I am looking for a DIY tube amp project and have been eyeing the Tubelab SSE and SPP, the Poddwatt, The Red light District amp and some others, but I'm having trouble deciding which topologies would make a good match with my speakers.
The speakers in question are Epos Epic 5 floorstanding speakers. They are reasonably sensitive (92dB / 2.83V@1m) 2.5-way 4 ohm speakers (I think they dip down to about 3.6ohm).
They are currently powered by a TPA3116 class D amp that delivers maybe 2x15W on its current power supply, giving more than enough volume.
For the tube amp I don't need ear-shattering volume levels but I do want a good presence, and the bass should not be lacking.
I think the Epos 5's sensitivity should be ok for an EL84 PP or maybe even SE amp, but the impedance worries me; to my understanding low impedances are hard to serve for a tube amp.
Would something like the Tubelab SSE be an option at all with these speakers or should I look at push-pull circuits only? And if so, which one would be comfortable driving these speakers and have a rewarding sound? Should I get all the wattage I can (PP pentode mode like SY's RLD) or will lower output triode mode suffice (like Podwatt)?
Any suggestions are much appreciated!
The speakers in question are Epos Epic 5 floorstanding speakers. They are reasonably sensitive (92dB / 2.83V@1m) 2.5-way 4 ohm speakers (I think they dip down to about 3.6ohm).
They are currently powered by a TPA3116 class D amp that delivers maybe 2x15W on its current power supply, giving more than enough volume.
For the tube amp I don't need ear-shattering volume levels but I do want a good presence, and the bass should not be lacking.
I think the Epos 5's sensitivity should be ok for an EL84 PP or maybe even SE amp, but the impedance worries me; to my understanding low impedances are hard to serve for a tube amp.
Would something like the Tubelab SSE be an option at all with these speakers or should I look at push-pull circuits only? And if so, which one would be comfortable driving these speakers and have a rewarding sound? Should I get all the wattage I can (PP pentode mode like SY's RLD) or will lower output triode mode suffice (like Podwatt)?
Any suggestions are much appreciated!
Tube amps don't exhibit the large damping factors found in SS amps. It's not a low nominal impedance that's the problem. The problem is dips in the impedance curve. The numbers you provided are favorable. Just use proper O/P "iron".
The "true" sensitivity of the speakers is 89 dB. 2.83 V into 4 Ω is 2 W., not 1 W. Paul Joppa's 102 dB. rule indicates that upwards of 30 WPC is what you need. You are currently underpowered (slightly). PP EL84s will yield about the same power you currently have. You can go SE, with a full pentode or UL mode KT88 and get a similar yield.
The "true" sensitivity of the speakers is 89 dB. 2.83 V into 4 Ω is 2 W., not 1 W. Paul Joppa's 102 dB. rule indicates that upwards of 30 WPC is what you need. You are currently underpowered (slightly). PP EL84s will yield about the same power you currently have. You can go SE, with a full pentode or UL mode KT88 and get a similar yield.
Here is the impedance curve of the Epos 5 (provided by Stereophile):
Red and yellow traces being the impedance modulus, blue being phase.
Looks quite uneven to me but I don't know what the norm is.
You're right about the actual sensitivity being lower, and I guess to get anywhere near the suggested 102dB I should probably be looking at PP circuits. It might even make more sense to just stay with tube preamp and solidstate poweramp which I use now with good results, but I have an itch to build a tube power amp 🙂
Red and yellow traces being the impedance modulus, blue being phase.
Looks quite uneven to me but I don't know what the norm is.
You're right about the actual sensitivity being lower, and I guess to get anywhere near the suggested 102dB I should probably be looking at PP circuits. It might even make more sense to just stay with tube preamp and solidstate poweramp which I use now with good results, but I have an itch to build a tube power amp 🙂
15 WPC will not get you to a 102 dB. SPL @ 1 M. That's why I said you currently are slightly underpowered. If you match that SS 15 WPC with tubes, you will be slightly better off. Tube amps compress, before hard clipping sets in. SS immediately hard clips. More speakers have been damaged by underpowered amps clipping than being over driven by lots of power. A tube amp can be safely pushed into the verge of clipping, but it's unsafe to do so with SS. Hard clipping "fries" tweeters. 😡
You should do fine connected to 4 Ω speaker taps. The worst dip in that impedance curve is (fortunately) not in the deep bass and the deep bass is where bad things happen.
The power section of the 20 WPC Sherwood S5000 (schematic uploaded) could be a good point of departure for this project. The 7199 is more or less extinct, but you can "score" a stockpile of highly suitable 6GH8s off "EBone", before that type too disappears. The ONLY O/P tube to use in that setup is the Russian 6П14П-EB (6p14p-ev), AKA EL84M, which is a very tough 7189 equivalent. The Russian tube sounds pretty darned good too. 🙂 FWIW, my preference is to buy tubes from reliable dealers, whenever possible. Jim McShane is my go to guy, but he's definitely not the only "straight shooter" out there.
Circuitry, like the S5000, that employs global NFB must be built with O/P "iron" that exhibits substantial magnetic headroom. The headroom is needed to avoid encountering core saturation from the deep bass error correction signal. 🙁 Edcor's CXPP50-MS-8K, with its 50 W. rating is a bit overkill, but much better too much "iron" than not enough. That core will NOT saturate. 😀
You should do fine connected to 4 Ω speaker taps. The worst dip in that impedance curve is (fortunately) not in the deep bass and the deep bass is where bad things happen.
The power section of the 20 WPC Sherwood S5000 (schematic uploaded) could be a good point of departure for this project. The 7199 is more or less extinct, but you can "score" a stockpile of highly suitable 6GH8s off "EBone", before that type too disappears. The ONLY O/P tube to use in that setup is the Russian 6П14П-EB (6p14p-ev), AKA EL84M, which is a very tough 7189 equivalent. The Russian tube sounds pretty darned good too. 🙂 FWIW, my preference is to buy tubes from reliable dealers, whenever possible. Jim McShane is my go to guy, but he's definitely not the only "straight shooter" out there.
Circuitry, like the S5000, that employs global NFB must be built with O/P "iron" that exhibits substantial magnetic headroom. The headroom is needed to avoid encountering core saturation from the deep bass error correction signal. 🙁 Edcor's CXPP50-MS-8K, with its 50 W. rating is a bit overkill, but much better too much "iron" than not enough. That core will NOT saturate. 😀
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