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Woo3 Modified

post #1 of 244
Thread Starter 
Woo3: I could not help myself, I have to modify.

This amp is really singing now. It is hard for me to keep my hands off of anything, even if it appears that there is little to be done, but even before I got the Woo3, I knew it would be a good, though small, platform to work with. Out of the box this is a rewarding and enjoyable auditory experience. The price belies the value you are receiving. This amp is dimensional, tonally very musical, i.e.: as in real music. Within 24 hours of receiving the unit I had to pop it open and look around.

Inside it is well laid out with Teflon wiring and very clean and shiny solder. The capacitors are photoflash, which I don’t see commercial producers of audio equipment using very often but are reputed to work very well in a power supply application, which they are here. The supply for the 6080/6AS7 and the drive tubes the 6922, use the photoflash capacitors for the B+. The rest of the parts are of good quality but you won’t find any boutique parts here nor should you expect to (they are often overrated anyway).

So why modify? Because I must.

First off I noticed that the input to the 6922 has a dc blocking capacitor. This used to be popular but most sources do not put out dc on the signal. This capacitor is only going to degrade the signal, even if slightly. The easy fix for this is to just move the wire from the volume control to the other side of the capacitor, which bypasses it. I also noted that the bias for the tube on pin 8 is set at 1.4 volts. This is a common bias for a 6922/6DJ8. A resistor, unbypassed by a capacitor (I normally use a 470uF cap in conjunction with the resistor, which increases bass response but can also add its own color) is used. My preference is a NiMH battery for bias on signal tubes. I have compared this head to head with a resistor, resistor with a Black Gate capacitor and other battery types and the NiMH is by far the best and relatively inexpensive compared to the Black Gate capacitor, that I preferred to using only a resistor. The NiMH will remain charged by the current on the cathode and will trickle charge. The battery will settle to around 1.35 volts, which is fine for the application and should last 5 to 7 years.

Now to the power supply. There is a photoflash capacitor for each of the 6922 tubes and for the B+ going to 6080, which will also go on to feed the plates of the 6922 tubes. I used 15uF Solen Fast Caps bypassed with a .01uF polypropylene SBE 716 for the photoflash going to the 6922 and a 12uF for the B+ going to the 6080 also bypassed. I cannot stand the sound of Solen capacitors unless bypassed. Once bypassed they loose the grainy quality they can impart to the sound.

The batteries and capacitors are held in place with nylon ties secured to a sticky sided mounting made for this purpose. I have also noticed that there is a grid stopper on the input tube after the volume control. But for some reason it has a very long leg to the pin of the tube. These should be mounted as close as possible to the pin in order to avoid picking up any signal that they are trying to get rid of in the first place. These will be replaced with some nice 1 watt nos tantalum 220 ohm resistors that I have on hand.

Now to the sound of these changes.

After the above change and as the hours went by, the amp opened up more and more. Layering increased with the recording space being reproduced in a more and more convincing manner. I was listening to Diana Krall, “All For You”, noticing the subtle changes in her voice and her palpable presence. Saxophone on my jazz recordings has a throaty and tangible quality. I have also noted that the depth and width of the recording landscape increased, much to my listening pleasure. Bass impact has increased and the perception of “speed” in the leading edge of notes and of the plucked string gained in realism and tightness.

Noting the above changes, I wish to state that the stock Woo3 is excellent and within the constraints of its price an exceptional buy. I find that the visual presentation in fit and finish to show no compromise. That some small changes can add to the musical enjoyment, for me, only goes to show what a good design it is to begin with.



Woo3 with Amperex PQ 6DJ8 gold pin, WE 421A



The heart of the tube, the heater.



Added caps and resistor changes.



Non inductive high quality resistors in the power supply.

John
post #2 of 244
good work pictures please!
post #3 of 244

Interesting!

