F4 power amplifier

[flocchini]

F4 Headphone Amp Up and Running

Thanks to Choky's patience in helping me debug a "bad" board my balanced F4 headphone amp is running. This is from Choky's schematic in post 3026 by generg. Thanks Nelson for the incredible current buffer. Preliminary listening (Buffalo II to XP10 to F4) says this is a keeper. As you can see "case isn't quite done.

The basement compartment contains transformers, first bank of caps and inductors.

 

[Zen Mod]

nice 'sinks

 

[flocchini]

Forgot to mention bias is set at 300mA
Only change to schematic is that R9 was reduced from 10k to 5k

Sinks might be overkill 🙂

 

[Nelson Pass]

I thought I recognized him lurking around the trash cans....

😎

 

[flocchini]

those trash cans would be like heaven😀

 

[Zen Mod]

 

[intel386]

Hi everyone !

ZenMod is an alien lightyears before us.........

IRFZ24N and IRF9Z24N could be used here as a replacement for IRF610 and 9610 ? If I want to build this cans version of F4 with +/- 24V rail voltage, which resistor values have to change ?

 

[Zen Mod]

with just quick look at their data - you can

resistor values - use same as in original F4 , except higher source resistors for outputs

 

[intel386]

with just quick look at their data - you can

resistor values - use same as in original F4 , except higher source resistors for outputs

Thanks for help, Zen Mod.

Please help me understand the bias trimpot : P2 is to bias the DC Offset at the output and P1 is to bias the Vgs of the MOSFET ? ( adjust until Vgs = 1/2 Vcc ? )

I have tried to simulate this circuit in LTSpice, but i'm a newbie in SPICE programs, so the result is very weird 🙁.Someone help me to fix my spice file, please ?
Spice file attached.

 

[Zen Mod]

for starters - read F4 manual ; it's written with that purpose

much better explained than I can do

P1 bias , P2 offset

 

[intel386]

for starters - read F4 manual ; it's written with that purpose

much better explained than I can do

P1 bias , P2 offset

I found that F5 manual has more info than F4 😀.Read F4 manual, I can only find the quiescent current setting and the matching requirement of the devices.

How should I adjust P1 ? Adjust it until Vgs = 1/2 Vrail or else ?

Ah, one more thing : I can only get touch on 0.3V matched mosfets and jfets, will they work well ?

 

[Zen Mod]

for Jfets - take what you can

for outputs = if you are making it for cans , one output pair is enough

so , no need for matching them

use schematic mentioned in post #3341

when you have that completed , ask again for biasing procedure , prior to first powering on

 

[intel386]

so , no need for matching them

use schematic mentioned in post #3341

I don't have to match the FETs ? Why ? 😕 What about the DC Offset ?

Schema metioned in above post has changed some resistor values and runs on +/-15V rail voltages.If I want to run my canned F4 on +/-24V rail, should I keep the original resistor values or follow the above schema ?

 

[neoinc]

I am building a crippled F4 with BA3 for front end but not sure if i am doing it correct.

To remove the F4 input buffer, R1,R2,R3,R4,Q1,Q2,D1 and D2 are not soldered. The BA3 output will goes between C1 and C2 on F4. Is this correct?

For the output MOSFETs, I have both Fairchild and Vishay devices. Is there a preferred one for this amp?

 

[Itsmee]

To remove the F4 input buffer, R1,R2,R3,R4,Q1,Q2,D1 and D2 are not soldered.

You do need D1 & D2, you don't need D3 & D4, you also don't need R24, R25, C3 & C4.

The BA3 output will goes between C1 and C2 on F4. Is this correct?

Yes.

 

[neoinc]

Thanks Itsmee, I read the wrong diodes, should be what you mentioned D3 and D4. But it is interesting that R24, R25, C3 and C4 not required as well. How does this four components work the JFETs? For biasing purposes?

 

[Itsmee]

C3/R25 and C4/R24 are bootstrap networks for the front end.
They slightly improved the maximum output and bandwidth, but
their primary purpose is to protect the JFETs from over-voltage.

😎

For the output MOSFETs, I have both Fairchild and Vishay devices. Is there a preferred one for this amp?

The Fairchilds work fine. They have a slightly higher Vgs and
the distortion of the P channel devices is a bit lower, although
not enough to rule out the IR parts as followers.

😎

 

[neoinc]

Thanks for pointing the answers out 😛

 

[flocchini]

F4 headphone amp

I have been listening to my balanced F4 driven by Pass X10 and fed by my Mc through a Buffalo II for about 3 weeks now. Running with 300mA bias at 15V.

I have to say this setup is absolutely superb with my HiFi Man 500s and with modded Denon 2000s, The bass is low and tight. There is very nice detail and the female vocalists (Etta James, Eva Cassidy, Jacintha, Nora Jones ) sound incredible. Why did I wait so long to do this. Highly recommended.

Thanks Choky and all who contributed to this thread/project.

I wonder what it would sound like with a MAGMA front end 😀

Best

Bob

 

[Zen Mod]

pardone moi .......... whazzat Magma?