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Modify your Woo 6. . Sophia and EML 274B . Images pages 32, 33, 34 of int. and ext. and... - Page 6

post #76 of 893
Thread Starter 
The silver and oil I have are in storage in Tucson, AZ so I don't think I will most likely be doing that. The tinfoil caps from Mundorf also look interesting and as you mention, they are a very good price.
post #77 of 893
Quote:
Originally Posted by jamato8 View Post
The silver and oil I have are in storage in Tucson, AZ so I don't think I will most likely be doing that. The tinfoil caps from Mundorf also look interesting and as you mention, they are a very good price.
I am very torn about the Mundorf Zn. It is such a great cap, yet it's kind of like that technically perfect young genius violinist who doesn't quite have the soul of a master. I updated my cap shootout with the Zn at the end...

http://www.head-fi.org/forums/f21/or...thread-284863/
post #78 of 893
I'd like to direct your attention to the 5AR4 rectifier tube datasheet, which can be found here(PDF file). Note the maximum ratings, specifically the rating for maximum capacity with a condenser input filter. This number is 60uF. In other words, with a capacitor input filter, which is what the Woo 6 uses, the first capacitor following the rectifier may not exceed 60uF. Any larger and it exceeds the maximum ratings of the rectifier tube, which leads to shortened tube life and possibly arcing. It's also why the rectifier tube seems to have a lot of effect on the sound from what owners are reporting, the tube is being heavily stressed and only the best ones are holding up to the abuse. This blatant design mistake needs to be corrected unless you have too much money or enjoy burning through rectifier tubes.

Fix the circuit first, then go play around with premium boutique parts, not the other way around.
post #79 of 893
Thread Starter 
Your concern is valid but in practice there aren't many designers who have followed this very closely, so Woo can't be faulted in a way. Cary Audio had 1000uf behind 2 GZ34's in their SLA50 and a good GZ34 would and does last for years in the circuit. Now directly heated tubes that come up to rectification fast do fail but not the indirectly heated GZ34's.

Turn the Woo 6 on and meter the DC as it comes up and has to fill the caps. It takes a good 15 seconds or maybe a little less. Now that is a slow ramp up of the voltage, which is great for the tubes (6DE7) getting the DC as their heaters are also coming on and the tube is not being hit with a lot of current all at once. Also the cap following the GZ34 can only be filled as the tube comes up to spec and it doesn't matter if it has 10 volts or 50 as it ramps up the cap is still being charged so since the 34 comes up slow it really isn't being stressed all that much. Also once everything is up and running there is no stress and it doesn't matter about the size of the cap as it is now charged (within reason). Is 60uf or less ideal, sure but remember the manufacture was also trying to be conservative. For something like the 274B you would need to change the circuit to a 8 or less uf cap as it is directly heated and is known to be a more easily stressed rectifier. So my experience over the years has shown that the GZ34 will be and is fine in this circuit but that the directly heated tubes will be a little more effected.

Changing this to a 8uf cap followed by 100ohms and then to the caps would work fine and would be very easy to do. The initial current would be slowed by the 100 ohms, as in a CL90 thermister, which is what I put in the Cary Audio amp so I could use directly heated rectifiers. The following resistor would then be decreased. You might even want to use 800 ohms for each side of a dual power supply or a 400 or 450 in a stock type configuration. The 6DE7's can take more voltage than what they are getting so a smaller power dropping resistor might not be bad. With a 8uf cap as the first one you could use any rectifier that would spec ok for the circuit needs like the 274B from Sophia.
post #80 of 893
Quote:
Originally Posted by jamato8 View Post
Your concern is valid but in practice there aren't many designers who have followed this very closely, so Woo can't be faulted in a way. Cary Audio had 1000uf behind 2 GZ34's in their SLA50 and a good GZ34 would and does last for years in the circuit.
This is why I maintain that the vast majority of "designers" are hacks, they can't even read and follow a manufacturer datasheet.

Quote:
Now directly heated tubes that come up to rectification fast do fail but not the indirectly heated GZ34's.
They all fail. Think about what happens in a momentary power interuption lasting maybe one to five seconds. The capacitors discharge yet the rectifier tube(s) are still hot, when the power comes back on it arcs over and fries.

