A guide to building the Pass F4 amplifier

[6L6]

Wow! Genuinely beautiful!

Well done, Sir!

Thank you for taking such good photos.

 

[qwertyl]

Wow! Genuinely beautiful!

Well done, Sir!

Thank you for taking such good photos.

Thank you. And thanks everyone. I wouldn't make it without this forum...

 

[Zashoomin]

Thank you to everyone who helped out as well. It is now biased to the correct 200mv and is singing like no other. My god this thing sounds good.

 

[qwertyl]

R3/R4

Just measured voltage across R3 and R4 - it is 96mV, which gives 4.4mA (96mV / 22.1 Ohms). It seems a bit low. I was expecting about 7mA. Are R3/R4 supposed to be 22.1? I was using schematic from Post #1 of this thread...

 

[6L6]

You can play with the source resistors... Change them to 10ohm and try again.

But remember the input stage is a buffer, so if it's working, there probably won't be much change.

 

[mvdventura]

Hello,

Greetings from Spain.

I´m wondering if I can drive an F4 using an Eastern Electric BBA.

Specs here:

Morningstar Audio Imports, Inc.

Loudspeakers would be Zu Druid MK IV.

Regards,

Daniel

 

[Zen Mod]

Specification

• Maximum input: 6 V
• Gain: 0dB to +18dB
• Input Impedance: 220K ohm
• Output Impedance: 800 ohms- 10K ohms
• Signal to Noise: 95dB to 85dB

18db will cover probably , but output impedance (10K) is puzzling thing

?!

 

[Triodethom]

18db will cover probably , but output impedance (10K) is puzzling thing

?!

That may be the range of desired impedance of the amp other than that it a real puzzle . In the ad it states 100k down to 600 ohm amps . 10 k may be a miss print should have been 100k the range of amp input drive . That's a guess on my part .

 

[AndrewT]

maybe they are telling us the output impedance is 800ohms and that the optimum load is 10kohms.

 

[6L6]

Because that widget is an "impedance interface," (whihc really means "tube tone effects box") I bet there is a pot somewhere not-normal to change the operating point and therefore output impedance, thereby having a big inpact of the sound without large gain swings.

 

[mvdventura]

Thank you all for the advice.

The thing is that I´ve been using the BBA with a First Watt F5 clone (now in rebuilding process) and I liked the combination a lot (my other amp is a Leben CS-300). Actually I preferred the BBA+F5 vs the Leben.

My setting with the BBA driving the F5 was: Gain at 11 and Volume at 9.

As I´d like to build an F4, and this has no gain like the F5, my concern is if the BBA might or not might be a good match.

Thank you again.

Daniel

 

[patkhan1]

Hello guys,
I am gathering the materials to build the F4, I will be using this power supply (the one from diyAudio Store used for the build in this thread) and I have a doubt about the line input capacitor that is shown in this picture:



It is the small blue cap across the power input lines. I am not sure about it's value, is it 0.0033uF 120v? or something different? Any help will be appreciated.
Thank you.
P.

 

[6L6]

It's a .0033uf (3300pF) cap that must be x1 (or x2) rated for across the line use.

Here's a link to an appropriate part-

WKP332MCPEJ0KR Vishay / Roederstein | Mouser

 

[patkhan1]

It's a .0033uf (3300pF) cap that must be x1 (or x2) rated for across the line use.

Here's a link to an appropriate part-

WKP332MCPEJ0KR Vishay / Roederstein | Mouser

Aweseome, 6L6. You truly excel as a diyAudio community member. It's really appreciated.
Thanks for all you do to keep up this threads.

 

[valvesound]

The reference to the schematic on that capacitor

 

[AndrewT]

It's there to help reduce the sparking across the on/off switch when the amp is turned OFF.

 

[AndrewT]

Which prompts the next question:
would it be better to keep the capacitor and ADD a snubber in parallel to absorb the energy of the ringing?

 

[Marra]

My F4 which is slowly taking shape.The heatsinks are on there third amp and are from Fischer 265mm wide x 200mm long with fins of 75mm with a 12mm thick base.Toroidal is a 500VA from Air Link in the UK.

 

[WalterW]

Looks nice Marra!
What's there under the white PSU caps? Any special rectifiers used?

 

[Marra]

Hi Walter;just standard bridges for the moment.I have schottkies and MUR 3020's to try later.There is a soft start board from Connexelectronic underneath the caps but I had to lift them anyway to clear the toroid.