this is going be a long post explaining myself
I am traveling down a path of learning and thought i want to do away with the lineout converter in my vehicle. I could easily order a high end LOC but why not look into creating my own.
What got me going was learning crossover network design and improving the audio reproduction in my vehicle. Currently I'm slowly redesigning the front and rear sound staging in my truck (10' F150 Platinum) and going for SQL. SQL is extreme high fidelity with moderate volume levels. I have always had a fair stereo in my vehicles because factory systems suck even in high end cars. I have never owned or seen anyone with DSP's or crossover networks I always relied on sound treatments and amplifier filters. Most folk I know use the filters on the amp or built there own crossovers.
The experience of learning and designing crossover networks and amplifiers physically is what I'm after. I really enjoy building stuff with my youngest and we like challenges and do stuff together all the time.
so regarding the tube preamp question, my goal is to produce a better "Line-Out Converter". knowing the quality of tonality tubes can provide, I want to make my own "LOC" using a tube configuration.
My truck's factory radio produces 4v on front and rear channels & 2v on subwoofer channel. I deleted the subwoofer channel, the only use for the rear lines are for rear fill as Sony implemented a factory 2nd order Butter-Worth low pass filter set at 50Hz.
none of my amps have high level input ability so I must use a multi-channel LOC as my input.
I will need 9 channels in total for my sound stage by completion.
once design is functional on the program I can produce the product. I would only use the front speaker lines as it is full range with no filtering other than non-adjustable stuff in the factory Sony DSP. I like my factory radio so don't want to change it out until I have to even then i'll play with this idea for quite some time.
all the tube LOC needs to accomplish is converting my front speaker lines signal to 9 RCA output channels. my thought is the Tube can help maintain a clean High Fidelity signal, and increase the RCA voltage. I would like to be able to improve max voltage output from 4v to 7.5v without distortion in the signal. this lets me deliver maximum input voltage requiring less gain, letting my amplifier's produce rated power output with the least amount of gain adjustment which lets me produce a cleaner signal to my loudspeakers.
As far as amplifier is concerned, like many I have always wondered about combining Class A with Class D or higher to produce a amplifier that uses the best of both worlds. Class A produces the best possible sound quality but with no Eff, while Class D and up run very Eff. Korean Class D amp's can be up to 95% Eff which is just amazing.
years of searching brings up no designs in use or schematics shared, only comments about designing and others destroying the designing and production of a amplifier by dropping comment after comment of the complexity needed to build one and all the potential short-coming's one would run into.
with that I think the best option for some step of success would be to start with LOC that uses a Class A Tube configuration to give adjustable voltage control and the ability to increase voltage output of the high level from 4v to 7.5v with no distortion to the RCA outputs. I think as a whole this idea is far more capable than reinventing the amplifier wheel with a amplifier that wont exist as advances in technology move far to fast.
I don't join to many forums but figured your always doing stuff with tubes you might be a great starting point for figuring if the theory is possible and if so can you help with circuit designing? If I need to join somewhere to acquire help designing the circuitry can you point me in the right location. I pondered using an AI circuit design program but using AI makes me nervous to reply on.
I do have proto on my android and programs like LTSpice, EasyEDA, KiCAD, XSIM, PCB Editor, QUCS and a few other programs for laying out the circuit.
i can find tons of schematics for various things i want to learn but nobody has done a LOC tube coupled together or if they have noones talking about it or posting schematics or designs or circuits lol.
I can design audio high/low pass filters of various types like bessel,butterworth,chebychev,sallen-key,QB3,SBB4,B4, audio zobel circuits, pi filters. so the basics I am ok with. current reading and studying about Parametric EQ's and how to implement open source software for configuring the EQ
sorry the for long post and the circus of theory and questions I asked but any help from you is greatly appreciated
Ok, fair enough - let's take one question at a time.
If I understand correctly, you want to take two speaker level outputs and convert that to nine line-level signals to feed that into other amps?
yes my left and right front speaker lines will turn into multiple RCA outputs
That's easy enough, there are plenty of speaker-level to line-level converters out there. If you want to go from two to nine, you'll need to first determine how you're going to mix the two channels down, unless you want 18 total outputs. After you get the line levels, then it's simply a matter of buffering it and feeding it into the requisite number of amplifiers. For the most part, line is high impedance so putting a blocking capacitor after the plate and feeding your signal into the appropriate resistor will give you the impedance you're looking for.t
In regards to the comment you posted on mine about noise and tubes -
Tubes are fun to use and they're a cool thing. But they're also power hungry, generate a lot of heat, and require higher voltages than you're going to find in a car. For most common applications, say a 12AX7 triode line-level amp, you're going to need 200mA of regulated 12V for the filaments (needs to be regulated, your alternator floating all over the place will burn them out quickly) and 180-250VDC of plate voltage.
So not only are you now concerning yourself with a relatively fragile heater in a glass bottle, you need two more circuits to generate the appropriate voltages. Using solid-state supplies here can generate a lot of what's called hash noise, so you're going to struggle getting a clean voltage to not make your tubes whine.
Don't buy into the hype that tubes are somehow better - a simple good quality op-amp circuit will do the same thing, be cleaner, and work better.