Klimon said:
Well, I did.. I'm just not sure what is the 'real' line level as there is contradictory info about it.
I have thought about that, too. I'm just wondering what is the 'normal' line level and what devices use it.
Is it the 2Vpp of CD players or the 0.9Vpp said in wikipedia or what. But I'm wondering if it could be possible to build the amp so that you could turn the buffer amp on with a switch, and you could bypass it when you don't need it without making it a separate device..
Hello Joku,
Why? You´re running your F2a in triode mode. So pentode drives triode. Take a look at this one.
Also Pete Millet is very fond of pentode drivers. You can find this amp on his page in which he uses a D3a in pentode mode to drive a KT88.
Kind regards,
Martin
Why? You´re running your F2a in triode mode. So pentode drives triode. Take a look at this one.
Also Pete Millet is very fond of pentode drivers. You can find this amp on his page in which he uses a D3a in pentode mode to drive a KT88.
Kind regards,
Martin
Line level
The Wiki article is a little confusing and inaccurate. The description
of "sine wave amplitude" doesn't make sense. The nominal levels
given in rms apply to sine waves also, not only "general signals",
whatever those are! (I think they are giving peak voltage at the
crest of the sine wave in the article as "amplitude", RMS x 1.414)
Anyway, the nominal levels are just that; nominal. In a pro recording
studio, +4 dBu should move the VU meter to "0". The highest peak
level can range from +18 to +30 dBu. If the nominal level is +4 dBu
and the peak level is +18 dBu, the system is said to have 14 dB of
headroom, i.e. it will pass undistorted a sine wave signal of +18 dBu
amplitude or about 6.2 VRMS. Studio gear is available which will pass
over +30 dBu sine wave signals, ~ 25V RMS
For consumer gear the nominal level is -10dBv which is 0.316 VRMS
(sine wave or otherwise) The "2V" we keep hearing about is 2VRMS
max undistorted sine wave signal. This means that the nominal level
is .316 VRMS and the max level the circuit will pass is 2 VRMS, giving about
16 dB of dynamic headroom.
In a nutshell, depending on the way the program is mixed at the
studio, the average level output by a CD player, receiver, Phono
preamp, etc. should be about 0.316V RMS for the louder passages,
which allows the headroom needed up to 2V RMS equivalent, to pass
the drum hits and string attacks etc. without clipping. This is of
course at full volume setting or without any attenuation.
There is no need for your amplifier to have more gain than that needed
to pass the peak level from your source without clipping. With
tube amps maybe you can make use of more gain than that
due to the soft clipping, say another 3-6 dB (1.5-2x more gain)
than that minimum. Lars' suggestion of 0 dBU (.775V RMS input at
clipping) sounds pretty sensitive and could be easily done in one
gain stage.
Real output levels are all over the map, and there is currently
tremendous pressure from audio device (MP3...) manufacturers to
reduce the 2 VRMS to a lower level that can be provided by 3.3V
supplied circuits. This may be why your powerbook doesn't even
come up to the nominal level.
http://www.audiodesignline.com/howto/210500003
(TBTW, this article shows a lack of understanding of level structure)
I have all kinds of issues plugging single ended laptop outputs into
my gear, commercial, pro, or DIY, due to excessive hum and noise.
If I unplug the AC adapter, it all goes away. I would think about some
kind of isolated buffer with gain if I wanted to use my laptop as a
signal source. How about SPDIF to an external DAC? Maybe powerbooks
don't have this problem.
Cheers,
Michael
The Wiki article is a little confusing and inaccurate. The description
of "sine wave amplitude" doesn't make sense. The nominal levels
given in rms apply to sine waves also, not only "general signals",
whatever those are! (I think they are giving peak voltage at the
crest of the sine wave in the article as "amplitude", RMS x 1.414)
Anyway, the nominal levels are just that; nominal. In a pro recording
studio, +4 dBu should move the VU meter to "0". The highest peak
level can range from +18 to +30 dBu. If the nominal level is +4 dBu
and the peak level is +18 dBu, the system is said to have 14 dB of
headroom, i.e. it will pass undistorted a sine wave signal of +18 dBu
amplitude or about 6.2 VRMS. Studio gear is available which will pass
over +30 dBu sine wave signals, ~ 25V RMS
For consumer gear the nominal level is -10dBv which is 0.316 VRMS
(sine wave or otherwise) The "2V" we keep hearing about is 2VRMS
max undistorted sine wave signal. This means that the nominal level
is .316 VRMS and the max level the circuit will pass is 2 VRMS, giving about
16 dB of dynamic headroom.
