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In Reply to: RE: Tube coupling caps reduced from 2.7uF to 1.5uF posted by Mendel on July 16, 2024 at 21:32:33
which will *tend* to lead to "faster" sound.
After complete break-in, if you still feel like "little light on bass and a little thinner in tone," I would try taking out all the bypass caps (both to coupling cap and PS caps) and listen. If still not there, I personally then would add back some small paper-in-oil bypass caps to the coupling cap..
Follow Ups:
Not sure if it's the burn in or my getting used to the sound, but everything is sounding very good. Much more transparent and faster sounding than before, seems to be less noise (lower noise floor). The tone seems to have filled out and the bass is there, tighter and less rounded than before.
Will be adding powered subwoofers to the system soon (getting 2 new 20 amp lines installed in August, one will be for my Acoustats and the two subs) so low bass response of the amp will be irrelevant anyway.
The best option is always to give it your best shot with the best coupling cap you can and call it good.
The more resolving your system is, the easier to hear that this is so. FWIW its also measurable.
Thousands of people, including many many manufacturers use bypass caps. Large caps are inductive and usually do not do the speed and high frequencies perfectly. Audio Research, GR Research.....on and on have used bypass caps. Me too. As capacitors have gotten better over time.....and if you use the very top of the line ones....then you can many times get away with just one cap. You have to experiment to know what is true or not. Do not believe me or anyone. Find out for yourself. Audio is very complicated. When I see someone say something is "only this way"....then most of the time.....it is not true. Very complex is audio.
My friend has an Apogee Duetta speaker that has Vcap Odam caps in his xover.....however, every stack is bypassed by a small value copper foil V-Cap Teflon for even better sound.
But not so much coupling caps. The more resolution your system has the easier this is to hear.
Hi Ralph.
Thanks for your response. I can't argue with your comments, you obviously know far more about amps than I do. However, the sound I am getting from the modded amp does not seemed smeared, on the contrary the amp sounds faster, and more resolving now, the way it was before seemed smeared. Obviously the new Mundorfs are more resolving than the old ones, and this more than makes up for any problems caused by the Dynacap bypass caps I guess.
I like what I'm hearing but now I'm very interested in trying the amp without the bypass caps. Is this something that I could do myself? I just can't keep lugging this 65 pound amp back and forth to my tech. I do have a very basic soldering gun, but no other equipment. Do you need a tool to suck up solder when you remove something? I assume the bypass caps are soldered in place. I think removing bypass caps would be pretty simple, but I have zero experience working inside of amps. Maybe I should just leave things be and enjoy the new sound I am getting.
The amp is definitely quieter since the mods, and power transformer mechanical hum (not through the speakers, just near the amp) has been cut way down. I put that down to the bypass caps on the power supply caps. Those are definitely staying.
isn't fixed by bypass caps. Its more likely that the screws that hold the end shells to the laminations were loose. That can happen over 20 years and can cause the transformer to rattle.
You don't need to solder to remove the pesky bypass caps around the main coupling caps. A set of diagonal cutters will do the job nicely. But if you're not comfortable knowing your way around the insides of the amp I'd take it to someone who does!
You'll hear no loss of highs, but you may notice it seems smoother.
Were the power supply filter caps replaced when you had this work done? The amp is old enough that would be a good idea. The 'half life' of the filter caps in tube amps ('half life' meaning about half of them are ready to fail) is about 20 years (due to heat).
Thanks again Ralph for the info.
Regarding the power transformer, not only are the screws tight, the previous modifications done 10 years ago included some kind of rubber padding to help reduce mechanical noise in the PT. I don't know what they did in the current modification (I don't think they did anything to the PT), but the buzz is now much reduced. So I assumed it was because of bypassing the power supply caps. As for the power supply caps, they were upgraded 10 years ago.
Regarding cutting the bypass caps, wouldn't that ruin them for future use? What if I liked the sound better with them in? They are about $30 each, seems wasteful to destroy them.
Question. Why would Rogue include bypassing the coupling caps in their upgrade package for the Stereo 90 if it is so bad to do so. That's why I did it in the first place.
Those power supply caps can hold a significant charge, possibly lethal! All you need to do is make contact with one positive terminal and any other metal part of the amplifier to possibly electrocute yourself or at least learn the lesson that electricity can hurt. The power supply bypass caps have nothing whatsoever to do with transformer hum and probably not much to do with the sound of the amp. Leave them be.
Despite your testimony to the contrary, I have a hard time understanding why anyone, trying to improve the sound, would bypass a quality capacitor (Mundorf SIO) with a lower quality cap. It just makes no sense at all, financially or technically. Maybe they don't really like the sound of the higher quality cap and want to mitigate its contribution. I would ask the tech.
berate is 8 and benign is 9
In my preamp I have recently changed/renewed the 1,0uF line coupling caps with Mundorf MCap Supreme Silver Gold Oil. After burn in (more than 300 hours) I have bypassed them with the Duelund JDM 0,01uF pure silver axial cap and I am very satisfied with the result.
The Duelund JDM cap has dropped in price and they are now less expensive than before (USD 54 incl. VAT).
You can read reviews about the Duelund's among many other brands at Humble Homemade HiFi. When a cheaper cap was needed in a lower quality speaker/amp or a higher quality cap in a high end speaker/amp I have used his reviews as a guideline. I think his reviews and gradings are very spot on.
https://www.humblehomemadehifi.com/Cap.html
mojul
If you can get them unsoldered that would be better. But again, if you're not comfortable knowing your way around the innards of the amp, take it to someone who does. Knock-on effects aren't worth the trouble!
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