Long time reader, first time poster, as they say. I have learned so much from this forum and it really has helped me get my new SSE put together.
I have a couple questions that I'm having a bit of a hard time fully understanding, I've done research, but the answers seem a little conflicting / vague. If you folks have time, would you mind clarifying the following?
- A few amp specs first:
Edcor CXSE25-8-5K OPSs
KT88 Tubes
440v at the plates
455v B+
560 ohm cathode resistors
Connected to Klipsch Heresy speakers.
- Regarding cathode feedback, how do I know when this is necessary? When I flip the switch on, the amp gets quieter, as it should. Other than this, I'm not sure that I can detect any other sonic differences (I might not have the golden ears...). What should I be detecting from a sonic perspective, or in other words, if it was off, what sonic clues would tell me, "hey man, you need some feedback on that amp"?
- I've looked at the chart on tubelab.com regarding simulations, did not see any documentation of KT88 tubes. What cathode resistors are the best choice considering the above voltages.
- The room that I have these speakers in is somewhat big, and even though they are at the upper range of mid-efficiency, I'd like to have all the clean volume possible. I know how to test for distortion with a dummy load, how do I find the max clean volume with speakers attached and music playing (real world vs. test tone). I have not grown a pair of golden ears yet, so determining max volume is not easy for me.
That you for your patience with my long-winded post, and thank you in advance for your thoughts.
-- Pete
I have a couple questions that I'm having a bit of a hard time fully understanding, I've done research, but the answers seem a little conflicting / vague. If you folks have time, would you mind clarifying the following?
- A few amp specs first:
Edcor CXSE25-8-5K OPSs
KT88 Tubes
440v at the plates
455v B+
560 ohm cathode resistors
Connected to Klipsch Heresy speakers.
- Regarding cathode feedback, how do I know when this is necessary? When I flip the switch on, the amp gets quieter, as it should. Other than this, I'm not sure that I can detect any other sonic differences (I might not have the golden ears...). What should I be detecting from a sonic perspective, or in other words, if it was off, what sonic clues would tell me, "hey man, you need some feedback on that amp"?
- I've looked at the chart on tubelab.com regarding simulations, did not see any documentation of KT88 tubes. What cathode resistors are the best choice considering the above voltages.
- The room that I have these speakers in is somewhat big, and even though they are at the upper range of mid-efficiency, I'd like to have all the clean volume possible. I know how to test for distortion with a dummy load, how do I find the max clean volume with speakers attached and music playing (real world vs. test tone). I have not grown a pair of golden ears yet, so determining max volume is not easy for me.
That you for your patience with my long-winded post, and thank you in advance for your thoughts.
-- Pete
Attachments
I have a very similar setup to you. KT88's with 580R. My B+ is a little lower than yours (425'ish when loaded). My Polk rt600i speaker are about 89db sensitive and I too, have wondered about CFB. I dismissed UL as I don't need the extra volume.
After posting a similar question, it seems that CFB only really has noticeable benefits with smaller output transformers. For this reason, I have changed my CFB/UL switches to serve as cathode resistor selectors, which is allowing me to run different tubes.
Charlie
After posting a similar question, it seems that CFB only really has noticeable benefits with smaller output transformers. For this reason, I have changed my CFB/UL switches to serve as cathode resistor selectors, which is allowing me to run different tubes.
Charlie
Pete,
Scroll down George's list of simulations, the KT88's follow the simulations for 6L6 tubes.
Charlie
Oh boy, I'm blind, for as many times as I've read those pages, I can't believe that I skipped over the KT88 section!
Now that I have the info to compare EL34s and KT88s, I'm going to have to ponder over the charts before asking any more beginners questions.
I'm still trying to understand what feedback does in an audio sense. In the physical wiring sense, I understand that some of the output is fed back into G3 as opposed to it being grounded as a supressor frequently is.
I also understand that non-tube amps frequently use a lot of it, and some say that the more a tube amp uses, the more it sounds like a solid state amp.
Hopefully I'm right on those statements? That seems to be where my understanding stops, could somebody take it from there and go a bit farther?
Regarding the open nature of the build... The first amp I made was a Dynaco ST-70 clone... I was hoping to use my test equipment to follow the signal and better understand how everything works, unfortunately, that amp packs components in so tight that it's a pain get probes attached in many places. For this amp, I wanted everything to be easy to get to for learning / testing. The plan is to make a rigid metal mesh cage to go over the exposed components, with holes cut for the tubes to protrude. Just haven't got that done just yet.
-- Pete
Now that I have the info to compare EL34s and KT88s, I'm going to have to ponder over the charts before asking any more beginners questions.
I'm still trying to understand what feedback does in an audio sense. In the physical wiring sense, I understand that some of the output is fed back into G3 as opposed to it being grounded as a supressor frequently is.
I also understand that non-tube amps frequently use a lot of it, and some say that the more a tube amp uses, the more it sounds like a solid state amp.
Hopefully I'm right on those statements? That seems to be where my understanding stops, could somebody take it from there and go a bit farther?
Regarding the open nature of the build... The first amp I made was a Dynaco ST-70 clone... I was hoping to use my test equipment to follow the signal and better understand how everything works, unfortunately, that amp packs components in so tight that it's a pain get probes attached in many places. For this amp, I wanted everything to be easy to get to for learning / testing. The plan is to make a rigid metal mesh cage to go over the exposed components, with holes cut for the tubes to protrude. Just haven't got that done just yet.
-- Pete
The KT88's are quite a different sound than the EL34's. I just wired a couple of cathode resistor switches. With 910R on the board, the EL34's sound warm and full, maybe "lush" is a good word for it. With a cathode switch flipped, I put around 535R between cathode ground with the KT88's. The sound is crisp, with good extension of treble and bass. The music sounds more open and defined, however, the warmth is gone.
I can well imagine that some music will sound great with the KT88's, while other music will be better with the EL34's. I am thinking that Queen's Night At The Opera will be stunning with the KT88's, while a late evening glass of scotch with Coltrane will demand the EL34.
The question is, which single malt should I try???
Charlie
I can well imagine that some music will sound great with the KT88's, while other music will be better with the EL34's. I am thinking that Queen's Night At The Opera will be stunning with the KT88's, while a late evening glass of scotch with Coltrane will demand the EL34.
The question is, which single malt should I try???
Charlie
I like your analogy and switch idea. I'm thinking about putting in a switch and a four pole connector so that it's possible to put various resistors in parallel with the 560 for the purpose of experimentation. However, since I just got this thing working a few days ago, I suppose I should leave it alone and enjoy it for a while.
If you get a chance Charlie, would you post a pic of your amp?
-- Pete
If you get a chance Charlie, would you post a pic of your amp?
-- Pete
To answer one of the OP original questions about feedback.
Running CFB & UL I get tighter bass response, but I have HUGE speakers so I'm always looking for ways to improve the low end. With SE it's I think the hardest part to get right. I have 15" woofers so sloppy bass will shine thru, the UL and CFB help with that for me.
Cheers,
Bob
Running CFB & UL I get tighter bass response, but I have HUGE speakers so I'm always looking for ways to improve the low end. With SE it's I think the hardest part to get right. I have 15" woofers so sloppy bass will shine thru, the UL and CFB help with that for me.
Cheers,
Bob
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