Hello there,
I have browsed through the designs in this forum to find a line stage pre-amp to place between my 500mV phono stage and my 45 SE power amp.
As per the power amp designer, the line needs a 15÷20 dB gain, which seems pretty rare around here. Maybe the only DIY solutions I have found are Ale Moglia's 2P29L or 4P1L DHTs, but I haven't gotten a confirmation on the actual gain yet, and besides those projects may be too far beyond my skills to build.
I like the JE Labs line stage but that only gives me 8x / 9dB, as most designs seem to. I am looking for a simple design that is linear, quiet and transparent without needing any exotic or very expensive parts.
Any suggestions?
Thanks.
I have browsed through the designs in this forum to find a line stage pre-amp to place between my 500mV phono stage and my 45 SE power amp.
As per the power amp designer, the line needs a 15÷20 dB gain, which seems pretty rare around here. Maybe the only DIY solutions I have found are Ale Moglia's 2P29L or 4P1L DHTs, but I haven't gotten a confirmation on the actual gain yet, and besides those projects may be too far beyond my skills to build.
I like the JE Labs line stage but that only gives me 8x / 9dB, as most designs seem to. I am looking for a simple design that is linear, quiet and transparent without needing any exotic or very expensive parts.
Any suggestions?
Thanks.
Yes, it would be optimal to have an output gain stage only in that phono pre. A phono pre with higher output voltage would also be a solution. It is only the phono pre that has non standardized line level so why have all the sources extra amplified? A big bonus is the that all sources including the phono pre are then about the same volume (when switching sources). Anyone having experienced the CD introduction will know what I mean. CD suddenly had 2V rms and an FM tuner was about 0.5V rms. Switching from moderate volume while playing a CD to tuner resulted in shock effects 🙂
Modern sources don't need extra amplification in general. If you will use a hi gain preamp you'll have more noise, possibly nervous volume control, maximum volume at 9 o'clock etc. when using CD/DAC/DAB+/Audio player.
Modern sources don't need extra amplification in general. If you will use a hi gain preamp you'll have more noise, possibly nervous volume control, maximum volume at 9 o'clock etc. when using CD/DAC/DAB+/Audio player.
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That sounds like an excellent idea. I kind of had the feeling I was going a nonstandard route.
All of a sudden the 15dB value I was suggested makes sense. 0.5->2V is a 4x amplification, i.e. 6dB, which adds up to a standard 9dB line pre to make 15.
Do you have any "phono booster" schematics that you would suggest? I could also integrate that in the line stage enclosure and hook it to a dedicated "phono" input.
I have a little DAC that I almost never use but it would be nice to have the same unput level at the channel selector, as you mention.
Thanks.
gm
All of a sudden the 15dB value I was suggested makes sense. 0.5->2V is a 4x amplification, i.e. 6dB, which adds up to a standard 9dB line pre to make 15.
Do you have any "phono booster" schematics that you would suggest? I could also integrate that in the line stage enclosure and hook it to a dedicated "phono" input.
I have a little DAC that I almost never use but it would be nice to have the same unput level at the channel selector, as you mention.
Thanks.
gm
Well it seems most go that nonstandard route which makes it the standard way 😀 Errors are more copied than good ideas.
When one sees this in practice with many tube device owners one can not avoid to think how silly this approach is adding hum, noise and what not. It was solved in the solid state world in the 1980's already when CD was introduced. That is 40 years ago so not exactly a fresh idea. I would not accept large volume differences and totally unnecessary addition of noise and hum in any case.
When one sees this in practice with many tube device owners one can not avoid to think how silly this approach is adding hum, noise and what not. It was solved in the solid state world in the 1980's already when CD was introduced. That is 40 years ago so not exactly a fresh idea. I would not accept large volume differences and totally unnecessary addition of noise and hum in any case.
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Wait a minute... The JE Labs has an 8x voltage gain, that makes 18dB then, right? That would be plenty for my phono. I even see options with lower gain tubes if I don't need that much gain.
And if I can get the line amplification to roughly 4x, I could wire the 2V digital source inputs to bypass the amplification altogether, and have a passive line stage for those. Would that sound right?
Signal levels pre-digital are complicated, and were specified very differently than the current "full scale equals 0dB equals X volts". For analog media, both vinyl and mag tape, levels were specified for an "averaged" working level ("0VU") and the media needed to supply a considerable overhead capacity for peaks. +20dB was considered a professional overhead, and +30dB was possible for the very best media, including vinyl records.
Coming from a radio station tradition, recording folk worked from meter levels specifically averaged and ballistically damped to reflect the subjective loudness of various sources to allow them to be mixed and faded together in real time, called VU meters. This VU meter tradition was incorporated into recording, and so recording levels were specified in dBVU. "0 VU" is a level undefined in voltage, but defining an averaged signal level. Recording levels to vinyl or tape are specified referenced to 0VU.
For example, a phono cartridge's output is specified in milliVolts at 0VU = 5cm/s (although this varied over time between 5cm/s horizontal and 5cm/s per channel and is seldom specified although 3dB different - but who's counting?). Peak cutting velocities can be 20 or 30dB higher than this, and limited only by the mechanical limitations of the cutter head and the playback tracking ability.
