Hi,
I'm looking for a preamp recommendation for a pair of LJM L12-2 power amp modules. I've considered a few options such as the LJM Preamp P9, P8, P7, or just a volume pot, but I'm not sure which way to go. @ljm_ljm please respond with some recommended combinations.
I've built LJM L12-2 amp boards, MX50 SE amp boards, and a power supply. All fun kits to build and no issues.
Thank you
I'm looking for a preamp recommendation for a pair of LJM L12-2 power amp modules. I've considered a few options such as the LJM Preamp P9, P8, P7, or just a volume pot, but I'm not sure which way to go. @ljm_ljm please respond with some recommended combinations.
I've built LJM L12-2 amp boards, MX50 SE amp boards, and a power supply. All fun kits to build and no issues.
Thank you
I'm powering the L12-2 amp modules with a single 20-0-20 160VA transformer. The power supply has four 6800 uF filter/smoothing capacitors. Typical North American household voltage of 120 VAC.
Since my initial post. I've tried an LJM Preamp P9 with a 50K pot. I could only turn the pot up a tiny amount before the volume level was much to high. I also tried using just a 10K volume pot as preamp. That works very well with plenty of range for quiet and loud volume levels. It also sounds very good. I have an LJM P8 preamp on order and will try that when it arrives.
Since my initial post. I've tried an LJM Preamp P9 with a 50K pot. I could only turn the pot up a tiny amount before the volume level was much to high. I also tried using just a 10K volume pot as preamp. That works very well with plenty of range for quiet and loud volume levels. It also sounds very good. I have an LJM P8 preamp on order and will try that when it arrives.
The LJM P8 Preamp arrived as a kit. I assembled and tested it right away. No issues with construction or quality of parts supplied. The 5532 chips were unmarked but that's fine. The were installed in swiss milled sockets. Nice touch. I may replace them with new ones.
Similar to the P9 mentioned in previous post, the P8 adds too much initial gain before the power amp modules. I also replaced the power amp 20-0-20 transformer with another 17-0-17 transformer. Not much if any difference on the volume knob range. Both the P8 and P9 preamps use a 50K log pot.
It's possible the L12-2 are just over-sized for my bookshelf speakers. If you see Michael Beeny video entitled "Integrated Amplifier. Using L15. FET amplifier boards and NE5532 Preamp." He places a 50K log pot before a single 5532 chip preamp, and a second 50K log pot between the preamp and L15 power amp modules. I'll try that next and report back.
Similar to the P9 mentioned in previous post, the P8 adds too much initial gain before the power amp modules. I also replaced the power amp 20-0-20 transformer with another 17-0-17 transformer. Not much if any difference on the volume knob range. Both the P8 and P9 preamps use a 50K log pot.
It's possible the L12-2 are just over-sized for my bookshelf speakers. If you see Michael Beeny video entitled "Integrated Amplifier. Using L15. FET amplifier boards and NE5532 Preamp." He places a 50K log pot before a single 5532 chip preamp, and a second 50K log pot between the preamp and L15 power amp modules. I'll try that next and report back.
The P8 and P9 have a gain of 10. The L12-2 has a gain of 31, so the last thing you want is a preamp with gain.
What version of the P8 do you have? The new version looks like it has trim pots to set the gain. The old version can be turned into a buffered volume control by changing the two 1k resistors to 10k.
What version of the P8 do you have? The new version looks like it has trim pots to set the gain. The old version can be turned into a buffered volume control by changing the two 1k resistors to 10k.
Ah, that's the P8 Mini. It has a gain of 5 (still too much). Completely different than the regular P8. I also see I was wrong earlier. It's the old P8 Mini that has gain adjustment trimmers. The listings on ali/ebay are confusing.
It's getting late for me and my brain is getting foggy. Can't really decipher the circuit by the pics right now. I'll come back to this later.
It's getting late for me and my brain is getting foggy. Can't really decipher the circuit by the pics right now. I'll come back to this later.
Are you thinking of the P7 Mini? It is similar, but with one 4580 instead of two 5532s.
I swapped out the P8 preamp for the P9 preamp. The P9 has no opamps. Instead it's Class A with discrete components. Many of them are surface mount on the bottom of the PCB. Similar results with both volume knobs at about 10:30.
No, I was again confusing the P8 Mini against the two different versions of the P8.
Expected since they both have a gain of 10x.
The P9 is beyond me to figure out how to lower its gain and I'm having a hell of a time trying to figure out the circuit of the P8. The DIP sockets obscuring the layout are throwing me for a loop.
Despite all this confusion, what you want is either a unity gain buffer or just a plain old passive volume control using just a pot or stepped attenuator.
I asked the ebay seller about the two different versions of the P8. One with trim pots and one without. I was told the version with trim pots was discontinued.No, I was again confusing the P8 Mini against the two different versions of the P8.
Expected since they both have a gain of 10x.
The P9 is beyond me to figure out how to lower its gain and I'm having a hell of a time trying to figure out the circuit of the P8. The DIP sockets obscuring the layout are throwing me for a loop.
Despite all this confusion, what you want is either a unity gain buffer or just a plain old passive volume control using just a pot or stepped attenuator.
I contacted an Ali seller and asked which resistors to change to lower the gain on the P8. I think something was lost in translation as they replied with "10K/1.5K=6.6". That was all I needed though. So you just need to change the two 1.5k resistors to 10k.
The fact they advertise it as having a gain of 10 but in reality it's 6.6 is part of the reason I was having trouble figuring out the circuit.
I replaced the sanded-down P8 opamps with genuine NE5532 chips from Digi-Key. However, no immediately noticeable difference in sound quality. The original opamps failed the diode test between pins 2 and 3, and between pins 5 and 6. See Michael Beeny's youtube video "Testing NE5532. Fake or Real?"