Hello everybody,
I would like to build an tube amp for my bookshelf speakers. I currently own a pair of Wharfedale 220, 25w
minimum power recommended. Sensitivity 86db w/m. I currently listen trough a Yamaha as301.
I have narrowed to these, OddBlock kt88, KT88 Williamson design, Dynaco st70 (vta board) with kt88.
I like the Oddblock as it will be the most cost effective, but i don't know how good it would drive my not so sensitive speakers.
Could you please recommend one from your experience ? I am interested in sonic quality and the ability to drive the speakers. I usually listen at lower volume, i think i'm not dialing the knob more than 11 a clock.
Any other suggestions are welcome
Thanks
I would like to build an tube amp for my bookshelf speakers. I currently own a pair of Wharfedale 220, 25w
minimum power recommended. Sensitivity 86db w/m. I currently listen trough a Yamaha as301.
I have narrowed to these, OddBlock kt88, KT88 Williamson design, Dynaco st70 (vta board) with kt88.
I like the Oddblock as it will be the most cost effective, but i don't know how good it would drive my not so sensitive speakers.
Could you please recommend one from your experience ? I am interested in sonic quality and the ability to drive the speakers. I usually listen at lower volume, i think i'm not dialing the knob more than 11 a clock
.Any other suggestions are welcome
Thanks
I think you should build something with a KT88 .
The self inverting push pull style Oddblock gives up some power in comparison to true push-pull, IIRC. I once read a very good explanation from Eli Duttman on the topic and from what I remember, the SIPP operates more like an actively loaded single-ended stage than a differential driven push-pull. Makes sense looking at the schematic.
That said, the Oddblock is very simple and would probably be a great project for a beginner. The Williamson and Dynaco will outperform it in power and THD but that will be at the cost of a more complicated build.
Unless you're listening in a very large room or from far away (both unlikely if you are using bookshelves), any of these amps will probably give you satisfying volume and decent dynamic headroom.
.The self inverting push pull style Oddblock gives up some power in comparison to true push-pull, IIRC. I once read a very good explanation from Eli Duttman on the topic and from what I remember, the SIPP operates more like an actively loaded single-ended stage than a differential driven push-pull. Makes sense looking at the schematic.
That said, the Oddblock is very simple and would probably be a great project for a beginner. The Williamson and Dynaco will outperform it in power and THD but that will be at the cost of a more complicated build.
Unless you're listening in a very large room or from far away (both unlikely if you are using bookshelves), any of these amps will probably give you satisfying volume and decent dynamic headroom.
The 220 specs. Wharfedale supplies are discouraging. Notice the 4.1 ohm impedance minimum. That requires the speakers be derated to 83 dB. sensitive, when they are mated to tubed power amplification. 2.83 V into 4 ohms is 2 W., not 1 W.
Paul Joppa's 102 dB. rule suggests that upwards of 70 WPC is what those speakers need. Class "AB2" KT88 finals will do that. The Heath W6M, a variation on the Williamson theme, is a reasonable guide to that sort of circuitry. Personally, I'd adjust the small signal complement to improve gain structure and gm.
BTW, even if SS power amplification is retained, the 56 Hz. 3 dB. down spec. strongly indicates that a subwoofer be added to the system.
2.83 V into 4 ohms is 2 W., not 1 W.Paul Joppa's 102 dB. rule suggests that upwards of 70 WPC is what those speakers need. Class "AB2" KT88 finals will do that. The Heath W6M, a variation on the Williamson theme, is a reasonable guide to that sort of circuitry. Personally, I'd adjust the small signal complement to improve gain structure and gm.
BTW, even if SS power amplification is retained, the 56 Hz. 3 dB. down spec. strongly indicates that a subwoofer be added to the system.
Attachments
- PCB available to simplify build process
- Designer is an active member here: pmillett
- Built and scrutinized by many experienced members here
- Scalable from 18W to 125W per channel
- Cheap tubes, most likely 1/10th the price you will shell out for KT88s
Here you go, Engineer's Amp aka DCPP
http://www.diyaudio.com/forums/tubes-valves/151206-posted-new-p-p-power-amp-design.html
- Designer is an active member here: pmillett
- Built and scrutinized by many experienced members here
- Scalable from 18W to 125W per channel
- Cheap tubes, most likely 1/10th the price you will shell out for KT88s
Here you go, Engineer's Amp aka DCPP
http://www.diyaudio.com/forums/tubes-valves/151206-posted-new-p-p-power-amp-design.html
The 220 specs. Wharfedale supplies are discouraging. Notice the 4.1 ohm impedance minimum. That requires the speakers be derated to 83 dB. sensitive, when they are mated to tubed power amplification.
