I have successfully completed construction of my Tubelab Simple SE amp. No problems so far and, in general, it sounds fantastic except for the very high end. Using the amp with either 6.5 in or 12 in very efficient Audio Nirvana full range Supers, I get significant harshness/distortion at the high end of the frequency range -- sort of like ice picks to the ears especially at higher volume levels but also there even at modest volume levels. I am running EL34s at about 23 Watts dissipation in Triode mode and the output transformers are Edcor GXSE15-8-5. Would using cathode feedback (without UL) be likely to get rid of the high frequency harshness?
Thanks
Thanks
No replies yet which makes me wonder if this is this just too stupid of a question to ask?
I forgot to mention that a lower powered SE triode amp ( a SPUD amp) that I have been using with these same speakers does not show the same high frequency distortion that I am getting with the Tubelab SSE. I would like to be able to use the Tubelab SSE since I have invested significant time and money building it, but I need help figuring out how to fix the high frequency problem. Sorry, but I don't have any diagnostic equipment other than a DMM.
I forgot to mention that a lower powered SE triode amp ( a SPUD amp) that I have been using with these same speakers does not show the same high frequency distortion that I am getting with the Tubelab SSE. I would like to be able to use the Tubelab SSE since I have invested significant time and money building it, but I need help figuring out how to fix the high frequency problem. Sorry, but I don't have any diagnostic equipment other than a DMM.
Hi wcakey. Cant say if what I noticed with my build is similar to yours, but I had harsh sounding 'in your face' midrange in Triode.
In UL it is a completely different sounding amp. Don't have CFB and max B+ is 360v ~ 18W.
In UL it is a completely different sounding amp. Don't have CFB and max B+ is 360v ~ 18W.
The only time I have noticed any sort of high frequency harshness with my SSE is when I have neglected to pay any attention to oxidation on tube pins - the driver tube in particular.
I have experienced the "in your face" midrange that sunil describes - this was all down to EL34 output tubes, which I have learned I simply do not like in this amp at all. Swap in some 6L6GC or some (extremely good value) Russian 6P3S-E (AKA "Sovtek 5881") and it is like a completely different amp. Super smooth and balanced.
I have a UL switch on my amp and it honestly sounds incredibly boring to me compared to plain old triode - no feedback in either case.
Note: in my case I am running Transcendar OPTs driving medium-high efficiency full-rangers. B+ is 415-430v depending on what rectifier I am running.
I have experienced the "in your face" midrange that sunil describes - this was all down to EL34 output tubes, which I have learned I simply do not like in this amp at all. Swap in some 6L6GC or some (extremely good value) Russian 6P3S-E (AKA "Sovtek 5881") and it is like a completely different amp. Super smooth and balanced.
I have a UL switch on my amp and it honestly sounds incredibly boring to me compared to plain old triode - no feedback in either case.
Note: in my case I am running Transcendar OPTs driving medium-high efficiency full-rangers. B+ is 415-430v depending on what rectifier I am running.
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Thank you sunil and cogitech for responding. I had Rk at 560R which, with a B+ of 438V, brought me close to the max dissipation value for EL34 (25 Watts). I decided to try using a slightly larger value for Rk (600R). For some reason that seems to have gotten rid of most of the harshness that I was experiencing at the top end, but it also left it somewhat devoid of life. I happened to have a pair of 6L6GC's and tried them out with no other changes. Definitely an improvement over the EL34's.