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Does the audio signal pass through a coupling cap? Why do I hear changes in sound quality between different caps?
The first is a good question, the second I cannot answer. "Does the audio signal pass through a coupling cap?" Pass through to me means there is a current. In a crossover there is certainly a substantial current that can be several amperes. Indeed things like ESR make a big difference. Dielectric absorption (DA) also makes a difference as the low frequencies are absolutely pumping the dielectric material up and down with many volts. The louder you play the speaker, the lower the impedance, the larger the effects. Yes a big bass transient leave behind a "ghost voltage"in the tweeter series cap due to DA. Lets not have that. I advise people to change caps in their crossoves without reservation. However, I go further to encourage them to save that money and get and electronic crossover (where the caps pass no current) and go direct to their drivers. Crossovers overboard! . Of course, changing the caps is easier. How many are willing to take that big step and make a big difference in their systems. The point about multi-amping is that you can choose specific amps for their specific job. I just hooked the OTL-1 to my horribly inefficient (less than 80 dB/watt) ESL speaker. By design that amp only sees 100 Hz up and a 500 watt transistor amp of no distinction plays 100 Hz down. Even with that inefficient ESL I can play plenty loud. With a conventional speaker of that low efficiency playing full range I would be running out of power in the bass region. I recall the whole boutique cap thing started in crossovers and with that I totally agree. Damn the 10 cent electrolytics with their high ESR and loss of capacitance over time. They are usually 10-20% accurate in value so the crossover points and slopes can vary widely. Bypass them but that won't fix the DA problem because the bypass is to small, but it will help the ESR.Having said all that in my honest opinion as one who does understand how electrons get about in a system, there is virtually no current (a few microamps) at best and no voltage (the cap has little or no reactance at audio frequencies) that the audio signal does not pass through the anymore than it passes through a wire. (I am not inviting a discussion of hook up wire in an amp )Are you saying that coupling caps in an amp make as big a difference in your hearing as crossover caps?The best analogy I can think of right now is that high octane gas vs low octane gas will make a big difference in a high compression engine. It will make less difference in a low compression engine and will make no difference, in my experience, in starting a fire.
Looking at different amps/preamps and gestalt on the net, it seems like you're a minority of 1. I'm not an EE or a circuit designer and certainly don't understand every possible movement of electrons, but it seems virtually everyone else hears significant differences using technically superior coupling caps.
It is interesting to hear that some boutique caps made it worse some made it better. All in all I guess you ended up spending as much or more on the caps than the original Bottlehead amp. I know the V- caps are very expensive, especially in the large sizes. I bought some for customer at his request. As I said, I don't mind doing it, I don't feel its the best use of money when other more important things can be done in a system. As to what you heard. The 1 uF output coupling cap is conducting current so that is the one that should make the most difference. The difference in current is more than ten thousand to one vs the interstage cap. The output coupling cap is driving a load of a few thousand ohms, the interstage cap is driving something like 470,000 ohms and at lower 15 times lower signal level (15 is the mu of tube).I also think the output coupling cap should be a lot bigger. If you are driving a 3000 ohm transformer the -3 dB down point is 53 Hz with 1 uF. This should be a problem, however 32 ohm phones move the -3 point down by 4 to 1 is the inductance of the output transformer is sufficient. Has anyone measured that? I clicked on specs but couldn't find any.I never use less than 33 uF in my rather similar 6EM7 parafeed amp. Why is that cap so small? These are the things that I think need attention.Here is a nice calculator for that sort of thing. http://www.sengpielaudio.com/calculator-XLC.htmI am not surprised to hear the current source mod made a big difference. That is a major circuit change. In my mind it has much more influence over the sound than a cap change. A current source unloads the input triode reduces distortion and raises gain. Did you notice the gain change?If you had a variety of output transformers and chokes to try you would hear bigger differences and it's not about the materials. Magnequest promoted some unusual expensive iron some time ago, where is it now? Seems everyone making parts has become a self appointed materials