F-5 boards

Switches things on and off again
Joined 2000
Paid Member
We don't have great information records for previous board revisions, I believe the V3 boards only functionally changed by adding P3. However importantly for you, I think they switched to using the article part numbering instead of BOM part numbering, so please do double check everything. Measure twice cut once and all that...
 
Member
Joined 2006
Paid Member
Thanks Jason, will do.

We don't have great information records for previous board revisions, I believe the V3 boards only functionally changed by adding P3. However importantly for you, I think they switched to using the article part numbering instead of BOM part numbering, so please do double check everything. Measure twice cut once and all that...
 
XLR Input for F5

Hi Everyone,

Can a single XLR input be added to the F5, similar to the wiring in the AmpCampAmp (see attachment), to run two F5's in mono? Or is there something in the F5's circuit which prevents doing this?

You info/assistance is greatly appreciated...Thanks!

Harry
 

Attachments

  • xciacvVWlTGfISa1.huge.jpeg
    xciacvVWlTGfISa1.huge.jpeg
    185.2 KB · Views: 361
What do I do with power supply?

Hi Guys,

Riddle me this. What is the correct Universal Power Supply V+ to V- voltage? I have seen 23V and change when not connected to amp boards, and I have seen 46V-50V.

I built my Universal Power Supply with TO-247/TO-3P diodes on the board, with the heat sinks, which results in a rectifier using parallel diodes (see PSU schematic). I hooked up the AnTek 5218 2X18V transformer in this setup and got 48V across V+ and V-. Does this have any bearing on my reading?

The 46V-50V range doesn't seem correct since the voltage into the amp board is 23V. Or am I wrong? The schematic for the amp shows +23V and -23V. Does mean 46V going into the amp (the latter voltage from the first paragraph)? I know this is evry basic, but it's been almost 50 years since I took classes in electronics, so I am not sure.

Thanks,
Dave Chorney
 
My first amp build - F5 V3 - bias way too high?

I just finished wiring up my first amp - an F5 V3 board. I actually started with a no-name ebay clone and let the smoke out due to a poorly labeled PCB - learned my lesson and got the real thing with good documentation. I've worked with electronics in the past but mostly digital/arduino stuff so this is stretching my brain in a good way.

I'm at the bias setting stage and I think I have everything wired correctly, however when I bump the power on (and i'm gun shy on this because of the previous boards getting smoked) the two multimeters across R7 and R8 (0.47 3W) I am getting ~2.5V before I panic and shut the power off. It appears to be happening on both of the F5 boards.

P1 and P2 are both fully turned counter clockwise and are soldered in the same orientation as the build guide - in case that matters with this layout. I did populate P3 but it's set to the center of it's adjustment range.
 
I have a quick question (I hope) about biasing...

I have both R/L channels fluctuating around 0mV and am currently targeting 550mV measured at the resistors. On the left channel, I have the pots set so the measured values are -549mV and 551mV, meaning there is roughly a 2mV spread measured at the resistors to achieve 0mV at the output. On the right channel, The pots are set so the measured values are -545mV and 555mV with 0mV, which is roughly a 10mV spread.

In both cases the average voltage is 550mV, and I may leave it at that bias setting. I don't imagine the variance in spreads is going to be too much of an issue, but the v2 guide says if you have decently specced parts (I used the F5 parts kit from DiyAudioStore), then the + and - voltages for each channel should be equal when measuring 0mV at the output.

So which components on the amp boards would account for the voltage spread seen on my R channel? The output resistors? FETs? Something else? And is it worth trying to do better than this by swapping something out?

Thanks in advance!
 
I have the F5 V3 amp all built, power supply was tested before being hooked up to the amp boards and it checks out fine. So, I am reading the manual at the First watt site and it says to make sure the trim pots are set to their minimum and to verify with an ohm meter before powering up. Perhaps I have missed it somewhere, but how where in this circuit do you get a reading from the trim pots once installed on the pcb? I tried getting readings directly from the pots themselves but nothing changes there no matter which way it's adjusted.

I have seen builds in videos where it seems they are going to show this little detail and then poof, they're onto the next part with the amp powered up.
 

6L6

Moderator
Joined 2010
Paid Member
Set meter to ohms and place across R5, then adjust P1 until it reads minimum ohms.
Do the same with R6 and P2.

The potentiometers do not necessarily turn the proper way for “up” and “down”, so mark the pots showing the direction of turn for up.
 
Set meter to ohms and place across R5, then adjust P1 until it reads minimum ohms.
Do the same with R6 and P2.

The potentiometers do not necessarily turn the proper way for “up” and “down”, so mark the pots showing the direction of turn for up.

I had tried to measure across all of the resistors on the board. The issue was, the pots were spun so far out of range, that I had to turn them for a long time to even get them to make any change. One board, the two pots showed change as soon as I started to turn them. I thought I had faulty pots or roasted them while soldering. I reckon that next time, I ought to check them before installation.