Aikido 5687 PCB - Headphone and C3

[eeyore]

Hi, just going through the 5687 manual and configuring it for headphone use. Just wondering how does C3 change the operating parameters of the circuit. I assume it allows for more current at the output, but does it change it to Class AB (which is implied in the manual).

Would omitting it cause it to be unable to drive low impedance headphones, or conversely, would including it make is not suitable as a line stage. I am little confused as there is a also a diagram fro wiring it up for either a HP amp or a Line amp, and this mode, I am unsure whether C3 is in or out, to allow it to function as both.

[Stixx]

It would be helpful to include the mentioned schematic with so many Aikido schematics and manuals floating on the net.
The Rev D manual doesn't list C3 anymore, and as far as I recall C3 in the previous manuals was just a filter cap for the input section and doesn't affect operating conditions at all. Saying this out of memory... maybe someone else can clarify.

[eeyore]

C3 in the version of the 5687 board I have is the cathode bypass for the lower triode of the output pair. From reading through, this is to lower impedance to get decent current and output to low impedance HP. I read also that the cathode resistor to the top output triode can be/is left out also to reduce impedance. From the same place, I read that this resistor can be left in, and the C3 (lower cathode bypass) can be left out, first, to test for bass response. If this is okay, I can remove and add as necessary to tune to desired bass response for my HP.

I mainly have 300R and 600R HP, I guess that it'd be okay to start with the the upper cathode resistor in and the lower cathode bypass cap out.

[jono1]

Does anyone have a link to the Aikido 5687 manual?

[vanofmonks]

I would dig a link too.

[DavesNotHere]

here you go:


http://www.tubecad.com/Product_PDFs/...ereo_Rev_C.pdf

[Stixx]

C3 in the version of the 5687 board I have is the cathode bypass for the lower triode of the output pair. From reading through, this is to lower impedance to get decent current and output to low impedance HP. I read also that the cathode resistor to the top output triode can be/is left out also to reduce impedance. From the same place, I read that this resistor can be left in, and the C3 (lower cathode bypass) can be left out, first, to test for bass response. If this is okay, I can remove and add as necessary to tune to desired bass response for my HP.

I mainly have 300R and 600R HP, I guess that it'd be okay to start with the the upper cathode resistor in and the lower cathode bypass cap out.

OK, now I am seeing it more clearly...
Well, Broskie says to use the upper cathode resistor and bypass cap when using the schematic as line amp (running at 10mA or so). This is known as the Aikido totem pole arrangement.
When driving headphones (even 300R cans are considered low impedance) he suggests to leave out the upper cathode resistor and the bypass cap which changes the output stage to a WCF (white cathode follower) with the ability to provide more current (up tp 30mA with suiting output tubes).

I am running my Aikido headphone amp (using 6N23P and 6H30 DR) in the latter topology... but I guess its up to you to try it both ways. But since you are running 5687's that are happy to deliver higher currents I would do as recommended... configure it as headphone amplifier as well