Paul Joppa's 102 dB. rule suggests that upwards of 70 WPC is what those speakers need. Class "AB2" KT88 finals will do that. The Heath W6M, a variation on the Williamson theme, is a reasonable guide to that sort of circuitry. Personally, I'd adjust the small signal complement to improve gain structure and gm.
BTW, even if SS power amplification is retained, the 56 Hz. 3 dB. down spec. strongly indicates that a subwoofer be added to the system.
Oh, i didn't knew that.
The speakers lack some bass on ss as301. I would probably change them next year, either a bookshelves with a bigger cone and better sensitivity, either to a standfloor set.
In regard to the Williamson variation, i was thinking of Loren42 kt88 version. What do you think?
An externally hosted image should be here but it was not working when we last tested it.
Elekit Japan is a good option. I made their TU-8200 that is 10W + 10W with KT88. Driving my 6ohm, 89dB Jamo nicely. I used to use them with Yamaha AX496 but now sound is very sweet and not over powering. This is my setup with Elekit TU-8500 pre-amp https://www.flickr.com/photos/64618899@N04/25640638202/in/dateposted-public/ . The kit is neat and after assembly no one would say it was a DIY.
Elekit are bringing out a new and more powerful amp and i think is based on KT150 tubes. vkung has put up some details in this forum.
Elekit are bringing out a new and more powerful amp and i think is based on KT150 tubes. vkung has put up some details in this forum.
here's another one that i came across Velleman, Inc. - Item - Details - K4040 . And another Edison 60 kit
I settled with Elekit though.
I settled with Elekit though.
2.828 Vrms into 8 Ohms is 1 Watt. A sine wave of 4 volts peak into 8 Ohms is 1 Watt.
2.000 Vrms into 4 Ohms is 1 Watt. A sine wave of 2.828 volts peak into 4 Ohms is 1 Watt.
Connect your loudspeakers to the 4 Ohm Tap on the output transformer. That works for most vacuum tube amplifiers.
Most Solid State amplifiers do not have this setting. They just have to provide
more current to 4 Ohm speakers than to 8 Ohm speakers.
If you listen quietly in a small room, you might not need lots of watts.
If you listen loudly, or in a large room, or both, you Will need lots of watts.
If you have an oscilloscope and probes, you can measure the peak volts into your
speakers, while they are playing at the volume you like to listen.
Although they are not 4 Ohms at all frequencies, you can calculate the approximate power into them: (V)squared / 4 Ohms = peak watts. Amplifiers are rated in rms, not peak watts.
So, Volts Peak/(2 times 4 Ohms) = ~ rms power (Vp/8 = ~ rms) for a 4 Ohm speaker.
2.000 Vrms into 4 Ohms is 1 Watt. A sine wave of 2.828 volts peak into 4 Ohms is 1 Watt.
Connect your loudspeakers to the 4 Ohm Tap on the output transformer. That works for most vacuum tube amplifiers.
Most Solid State amplifiers do not have this setting. They just have to provide
more current to 4 Ohm speakers than to 8 Ohm speakers.
If you listen quietly in a small room, you might not need lots of watts.
If you listen loudly, or in a large room, or both, you Will need lots of watts.
If you have an oscilloscope and probes, you can measure the peak volts into your
speakers, while they are playing at the volume you like to listen.
Although they are not 4 Ohms at all frequencies, you can calculate the approximate power into them: (V)squared / 4 Ohms = peak watts. Amplifiers are rated in rms, not peak watts.
So, Volts Peak/(2 times 4 Ohms) = ~ rms power (Vp/8 = ~ rms) for a 4 Ohm speaker.
Wow, i didn't thought of that. Unfortunately i don't have an oscilloscope. But i did find a thread where is explained how to check the peak with a multimeter.
http://www.diyaudio.com/forums/mult...much-voltage-power-do-your-speakers-need.html
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