Woo Audio 6

[regal]

I have been a long time supporter of DIY tube amps. I want to try an SET headphone amp. What I am finding is you can buy a new WA6 for less than building a proper SET amp because the air gapped headphone OPT's cost so much.

Is the WA6 a well designed amp, does anyone know the topology? I'm on the fence with this one, any feedback would be appreciated.

[n_maher]

SET amps are not necessarily transformer coupled. SET just means single ended triode.

[regal]

Yes but I have several OTL, want to try an SET OPT head amp.

[n_maher]

Woo is a good choice in my book. I haven't spent any extensive time with them but as far as I can tell they are built well and seem to be well liked. That's about all I can offer.

[aerius]

Is the WA6 a well designed amp, does anyone know the topology? I'm on the fence with this one, any feedback would be appreciated.

2 stage grounded cathode amp with RC coupling and transformer output. Cathodes are bypassed with generic electrolytic caps. Power supply violates the maximum capacitor size limit for a 5AR4. Max capacitance for a 5AR4 using a C input filter is 60uF going by the datasheet, the Woo is 330uF.

[bdr529]

Do you know why he would want to do that? Would this be overcompensating a different weakness (no choke filter)?

Sorry if I am completely wrong, i am struggling to remember electronics class.

[aerius]

To be honest I don't know why. Could be compensation for lack of a choke, insufficient filter stages, or lack of some form of regulation. Or maybe he had a solid state rectifier in the prototype and switched it to a tube without making sure everything was still in spec. Could be one of dozens of things, and no one other than the designer knows for certain.

[dreamwhisper]

I'm disappointed, I always held the Woo6 in high esteem.

It won't necessarily sound worse as a result but it does seem sloppy to me.

Anyone know if his other designs have similar problems in topology?

[peanuthead]

Here is Takezo's response from the other site:

"wooaudio has told me in the past that the wa6 implements a soft-start when initially

turned on... and the amp puts only 180v on the rectifier anode plate normally (much lower

than the characteristic 450v, with max. of 550v.) contributing to the safe use of these

rectifiers on the wa6... having said that, i'd lower the first caps to 22uf or lower, just to

be on the safe side. the wa6SE implements a choke in their C-L-C path with the first cap

being 10uf, with a delay circuit added on also, so should be fine. "

[jantze]

Here is Takezo's response from the other site:

"wooaudio has told me in the past that the wa6 implements a soft-start when initially

turned on... and the amp puts only 180v on the rectifier anode plate normally (much lower

than the characteristic 450v, with max. of 550v.) contributing to the safe use of these

rectifiers on the wa6... having said that, i'd lower the first caps to 22uf or lower, just to

be on the safe side. the wa6SE implements a choke in their C-L-C path with the first cap

being 10uf, with a delay circuit added on also, so should be fine. "

I also modified my WA6 based on takezo's comments. No sparks or any other problems.

[bdr529]

Very cool, thanks for the pics/link. Nice job on your amps.

[cetoole]

Here is Takezo's response from the other site:

"wooaudio has told me in the past that the wa6 implements a soft-start when initially

turned on... and the amp puts only 180v on the rectifier anode plate normally (much lower

than the characteristic 450v, with max. of 550v.) contributing to the safe use of these

rectifiers on the wa6... having said that, i'd lower the first caps to 22uf or lower, just to

be on the safe side. the wa6SE implements a choke in their C-L-C path with the first cap

being 10uf, with a delay circuit added on also, so should be fine. "

The maximum capacitance limits are about current, not voltage.

[OPTiK]

Are those cold joints i see?

[regal]

I decided to build a SOHA II to hold me over till the Stacker II is done, they Stacker II is basically a SET OPT amp with a solid state circuit acting as the OPT. The SOHA II is the same but the first stage is a cathode follower and the tube B+ / current is restricted.