expert. However who wants to fool around with changing transformers, though yours are pretty easy to get to. Do you know the primary and choke inductance values. They had better be large. Why dont people fool with transformers more than capacitors. The have a bigger chance of making a difference. I will propose that a tranformerm is too difficult and varied to specify. You have to express the impedance ratios, the input inductance, the leakage inductance, the copper loss, the iron loss, the Low frequency saturation point. A cap is easy to specify, capacity and voltage, done. The rest is going on and on about exotic materials, winding techniques, leads, yada, yada , yada. How about changing the 6DN7 to a 6EM7 which has the same pinout but lower output impedance. You would have to change the cathode resistors but little else I imagine. The output impedance is 750 vs 2000 ohms, almost 3 times lower. That will make a big difference.I am simply stating that there are bigger things to do that fooling with caps, however, for some reason fooling with caps has become very popular perhaps only one step below tube rolling. I think it is obvious in any hobby that people change the things that are easiest to change, while leaving the more difficult yet more important things alone. I could make you some iron that would blow the socks off the Bottlehead stuff. Look at the pricing of the kit. Break it down by the parts you know the cost of and you will see that the two output chokes and two output transformers can only cost about $25- $50 each. If you have $250 to spend on a Vcap how about the same for a transformer or audio choke?How about replacing that $2 volume control with a Noble or Alps. I really don't understand how more resolution caused listener fatigue. I find the more detail I get the more I can turn down the volume and that certainly reduces fatigue. Of course the good recording sound better and the bad recordings sound worse. So go play the bad ones in the car.
It takes big expensive machines to make capacitors of the highest quality construction. "boutique" capacitors (unless custom manufactured by a major manufacturer) are seldom of the highest quality construction.
I bought the V-caps out of curiosity. I probably wouldn't spend that much on them again although I do think they sound excellent.I don't have the current version of the the Sex amp which is version 2.1. Mine is the previous 2.0 version. Mine has off the shelf chokes and ouput transformers that have since become discontinued. I believe the choke is 30mH and the OT is 8K. The newer version has custom-made iron. Bottlehead does offer their version 2.1 iron as an upgrade. They don't post the values so I can't comment on that. Magnequest still offers upgraded sets as well and uses Nickel as the special metal to increase the price. According to the bottlehead guys the more nickel the better the sound. I think they wrote some more about it but I can't seem to find it.I was planning on getting the upgraded bottlehead iron as it's only $200. If you can make better iron then I would certainly be interested. They supplied 1uF for the outputs but also recommended 2uF as an option; especially with the upgraded iron.Switching to 6EM7 sounds like fun too. The bottlehead guys did tinker a bit with the 6EM7 tubes and posted the needed changes although I haven't heard of anyone actually doing it. The whole point of the kit was that it was flexible enough to try various circuits/ tubes.The current source did improve the amp considerably. I do recall a bump in gain.I do think you're right about why people mess with caps. They are easy to figure out the values needed and swap out. As a seemingly never-ending novice to this stuff I can personally confirm this. The bottlehead gear is designed for guys who want to put the puzzle together but don't necessarily want to figure out the details behind each piece. I've considered upgrading the volume knob but usually I just max it out as I have a separate preamp connected upstream. The sex amp only has one input whereas my preamp has two. Yeah, the MR caps being too revealing really threw me. It did sound fantastic but at the same time irritating after a while. I have the MR caps in my preamp and don't get the same effect. It's weird. Maybe I need a Shakti stone or ultrasonic filter.
Roger - I think this question may have inadvertantly gotten lost in the recent large posts, so I will ask again.How about adding a smaller, quicker bypass cap to those large value electrolytics in the power section of an amp or preamp or CD player or whatever? IYO is there any benefit to that?
How about adding a smaller, quicker bypass cap to those large value electrolytics in the power section of an amp or preamp or CD player or whatever? IYO is there any benefit to that?
On this one, I have settled with unbypassed Clarity TC caps rather than use any electrolytics at all. They are expensive and large, but the results have been worth it imo.
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