There are several triodes that will do fine duty in the ~3-6x delivered gain regime. The 12B4 for one. Output Z can be lowered well below the plate with a cascode CCS and the output taken from the lower element source( the mu follower output ).
If going further is required, a 70V line auto former can be put on the output, and gain adjusted with tap selection.
Not all amps can deal with just a 2V signal. In combination with a low source output, gain is good...🙂
cheers,
Douglas
If going further is required, a 70V line auto former can be put on the output, and gain adjusted with tap selection.
Not all amps can deal with just a 2V signal. In combination with a low source output, gain is good...🙂
cheers,
Douglas
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A reasonable amount of gain is good, yes. I like to have a few dB of gain in my line stages, but no more than about 12dB of gain. First design I built used a 12AU7 and had about 30dB of gain. Completely useless for most power amplifiers, and all that kind of gain does is raises your noise floor.
I'm inclined to say exactly the opposite. You want to make a great record, who cares how much distortion your mic pre adds? It's as much an instrument as your guitar amp.
For a live setting, yes, you want clean. But in a studio, you kind of want to use what sounds nice, since that's what counts in the end. If you look at the list of records recorded through Neve 80xx series consoles, it tells you that Rupert Neve must have gotten something right.
If the load is balanced, a LTP is also a very fine circuit. Gain( per plate to ground) is half what a SE stage would deliver. I much prefer triode-strapped EL84 vs 6SN7, even though mu is very comparable. Current implementation is with a B+ of 500V, 20k Plate loads, and about 18 mA/section. Lots of heat given from the plate loads.
cheers,
Douglas
cheers,
Douglas
I concur with your first paragraph, about people (generally) liking distortion.
Your second paragraph, maybe not so much. Let me explain. My own DIY linestage experiments have lead me to some interesting, counter-intuitive, conclusions. It's not simply that people prefer a distorted signal, it's that the distortion needs to be of a certain character and dynamic behavior. Vladimir Lamm has postulated that the distotion level should constant versus frequency, vary linearly in proportion with the signal level, and be dominated by the second harmonic. If you check the test reports published in stereophile, the preamps typically producing the most positive subjective sonics generally fit that profile.
I think it no coincidence then that triodes and feedback free circuitry are highly prized by many audiophiles for their subjective sound character. Lovers of such products often express the belief that such circuitry sounds good despite it's distortions. I think the elephant in the listening room is that such circuits sound good BECAUSE of their distortions. I've found this situation more intrigung than I at first might expected. While high levels of even order distortion can sound euphonic, lower levels, with the right dynamic behavior, make the reproduction sound more naturally realistic, clearer sounding, less ear fatiguing and, seemingly, lower in distortion than an actually low distortion circuit. Why this should be, I'm unsure. I often find objectively very low distortion circuits to make the music sound boring - which is among the greatest of playback system sins.
Maybe this Audiopax article Whysingle-endedtubeamplifiers.pdf can shed a bit of light. A quote :
"In figures 1, 2 and 3 we can see what happens with a loudspeaker driven by a low distortion amplifier and by a single ended amplifier of high 2nd harmonic distortion with both polarities. In this case the speaker alone has around 2% of distortion between 100 Hz and 1000 Hz with 2.83 Vrms in the input (that corresponds to 1W in an 8 ohm load). We can see this in figure 1. In figure 2 we connect it to a SE amplifier with an average 0.8% 2nd harmonic distortion at this output level. It is easy to see the distortion addition between 150 Hz and 300 Hz and subtraction around 900Hz. We could say that, as an average, the distortion has increased. Figure 3 shows the same set up with the other polarity. We can see that the whole 150 Hz till 300 Hz region has reduced distortion and that around 900 Hz we have an increase in it. The overall effect seems to be a reasonable decrease in distortion."
A similar attempt done using SS shared in ClassB+a mosfet amplifier by diegomj1973.
Partial approach. You are an engineer, how much THD do you measure on your acoustic output? And what do you do to minimize overall distortion?
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Yeah, but if it doesn't waste a lot of power and run hot, then what exactly is the point? 😀
Common practise is you record clean and add distortion / effects when mixing. That way you can go back to correct effects when it does not suit other sounds or fit to the total mix. A middle way may be by adding little coloration when recording to achieve a specific sound from an instrument. I'm thinking tone control for guitars and little compression on toms for instance, to obtain max S/N.
Agreed, once the track is laid, it’s laid (unless you re record it).
You can mess around with it endlessly during mixdown and mastering to get a sound that will sound well enough across a broad range of systems.
