I could use some help. I'm looking for a relatively straightforward, compact, pre-amp (balance and source selection optional) + tone control (2-3 band) solution for use with a small Class D amp on my desk. I'd like to keep it solid-state (no tubes).
I'd like it to, um, not suck, by which I guess I mean: I'd like it to have no easily discernible impact on the output when the controls are set to a neutral position, and to introduce a minimum of noise and distortion when boosting or attenuating a band. As for the controls, I'd prefer knobs (whether pots or rotary encoders) with neutral effect at their midpoint.
If the controls are digital, I'm fine with a single knob, as long as its easy to switch modes, to identify the current mode, and to see where in the range it's set. I'd rather have individual LEDs to indicate the mode, and some sort of multi-segment bar to show the setting, rather than a chunky dot-matrix LCD display. I realize that I may need to be flexible on this want.
My first choice would be an inexpensive (less than $20) finished board. Second choice is a similarly priced kit. Third choice is reference to a good IC (or two) with proven designs that I can build from.
In all cases, I'd prefer something that can run from a single supply rail, or, barring that, something that would work well with a virtual ground within the 19-24v supply used by the power amp.
On my own I've found a lot of finished boards and kits I don't want to use, thanks to their use of rather noisy old ICs (ie LM1306, TDA1524) or ICs that I can't find much hard data on, but I'm suspicious of (ie XR1075).
I've also found boards, kits and projects based on more modern chips with digital controls. Unfortunately, the ones I've found are either past the upper range of my budget and/or require more integration/programming than I want to do at this point.
One kit I have considered is this XY HiFi kit, which uses discreets and a few (upgradeable) op-amps. I'll probably buy one and try it out, but I'd appreciate any pointers that would help me learn more about it (like whether the circuit it implements has a name).
I've been looking at forum posts. They've helped me rule some things out, and pointed me towards a few things with potential, but that seem to exceed my time and materials budget for this little project.
So, now I'm hoping that some of you can help point me to things I've missed so far. That includes informing me that what I'm asking for isn't realistic (which I'm already suspecting is the case for anything with a modern IC solution with integrated controls). Thanks!
I'd like it to, um, not suck, by which I guess I mean: I'd like it to have no easily discernible impact on the output when the controls are set to a neutral position, and to introduce a minimum of noise and distortion when boosting or attenuating a band. As for the controls, I'd prefer knobs (whether pots or rotary encoders) with neutral effect at their midpoint.
If the controls are digital, I'm fine with a single knob, as long as its easy to switch modes, to identify the current mode, and to see where in the range it's set. I'd rather have individual LEDs to indicate the mode, and some sort of multi-segment bar to show the setting, rather than a chunky dot-matrix LCD display. I realize that I may need to be flexible on this want.
My first choice would be an inexpensive (less than $20) finished board. Second choice is a similarly priced kit. Third choice is reference to a good IC (or two) with proven designs that I can build from.
In all cases, I'd prefer something that can run from a single supply rail, or, barring that, something that would work well with a virtual ground within the 19-24v supply used by the power amp.
On my own I've found a lot of finished boards and kits I don't want to use, thanks to their use of rather noisy old ICs (ie LM1306, TDA1524) or ICs that I can't find much hard data on, but I'm suspicious of (ie XR1075).
I've also found boards, kits and projects based on more modern chips with digital controls. Unfortunately, the ones I've found are either past the upper range of my budget and/or require more integration/programming than I want to do at this point.
One kit I have considered is this XY HiFi kit, which uses discreets and a few (upgradeable) op-amps. I'll probably buy one and try it out, but I'd appreciate any pointers that would help me learn more about it (like whether the circuit it implements has a name).
I've been looking at forum posts. They've helped me rule some things out, and pointed me towards a few things with potential, but that seem to exceed my time and materials budget for this little project.
So, now I'm hoping that some of you can help point me to things I've missed so far. That includes informing me that what I'm asking for isn't realistic (which I'm already suspecting is the case for anything with a modern IC solution with integrated controls). Thanks!
Most tone controls are based on the classic 'Baxandall' arrangement. Have a look at some of these.
Single rail designs tend to have fallen from favour but you can easily use a 'DC-DC' convertor to power any of these.
This is just an example of a convertor. 24 volts in and -/+15 volts out.
POWERPAX - 1PA2415S-WR - 1W UNREG SIP SCP 24V IN / + - 15VOUT | CPC UK
Audio Designs With Opamps -2
ESP Projects Pages - DIY Audio and Electronics
Hi-Fi Preamplifier
Single rail designs tend to have fallen from favour but you can easily use a 'DC-DC' convertor to power any of these.
This is just an example of a convertor. 24 volts in and -/+15 volts out.
POWERPAX - 1PA2415S-WR - 1W UNREG SIP SCP 24V IN / + - 15VOUT | CPC UK
Audio Designs With Opamps -2
ESP Projects Pages - DIY Audio and Electronics
Hi-Fi Preamplifier
Thanks, Mooly!
After writing all that, yesterday, I've been thinking about it more, and I'm realizing that my conviction that I need/want tone control is waning. Pretty much all my sources are digital, so I can apply EQ in the digital domain. Most will be paired with a particular amp/speaker setup, so I won't be changing profiles often. In a few situations, I might want a volume control (in some cases passive, in some cases active) that I set once. That's a simpler problem.
I appreciate the pointers, because chances are, I'll be sucked into this question again 🙂
After writing all that, yesterday, I've been thinking about it more, and I'm realizing that my conviction that I need/want tone control is waning. Pretty much all my sources are digital, so I can apply EQ in the digital domain. Most will be paired with a particular amp/speaker setup, so I won't be changing profiles often. In a few situations, I might want a volume control (in some cases passive, in some cases active) that I set once. That's a simpler problem.
I appreciate the pointers, because chances are, I'll be sucked into this question again 🙂
Unfortunately, by being practical and clearheaded I've deprived myself of justification for an interesting project. I think I'm still going to pick up a kit or do a protoboard build of P97 to tinker with.
People buy those kits and mod them. You can change the capacitors to move the turnover frequencies or use different film capacitors. Changing resistors can move the turnover frequencies and/or change the maximum boost and cut. And of course you can put different op amps in them.
I built a tone control/preamp board for single ended power supply. It uses TLE2426 for bias only. The signal ground ties to V-. The rest is a straightforward shelving equalizer. Nichicon Muse coupling capacitors and MKP capacitors in the tone circuits make for a very nice tone control. It doesn't distort the sound like some do. It works A-OK from 12-30 volts and has enough decoupling (inductors and resistors) to be powered by a computer power supply. People like it.
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