A few years ago Danny Richie over in the GR Research circle created an experiment that anyone could test out. On an inexpensive pair of speakers Danny installed 2 separate crossover boards and made them instantly switchable. The parts for one crossover were generic parts and the other crossover was made with so-called "boutique" parts of higher quality construction. Both crossovers have identical measurements and identical measured output from the speaker. Yet they sound different. I think he still has them available.
At the very least here's the thread.
As I have said many many times. A crossover is one place where caps can
make a difference and I do
believe anyone who says so. The problem I see is that audio enthusiasts have taken this to apply to all capacitor applications. Coupling caps in an amplifier are not doing the same thing.
They have virtually no current going through them and no voltage drop across them.
The boutique capacitor thing has gone viral. It may never end. Very few designers are willing speak out against it. We have a lot of capacitors being made by companies who have little experience. The equipment and the materials to make them is very inexpensive. You could start a Boutique cap company in your garage for $10,000 and make $100 caps that have $1 in materials. Snake oil has a long and sordid history.
I ask this question: If resistors
made a big difference, and they do, who is going to make Boutique resistors and who is going to put them in? They are much harder to make than capacitors and require far more expensive equipment and difficult processes. Resistors do have some problems not discussed such as drift with temperature, drift with time and voltage coefficient (change in resistance with voltage causing distortion).
In the ESL amps we use a $25 Caddock resistor in the feedback network because it has the lowest voltage coefficient available. There are 4 of these in the amp. They are beautiful with gold plated leads. They are non-inductive. This resistor swings 5000 volts of signal across it and that resistor alone is a major contributor to making the amplifier low distortion. Using a standard resistor would increase the distortion measurably. Of course I could blindly apply this discovery to every resistor in the amps and double the price of this amplifier. I could put them where their exceptional qualities would make no difference.
There are some resistors that have no voltage across them and their value can change 100% and not make any difference in how the amp works. There are other resistors that have so little voltage across them that these qualities are vanishingly small. In the OTL-1 the DC considerations are larger than in most amps so I want resistors that won't drift over time so I use the mil-spec Vishays. They cost only ten cents vs 3 cents for common MF resistors. There are about 50 of them. The $25 Caddpcks would make no
difference where they are swinging 0-15 volts vs 5,000 volts. They would
make a $6,000 difference in the price of this amp. [/b][/b][/b]
In all our amps we use precision metal film resistors with low temp and voltage coefficients. In the OTL-1 we are using all Dale/Vishay mil-spec resistors in the signal path. I know this makes a difference, so this is where I spend the money. Botique caps to the back of the room.
If you could buy these resistors would you be willing to find the values of 50-100 resistors in your amp and replace them? At what cost? Capacitors are easy to read, they stand out, the new ones are very pretty and usually there are only 4 in a stereo power amp.
We worked on an RM-10 where the coupling caps were replaced by the owner. He thought it sounded great. It came in for another problem which we fixed. When testing the amp on the bench I noticed one channel had high distortion and less than half power. I found one capacitor had been connected to the wrong terminal and one output tube was not being driven at all. The push-pull amp had become single ended in that channel. At very low power the problem was not noticeable but that channel clipped at 3 watts vs 35 watts for the good channel.
I have an additional theory about upgrades. The Audio Enthusiast will spend the most money on the thing that is easiest to replace. Cables, power cords, fuses are easy to upgrade and have little or no risk of harming the equipment.
If I thought Botique caps made my amps sound better why wouldn't I use them. Do you think I do all this work to make a great sounding amp and overlook something like caps?