I think the colour of the resin is irrelevant, LJM himself shows a blue board which he states is a fake. In fact I believe the "ferrite bead board" is the latest version, but who knows.
The Sanken 2SA1295 & 2SC3264 have been declared obsolete by Sanken and are no longer manufactured. If you are getting these from China then they are without doubt fake -don't waste you money.
The Sanken 2SA1295 & 2SC3264 have been declared obsolete by Sanken and are no longer manufactured. If you are getting these from China then they are without doubt fake -don't waste you money.
Profusion in England still has the 1195/1216, if you still want to have the large Sanken outputs.
I saw them in stock at digikey too I think.
They give better distortion measurements than others I tried, so I they may be the real deal. I think they are worth the extra cost for the improved performance alone.
They give better distortion measurements than others I tried, so I they may be the real deal. I think they are worth the extra cost for the improved performance alone.
Blue single sided board with ferrite bead is genuine old version of the board that is still sold. New boards don't have ferrite bead, are double sided and could be green or blue colored. Boards don't have bias trimpot because they have fixed bias and no bias setting is needed.
Ta, Rallyfinnen, I think you're right re:the latest version.
On a slightly different note, because I need to drive 4 ohm loads with +/-35V I run all my MX50-SE's with 2 pairs of output transistors (Toshiba's 5200/1943's from Mouser) except the tweeter amps which only needs to provide 10W. It's an active speaker pair with ten amplifiers in total, each speaker has a tweeter, two 5" mids and two 8" bass drivers (earth movement is handled by a 15" sub). At one point I did waste some money and bought a pair of L20-SE's which are basically MX50-SE's with an extra pair of output transistors only twice the price and little if no performance benefit. Recently I've blown a driver transistor (can't remember if it was a 649 or a 669), I had spares and replaced with no issues. I also note that the old MX50x2 (a current f/b version of the Musical Fidelity MF-XA50 and a much better amp than the MX50-SE once you add some decoupling to sort out the parasitic oscillation, but unfortunately twice the price of the -SE) has 2 pairs of 649/669's drivers.
So question: You have stated previously that you have added an additional pair of output transistors but did you change the 669/649's drivers? Slowhands once published a cct for this mod but states that he hadn't actually tried it but also suggests changing the pre-drivers (not sure what pre- means) to MJE340/350, presumably one pair like for like. Thanks, Clive.
On a slightly different note, because I need to drive 4 ohm loads with +/-35V I run all my MX50-SE's with 2 pairs of output transistors (Toshiba's 5200/1943's from Mouser) except the tweeter amps which only needs to provide 10W. It's an active speaker pair with ten amplifiers in total, each speaker has a tweeter, two 5" mids and two 8" bass drivers (earth movement is handled by a 15" sub). At one point I did waste some money and bought a pair of L20-SE's which are basically MX50-SE's with an extra pair of output transistors only twice the price and little if no performance benefit. Recently I've blown a driver transistor (can't remember if it was a 649 or a 669), I had spares and replaced with no issues. I also note that the old MX50x2 (a current f/b version of the Musical Fidelity MF-XA50 and a much better amp than the MX50-SE once you add some decoupling to sort out the parasitic oscillation, but unfortunately twice the price of the -SE) has 2 pairs of 649/669's drivers.
So question: You have stated previously that you have added an additional pair of output transistors but did you change the 669/649's drivers? Slowhands once published a cct for this mod but states that he hadn't actually tried it but also suggests changing the pre-drivers (not sure what pre- means) to MJE340/350, presumably one pair like for like. Thanks, Clive.
Hello Clive!
Big project 🙂 Ever consider class D for the 8" woofers?
Yes, I tried double outputs, but only as a temporary test, and I did not measure much back then. I only connected them in parallel with current sharing resistors. I got the LJM12-2 as a 'beefier MX50SE', but for some reason I did not like the sound much. Sounded too bright, but measured well, especially in class A.
I also have a pair of the MX50x2, but they are in the same 'leftover' box as the 12-2 boards..(together with some LJM Naim clones etc) If i remember correctly, the 50x2 are a completely different topology, not the 'D. Self type'. Maybe I should take another look at them, based on your statement.. I did not like the sound of those either, and distortion measurements were not impressive either.
Have you written about them somewhere? Easy fix?
Big project 🙂 Ever consider class D for the 8" woofers?
Yes, I tried double outputs, but only as a temporary test, and I did not measure much back then. I only connected them in parallel with current sharing resistors. I got the LJM12-2 as a 'beefier MX50SE', but for some reason I did not like the sound much. Sounded too bright, but measured well, especially in class A.
I also have a pair of the MX50x2, but they are in the same 'leftover' box as the 12-2 boards..(together with some LJM Naim clones etc) If i remember correctly, the 50x2 are a completely different topology, not the 'D. Self type'. Maybe I should take another look at them, based on your statement.. I did not like the sound of those either, and distortion measurements were not impressive either.
