F5 power amplifier

[alazira]

Originally Posted by Zen Mod

perfect opportunity to replace crystal ball with little mosfet testing setup

Hey Zen Mod,
Who uses a crystal ball? Tea leaves only!

Certainly a mosfet/jFet testing setup is on my to do list after DAC, open-baffle speaker, battery-powered F5

I'm guessing if I have +DC offset then the N-channel is toast? Hoping to save a swap-out of the working channel mosfet...

[bear]

My batches of Toshiba 2SJ201 and 2SK1530 have been run through my Tektronix curve tracer as of a few minutes ago.

(I thought someone was still relatively current on offering up the same devices in Swap, but I didn't find the thread using the search...?)

Anyhow, I will have a fair number for sale.
That's the good news.

The not as good news is that the two batches did not "group" in a manner where the distribution curves overlapped as much as I had hoped. This means that there are not very many dead on device matches to be had out of the batch. There are a fair number of Pch matches and Nch matches - but they will bias up at different points. That won't be a huge problem as already mentioned in the thread.

This means that my price will of necessity be closer to cost except for the sets (if any that I can sell) that are matched Nch to Pch.

Please wait for my post in Swap Meet, I'll list the available devices and prices early in the week, before jumping in, thanks.

Anyone with a number of J201s that when static bias tested need LESS voltage to reach 1.3amps OR with a number of K1530 that need MORE voltage to reach 1.3amps should contact me for a swap out to get matched sets out of it. PM me if you have a reasonable (4-12 or more) number of "orphans" to offer up...

_-_-bear

[jameshillj]

Prooptiki,
In addition to Andrew's post above (#7643) the actual current pulses that charge the power caps via the diodes is MUCH higher that that again (often 10 times) so the ability of the Torroid to supply these high instantaneous currents is a spec that's rarely included.

So, the 300VA will "run out of steam" for just one channel, unfortunately.

However, you can reduce these pulses by adding a small series resistor between the diodes and power cap (generally about 0.1 - 0.15R) - sound will be much "smoother" and trannie will run cooler.

This is why the use of a 300VA transformer / channel gives better results.

[juma]

Originally Posted by jameshillj

....
So, the 300VA will "run out of steam" for just one channel, unfortunately.
.....

If that is true, I wonder why Mr. Pass is using single 300VA toroid in commercial (stereo) version of F5 which doesn't "run out of steam" even when amp is driving the 2 Ohms load ?

[osscar]

I think that the commercial F5 uses 400W transformer but maybe iam wrong.

[AndrewT]

Originally Posted by jameshillj

the actual current pulses that charge the power caps via the diodes is MUCH higher that that again (often 10 times) so the ability of the Toroid to supply these high instantaneous currents is a spec that's rarely included.

These are always included. That is precisely why the transformer manufacturer tells you, me and everyone else to de-rate the transformer to about 60% to 70% when feeding a capacitor input filter.

That's why the 8.3Aac transformer ends up supplying a maximum continuous 4.2Adc after rectifying and smoothing.

[jameshillj]

yes, thanks, Andrew.

Juma,
So, the 300VA will "run out of steam" for just one channel, unfortunately.
Sorry, mistake - I meant single 300va for both channels

My apologies. In hindsight, "runs out of steam" is a poor choice of words - obviously, Nelson's amps work just fine with single 300VA units - my production F3 is also fitted with a single 300va transformer, block bridges, etc and it works quite well - commercial products have different criteria to DIY.

Now, when DIY, a 300VA / channel for the F5 made a significant change/improvement in the amp's performance that is worth the extra initial design/investment (IMHO) - the same thing applies to the whole power supply, diodes, caps, wire, etc.

For many people, the F5 is the last amp they'll ever build.

Suggestions & observations, not criticism.

[kalinowski]

hello everybody,
I've got 8 of those cool kendeil 4700uF capacitors. What would be the consequences of using only about 20mF per rail instead of 40mF? The reason I ask is I cant get any more of them and I really want them sitting in my PSU.

[Nelson Pass]

I think you already know the answer.

[umut1001]

I have rifa peh169 caps 63v 10000uf x10 pieces.I will parallel them.They are big caps but very high quality.What do you think about it?Are they much more for F5 amp?