However, the load on the power supply rails at rest is 1.3 amps, rather than the load being nil or nearly nil for a class B or AB (low bias) amp. So there will not be a "dive" in the rail voltage as the amp draws current during normal signal excursions.
This might have some sort of sonic effect as a drop in rail voltage will also cause an effective drop in gain which in turn must be made up by additional gain (assuming feedback) in order to maintain linearity.
_-_-sleepy bear
why does a ClassAB amplifier modulate the supply rails?
Hint: something to do with supply impedance at the frequencies that the amplifier modulates the amplifier rail current.
Why should a ClassA amplifier modulate the supply rail voltage exactly like a ClassAB amplifier?
Hint: because the PSU also has a supply impedance at the frequencies that the amplifier modulates the amplifier current.
The big difference is that the ClassAB modulation consists of halfwaves which have HF content way above audio frequencies.
ClassA modulates the current at audio frequencies and the HF only becomes signficant if or when it moves out of ClassA into ClassAB, i.e. on transient current peaks.
Hi there
I am currently at page 176, only another 438 and counting!
I have built various chipamps over the last couple of years and now fancy having a go at Nelson's 'F'-series. I have heard that several versions can use the same unregulated power supply. Can I build one power supply to work with entire range? If not, which models are compatible with the supply below?
I am also trying to source an enclosure with a suitable heatsink.
modushop.biz
Would someone be kind enough to check the attached PDF and let me know which model would be suitable?
I will also be driving a pair of Brines FT-1600 Mk2 Speakers
Thanks for your help
I've build a F5 with a 3u case (40 cm) long and it is not very warm. I am planning to see if a 2u case will suffice. IMO a 5u must be overkill.
- F
Hi Folkeb,
Do you have the amp outside in the snow??? Just kidding
I have used the 40cm 4u and 30cm 5u and both get hot enough for me to not contemplate on going down in sink area. The 40cm 3u is probably very efficient compared to the others because it is relatively long compared to the height.
Christian
Banned
Joined 2002
Here is a nice selection of cases,
Chassis case item
Drop down to this one, its 160$ i think for the case, with sinks and all :0
PWAD-A40 Alum. Chassis for power amp.
Heat sink suitable for 30W+30W stereo or 60W under Mono Class A,
Overall size: 48cm(W) x 26cm(D) x 11cm(H)
Body size; 47 cm (W) x 25cm(D) x 10cm(H)
Panel size: 48cm (W)x 11cm(h)
Thickness: body(1.1mm), panel (6mm)
Heat sink size: 25cm(D) x 10cm(H) x 3.5cm(Thick) , with
2 pcs of heat sink
Pre-cutout/hole:
Panel Main switch; 23 x 13mm( recess 38 x 23 mm)
Led hole: 3mm dia
Back Panel; 2 hole for inputs(10mm dia)
2 set of speaker out(each with 4 hole of 10mm dia.)
Power Switch: 28 x 20 mm cut out
fuse hole in 12.5mm dia.
I don't the PWAD-A40 heatsink is large enough. It appears to be less than half of the dissipation recommended for the F5.
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Banned
Joined 2002
The quality of the variable output may not be extremely good - depends on which player you have of course. I currently use the F5 with a passive preamp - works nicely, but you may need some gain if you want to get the full swing.
Attennuator on your CD is probably buffered
Its there, and if you cant bypass it, by say a second output with full output,
You may just as well use it, fore the time being, until you know how your F5 works with your speakers
That will determine whether you will need a preamp with gain
I may try Broskie new CCDA tubepre
But I will have a "passive" Lightspeed and B1 as well
A Seifert KL145 sizes 200mmx40mm, has 19 ribs, 100mm length does 0.6C/W
A Seifert KL146 sizes 300mmx40mm, has 29 ribs, 100mm length does ~0.4C/W
The PWAD-A40HS sizes 250mmx39mm, has 24/25 ribs, 100mm length should be around 0.5C/W
That figure is not yet corrected for 50-55C range operating.
Very unlikely that a single of those heatsinks will suffice to handle the +60W of an F5 channel without crossing the 55C mark, it will need a band-aid to do so.
The PWAD-A40 is a 35mm type, ribs are 4mm shorter (or the base plate is much thinner), not a chance in H it'll be good enough for an F5 channel.
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