I have followed member Andy’s exploration of the “26 preamp” with great interest, with its various iterations. I also remember “a Mike” with an “Andromeda preamp” based on a 27/e83f arrangement.
These days, we need little else from a preamp other than switching and we possibly need little amplification and of course the attenuation.
My question: If you would start your “ideal tube preamp” now, what would you be looking at, starting from a belief that the old low mu, low gain tubes are best.
These days, we need little else from a preamp other than switching and we possibly need little amplification and of course the attenuation.
My question: If you would start your “ideal tube preamp” now, what would you be looking at, starting from a belief that the old low mu, low gain tubes are best.
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I am currently working on my ideal tube preamp using early 01a tubes, CX-301a specifically with thoriated filaments. Following the path laid down by Ale.
My main amp is an F4 so i do need a pre amp with some gain, and it will also have a 3 selectable inputs and 3 selectable outputs as i am done with switching interconnects around between headphone and speaker amps.
My main amp is an F4 so i do need a pre amp with some gain, and it will also have a 3 selectable inputs and 3 selectable outputs as i am done with switching interconnects around between headphone and speaker amps.
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I don't need a preamp as such in my system and haven't for many years. My DAC goes straight into my 2 stage amplifier. I'm using the 01A as the driver stage. I think this is probably my favourite DHT. I like the 10Y and the 46 as well, but I'm just comfortable with the 01A. It's clear, neutral and subtle in its detail and tonality. The 10Y is more dynamic and you can put a lot more current through it. The 26 is warmer, but I don't find it as natural and attractive sounding as the 01A.
Since I don't really have any interest in "preamps" as such I don't know what the main point of using one is - amplification, tonality, step-down......?
Since I don't really have any interest in "preamps" as such I don't know what the main point of using one is - amplification, tonality, step-down......?
A fair number of threads, both here and other fora, are about "buffers" to alter the voice of all sorts of SS equipment. FWIW, I decline to deal with "effects machines" in this thread and restrict my remarks to HIFI.
Close attention to overall gain structure is (IMO) a key area. Amplifying a signal only to later attenuate it has an adverse impact on S/N performance. Whenever possible, avoid that scenario.
System synergy is "the name of the game". What works well in a particular listening venue, with a given set of speakers, and some grouping of electronics need not, and all too often does not, work well in a different venue, etc.
There is no absolute best. Rather, a set of proven performers is available to be subjected to empirical determination of what works well in any given situation.
Close attention to overall gain structure is (IMO) a key area. Amplifying a signal only to later attenuate it has an adverse impact on S/N performance. Whenever possible, avoid that scenario.
System synergy is "the name of the game". What works well in a particular listening venue, with a given set of speakers, and some grouping of electronics need not, and all too often does not, work well in a different venue, etc.
There is no absolute best. Rather, a set of proven performers is available to be subjected to empirical determination of what works well in any given situation.
My feelings entirely. Why add any more gain than you need? I've always experienced a subtle or not so subtle loss of absolute clarity when adding a stage. Surely you only need about 20% or so above your normal listening level? What's the point of further amplification?
And if you're seeking a different tonality, why not put it in your amplifier? Instead of a tube preamp into a solid state amp, why not just build a hybrid amp?
The need for a 'pre amplifier' might arise from the necessity to connect many sources or to drive a modern low input impedance power amplifier. It is a valid idea to build a universal pre unit to power your (many) power amplifiers with just a single input.
You can have any linear valve for voltage amplification (but there is no need for a high or even medium mu type) and buffer the gain with a cathode follower or MOSFET. Feedback from anode to grid reduces excess gain, if needed.
You can have any linear valve for voltage amplification (but there is no need for a high or even medium mu type) and buffer the gain with a cathode follower or MOSFET. Feedback from anode to grid reduces excess gain, if needed.