With playback, do what you like, it can all be undone, updated, compared and replaced.
Very different situations.
You can mess around with it endlessly during mixdown and mastering to get a sound that will sound well enough across a broad range of systems.
With playback, do what you like, it can all be undone, updated, compared and replaced.
Very different situations.
So what yer saying is that it would be Right to build a linestage around 304TL, or better yet, 851's?
Delicious🙂
cheers,
Douglas
To each their own. I would consider a preamp to be that "little" bit of a coloration, but that's just me. Some of it depends on what's being recorded too. Of course, there are 1x10^4 ways to skin a cat.
Back onto the topic of line stages.
I may play around and see if I can come up with a LTP-based line stage that simulates well. I think the idea has potential.
I'll be honest, I think that a good tube line stage with perhaps 10-12dB of gain and decently low output impedance could be quite nice for a lot of people.
Look at something like a triode connected 6P43P-E, they look like a promising tube triode connected at ~165 volt supply, gain of ~7, Rp of 1k or so with 100 volts on the anode. I might try a build of Salas 6V6 preamp with one to drive a baffle step compensation circuit.
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H713 said:
I haven't built it, but I was playing around with a 5687 or 6N6P LTP as a line stage for single-ended sources to drive amps with balanced inputs. Using a CCS in the tail, you can get very low distortion from either tube, and output impedance should be in the 2k ohm range. It might have too much gain, though.
I figure a pair of 6V6 (or 6AQ5 or 6P1P) wired triode and run as a LTP could be fun.
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I had many similar concerns when I was thinking about building a preamp. I settled on a design that made use of the best of all worlds I could think of - passive preamp, headphone amp, and active preamp, all in one:
The design is based around an Aikido All-in-One with 6CG7/ECC99 primarily serving as a headphone amplifier. The stepped attenuator is also one of Broskie's designs, the A3 Stereo with 20K impedance to work for both passive preamp duty as well as active stage attenuation. The headphone amplifier stage has polypropylene output capacitors, and the same board holding those capacitors contains the relays to do front panel control switching. All of the controls work as expected and give a lot of flexibility: Without any power (even unplugged) it works as a passive attenuator and line source selector. With power, it can be a headphone amplifier or (active mode) active line stage, both driven from the Aikido circuit. A line mute function gives the option to leave the power amp or downstream components on-line and only have headphone output active. It has about 20dB of gain, depending on the headphone load, of course. I find that to be plenty, perhaps excess for hot sources and strong power amplifiers, but the overlap between passive/active mode is nice with adequate, but separated, attenuation range for both.
This design I still feel to be the best feature set, and truly what I wanted from a versatile preamplifier.
The design is based around an Aikido All-in-One with 6CG7/ECC99 primarily serving as a headphone amplifier. The stepped attenuator is also one of Broskie's designs, the A3 Stereo with 20K impedance to work for both passive preamp duty as well as active stage attenuation. The headphone amplifier stage has polypropylene output capacitors, and the same board holding those capacitors contains the relays to do front panel control switching. All of the controls work as expected and give a lot of flexibility: Without any power (even unplugged) it works as a passive attenuator and line source selector. With power, it can be a headphone amplifier or (active mode) active line stage, both driven from the Aikido circuit. A line mute function gives the option to leave the power amp or downstream components on-line and only have headphone output active. It has about 20dB of gain, depending on the headphone load, of course. I find that to be plenty, perhaps excess for hot sources and strong power amplifiers, but the overlap between passive/active mode is nice with adequate, but separated, attenuation range for both.
This design I still feel to be the best feature set, and truly what I wanted from a versatile preamplifier.
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My preference is to keep the headphone amp a separate entity, but I realize that most people find that cumbersome.
Who did you use for the front panel? It looks very professional, much better than my solution (label maker).
Who did you use for the front panel? It looks very professional, much better than my solution (label maker).
Front Panel Express
They do wonderful work, if a bit pricey. I've never been disappointed with them for my projects.
The advantage of this design was that it was targeted as a headphone amplifier first, with the preamplifier bits (line switching and attenuation) tacked on to it. A headphone amplifier can actually make a wonderful active line stage.
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Wow, that is exceptional. Really nice work, and really nice function-driven mechanical design.
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Wow, that is exceptional. Really nice work, and really nice function-driven mechanical design.
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Thank you so much. The only consideration in the physical build was noise floor. I am very happy to report that with a few earth grounding tricks and using schottky rectification, the hum is zero, even on headphones. A properly tuned Aikido circuit can do wonders to remove power supply noise for sensitive sources and drivers.