored PCBs and oxidized solder joints you often see in vintage gear. If there is a place to put a bigger heat sink on it, by all means do it.
Have checked fleabay and Aliexpress and don’t find any heatsink that supports 2 trannies in that size. Can only be higher. Packed with components around. Thinking of extending original sink with some copper fins/plates.
Whatabout the main psu caps, they seem a bit on the small side considering ”big amp”... footprint of them is 30x52mm so any bigger wont fit, for example 5600uf/100v is 35mm
Whatabout the main psu caps, they seem a bit on the small side considering ”big amp”... footprint of them is 30x52mm so any bigger wont fit, for example 5600uf/100v is 35mm
The +/-17v heatsinks are quite small they get hot as heck including 2pcs 1k/1w fusible resistors.
Also the other heater have 4x100R /1w fusible too and you can boil egg on those.
A1493/C3788 that are sitting pushed down on each channel doesn’t have a heatsink at all and can’t barely touch them with my fingers.
What was Nad thinking? The S200 looks the same
Also the other heater have 4x100R /1w fusible too and you can boil egg on those.
A1493/C3788 that are sitting pushed down on each channel doesn’t have a heatsink at all and can’t barely touch them with my fingers.
What was Nad thinking? The S200 looks the same
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