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Having had many similar discussions the test to end discussions is the straight wire test. Compare the built device with a straight wire. In my experience preamps are rarely needed in this day and age except for the odd device that needs gain. Source selection and volume control maybe followed by a buffer (depending in input impedance of the power amplifier) is what is needed in most cases. It always strikes me that many choose an effect generator over neutrality 🙂 "I finally hear music again" etc. A completely different subject but I see this also with Spotify MP3 against lossless FLAC...
Although I agree I also do not agree. In the tube world it is fully accepted to "adapt" stuff to each other in part for that synergy. It is not defined by building stuff that always is compatible and often is decided by hearing and not by design (which would easily make clear what the issues can be). More often than not I was witness of stuff that only worked OK when used together. Especially drive capability is a weak point. Using tube gear together with solid state stuff reveals this: not enough drive, way too much gain because of wrong design choices, absurd focus on capacitors instead of topology, no muting, not using modern PSU techniques that would really improve the device "but they are silicon", strong reluctance against often very good modern parts, absolutely unsafe and wrong PE/GND techniques etc. The use of low gain devices is what is needed in 99% of cases (any source younger than 20 years has 2 Veff output) and capable of 10 kOhm loads like your 12B4a design.
In short: when normal gain tube or solid state high input impedance i.e. 50 kOhm power amplifiers are used one is better off with source section and volume control in that device instead of building a external superfluous device that does not make anything better.
Although I agree I also do not agree. In the tube world it is fully accepted to "adapt" stuff to each other in part for that synergy. It is not defined by building stuff that always is compatible and often is decided by hearing and not by design (which would easily make clear what the issues can be). More often than not I was witness of stuff that only worked OK when used together. Especially drive capability is a weak point. Using tube gear together with solid state stuff reveals this: not enough drive, way too much gain because of wrong design choices, absurd focus on capacitors instead of topology, no muting, not using modern PSU techniques that would really improve the device "but they are silicon", strong reluctance against often very good modern parts, absolutely unsafe and wrong PE/GND techniques etc. The use of low gain devices is what is needed in 99% of cases (any source younger than 20 years has 2 Veff output) and capable of 10 kOhm loads like your 12B4a design.
In short: when normal gain tube or solid state high input impedance i.e. 50 kOhm power amplifiers are used one is better off with source section and volume control in that device instead of building a external superfluous device that does not make anything better.
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Adapting to obtain synergy is being empirical. 
Very rarely do 2 VRMS digital signal sources need additional gain in the system control center, AKA "line stage". Where a small amount of line stage gain can be valuable is in combination with a not so high gain MM phono preamp. A simple passive EQ setup built around 6922s is such a phono preamp. The Korean made, battery powered, "Little Rat" SS phono preamp sounded surprisingly good working into a BottleHead "Foreplay" or other tubed line stage with gain.
Getting phono and digital to work with the volume control in approx. the same place is a PITA. The digital sources have to be "padded" down and some S/N damage is inevitable. Top quality "padding" resistors minimize the losses.
Very rarely do 2 VRMS digital signal sources need additional gain in the system control center, AKA "line stage". Where a small amount of line stage gain can be valuable is in combination with a not so high gain MM phono preamp. A simple passive EQ setup built around 6922s is such a phono preamp. The Korean made, battery powered, "Little Rat" SS phono preamp sounded surprisingly good working into a BottleHead "Foreplay" or other tubed line stage with gain.
Getting phono and digital to work with the volume control in approx. the same place is a PITA. The digital sources have to be "padded" down and some S/N damage is inevitable. Top quality "padding" resistors minimize the losses.
A simple solution would be to have the phono pre updated to eighties standard 2Veff. A good use for those high mu tubes 🙂 All other sources are 2Veff already even DAB+/FM tuners. Adding gain to all sources (and creating the need for padding down well performing 2Veff sources with S/N damage) while only 1 source is the cause is not a technical effective solution but it is unfortunately in line with expectations.
Pssst: a simple stage with OPA1656 after the phono pre solves all at minimal cost/very good sound quality 😀
Pssst: a simple stage with OPA1656 after the phono pre solves all at minimal cost/very good sound quality 😀
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