F5 power amplifier

So, it biased nicely and sounds even nicer!

I do have a channel imbalance to the left though (i.e. the singer is clearly not center when it should be). Could it be that I didn't bias perfectly symmetrical? Though channel balance should be more related to gain in each channel (to my beginners brain anyways...), no?
 
I only changed the amp.

BUT I just tried changing the interconnects. They're DIY and I sillily made two left channel and two right channel pairs together, which of course ended up being slightly different in length. :cuss: Never seemed to have any noticeable effect though.

Anyways, I just swapped the cables so that each channel is the same length. Now it's the same as if using my headphone amp... i.e. nicely centred. Is it possible that the F5 is more sensitive to interconnect lengths?
 
Newly minted F5 with buzz/hum

Hey Guys,

Wasn't sure where to post this or if I should make a new thread—figured I'd keep it with the F5 thread in case anyone else can benefit from any proposed solutions. I considered rebooting some old threads—but no.

See pics. Let me know if more detail is required.

The quite audible buzz/hum sounds to me like what the transformer sounds like with ones ear in the case—definite "buzz", perhaps more than "hum", but both. It's just that it's coming through the speakers. Even under other audio, depending on volume and distance from the speakers of course. I'm tuned to it...so to me it's pretty annoying, and I can pick it out.

If I short the inputs, still have buzz/hum (this rules out environment correct?).

From other research and inputs from members—here's what I've tried:
- Connecting PCB grounds directly across the amp (ZenMod in some old thread)
- Connecting speaker grounds directly to PCB
- Connecting PCB grounds directly to star ground after CL-60 (this may not be a star ground—I've looked at so many drawings—it all starts to blur)
- Flipped the transformer—6L6 suggestion—still hums.

What I haven't tried is all of the above together, with the exception of the transformer flip. I saw an "if all else fails" drawing that showed all grounds from input/speakers/AMP boards/PSU board to a single grounding point on the chassis with a CL-60 in line to the IEC ground.

I'm going to replace the PSU to chassis CL-60, since it got a little toasty in a previous—now resolved—start-up attempt—it's visually discolored. I don't know if this could be a buzz/hum factor or not.

I also haven't messed with the input grounds based on some reading up here.
If I plug the amp into a preamp—B1K—I'd say the buzz/hum increases for a moment, then seems to return to normal—non-preamp hum.

The reputation of the F5 is that it should be quiet/silent... so I'd love to solve this? Anyone see anything—or have suggestions?

I'm going through this:
Audio Component Grounding and Interconnection

A lot of that article is a bit over my head at the moment...

Incidentally the Antek transformer isn't the shielded variety—I've read mixed things about this—but that it CAN matter—article above... I have another build in process—that one has a shielded Antek.. Should be interesting.

THX!!
 

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Last edited:
The blue and teal wires between your transformer and the diodes are the noisiest part of the amp. They're inside a ground loop with an input connected, but not with the inputs shorted.

Still it might be worth moving your red/green/power braid to the back of the case so that the blue/teal wires are between it and the transformer and see if that makes any difference.

It also might be worth twisting the blue/teal wires as another experiment.

Cheers,
Jeff.
 
The blue and teal wires between your transformer and the diodes are the noisiest part of the amp. They're inside a ground loop with an input connected, but not with the inputs shorted.

Still it might be worth moving your red/green/power braid to the back of the case so that the blue/teal wires are between it and the transformer and see if that makes any difference.

It also might be worth twisting the blue/teal wires as another experiment.

Cheers,
Jeff.

Thanks Jeff, To be clear—run the left channel V+, GND, V- braid, towards speakers around the IEC side of the amp, instead of right across under the secondary wires. Will twist those secondaries as well.
 
Official Court Jester
Joined 2003
Paid Member
I only changed the amp.

BUT I just tried changing the interconnects. They're DIY and I sillily made two left channel and two right channel pairs together, which of course ended up being slightly different in length. :cuss: Never seemed to have any noticeable effect though.

Anyways, I just swapped the cables so that each channel is the same length. Now it's the same as if using my headphone amp... i.e. nicely centred. Is it possible that the F5 is more sensitive to interconnect lengths?

no

that just means that your interconnects (causing different signal level) are utter Drek

:clown:

difference in length - only if one is foot long , while other one 33foot long