Traditionally, higher power tube amplifiers used coupling caps in the 0.22uF range. Smaller amplifiers used 0.1uF, and had no problem producing frequencies lower than 20 Hz. In the past generation, 0.47uF is the customary value, which produces more powerful low end performance. The issue that just about everyone overlooks is the sweetness of the amplifier gets lost as the coupling capacitor size increases. Whether you use 0.1, 0.22, or 0.47uF, there are benefits and trade offs. I tend to tilt back and forth between 0.22 and 0.47uF, neither is right or wrong, it depends on what you prefer at the moment. Those engineers of yesterday were a lot smarter than we realize. In fact, they knew a lot more than just about anyone around today
Yes. When tubes were all we had, we got downright ingenious with workarounds. Still, tubes are a 'lovable form of awful' in many cases of playback systems. Likely, you could go into Abbey Road or Warner Bros. sound stages, and the only vacuum tube you'd find is in the break room microwave oven. Yet, traditionalists celebrate their flaws and glowing little filaments. ;)
The first input tube of the Reisong amp probably has a 100,000 ohm input impedance so the choice of a 0.22 microfarad input cap is a sound engineering choice. But like all things hi fi, replacing the input cap to 2 microfarad one will certainly "fatten" the low frequencies and the Reisong will probably sound gorgeous when playing hip hop and electronic dance music tracks with lots of bass.
@@laurentzduba1298 sure it will 👍😄. The signal is already 3db down on 7.2hz, flat upto 14.4 hz. And the phase shit occurs 2 or 3 octaves above cut off. So choosing lower cutoff is definitely better.
@@laurentzduba1298 2uf is excessive. Just use a 0.47uf capacitor. You would be flat at 20hz, and it is a small enough value where you wouldn't have to sell your first born to buy a decent copper foil capacitor.
@@tristanjones7735 to my ears, silver air gap capacitors are probably the best sounding capacitors ever made. Sadly, it was very hard to get back in the 1990s and probably impossible to get now after the company making it closed shop back around 2002.
Hello and Thanks for your useful videos. I have some questions about the coupling capacitor in the final stage of amplifier. the big electrolytic capacitor that connect between push-pull transistors and the speaker. I have tried to test a self-made 300w amplifier with a 10ohm high power resistor to measure the output voltage and frequency on oscilloscope. In low power everything was quiet. but when I increased the input signal, some buzzy music sound came out from the board. the sound was similar to a little piezoelectric speaker, but there was no inductor to make the sound. the sound source was around the final big coupling capacitor. 1.Can an electrolytic capacitor make sound due to the changing current on it and is it effective on the quality of output signal and sound. 2.Why speaker manufactors dont put a big capacitor on their product in series to prevent unwanted dc current and fail the speaker. It became too long. Hope you patient to read it. thanks.
No corners cut it was a mistake in my submission corner frequency 7.2Hz not 72Hz but according to vcaps.com the capacitor value at input impedance of 100k ohms gives an optimal low frequency response of 72hz with a 7.2hz corner frequency. Anyway I upgraded to a 0.47uf and it sounds even better now. Reisong amps are very well built
Is there any system without caps and inductors in the signal path somewhere? Active speaker drive with high resolution DSP cross-over is possible avoiding the passive cross-over filter, and that’s all great, but the DAC output stage filter is another issue and the power amp can’t be class-D, but that’s ok.
Linn had produced a direct coupled capacitorless preamp back in 1995 - add extra for an RIAA phono preamp stage - but I've never seen it being reviewed by leading hi fi mags between 1995 and 2000.
Sure, the First Watt F5 is a good example of a direct-coupled amp. It'd pair quite well with full-range speakers, too. There are a lot of direct coupled products, but they just aren't common in the grand scheme of things, for a variety of reasons
.22uf is fine with a 100,000 input impedance. that works out to about 10 ohms at 72hz. perhaps your thinking of an output impedance. that would be a bit under 6 db at 72hz. maybe you meant .022uf
Before make your amp burn, check the recordings youre listen, many of them are rolled-off below 40 Hz in order to not to have a terrible buzzing room tone. You can load the file in you PC or Mac and check them on Audacity or iZotope. If you can listen the double basses on a Columbia 60's symphonic recording, your amp is working very good.
Output, not input: I have 8 ohm compression drivers that I actively cross over at 1250 Hz. I put 18 microfarad polypropylene caps in series with them to block some low frequencies in case they happen to find their way onto the wire.
A good opportunity to add *better* coupling capacitors also. Every little thing matters in an SET amp. If corners have been cut at that critical juncture, what else has also?
The 72Hz was a typo when sending the question. That has caused a lot of confusion. 7.2Hz is the -3db corner frequency with the optimal low frequency response being 72Hz according to : www.v-cap.com/coupling-capacitor-calculator.php
@@skularatna8136 You're correct, thanks for the clarification. Is the K42Y a Teflon dialectic cap? I've used a few K40Y-9s and have found the same, usually more perceived detail as well. The V-Cap CUTF is my favorite though. I've recently gone coupling-capacitorless with a Loftin-White DC SET and this has been the best overall to my ears.