Interesting! pls show some photoes.
post #4 of 244
Quote:
Originally Posted by jamato8
Now to the power supply. There is a photoflash capacitor for each of the 6922 tubes and for the B+ going to 6080, which will also go on to feed the plates of the 6922 tubes. I used 15uF Solen Fast Caps bypassed with a .01uF polypropylene SBE 716 for the photoflash going to the 6922 and a 12uF for the B+ going to the 6080 also bypassed. I cannot stand the sound of Solen capacitors unless bypassed. Once bypassed they loose the grainy quality they can impart to the sound.
Thanks for sharing your Woo mods with us John... well done. I also don't care for the sound of Solen Caps - I've used them in my speaker cross-over networks, and found them to be grainy and jagged sounding, so I avoid them whenever possible.
post #5 of 244
Thread Starter 
If bypassed by a .1 or .01 it gets rid of that but I will only use them in the power supply, where they can work quite well and are better than electroylytics except for Black Gates.
John
post #6 of 244
Quote:
Originally Posted by jamato8
Woo3: The supply for the 6080/6AS7 and the drive tubes the 6922,

At the risk of exposing my ignorance regarding the subject matter I have to ask for some clarification. I am confused by your statement “The supply for the 6080/6AS7 and the drive tubes the 6922” as I was under the impression that the 6080/6AS7 was a drive or power tube and the two 6922 tubes are the audio tubes for each channel.

Would someone please explain a function of the 6080/6AS7 and 6922 tubes.
post #7 of 244
Quote:
Originally Posted by WDC
At the risk of exposing my ignorance regarding the subject matter I have to ask for some clarification. I am confused by your statement “The supply for the 6080/6AS7 and the drive tubes the 6922” as I was under the impression that the 6080/6AS7 was a drive or power tube and the two 6922 tubes are the audio tubes for each channel.

Would someone please explain a function of the 6080/6AS7 and 6922 tubes.

You are correct. I think when he said the drive tubes, he meant, the 6922's drive/ supply signal to the 6as7 power tube.
post #8 of 244
Thread Starter 
The tubes that are the input or driver tubes are the 6922's and the power tube is the 6080. I am using some Amperex PQ A frame made in Holland. I was lucky when an old TV repair store, that hadn't dumped their tubes, had a bunch of nos Amperex 6DJ8's in PQ, Bugle Boy, A frame, white label, orange globe and gold pin. But out of all of these some of the best 6DJ8's I have heard are some that are marked Amperex that are Russian from 1982. These tubes are unbelievable and not all that common and often passed by when available. I also like the GE grey glass, an often overlooked tube.

The modifications I have made are breaking in more and the depth and width of the soundstage, dynamics and transparency, is very pleasing.

The next "try" will be to use a resistor to convert the volume control to a series shunt control where you send the signal through a single resistor allowing the volume control to only act as a shunt to ground. To do this instead of using the 3 poles of each signal control (right and left) you use the center tap and the ground. After the center tap you put, in this case, about a 70 or 80K resistor that goes on to the tube grid. The signal goes through this resistor but as the volume control is moved in the same direction as it has been and the signal is shunted less to ground, increasing the volume but only going through the one resistor. This is what I do with my preamp but I will have to see how the 6DJ8's handle this. On some tubes you can decrease the high frequency response and the exact resistor to use needs to be taylored to the volume needed.

I also note that the grid stoppers look to be 1/8 watt with long leads. I will try some tantalum with the connection to the grid pin of each 6922/6DJ8 as short as possible.

John
post #9 of 244
Thread Starter 

6080WA

Well so much for thinking that the cool looking ST shape 6AS7G had to be the best sounding of the power tubes for this amp. I just got a Bendix made 6080WA from the early 60's, (or it may be made by Tungsol that Bendix rebranded but I did not think Bendix rebranded). It has triple mica, copper support rods and extra getter between the top two micas. This tube throws a deep and very wide, as outside the headphones by a wide margain, soundstage. It is nice to be able to get power tubes nos that are cheap.

I have also changed out the bypass caps for the output electrolytic cap with a Jensen copper pio .22uF. This little amp is getting pretty stuffed but it does sound great.

John
post #10 of 244
Thread Starter 
I changed out the bypass cap for the high frequencies for the output caps with my favorite cap the Mundorf Silver Supreme. I used .56uF rated at 1200 volts dc. They are all rated at 1200 dc and 800 ac. I have also used them in the ac to clean it up.