In a nutshell, depending on the way the program is mixed at the
studio, the average level output by a CD player, receiver, Phono
preamp, etc. should be about 0.316V RMS for the louder passages,
which allows the headroom needed up to 2V RMS equivalent, to pass
the drum hits and string attacks etc. without clipping. This is of
course at full volume setting or without any attenuation.
There is no need for your amplifier to have more gain than that needed
to pass the peak level from your source without clipping. With
tube amps maybe you can make use of more gain than that
due to the soft clipping, say another 3-6 dB (1.5-2x more gain)
than that minimum. Lars' suggestion of 0 dBU (.775V RMS input at
clipping) sounds pretty sensitive and could be easily done in one
gain stage.
Real output levels are all over the map, and there is currently
tremendous pressure from audio device (MP3...) manufacturers to
reduce the 2 VRMS to a lower level that can be provided by 3.3V
supplied circuits. This may be why your powerbook doesn't even
come up to the nominal level.
http://www.audiodesignline.com/howto/210500003
(TBTW, this article shows a lack of understanding of level structure)
I have all kinds of issues plugging single ended laptop outputs into
my gear, commercial, pro, or DIY, due to excessive hum and noise.
If I unplug the AC adapter, it all goes away. I would think about some
kind of isolated buffer with gain if I wanted to use my laptop as a
signal source. How about SPDIF to an external DAC? Maybe powerbooks
don't have this problem.
Cheers,
Michael
We listen to the result of individual stages. Cancellation reduces mainly less offensive 2nd order harmonics. By looking at THD it might look OK. What we should look for is odd order harmonics. But in a RH/partial feedback amp high odd order harmonics are left and this is not that funny. So the harmonic spectra of each stage IS very imporant.
revintage said:
revintage said:
Yes, if there is minimal distortion in individual stages, then the outcome should also have minimal distortion. I would agree, that's it's easier to engineer this way. But it's still the overall result that matters, and sometimes this can be surprising (good or bad). BTW, I would include the power supply in this outcome too.
I do disagree with the general dismissal of the AT7, at least in one case. I had a pair of pp amps with AT7 as the input tube. Distortion profile was excellent (IIRC, at least 60dB down on 2nd, 10 more on 3rd, a little 4th, and very little higher order). This at about half way to clipping, as my sound card only did 1V RMS.). Very nice sounding amp.
Sheldon
Dear Joku
What about simply schematic from NEUMAN
http://www.diyaudio.com/forums/attachment.php?attachmentid=151694&stc=1&d=1261915060
In that way isn't the live easily???
Ivo-Cici
What about simply schematic from NEUMAN
http://www.diyaudio.com/forums/attachment.php?attachmentid=151694&stc=1&d=1261915060
In that way isn't the live easily???
Ivo-CiciAttachments
Sorry for answering to this old thread, but I have been busy (ie. exchange studying) and I'm now returning to this project.
Anyways, that Neuman's schematic uses F2a as a pentode and I don't have access to the EF804 in quantity. So, that is the reason I would like to use the ECC40 as a driver. I decided to design the amp around a 2Vpp input, so I'll plan to use the first section of the ECC40 as a normal voltage gain amp (gain around 25) and the second section as a cathode follower to drive the F2a. This is my revised schematic:
Opinions?
Anyways, that Neuman's schematic uses F2a as a pentode and I don't have access to the EF804 in quantity. So, that is the reason I would like to use the ECC40 as a driver. I decided to design the amp around a 2Vpp input, so I'll plan to use the first section of the ECC40 as a normal voltage gain amp (gain around 25) and the second section as a cathode follower to drive the F2a. This is my revised schematic:
An externally hosted image should be here but it was not working when we last tested it.
Opinions?
Last edited:
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