@@FireTriode oh nice! Did you construct the loftin white yourself. I found the only issue with that design is if your input tubes fail you affect the entire circuit meaning there is no protection for the output tubes ? Correct me if I am wrong?
The late Ken Ishiwata of Marantz had a reverence on paper in oil capacitors due to their dark inter-transient silences. But unless you are using military spec paper in oil caps, always regularly check when using one in a tube amp for DC leakage. To my ears, paper in oil caps subjectively sounds more musical than mylar and polypropylene capacitors.
I would love to hear an amp with working paper in oil caps. Because of the typical age of consumer devices that used paper in oil caps, I have never heard a device that had working ones. Other than some radios, which sounded like garbage to begin with LOL
@@graxjpg garbage sound is a sign to replace the paper in oil caps. Back in the 1990s, the Parts Connection used to sell surplus tested and working military grade paper in oil caps sourced from the closure of the USAF Strategic Air Command and the former Soviet Union. In use, these caps need to be monitored regularly since when they go bad they tend to leak DC. If you want an alternative that offer less attention and sound almost as gorgeous, high voltage polypropylene caps from the 1950s and the 1960s rated at 630 volts or higher.
@@skularatna8136 If you like the K42-y, you should give the K75-10s a try if you ever wind up opening it up again. I've yet to compare the two, but I've always been happy with the K75s where I've used them!
our brain reconstructs those low frequencies by subtracting the harmonics present above them; they don't need to be physically there for one to perceive them
So, all those pipe organs with 16' and 32' ranks of open pipes (which are hugely expensive) simply are unneeded? We can just reconstruct the tones in our cabezas? Moosedudu on the hifi path.
@@johnholmes912 Yes, some. But they call it 32 Resultant, not 32, and the low fundamentals don't exist in the air -- they are formed in our brains. (And they lack the voicing or a real 32 stop.)
0.22uf is perfectly enough. The problem lies not in the coupling caps, but in the output transformers. All those SET amps usually doesn’t have any negative feedback, that’s why in these circuits all the parts should be the highest possible quality. But those coupling caps actually are the less demanding components, that’s for sure. You can make those caps 1000 uf, but that won’t help at all ))
It's more like not stressing the OPT ! ..........and economic restrictions on the design. As well as a driver that lacks the necessary current to drive the grid of the following tube! The 100K grid resistor is very ( to) LOW .......... Also limitations of the power supply ..........
Yip. It's 7.2Hz, even the "Octave above" is still 14.4Hz, way below what the Audio Impedance matching transformers in just about any Valve amps can handle. Amazing how audiophiles are always gunning for Capacitors when the real audio changers in the chain are the Impedance matching transformers. I think it because it is the balance between the Valves and the Impedance matching transformers that gives the Valve amp it's distinctive sound, so they won't even open that Pandora's box.
Transformers are mostly gone except in power output tube amps. The trouble is, capacitors are still here, and many leak DC and change value with age. It's a partial reason that high priced caps may be money well spent in high end designs.
@@jimshaw899 My comments are based on the Amp mentioned in the video and like many other Valve amp examples, they are definitely not gone. These transformers have a massive impact on the sound reproduction and as mentioned, it plays a big part in what gives Valve amps their character. The lowest to highest frequency in the Audio Band (20hz to 20 kHz many, including me, will argue that its much more) has a ratio of 1000. Producing capacitors that has a flat response over this band, without any dips, peaks or ringing properties, is immensely more doable than producing Transformers that can do the same. Regardless of whether the transformer has an amorphous Iron or silicon-iron core, Coper (in all it's variants) or even pure Silver conductors and the best enamel coating on the conductors, they cannot come close to the ability of the capacitors to pass audio with minimal colouration. As for decay with age, it was not the topic of the video and indeed all components suffer from that. Valves (that are frequently replaced) are much more affected by age than Capacitors but even Transformers are affected as well. But yet those that are so pedantic about those evil capacitors, while pushing Valve amps, will not mention the issues with the output transformers. I think it's because the transformer is part of the kind of sound they like. The BHK signature amps (like some others) overcomes all this by being a Hybrid and having a MOSFET output stage. They therefore do not need the output Transformer. But then again, some will argue that they don't sound "Valve" enough for their taste. My point is that I believe that most people are going for a "type" of sound and that is not necessarily the purest form of the sound.
@@skularatna8136 Okay. I just find it weird that Paul would go with that clearly incorrect figure, and create an imagined justification for it, instead of instantly questioning its accuracy.
@@skularatna8136 -3dB @ 7.2Hz is fine. If you’re playing vinyl, rumble would become a problem @ 15Hz. Correct me if I’m wrong, but i don’t believe that pipe organs reach any lower than 10Hz or so
@@skularatna8136 feel only at that frequency. Very few subs can play that low cleanly anyway. Certainly no full range speakers can. Most subs that can go that low have their own amps, so this is just an academic exercise, don’t you think? I mean, how may angels can dance on the head of a pin? Does it matter?