The highs are different with these caps. There is a bit more natural bite and air to the music. More time is needed for these to break in, which can be a few hundred hours. I am also changing out the large decoupling caps, that are 470uF for some Black Gates. The Panasonic aren't bad but I have never heard anything as good as Black Gates, and that includes some poly and film caps. I still feel that in the stock form this is an outstanding buy.

John
post #11 of 244
Thread Starter 

Black Gate output cap upgrade

I installed Black Gate caps in the output in place of the Panasonic. As usual they sounded ok then so-so, then horrible for about 10 hours and now they are coming out of audio hell. BG's can take 400 or more hours to really break-in. These are already sounding better than the originals.

Bass is tighter and deeper. It feels like I have the speakers on, there is a real visceral feel to the bass without it being heavy. All other areas are great. There is a nice openess to the music, transparency and slam. More will be known after a few hundred hours but I have never had a down side to broken-in BG's.

These are a little larger than the Panasonics but still fit without a problem. I am using the Mondorf Silver Supreme .56uF bypass but I have found that with BG's they often do not require and sometimes do not do as well, with bypass caps.

Feels kind of funny answering my own posts but the changes are interesting and maybe someone will benifit from them if they want to modify their Woo3 or any other amp of this kind.

Next change will be to use Mills resistors. I already replaced the cathode bias resistor for the drive tubes with a Riken Ohm carbon. This is a very important resistor and what has been used is a metal oxide, often found in voltage dropping areas. This also yeilded an improvement.

John
post #12 of 244
Quote:
Originally Posted by jamato8
Feels kind of funny answering my own posts but the changes are interesting and maybe someone will benifit from them if they want to modify their Woo3 or any other amp of this kind.
Keep those posts coming.
post #13 of 244
How many hours do you have on the amp now and how many before you started you first mod?

The reason I'm curious is my Woo3 is still totally stock and improving all the time. I would guess that to have about 200-250 hours on it.


Quote:
Originally Posted by jamato8
I installed Black Gate caps in the output in place of the Panasonic. As usual they sounded ok then so-so, then horrible for about 10 hours and now they are coming out of audio hell. BG's can take 400 or more hours to really break-in. These are already sounding better than the originals.

Bass is tighter and deeper. It feels like I have the speakers on, there is a real visceral feel to the bass without it being heavy. All other areas are great. There is a nice openess to the music, transparency and slam. More will be known after a few hundred hours but I have never had a down side to broken-in BG's.

These are a little larger than the Panasonics but still fit without a problem. I am using the Mondorf Silver Supreme .56uF bypass but I have found that with BG's they often do not require and sometimes do not do as well, with bypass caps.

Feels kind of funny answering my own posts but the changes are interesting and maybe someone will benifit from them if they want to modify their Woo3 or any other amp of this kind.

Next change will be to use Mills resistors. I already replaced the cathode bias resistor for the drive tubes with a Riken Ohm carbon. This is a very important resistor and what has been used is a metal oxide, often found in voltage dropping areas. This also yeilded an improvement.

John
post #14 of 244
Thread Starter 
I have about 300 hours on it. I have left it often with music playing on repeat and some tubes I don't mind staying on. I agree that there will be changes and these can continue for some time. But through experience I know that there is a certain level to be obtained with the caps and resistors I use. I have used Mills, Black Gate, Riken Ohm, Tantalum resistors, Mundorf Silver Supreme, plus a few others for some time now. The Black Gates are a step way above any other electrolytic type of capacitor and as mentioned in one of my posts, I find that BG's can be as good as some film caps, which flies in the face of what most would say about electrolytics, but BG's do not fit the mold in any way.

The Woo3 is a bargain at twice the price but it is fun to work with. The biggest change so far is the Black Gates but it may be that the BG's are letting more of the change in sound that the other components have made throug. I do notice that when changing tubes I notice the difference more now.

John
post #15 of 244
We're all dying for pics here John!!
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