amp new PSU capacitors

If it ever goes wrong I'd consider that upgrade. But at the moment it does its job adequately.

That's still 400w average power.

There are life issues too, derate working voltage to 60 or 70% of spec and they last 10x longer. Similar issues with temp, 105degC caps last forever when derated.

Spec'd life at max temp and voltage on an electrolytic is rarely impressive.

foolish strategy.

I see HDMI doesnt contain analogue output :/ Trouble with using hardware to keep up with digital standards is they keep changing.

NT

draw =A0an "equivalent" circuit of any amplifier, you will see that the po= wer supply shows as being in series with the load.

r supply. This means that you should choose ps components as carefully as y= ou would for example speaker crossover components or any other component in= the signal path.

t your theory. Hang the cheapest on temporarily.

Actually for a sine wave the mean power is half the peak power. It is the voltages that are in the ratio of 1/root(2).

Not seen the initial postings in this thread as it has only just started being xposted to uk.rec.audio. However, the above depends on details like if the amp is single-rail or dual-rail.

For example, for 100wpc (mean for sinewave) into 8 Ohms you'd need +/- 40V rails as absolute minimum in a dual-rail design. If it were a single rail then you'd need 0V and a 80V rail as absolute minimum. In practice a real-world design would need headroom to drive the devices, so 0 - 80V single rail would get you somewhat less than 100 wpc (sinewave mean). Then if you also take into account that the PSU will probably 'sag' under sustained load you'd find that 80V single rail would be much less when you are trying to get sustained sinewave power from both channels of a stereo amp.

So in practice you might find that 0 - 80V single rail ended up giving you far less than 100wpc mean sinewave stereo. (Although peak levels for music could be somewhat higher.)

And as I see someone else has pointed out. You also would be safest choosing a cap whose spec voltage was well above the actual rail voltage when the amp isn't sagging the voltage. Hence an 80V cap would be sensible for use with a somewhat lower rail voltage.

Slainte,

Jim

Otherwise its about - with PSU sag and a safety margin the square root of two times half the voltage minus about 15v, so 24v rms Or in power terms about 132W into 4 ohms

Unless its split rail with two 80V caps, or an H bridge..in which case yes, its abut 400W.

?

wrong:

Oh dear. I guess the 16 years i spent designed audio power amps was completely wasted?

Fairly ordinary domestic power amps run with +/- 40 or 50 v rails.

The full rail voltage won't appear on the output ( unless the one of the Output Devices have gone S/C ).

on

Youre fond of asuming too much

"fred"

Electro life is not related to DC operating voltage, unless the rated limit is exceeded then it is VERY short.

Electro lifespan is all about the quality of the airtight seal in the end of the cap - cos the end of life occurs when most of the electrolyte has escaped as vapour through an imperfect seal. The rate of loss of electrolyte is a function of the local ambient temperature and ripple current ( if any) heating the electro.

Long life electros come in both 85C and 105 C types - all that is different is the quality of that seal.

..... Phil

"The Natural Philosopher"

1. If the filter electros are each rated at 80VDC working and one sensibly allows for higher than nominal AC supply - then the *unloaded* DC rails are likely to be +/- 74 volts.

2. If the AC tranny is of conventional design ( toroidal or E-core) then the regulation factor is such that the average DC rail will drop under load by about 12%.

1. If the capacitance is a typical value like 6800uF for one channel - then the p-p ripple voltage under steady load is about 4 volts - more if the audio test frequency is under 100 Hz.

2. An output stage is never able to swing to the full extent of the available DC rail voltage - particularly so if the output devices are lateral mosfets. Assuming a typical complementary Darlington output stage with emitters supplying the load - the output can swing within about 5 volts of the available supply with an 8 ohm load.

Adding this up we have:

So the "rms" power on sine wave into 8 ohms will be 210 watts.

..... Phil

No. 58 volts peak TO peak.

No, slightly over 50W.

Ok I see you are talking about split rails. I read the above too quickly. I don't think the OP mentioned that he had split rails.

So your analysis is correct for what equates to a +-60V supply.

However I have yet to see that sort of power and arrangement outside some pro audio kit.The semiconductor cost is pretty high above 100V.

?

wrong:

To be a pedant - its not a strategy, it was a heuristic ;-)

When you think that an amplifier is in its simplest analysis a voltage (or current) modulated variable output power supply, you appreciate the PSU is a fairly critical part that is actually in circuit with the load.

Fairly NON critical part actually. Since the feedback that controls the output is taken from across the load, not the power supply.

That is the trouble with 'simplest analyses'..