Quote:
Turn the Woo 6 on and meter the DC as it comes up and has to fill the caps. It takes a good 15 seconds or maybe a little less. Now that is a slow ramp up of the voltage, which is great for the tubes (6DE7) getting the DC as their heaters are also coming on and the tube is not being hit with a lot of current all at once. Also the cap following the GZ34 can only be filled as the tube comes up to spec and it doesn't matter if it has 10 volts or 50 as it ramps up the cap is still being charged so since the 34 comes up slow it really isn't being stressed all that much. Also once everything is up and running there is no stress and it doesn't matter about the size of the cap as it is now charged (within reason).
Wrong. Rectifier tubes do NOT deliver a steady state DC current when they're on, they deliver a spike of DC for the portion of the AC cycle where the voltage coming out of the rectifier exceeds the stored voltage in the capacitor. With a C-input filter there's a sharp current spike lasting anywhere from a few milliseconds to a few dozen milliseconds depending on the DCR of the transformer, the internal resistance of the rectifier, and the size and ESR of the input capacitor. With a full-wave rectifier, this happens 120 times every second. Which brings us to the next rating, Maximum Peak Current, in this case 750mA. This is the maximum current which can be allowed to flow on each AC cycle, given the size of the capacitors in the Woo 6 this rating is most likely being exceeded, and with low ESR Blackgates it's almost certainly exceeded.

To simplify a bit, the larger the input capacitor is, the shorter the current spike will be and the larger the current flow. Lowering the ESR of the capacitor has the same effect. This is how the manufacturer derived the maximum recommended capacitor size, if the cap is larger 60uF, the peak current flow will likely exceed the 750mA rated maximum given typical transformer and capacitor characteristics.

Quote:
Is 60uf or less ideal, sure but remember the manufacture was also trying to be conservative. For something like the 274B you would need to change the circuit to a 8 or less uf cap as it is directly heated and is known to be a more easily stressed rectifier. So my experience over the years has shown that the GZ34 will be and is fine in this circuit but that the directly heated tubes will be a little more effected.
Design center ratings are conservative but that's no excuse to use a 330uF cap when the recommended maximum is 60uF, it's more than 5 times larger. Design center means you can push the specs around 10-20% at most with reasonable safely, not 500%.
post #81 of 893
Thread Starter 
I know it doesn't deliver a constant DC or there would be no need for smoothing. It is a saw toothed type of DC but I don't feel like getting into all the fine specs. I have designed and built amps for years. We can agree to disagree. In practice the GZ34 is working as intended in the circuit. Few things in life are ideal. Again in practice I have seen and used a GZ34 in a 500uf cap following the GZ34 with no ill effects and no arcing. Does it arc directly heated rectifiers sure but then I don't normally use them in the circuit. Would I design my own circuit with a 10 or 20uf cap followed by a resistor? No, I would go directly into an inductor, then to the cap, which is what I do. I will take inductors any day. If there was room I would have the circuit as a LCRCR or a high current L for the last R but that is not practical due to size of a large current L for most home applications due to weight and size.
post #82 of 893
i may be mistaken but the vast majority of tube specs were
done for high gain, high voltage speaker amps...the wa6 is neither...

and in practice, i've yet to experience an arc or a fried rectifier...
even during a black out...of course, the lights didn't come back
for about 10 minutes...i don't doubt for a second that a tube
can fry if pushed intentionally, but in common use it hasn't come
up as an issue, yet..

my burn in rectifier is the rca 5r4gy which has a recommended input
cap specified at 4 uF...it measured 56/51 when i first purchased
it...after 2000 hrs. and countless on and off operation i measured
it today to see how it's changed...it tests as 54/51...oh, it's an
indirect type...the 5u4g and the 274b are the only rectifiers
that i know of that are directly heated...

i should specify, the first cap, a black gate, is a 150 uf/350v...
post #83 of 893
Thread Starter 
Actually high gain doesn't effect anything when rectifying. What you have is a circuit. There are parameters within that circuit and even if the amp or preamp, or dac or whatever circuit has demand of the rectifier, whether that is a solid state or tube, the demand when the circuit is activated will be the same for a given current demand. I had a preamp with series 6X4's (in series for a higher voltage capability) but the current demand due to too large of caps, would shorten their life. I implemented resistors in the line right after them to change this. Also the amount of demand from the circuit is also a factor and with the 6 there isn't that much of a draw, maybe around 90Ma total from the 6DE7's.

