Whats your heatsink temps at .55 volts? I am runnning I think .535, hitting 53 degrees, Just added some computer fans and temps are down to 40-42 ish
Hi 6sX7 would you or zman01 mind elaborating on this issue? I was looking forward to building another F6 as a balanced mono block and converting my existing F6 to the same. It’s been done here before, and apparently without issue - see the posts below for details.
Thanks in advance! -Glen
Post #887/890
Balanced F6
https://www.diyaudio.com/forums/pass-labs/258613-diyaudio-firstwatt-f6-89.html#post4382791
Post#1437
Balanced F6
https://www.diyaudio.com/forums/pass-labs/258613-diyaudio-firstwatt-f6-144.html#post4486087
The output impedance in the bridged amp doubles to 1 ohm (damping factor down to 8).
Whether that might be a problem depends on the impedance profile of your speakers.
Whether that might be a problem depends on the impedance profile of your speakers.
What Dennis typed. My experience with the ACAs interacting with the Curt Campbell designed Halcyons leads me to surmise the F6 monsterblocks won't have the control the Halcyons need. a single F6 channel output impedance is 0.5 Ohm and the Halcyon impedance dips down into the upper 3s. However, I have everything on hand except the 2nd pair of transformers and built PSU boards (which is needed anyways for any sort of 1st W balanced monoblocks) so I might as well try. Right?
But! Given the F5 output impedance of 0.1 Ohm, a pair operated in balanced mode would be a better match. Reading thru the various threads and coming from the hollow state world, I very much like these F6s and unsure if the F5 will not be to my liking.
So, jump over to the F5s or take the quick excursion? My time is limited so I'm not sure. It took me 3+ months to get the F6s built. Things will go faster since I have the chassis built and learned my way around Mr. Pass's designs but still...
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That might be a problem with a 3 ohm load. Got it, thanks.
That dashes my plans for the F6. Though the F6 sounds fantastic in my system to my ears, I was really hoping to add some magic utilizing a balanced configuration to go with a balanced preamp I’m building. I know a lot of people like the F5, I’ll have to check it out now!
hmmmm...
Any gotchyas I need to think about/account for? I'm running the ACAs as paralleled monoblocks, I don't recall anything special like trimming out offset between the two output boards within each amp. I do need to go check the DAC output impedance to see if I can comfortably drive the input of such a beast. However, all that is needed at this point are 2 more transformers and a bunch of resistors and caps which I'm ordering next month (5 days away and counting).
And the Schiit Bifrost has an output impedance of 75 Ohm. Easey-peasey.
Does the F6 invert phase?
Does the F6 invert phase?
easey-peasey is right! I totally overthought everything and posted too fast. All I need is a pair of xformers, a handful of resistors and a basket full of caps. And the where with all to "once more unto the breach, dear friends."
Be very careful about paralleling two F6. The output stage is DC coupled and there could be thermal issues with such a solution because the current might not flow equally between the pairs.
One other solution is to lower the output impedance by using the modified bias circuit suggested by 2picoDumbs and then lowering (halving) values of the degeneration resistors. Then a bridged pair will work better if not perfect.
Absence of magic smoke not promised 🙂
Paralleling the ACA will work because of the output cap, no DC current can flow between the pairs.
One other solution is to lower the output impedance by using the modified bias circuit suggested by 2picoDumbs and then lowering (halving) values of the degeneration resistors. Then a bridged pair will work better if not perfect.
Absence of magic smoke not promised 🙂
Paralleling the ACA will work because of the output cap, no DC current can flow between the pairs.
The coupling transformer might not be able to handle the extra capacitance of the second pair without causing some HF degradation.
