A guide to building the Pass F4 amplifier

[66deg]

Thanks Dennis, much appreciated.

 

[JeffYoung]

The F4 manual includes drawings of how to hook it up using a flea-watt amp.

I also use Toroidy. I usually get a 500VA just because I feel better if the transformer is more expensive than the shipping, but a 300VA would do.

 

[cal3713]

You have to create your own cables that have speaker connections on one end and RCAs on the other. The speaker post that connects to ground (usually the black) connects to the outer part of the rca and the other (usually red) goes to the pin. The speaker connection attaches at your flea watt and you'll need to put a resistor (8, 16 ohms... Whatever is optimal for the amp) across the speaker connections too.

Hello DIY collective,




I am in the process of collecting parts for an F4 build and would like to ask a couple of questions. Before we get to them; my proposed setup will be, ARC Ref 3 pre amp - F4 -speakers or ARC Ref 3 PREAMP - Flea watt amp (TU 8100 PCL86) combined with F4 - speakers.
In the second scenario with the flea watt amp I am not sure how they are conected together and I think the flea watt needs to see a load whereas in the first scenario it would just be connected as normal i.e RCA in, speaker binding posts out.

Could I ask how to go about the construction of a flea watt seeing a load

what parts would be required and secondly how it is connected.


My other question concerns the toroid, I live in France so our eletrical supply is 230V - 50Hz and I am looking to order from Canterbury Windings, I think TM160A is the right one but would like to double check;http://www.canterburywindings.co.uk/standard_range.htmlhttp://
If this is not correct I have the option of a custom build. http://www.canterburywindings.co.uk/ordering.htmlhttp://
If this is my best option could anyone advise me on what would be the specifications for a custom build.
Merci.

 

[66deg]

Hi Cal,
Thanks for the info, as suspected I will make up 2 cables with banana plugs on one end and RCA male on the other. When you say put a resistor across the speaker terminals is this usually done just across from red to black on the inside of the Flea Watt amp or externally on the binding posts?

This is the rated ouput: 2W per channel into 6 ohms at 10% THD so I shall add 2 X 6ohms
resistors onto my order.


Thanks again.

 

[66deg]

I am ordering components and would be grateful if someone could check if this is correct to go across the binding posts on the flea watt amp MR5FT6L00-ND
As a beginner I find the choice of components a little bewildering.
Merci.

 

[syracuze]

I am ordering components and would be grateful if someone could check if this is correct to go across the binding posts on the flea watt amp MR5FT6L00-ND
As a beginner I find the choice of components a little bewildering.
Merci.

That is only 6 mOhm, it is very low as such. You probably want something like 8 Ohm or maybe 16 Ohm, depending on what your flea watt amplifier would be happy to see as a load.

Just to give you an idea what this serves for F4 has an input impedance of 47 kOhm which much higher than any typical speaker load that flea watt amplifier is designed for, so you want to put a resistor in parallel to F4 input so that your tube amp thinks it sees a proper load similar to a speaker.

 

[66deg]

Thanks Syracuze, I will order some a little larger.

 

[cal3713]

On the speaker binding posts... you can read a bit more about it at the 6moons review of the F4 (6moons audio reviews: FirstWatt F4). From the 6moons article, here's an image of one cableing solution:

Hi Cal,
Thanks for the info, as suspected I will make up 2 cables with banana plugs on one end and RCA male on the other. When you say put a resistor across the speaker terminals is this usually done just across from red to black on the inside of the Flea Watt amp or externally on the binding posts?

This is the rated ouput: 2W per channel into 6 ohms at 10% THD so I shall add 2 X 6ohms
resistors onto my order.


Thanks again.

 

[cal3713]

Thanks Syracuze, I will order some a little larger.

If possible, note the distortion numbers of your amplifier at different load values. It is often the case (for SETS?) that a higher load (e.g., the 16ohm) will allow the amplifier to operate with less distortion.

 

[66deg]

Those images are just what I needed to see, a great help. I can now finalize all orders then twiddle my thumbs until everything arrives.

 

[66deg]

The only part not in stock at Mouser / Digi Key is this, 71-RN60D7500F/R RN60D7500FRE6Vishay Metal Film Resistors - Through Hole 1/4watt 750ohms 1% 100ppm

Apparently not in stock for 40 weeks so I would like to check if this is OK instead.750r 0.25W Royal Ohm Metal Film Resistor 100 Units on Cut Tape | eBay

 

[albertNL]

No need to buy RN60. The RN55 are fine and available. I found these at mouser:
RN55C7500FRE6

The only part not in stock at Mouser / Digi Key is this, 71-RN60D7500F/R RN60D7500FRE6Vishay Metal Film Resistors - Through Hole 1/4watt 750ohms 1% 100ppm

Apparently not in stock for 40 weeks so I would like to check if this is OK instead.750r 0.25W Royal Ohm Metal Film Resistor 100 Units on Cut Tape | eBay

 

[66deg]

Thanks albert.

 

[JeffYoung]

I also use the RN55's.

 

[Lukyk]

Higher idss fets

Any disadvantages using fets with idss around 10,7 with this design? Will there be any bias or other limits? Are there any part changes needed?

 

[6L6]

Will work very well.

 

[Lukyk]

Thank you very much, exactly what I wanted to hear

Looking forward to try F4 with my newly built Ale's 01a pre. It already sounds fantastic with F6, but there is too much gain.

 

[ItsAllInMyHead]

Now I need a chassis...

Jim, thank you once again for a fantastic build guide! It'll likely be a week or two before I get it in a chassis and give it a listen, but I had some time this morning to stuff the boards.

 

[Zen Mod]

F4 is for Sissies !

 

[ItsAllInMyHead]

Proud to call myself a big ol' SISSY!