Tone Controls (probably unnecessary long)

I am interested in faithful reproduction, but am also looking for a particular sound.
Up until 1992, I had a tube radio from the sixties. I really liked its sound, especially with the tone controls set to max. If I could draw a light analogy, it would be the light that passes through a jar full of honey or an amber pendant. Or that bone warming heat coming from the fireplace. I knew that by setting the tone controls to their max values I was "coloring" the sound, but to me the music sounded much more pleasant. I was and I am willing to make this compromise when it comes to faithful music reproduction. What I liked the most about my old radio's tone controls was that unlike other systems I have listened to (all of them transistor) where upon turning up those dials brings some harshness, with the old radio's tone controls turning up the bass, starts first bringing warmth at a particular low frequency and then as I turn the potentiometer, it feels like the warmth spills across the whole frequency spectrum.
Now to my modern day dilemma: I own a Lepai 2020A+ which without its tone controls, I find tinny and having some of that transistorish harness. Once its tone controls circuit is engaged, it closely matches the “sound” of my old radio. My question is: Can you recommend a higher end circuit, or a commercially available preamp that renders the sound the same?
I am perfectly happy with the Lepai in the office, but need something more powerful for the living room. As a back up plan….I bought another Lepai and intend to trace and reproduce its tone control circuit. I wander if the warmth I am talking about is due mostly to the OP Amp in the tone control circuit, which brings me to my second question: How does one design tone controls circuit like that, which parameters are most important when it comes to “warmth”?

Thanks in advance.
 

rayma

Member
2011-04-29 8:37 pm
Can you recommend a higher end circuit, or a commercially available preamp that renders the sound the same?
How does one design tone controls circuit like that, which parameters are most important when it comes to “warmth”?

The Lepai tone controls are fairly conventional, with boost/cut around +/-10dB.
Warmth is from the lower midrange/upper bass region.
Check out the Baxandall tone control circuit here: Practical Tone Control circuit.
Look at the measurements of the Lepai here: Cheap Amps Face Off: Lepai LP-2020A+ vs. Topping TP30
 
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Thanks for the fast reply and thanks for the links.

I did open my spare unit and determined that tracing the PCB tracks isn't going to be as easy as I thought, due to the fact that it is at least a two-layer board.

Before, reinventing the wheel, does anyone have the schematic of the latest version of Lepai 2020A+? I searched, but all the schematics I found were related to the older versions of it.

Thanks in advance.