Hi,
I apologize in advance for my very novice knowledge of electrical engineering. I'm an audio and music enthusiasts / amateur musician who works as a mechanical designer in robotics. I have some exposure through my team and hobby to have just enough knowledge, or lack thereof, to be dangerous!
I have a pair of Carvin AG100D combo amplifiers which I use for my electric double bass along with my acoustic with a piezo pickup. I'm fond of this combo, as are a few other bass players, as it's a great sounding full range cab and fairly light. The amplifier section, however, isn't all it could be. Many use the cab only and power it with the new wave of compact class D bass head units. The nominal impedance of the cab is 8ohms. They are wired from the factory to daisy chain in series as the TDA7294 based amplifier section isn't stable enough to run sustained at any volume to support a 4 ohm load. It also is noisy and lacks headroom which becomes obvious at moderate volumes. Testing with Markbass Blackline 250 (150w rms @ 8ohms) was noticably less congested sounding at higher volumes in a not so blind a/b.
I was interested in seeing if I could leverage the +- 50v (data sheet for the chip says 40, Carvin schematic says 50, need to measure) power supply and the preamp stage with a more robust class D solution. My goal would be to ultimately fit both combos with a new amplifier setup as I leave one at home and one in the practice space, but for starters, just doing one would be fine. I will likely mess this up a bunch, so protecting the drivers especially is important. I also work for a startup, so I'm more financially constrained than I'd like to be. So with the odds being I might blow up a newly purchased amplifier board, cost is a factor.
It would seem that the LJM L12, L15, L25 or L50 might be good fits. The cabs power handling is rated at 300w, and others have reported good results using more robust amps, but given the propensity for staggeringly inaccurate power ratings and the seemingly endless appitite of musicians to believe them, it's hard to know if a real 300w rms into 8 ohm amplifier wouldn't destroy this thing.
I've attached the schematic of the Carvin's amplifier section. BTW, I do really like Carvin stuff, so this isn't my attempt to besmirch this amplifier, I'm very, very fond of it. It's great for playing in a jazz combo and even works well for electric guitar with a modeling preamp in front of it.
Thank you in advance for what is always thoughful and detailed advice.
I apologize in advance for my very novice knowledge of electrical engineering. I'm an audio and music enthusiasts / amateur musician who works as a mechanical designer in robotics. I have some exposure through my team and hobby to have just enough knowledge, or lack thereof, to be dangerous!
I have a pair of Carvin AG100D combo amplifiers which I use for my electric double bass along with my acoustic with a piezo pickup. I'm fond of this combo, as are a few other bass players, as it's a great sounding full range cab and fairly light. The amplifier section, however, isn't all it could be. Many use the cab only and power it with the new wave of compact class D bass head units. The nominal impedance of the cab is 8ohms. They are wired from the factory to daisy chain in series as the TDA7294 based amplifier section isn't stable enough to run sustained at any volume to support a 4 ohm load. It also is noisy and lacks headroom which becomes obvious at moderate volumes. Testing with Markbass Blackline 250 (150w rms @ 8ohms) was noticably less congested sounding at higher volumes in a not so blind a/b.
I was interested in seeing if I could leverage the +- 50v (data sheet for the chip says 40, Carvin schematic says 50, need to measure) power supply and the preamp stage with a more robust class D solution. My goal would be to ultimately fit both combos with a new amplifier setup as I leave one at home and one in the practice space, but for starters, just doing one would be fine. I will likely mess this up a bunch, so protecting the drivers especially is important. I also work for a startup, so I'm more financially constrained than I'd like to be. So with the odds being I might blow up a newly purchased amplifier board, cost is a factor.
It would seem that the LJM L12, L15, L25 or L50 might be good fits. The cabs power handling is rated at 300w, and others have reported good results using more robust amps, but given the propensity for staggeringly inaccurate power ratings and the seemingly endless appitite of musicians to believe them, it's hard to know if a real 300w rms into 8 ohm amplifier wouldn't destroy this thing.
