| SINGLEENDED |
EL 84 Pentode configuration.
Sound sweet and nice. Except 2 drawback.
Slow no speed .
Bass sound bloated.
Any suggestion . :smash: :D |
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| tkifowit |
I have questions.
Do you have a schematic?
Is it se or pp? |
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| Tube_Dude |
| quote: | Originally posted by SINGLEENDED
EL 84 Pentode configuration.
Sound sweet and nice. Except 2 drawback.
Slow no speed .
Bass sound bloated.
Any suggestion . :smash: :D |
Have you used negative feedback? |
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| SY |
| No NFB = High output Z. High output Z = Big, bloaty bass with speakers not specifically designed for that. And a frequency response that looks like a roller coaster. |
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| SINGLEENDED |
Found out the problem with the pacing.
Over size supply cable , changed to copper tin type.
Bass still bloated.
Schematic : www. Diyparadise.com/buildel84c.html
It's PP.:( |
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| ilimzn |
| Why ask questions, if you don't bother to read answers? |
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| phn |
| Scrap the UL. Try connect the screens directly to B+. |
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| SINGLEENDED |
| Still no good.:hot: |
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| dshortt9 |
| If you have 4,8, and 16 ohm output taps you could use them to apply cathode feedback to the EL84's like Audio Research does. This would tighten up the base. |
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| phn |
Try triode connect the EL84s. 100 Ohm resistor between screen and anode.
This will reduce gain. But it's a start. If this works you might have to use feedback if you want to run the amp in UL or as pentode. Triodes have internal NFB. Pentodes don't. |
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| SINGLEENDED |
| quote: | Originally posted by phn
Try triode connect the EL84s. 100 Ohm resistor between screen and anode.
This will reduce gain. But it's a start. If this works you might have to use feedback if you want to run the amp in UL or as pentode. Triodes have internal NFB. Pentodes don't. |
Triode o/p is 5-6watts
Pentode o/p is 15 -18watts
So triode is out . NFB after all the trouble . No way ... There must be something i'm missing. Let me cool it first.:hot: |
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| ilimzn |
| quote: | Originally posted by SINGLEENDED
There must be something i'm missing. Let me cool it first.:hot: |
Yes, there is - it's SY's answer to your original question - 4th from the top of the thread. |
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| have' |
Hi sigleended,
I have build the Simple EL84 with EL48 as driver quite a time ago.
The bass is realy deep, i think that the only tube amp that lat me feel the sub-bass.
My friends are now building it , and he said the same thing about the bass.
May be there's somethings missing? |
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| SINGLEENDED |
| quote: | Originally posted by have'
Hi sigleended,
I have build the Simple EL84 with EL48 as driver quite a time ago.
The bass is realy deep, i think that the only tube amp that lat me feel the sub-bass.
My friends are now building it , and he said the same thing about the bass.
May be there's somethings missing? |
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| SINGLEENDED |
| quote: | Originally posted by have'
Hi sigleended,
I have build the Simple EL84 with EL48 as driver quite a time ago.
The bass is realy deep, i think that the only tube amp that lat me feel the sub-bass.
My friends are now building it , and he said the same thing about the bass.
May be there's somethings missing? |
IF the bass is really deep , Let me know where have I gone wrong.??? |
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| Wavebourn |
| Use less voltage for screen grids, regulated. |
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| SINGLEENDED |
| quote: | Originally posted by Wavebourn
Use less voltage for screen grids, regulated. |
That helps a little bit. The power supply is fully regulated.The bass is deep and bloated but not tight .I have listen to system that is deep & tight and i am getting close but not close enough.
:cannotbe: |
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| ray_moth |
If you persist in using pentode-mode without NFB, you will never get good, tight bass. Screen supply regulation is important but it's only a drop in the ocean compared to NFB.
The speaker needs damping. Without adequate damping, the speaker cone does not stop dead when the music stops and that is most noticeable at the lower frequencies. You get 'overrun', a bit like an electric motor when the power is swithced off; if you connect a low resistance across the motor, it stops quickly, otherwise it will slow down gradually. A speaker is a kind of linear motor.