Have you written about them somewhere? Easy fix?
Yes, I've seen that mod. I've been running for 5 years without any problems, so I've probably just been unlucky. Retro-fitting 10 amplifiers is a bit of a mammoth task.
I run a class D for the Sub, since I needed 800W and couldn't cool an A/B in an elegant enclosure (not that a 15" sub is exactly elegant).
Agreed, the VAS on the X2 is a completely different design but I loved the sound particularly the low-end, but just too expensive in the numbers I need and especially considering that I would replace all the output transistors (I'm happy to have fake/clone smaller components but the big boys need to be genuine Toshiba's). The other performance factor for me is that all my builds are active so I'm always driving straight into an inductive load which probably suits LJM's inductor-less designs.
I wish I could speak Chinese, I'd love to have a proper conversation with LJM. For me he's a legend, a Doug Self for the masses. He obviously designs down to a price and implements a design simplicity that allows folks to purchase and assemble without the need for any tools or measurement capability i.e. the auto bias circuit (us sophisticates insert an adjustment pot 🙂). But I'd love to see how he would design a balls out, no holds barred, cost no object best amplifier possible.
Similarly, elsewhere I've seen him recommend SA1186/SC2837 based on their speed, although their Ic is significantly lower than comparable devices this comment has always bugged me, why does he think fT make such a difference? - I guess we'll never know.
LJM=Doug Self for the masses 🙂 Yes, you have a point there! Do you know if he ever designed an amp with emitter follower output stage? Most seems to be CFP.
I have actually dug out the mx50x2 boards, and looked up the (M.F.)schematic, and it seems to be what Self calls a quasi complementary Baxandall output. However, there is a difference from Self's example and the MF schematic. The Baxandall diodes are connected to the output in the MF amp, and to the collector resistor in Self's example. Not sure what difference it makes though.
I also remember liking the bass of the mx50x2, but I think I found them a bit 'rough' in the upper registers.
Will have a look at them. If you have some hints on the oscillation problems (how to find them, and how to solve them), I would be grateful.
I have actually dug out the mx50x2 boards, and looked up the (M.F.)schematic, and it seems to be what Self calls a quasi complementary Baxandall output. However, there is a difference from Self's example and the MF schematic. The Baxandall diodes are connected to the output in the MF amp, and to the collector resistor in Self's example. Not sure what difference it makes though.
I also remember liking the bass of the mx50x2, but I think I found them a bit 'rough' in the upper registers.
Will have a look at them. If you have some hints on the oscillation problems (how to find them, and how to solve them), I would be grateful.
mx50x2 is on the bench, and I did some masurements. Measures ok, and seems ok to drive low impedances too. Running it from a +-25V 1A bench supply, so no high power testing.
Can't really see any signs of oscillations so far in the output either.
At first glance I don't see something wrong, so it doesn't really explain why I did not like the sound.
Can't really see any signs of oscillations so far in the output either.
At first glance I don't see something wrong, so it doesn't really explain why I did not like the sound.
Hi guys,
i received this amp kit, i am going to assemble it. Since you already have experience with it, I ask if the values shown on the pcb are correct or should changes be made? the gain is better for it at 31 or 22 .. Thanks
i received this amp kit, i am going to assemble it. Since you already have experience with it, I ask if the values shown on the pcb are correct or should changes be made? the gain is better for it at 31 or 22 .. Thanks
Hi.
All values are correct on pcb.
By default gain is set to 31 with 330R supplied resistor.
For better bass (excellent on that amp) you can increase 16v470uF cap to 1000uF (6.3v should work perfectly) and increase mkp input cap to 10uF.
Have good time assembling it.
Best regards.
All values are correct on pcb.
By default gain is set to 31 with 330R supplied resistor.
For better bass (excellent on that amp) you can increase 16v470uF cap to 1000uF (6.3v should work perfectly) and increase mkp input cap to 10uF.
Have good time assembling it.
Best regards.
Hi
Mine is loaded with Sanken BJT.
I found it really nice at basses but upper frequencies are a bit "tasteless".
Not bad, not good, for the cost I didn't heard better though.
Mine is loaded with Sanken BJT.
I found it really nice at basses but upper frequencies are a bit "tasteless".
Not bad, not good, for the cost I didn't heard better though.
Hey guys I’ve put together like 4 of these kits and I think they sound really good however on each one there is a slight humming in the speakers but goes away completely with just a little volume. Dose anyone know how to correct that ? And I’m very happy with the sound of these amps thanks
Mark
Mark
The hum is likely due to the installation, I have no hum in mine (I also built one with 4 channels, and two stereo amps). Read up on ground loops (good info here on the forum) and you will probably find the cure.
Not sure about your volume control, maybe that has something to do with it too.
Not sure about your volume control, maybe that has something to do with it too.