I've attached the schematic of the Carvin's amplifier section. BTW, I do really like Carvin stuff, so this isn't my attempt to besmirch this amplifier, I'm very, very fond of it. It's great for playing in a jazz combo and even works well for electric guitar with a modeling preamp in front of it.
Thank you in advance for what is always thoughful and detailed advice.
IF you plan to feed a new Class D power amp from current power supply, you will have same power out as before .
As famous Tech Enzo once said, "the amp is just that thingie between power supply and speaker"
If you want higher power, you could leave current TDA7294 as_is, driving original speaker, and add a new smps supply + class D Poweramp similar to Ice Power modules, inside the bottom speaker cavity, feeding an extra speaker out jack.
In small places use amp as is, in larger ones add an extra cabinet for more power and more cone surface, a killer combination.
As famous Tech Enzo once said, "the amp is just that thingie between power supply and speaker"
If you want higher power, you could leave current TDA7294 as_is, driving original speaker, and add a new smps supply + class D Poweramp similar to Ice Power modules, inside the bottom speaker cavity, feeding an extra speaker out jack.
In small places use amp as is, in larger ones add an extra cabinet for more power and more cone surface, a killer combination.
You know, the power supply being the major limiting factor in terms of power / headroom never even really occurred to me. Wow, I feel dumb. Anyways, that’s a great insight. In regards to the smps power supplies, many of the LJM boards require dual voltage. There are numerous affordable examples on aliexpress, but as I’ve learned the hard way, most of the time you get what you pay for. I’ve had difficulty finding alternatives though. Any suggestions would be welcome. I’ve thought about just going ICE top to bottom too. Bergantino uses ICE amplifier modules and he makes a wonderful product.
The previous replies are correct but forget one thing. Class D amps are more efficient so even with the existing power supply you will get more power from a class D amp.
Whether the voltage is +/-40V or 50V, the power you get from a Class D amp will be higher that a Class A/B. The TDA7924 is a Class A/B MOSFET output stage chip and they are even less efficient than bipolar output stages. The ideal amp would be the LJM L15D for those voltages. You may need to either attenuate or boost the preamp output to match the new amp but that is relatively easy and could be achieved just by careful use of the volume.
If you are going to run at high volume continuosly you may need extra heat sinking. You may be able to attach the module’s heating to the chassis or existing heat sink on your amp.
You could go down the icepower route also. The 300AS1 would be ideal as you could ditch the existing power supply. Of course it is slightly more work.
Whether the voltage is +/-40V or 50V, the power you get from a Class D amp will be higher that a Class A/B. The TDA7924 is a Class A/B MOSFET output stage chip and they are even less efficient than bipolar output stages. The ideal amp would be the LJM L15D for those voltages. You may need to either attenuate or boost the preamp output to match the new amp but that is relatively easy and could be achieved just by careful use of the volume.
If you are going to run at high volume continuosly you may need extra heat sinking. You may be able to attach the module’s heating to the chassis or existing heat sink on your amp.
You could go down the icepower route also. The 300AS1 would be ideal as you could ditch the existing power supply. Of course it is slightly more work.
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That's a great point on the efficiency. I'm seriously thinking about ditching the amp board altogether as it's large and the power supply is integrated. It does step the voltage down however for the preamp and digital effects section. The noise floor is high on these amps too. I'm not sure if it's the preamp stage, the amp, both? I'm in the process of designing an enclosure for my Mac + Focusrite based "preamp" setup which I use as a front end into these things. I could almost just build an amp into that box and use the speaker inputs on the cabs and just leave the amp alone. I have to buy a power supply of course, but I'm starting to think that makes more sense. There's a "500" watt 120v input dual output power supply available on aliexpress. I've seen some youtubers and others link to what appears to be the same board and have some success. I'm thinking that with with a LJM15D and I could put two paralleled outputs to one of them to present a 4ohm nominal load. I can get it in 50, 55 and 60v dual outputs. I don't use the fancy shmancy computer based front end unless I'm playing electric guitar or bass guitar, so for most practices, I could just keep using my LR Baggs pre and my HPF-2 filter with the built in amp. That said, it would be nice to not add a ton of weight to the computer + interface box and always have a better sounding amp. Ahhhhh decisions, descisions...