NFB lowers the output impedance of the amp, so that the speaker will follow more precisely the signal that's being fed to it. With triode connection, where the OP impedance of the tube is only a few hundred ohms, that's not a big deal; however, with pentode connection, the OP impedance of which is many kilohms, it certainly is a big deal! |
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| Eli Duttman |
| Ray is correct! Loop NFB is a must when using pentode mode finals. Regulating the g2 b+ makes for linearity, but does nothing about the damping factor issue. When the open loop circuitry is reasonably linear to begin with, the closed loop error correction signals are small, which is good. So, regulate g2 B+ and use loop NFB. |
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| SINGLEENDED |
| Back to basic again. What value would U proposed that I used as i'm not really keen on nfb. Best if it is not used at all. I like the amp to sound natural. So kindly give me a value that is min.:) :( :) |
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| Wavebourn |
| quote: | Originally posted by SINGLEENDED
Back to basic again. What value would U proposed that I used as i'm not really keen on nfb. Best if it is not used at all. I like the amp to sound natural. So kindly give me a value that is min.:) :( :) |
The rule is: if you go with a global NFB use it as much as possible so your amp will sound more natural. |
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| Dave Cigna |
| quote: | Originally posted by Wavebourn
The rule is: if you go with a global NFB use it as much as possible so your amp will sound more natural. |
Did you mean to say use as little as possible? It's been a while since I played with PP pentodes and NFB, but my own experience was that zero NFB sounded the most natural. A little tightened the bass, but was less natural sounding. A lot of NFB squashed the sound. Dynamics and precision (in some sense) were there, but the music suffered. Live recordings sounded less live.
Anyway, my advice to SINGLEENDED is to just experiment. It's easy to try different levels of NFB. The classic place to apply it would be at the cathode of the driver tube, but it might be interesting to try the unused EL84 grid, though the feedback signal there would need to be large. A quick experiment you might try is connecting a 500R pot between the 'hot' speaker terminal and ground. Connect the wiper to the EL84 grid. If the amp squeals like a little girl then reverse the plate and screen connections on the OT.
-- Dave |
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| Eli Duttman |
| quote: | Originally posted by SINGLEENDED
Back to basic again. What value would U proposed that I used as i'm not really keen on nfb. Best if it is not used at all. I like the amp to sound natural. So kindly give me a value that is min.:) :( :) |
Look at my previous post. Please notice I said loop NFB, not global NFB. Short loops are less problematic than large loops. If by chance your O/P trafos have unused UL taps, you can try Bandersnatch's exolinear topology. You connect the load resistors of the driving electronics to the UL taps instead of B+. Exolinear is a form of "plate to plate" NFB. If UL taps are (as I suspect) unavailable, try the plate to plate method. A resistor 10X the value of the pentode's grid leak part is a reasonable place to start. If the bass is still too loose, decrease the NFB resistor value.
Edit: fixed typo |
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| Wavebourn |
| quote: | Originally posted by Dave Cigna
Did you mean to say use as little as possible? [/B] |
No.
Or zero, or as much as possible, if you want natural sound.
I.e. or do not change an order of a transfer function, or stretch it as stright as possible. |
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| SINGLEENDED |
Thanks PHN,
100R between screen & anode solved the bloaty bass problems.
Sound sweeter than when i have it up & running.
Amixture of solid copper wire and tinned copper helps in the speed.
Thanks to all U guys.:smash: :) |
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| alexmoose |
| quote: | Originally posted by have'
Hi sigleended,
I have build the Simple EL84 with EL48 as driver quite a time ago.
The bass is realy deep, i think that the only tube amp that lat me feel the sub-bass.
My friends are now building it , and he said the same thing about the bass.
May be there's somethings missing? |
I was going to build one this summer, exactly as you said, with EL84 drivers, do you seggest it? is it worth the money?
I may just used it to handle everything below 1khz, and use my EL34 SET for everything above, does this sound like a plan? I would love your input
-Moose |
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| SINGLEENDED |
| quote: | Originally posted by alexmoose
I was going to build one this summer, exactly as you said, with EL84 drivers, do you seggest it? is it worth the money?
I may just used it to handle everything below 1khz, and use my EL34 SET for everything above, does this sound like a plan? I would love your input
-Moose |
If U ask me , If it is worth the money , Yes /2 it is . Low fabrication cost sweet sounding & also hum free. As U know free from humming is my first goal. Most of the tube pre/power is usually humming or crackling.
Why do u want to use EL 84 PP & EL 34 SET combination to drive your speaker? I'm not sure it will match .It is best to have both running in PP or SET so timing is the same.
:smash: :smash: |
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