A guide to building the Pass F4 amplifier

[Tomcat1969]

Thanks again Jim. It is fab! With an 834 clone and BA-3 front end. It's like HD music!

Even my wife was smiling during the couple sides I played, and with a new Jico SAS stylus with about 2 hours on it. It's mental.

 

[Dennis Hui]

That's great! Much fun listening ahead.

 

[yoshida]

Thank you for your comment.

I chose the following rectifiers.
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This is a product from an electrical parts shop Akiduki-denshi.
A diode bridge is made up of four SBRT20U100SLP.
http://akizukidenshi.com/download/ds/diodeinc/SBRT20U100SLP.pdf
I chose this because I found some positive reports on the net.

Another candidate was a SIC rectifier, but I haven't compared it yet because they are weak against inrush current and requires soft start.
Maybe SIC is better than the one I chose this time. I will replace it with SIC someday.

The following is data sheet of MPC74 . It is a low distortion grade.
http://www.fu-futaba.co.jp/files/topics/35_ext_08_0.pdf
I can't find it now, but I've previously found a report that MPC (Metal Plate Cement) shows less increase in resistance when a large amount of current is applied compared to MOX/cement.
There should have been a difference of about 0.1% vs 1%.
I'm not sure if that explains low distortion.

Tomcat,
Congrats. I also listen all day long.

 

[tamra]

Nice build Yoshida san.
I am very interested in how F4 sounds like.
I have tried several diodes with Hypex UCD amp.
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This one was not good sound at all.
There was problem with Rohm SCS106AG from counter electromotive force.
Sounded OK though.
Also tried MSR1560 was good.
After few tests,I have completely satisfied with SCS310AG (3rd gen).
So I am trying to build with F6 but not finished yet.

 

[myleftear]

The following is data sheet of MPC74 . It is a low distortion grade.
http://www.fu-futaba.co.jp/files/topics/35_ext_08_0.pdf
I can't find it now, but I've previously found a report that MPC (Metal Plate Cement) shows less increase in resistance when a large amount of current is applied compared to MOX/cement.
There should have been a difference of about 0.1% vs 1%.
I'm not sure if that explains low distortion.

Thank you for clarifying.
I must admit the data sheet of the futaba MPC resistors is a bit challenging...
Since they are available and affordable, maybe I will just try them in a project sometimes.

 

[Tomcat1969]

Many thanks Yoshida. I have been spinning LP's all day. Wonderful.

Nice build!

 

[amandarae]

Hi everyone,
I am gathering parts for my build. Since the store have some of the items Sold Out, I am "out sourcing" some of the parts I need.
1.) For the PSU (DC), will this board be good enough 1pcs CRC 6 Capacitors PASS Amplifier Power Supply Board PCB | eBay. Of course if anyone has a spare of the Universal PSU board from the store that they will not be using anymore, I will be more than eager to buy it from you.

2.) What are the sizes for the Transistor screws (bolt and washer) and the brass PCB standoffs that can be seen on th build by 6L6?
3.) Trafo, since Antek AS-4218 is out of stock, will AS-4220 be okay? Any other recommendations here most welcome.
4.) Any recommendations on what to read regarding steps for "matching" transistors (particularly 2SK170 and 2SJ74)?

inputs much appreciated. Thank you!

Abe

 

[Dneu2011]

I’ve used these and like them in my Pass builds.

CRC Power Supply PCB PASS DIY F5 TURBO First Watt class A Power amp amplifiers 699987115670 | eBay

I also used AS-3220 so the 4220 would be even better.

As for screws and standoffs, go with m3.

 

[amandarae]

I’ve used these and like them in my Pass builds.

CRC Power Supply PCB PASS DIY F5 TURBO First Watt class A Power amp amplifiers 699987115670 | eBay

I also used AS-3220 so the 4220 would be even better.

As for screws and standoffs, go with m3.

Thank you! May I ask what rectifiers did you use? As for the M3 screws, 10mm length is okay (using DIY Audio Store 4u chassis)?

 

[mcandmar]

I used the AN-5218 in my build as the 400va version was out of stock. No harm in having a little more beef in the transformer.

 

[6L6]

With that PCB try these - LINK

MBR10100G

 

[amandarae]

Thank you guys!

Abe

 

[Dennis Hui]

For matching output mosfets, you can measure and match by Vgs as outlined here:

http://www.firstwatt.com/pdf/art_matching.pdf

For the jfets, you can measure and match by Idss. Some info is here:

JFET matching information – diyAudio Store

See also Borbely's articles:

http://www.linearsystems.com/lsdata/others/JFETs_The_New_Frontier_Part1_by_Erno_Bordely.pdf

 

[amandarae]

For matching output mosfets, you can measure and match by Vgs as outlined here:

http://www.firstwatt.com/pdf/art_matching.pdf

For the jfets, you can measure and match by Idss. Some info is here:

JFET matching information – diyAudio Store

See also Borbely's articles:

http://www.linearsystems.com/lsdata/others/JFETs_The_New_Frontier_Part1_by_Erno_Bordely.pdf

Thank you! That's the one I am looking for.

Abe

 

[Eric]

2.) What are the sizes for the Transistor screws (bolt and washer) and the brass PCB standoffs that can be seen on th build by 6L6?

Hi Abe,

Something I wish someone else told me years ago: Go to Bold Depot (or Mouser.com or McMaster.com) and order 100 screws in size M3 that are 15mm long. Use these to bolt mosfets to heatsinks. Order another 100 M3 that are 5mm long and use these to hold PCBs to hex standoffs. Order 100 M3 nuts, washers, and 100 hex standoffs that are 5mm long. Get all of these in stainless steel (hex standoffs will likely be aluminum). Order an M3 tap and drill bit to go with it and you'll be set for a long time with amp building.

 

[amandarae]

Hi Abe,

Something I wish someone else told me years ago: Go to Bold Depot (or Mouser.com or McMaster.com) and order 100 screws in size M3 that are 15mm long. Use these to bolt mosfets to heatsinks. Order another 100 M3 that are 5mm long and use these to hold PCBs to hex standoffs. Order 100 M3 nuts, washers, and 100 hex standoffs that are 5mm long. Get all of these in stainless steel (hex standoffs will likely be aluminum). Order an M3 tap and drill bit to go with it and you'll be set for a long time with amp building.

McMaster-Carr is local to me (Diamond Bar CA). Thank you for the tip!
Abe

 

[Erikgunnar]

Parallel vs Balanced

I am in my final stages of my F4 build.

I have two mono block chassis and two F4 amps per mono block. 650VA per block.

Speakers are 4ohm and 88db and I listen mostly to music with good bass

Shall I go balanced or parallel?

Balanced the amp will see the speakers as 2ohm and damping factor will be 20 instead of 40.

Will I lose bass punch with lower damping factor?

Will the amp go out of Class-A early due to 2ohm?

In Parallel mode the amp will see the speakers as 8 ohm so I guess the amp will not go out of Class-A early.

Will parallel give me a damping factor of 80 and a bit tighter bass?

Do any one havde good experience?

Many thanks in advance.

 

[6L6]

I’d suspect bridge balanced would work better for you, the F4 has no issues with current delivery.

 

[Erikgunnar]

I’d suspect bridge balanced would work better for you, the F4 has no issues with current delivery.

Thanks!

Balanced the amp will see the speakers as 2ohm and damping factor will be 20 instead of 40 so will I lose bass punch with lower damping factor?

Will the amp go out of Class-A at low watt due to 2ohm?

 

[TioFrancotirador]

My F4 is back to live. With traditional PSU this time: Transformer + Caps.