F5 power amplifier

[Nelson Pass]

The F5 sounds different.

It is more detailed, wider bandwidth, and is more aggressive regarding
dynamics and speaker control. The Aleph 30 is a little more laid back.

The decision would tend to revolve around the speakers and your
taste.

[Jozua]

Nelson

My Aleph30 clone when used with the Krell 7b pre-amp sounds exceptional with 1 meter long Newform ribbons. I find it extremely musical. With a 600 VA transformer the control is outstanding. I rate it as one of the musical amps I own.

I am collecting parts for the F5 and Aleph J for a possible bi-amp scenario. It would be interesting to see how a F5 with just two output devices per channel will compare,

Regards and many thanks for putting the design within the public domain.


Jozua

[tinitus]

Sounds like a low gain tubepre could be the soulmate of F5
I might try that

[Diomedian]

Originally posted by Jozua
many thanks for putting the design within the public domain.

To be clear, the F5 is _not in the public domain - it remains copyright First Watt (as far as I know). All we've been granted is use of the design for personal DIY use. But I certainly join you in the chorus of thanks to Mr. Pass for his generosity and for all his contributions to the community.

-j

[sangram]

Originally posted by tinitus
Sounds like a low gain tubepre could be the soulmate of F5
I might try that

If it's not too much trouble, could you share that separately? I'm looking for something similar eventually, and need all the help on tubes I can get. Thanks

[AndrewT]

Hi,
power just the mains side with ONLY the transformer connected through a bulb tester.

Switch off.
Add the rectifiers and ONE bank of smoothing.
Test again.
Progressively add each bank of smoothing and retest.

Now add one channel of amplifier and test.
Add the second channel and test.
Remove the bulb tester.
Power the whole amplifier from your Variac.
Start it up at low voltage and gradually bring up the voltage.
Periodically check the cap voltages.

When up to full voltage start increasing the bias current on one amplifier. Get is approximate, but on the low side.
Start biasing the second amplifier, again to the low side of final.

Remove the Variac.
Power up again and finalise the bias setting.
Check output offset and output mVac.
When you are happy, connect your source and recheck the offset and mVac.

Finally connect some cheap speakers and have a listen.

[Sisyphism]

What a nice advice!
Thank you AndrewT.

I think i should warm it up first was mentioned.
To let it run for 1h to 2h or so,
at just 0.4V instead of 0.59V (R11 and R12),
before setting it at final adjustment.

There is one thing i don't understand at this time:
Well DC-Offset ist measured in V DC i think,
but since i'm a "caveman",
i do not know what mVac means,
and what i have to do with it.

Just measure it at same connection as V DC with V AC?
As low as possible?

Thank you guys!

[pro]

You have to measure VDC (direct voltage). If you don't have a signal at the input, you won't have any VAC (alternate voltage) at output.

[nigelwright7557]

Originally posted by Sisyphism
What a nice advice!
Thank you AndrewT.

I think i should warm it up first was mentioned.
To let it run for 1h to 2h or so,
at just 0.4V instead of 0.59V (R11 and R12),
before setting it at final adjustment.

There is one thing i don't understand at this time:
Well DC-Offset ist measured in V DC i think,
but since i'm a "caveman",
i do not know what mVac means,
and what i have to do with it.

Just measure it at same connection as V DC with V AC?
As low as possible?

Thank you guys!

mVDC means millivolts DC.
A millivolt is a thousandth of a volt.

[AndrewT]

Originally posted by pro
You have to measure VDC (direct voltage). If you don't have a signal at the input, you won't have any VAC (alternate voltage) at output.

no,
there is always a DC voltage at the output and there is always an AC voltage at the output. It depends on whether one has the equipment to measure these voltages.
Both can be well below 1mVdc and below 1mVac.
adding the source instead of shorting the input is very likely to increase one or other or both.

It is always worth checking before connecting the speakers.

My dmm have a full scale reading of 200mVdc and 200mVac (over a very restricted bandwidth).
I have a resolution of 0.1mV on both scales. These can be bought very cheaply with tolerance of better than 0.5%.