The best thing for the rectifier would be a small cap to a resistor of around 100 ohms and then on to the rest of the circuit. In practice I believe the circuit will and is fine but I agree with Roam that many circuit disregard the specs at the cost of a shorter life for the rectifier. It is an easy fix and easy design to implement but why often ignored I do not know. I think one reason is for a fast rectification to a smooth DC with as little parts as possible.
post #84 of 893
thanks for the insights, both of you gentlemen...

john, have you inquired jack as to why he's using a 330uf for the
first cap on the stock wa6? roams' post raises an interesting Q as
to why woo audio is doing this on the stock unit...
post #85 of 893
Thread Starter 
I make different inquires. In the early life of tubes, 1930-1950 (1940 and 1950's the best years of tubes), often designs stayed within limits because it was part of what designers just "knew". They were steeped in this. I have a friend who worked for RCA and designed tubes. He has several patents and of course is long retired but he "knows" tubes like we breath air. Now tubes are are implemented but working knowledge is often different from then.
post #86 of 893
Quote:
Originally Posted by jamato8 View Post
The best thing for the rectifier would be a small cap to a resistor of around 100 ohms and then on to the rest of the circuit. In practice I believe the circuit will and is fine but I agree with Roam that many circuit disregard the specs at the cost of a shorter life for the rectifier. It is an easy fix and easy design to implement but why often ignored I do not know. I think one reason is for a fast rectification to a smooth DC with as little parts as possible.
It might be fine due to the internal resistance of the rectifier and the DCR on the transformer combined with the fact that the ratings are on the conservative side, however, it is by no means an ideal situation. There's the shortened tube life which I mentioned, but perversely enough a larger faster capacitor can actually generate more noise since it shortens and sharpens the top-up current spike near the peak of each AC cycle. There's less ripple & hum but more high frequency hash, and that noise is not easy to filter.

As for why so many manufacturers do it, it comes down to cheapness & ignorance. It's cheaper to upsize a capacitor than to add another stage of RC filtering. It's why LC filters are almost non-existent. Good design rules have been forgotten and lost for the most part. Audio has mostly become a style over substance business, people don't really care about nor understand good design, but they'll respond just like Pavlov's dogs when "more & bigger" "Blackgate" or "Teflon caps" are mentioned.

Thankfully there's still people like John Atwood (Artemis Labs) and Allen Wright (Vacuum State) who still design equipment the proper way. Once in a blue moon a good design also pops up in the headphone world, such as the Moon Audio Luna or Trafomatic Head One. Unfortunately, good designs are very few & far between.
post #87 of 893
Thread Starter 
I have around 30 hours on the Mundorf silver and gold and oil and they have turned dull. I am having to use my Ultrasone 780's as they are brighter in sound than my other headphones. That is ok, I expect this as the caps form. At 3 hours they gave a glimpse of the sound to come and it was good but then I am hoping, aren't I. ? :^)
post #88 of 893
Quote:
Originally Posted by jamato8 View Post
I have around 30 hours on the Mundorf silver and gold and oil and they have turned dull. I am having to use my Ultrasone 780's as they are brighter in sound than my other headphones. That is ok, I expect this as the caps form. At 3 hours they gave a glimpse of the sound to come and it was good but then I am hoping, aren't I. ? :^)
I usually cook my caps for a week before installing, but the one time I didn't was with Mundorf silver/gold (non oil). It did turn dull for a while before coming back in full force, so I wouldn't worry...yet
post #89 of 893
Thread Starter 
Yeah I am not worried. I am very used to this happening.
post #90 of 893
Thread Starter 
Ok, the sound is coming back but needs some smoothing but the quality is returning and the details are there. A little closed in right now but not concerned. I am very curious how these silver and gold play out. The 6 with the split power supply would seem to be a player in the big league.
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Head-Fi.org › Forums › Equipment Forums › Headphone Amps (full-size) › Modify your Woo 6. . Sophia and EML 274B . Images pages 32, 33, 34 of int. and ext. and discussion of the SE . . .