This is a whole different critter than a digital source whose output is specified at an inviolate clipping level of 0dB. And this difference causes all kinds of confusion, not even counting the massive compression, for artistic reasons?, of modern digital recordings, which clouds and confounds the issues.
All good fortunes,
Chris
Coming from a radio station tradition, recording folk worked from meter levels specifically averaged and ballistically damped to reflect the subjective loudness of various sources to allow them to be mixed and faded together in real time, called VU meters. This VU meter tradition was incorporated into recording, and so recording levels were specified in dBVU. "0 VU" is a level undefined in voltage, but defining an averaged signal level. Recording levels to vinyl or tape are specified referenced to 0VU.
For example, a phono cartridge's output is specified in milliVolts at 0VU = 5cm/s (although this varied over time between 5cm/s horizontal and 5cm/s per channel and is seldom specified although 3dB different - but who's counting?). Peak cutting velocities can be 20 or 30dB higher than this, and limited only by the mechanical limitations of the cutter head and the playback tracking ability.
This is a whole different critter than a digital source whose output is specified at an inviolate clipping level of 0dB. And this difference causes all kinds of confusion, not even counting the massive compression, for artistic reasons?, of modern digital recordings, which clouds and confounds the issues.
All good fortunes,
Chris
It would be nice if that old analog source and that recent digital source have more or less the same volume level and not with the large difference there is now, regardless of all history. Since 40 years we have the 2V rms/10 kOhm standard and it would be wise for those stubborn tube guys to give in and build/adapt/modify stuff to the same standard. Fits better on the time axis of matters too.
I see 8V rms output tube DACs coupled to 150 mV sensitive tube power amplifiers and everyone pretending this to be normal 😀
I see 8V rms output tube DACs coupled to 150 mV sensitive tube power amplifiers and everyone pretending this to be normal 😀
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Sure, and the modern trend to heavy compression complicates the "same" part. But such is life.
All good fortune,
Chris
All good fortune,
Chris
I've found that a phono preamp with about 44dB gain (give or take a dB or two) with a typical MM cartridge with 5mV cm/dyne output gives me playback from LP at about the same subjective volume level as playback from CD or DAC.
Many phono preamps are designed to provide about 35dB of gain at 1kHz.
This means that if I have one of those preamps and having my LPs play back less loud than my DAC really bothers me, I would need an additional 9dB of gain to boost that 35dB of gain up to 44dB.
That's about 2.83X gain.
Now go look for a tube preamp with 'zero negative feedback' that has 3X gain without introducing another volume control.
I don't know of any.
Many phono preamps are designed to provide about 35dB of gain at 1kHz.
This means that if I have one of those preamps and having my LPs play back less loud than my DAC really bothers me, I would need an additional 9dB of gain to boost that 35dB of gain up to 44dB.
That's about 2.83X gain.
Now go look for a tube preamp with 'zero negative feedback' that has 3X gain without introducing another volume control.
I don't know of any.
Something with a 12B4a will work.
An opamp also would work 🙂 ECC1656 for instance. I bet one will be quite satisfied with this one.
An opamp also would work 🙂 ECC1656 for instance. I bet one will be quite satisfied with this one.
12B4 with the cathode resistor bypassed would have a little more gain than that, but yes, that'll certainly work. There's a bunch of threads on that topic.
https://www.diyaudio.com/community/...the-12b4-better-than-the-grounded-grid.68267/
https://www.diyaudio.com/community/threads/12b4-preamp.137771/
https://www.diyaudio.com/community/threads/diy-12b4-preamp-any-good.317693/
https://www.diyaudio.com/community/threads/12b4-preamp-design-pre-build-questions.287521/
https://www.diyaudio.com/community/threads/12b4-line-stage-amp.141025/
Another tube along those lines would be a triode-wired 12P17L.
I'm working on a 12AT7 inverter stage, DC-coupled to a MOSFET source follower, with NFB from the MOSFET source to the grid of the 12AT7. It should tick all the boxes. It uses a triode for voltage amplification, has low output impedance, sinks 5mA of current so it won't slew limit into 1nF of cable capacitance, has very low distortion, and its gain can be 3X if I want it to be. But of course, it uses... (gasp!) ... NEGATIVE FEEDBACK to do all that.
The horror.
https://www.diyaudio.com/community/...the-12b4-better-than-the-grounded-grid.68267/
https://www.diyaudio.com/community/threads/12b4-preamp.137771/
https://www.diyaudio.com/community/threads/diy-12b4-preamp-any-good.317693/
https://www.diyaudio.com/community/threads/12b4-preamp-design-pre-build-questions.287521/
https://www.diyaudio.com/community/threads/12b4-line-stage-amp.141025/
Another tube along those lines would be a triode-wired 12P17L.
I'm working on a 12AT7 inverter stage, DC-coupled to a MOSFET source follower, with NFB from the MOSFET source to the grid of the 12AT7. It should tick all the boxes. It uses a triode for voltage amplification, has low output impedance, sinks 5mA of current so it won't slew limit into 1nF of cable capacitance, has very low distortion, and its gain can be 3X if I want it to be. But of course, it uses... (gasp!) ... NEGATIVE FEEDBACK to do all that.
The horror.