I also got a pair of these boards recently. Very happy with the sound for this money. Controlled, dynamic and detailed would be the key words in my opinion.
Using them with a scrapped surround amp case, transformer and heat sink + added some giant filter caps for the PSU. Voltage is +-37VDC.
I have also tested LJM's NAP250 MOD & L7, but the MX50SE is my favorite so far. Waiting for LJM 12-2 to arrive.
Have only tested them with some inexpensive 8ohm speakers yet. Most of my speakers are lower impedance due to d'appolito parallelled drivers etc. Thinking of buying more and using them in my active setup with one per driver.
Even the cheaper speakers did things I never heard them do before with the MX50. A pair of modified old Mission 737's suddenly sounded really good!
MODS:
-Bias trimmer
-Added a 10ohm HBR? (hum breaking resistor). Did not notice any diffrence.
-Changed outputs from D1047/B817 to Toshiba 2sa1962/2sc5242 (from scrapped Onkyo). Impression is improved transients and smoother mid/highs.
Based on the test with different outputs, I would go for the Sanken-version next time.
Using them with a scrapped surround amp case, transformer and heat sink + added some giant filter caps for the PSU. Voltage is +-37VDC.
I have also tested LJM's NAP250 MOD & L7, but the MX50SE is my favorite so far. Waiting for LJM 12-2 to arrive.
Have only tested them with some inexpensive 8ohm speakers yet. Most of my speakers are lower impedance due to d'appolito parallelled drivers etc. Thinking of buying more and using them in my active setup with one per driver.
Even the cheaper speakers did things I never heard them do before with the MX50. A pair of modified old Mission 737's suddenly sounded really good!
MODS:
-Bias trimmer
-Added a 10ohm HBR? (hum breaking resistor). Did not notice any diffrence.
-Changed outputs from D1047/B817 to Toshiba 2sa1962/2sc5242 (from scrapped Onkyo). Impression is improved transients and smoother mid/highs.
Based on the test with different outputs, I would go for the Sanken-version next time.
The best option is to use 10k log pot at the input and to increase input resistor to 47k. In this case you would also have to increase feedback resistor to 47k and to change value of the gain setting resistor to a value that suits your needs. But you would have to find these three resistors on the pcb.
Q2/Q10 = 2MJ2955/2N3055?
Hi,
Can it be for Q2/Q10-MJ2955/2N3055?
Are there any changes to the shematic (circuit)?
See shematic...
Thank you!
Hi,
Can it be for Q2/Q10-MJ2955/2N3055?
Are there any changes to the shematic (circuit)?
See shematic...
Thank you!
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My MX50SE is built with parts from the kit (except output transistors). PSU voltage is +/-31VDC at idle. I am pleased to report that with fixed resistor bias circuit I have 13mA bias at one channel and 20mA bias at the other. The difference is not such that trimpot is needed. Also I have DC offset of +1mV at one channel and -1mV at the other. This is very fine result!
I've been reading some amp-books, and it seems doubling the outputs is a good thing for both current/power and distortion, so I'm starting some mods on my MX50SE boards.
I'm now trying to double the output transistors (toshibas as mentioned before) using 4x0,27 Ohm emitter resistors (per amp) I had 'in the bin'. I tried simulating this on in LTspice using the model from this thread, but I have not used Spice since school, and that was abt 20 years ago..(I remember I had to add components to the network via text commands!) It seems to work from what I can see but maybe I'm doing it all wrong.. My gut feeling is that it should work, and they will just share the currents. Ok, maybe not 50/50, since they are not well matched, but should be 'ok'. Should I worry about load on the drivers? Added capacitive load on drivers? Or is it too low to be a concern? Stability of the amp?
What do you think? Will it work? Would I have to change some resistors too? I'm new to modifying amps in this way, so advice is welcome.
I modified one and powered it up with a lab supply. Seemed fine, no oscillations (no load, no input signal).
A bit funny on the 'turn on' when I adjusted idle current. One transistor would turn on before the other, and Idle currents through the paralleled transistors was not equal (Vbe & hfe diff?). I guess it would even out as current goes up and they are more in the linear working range. However I could not verify this since I have no heat sink right now. How critical is it to get both paralleled transistors to get past the 'knee' and pass current at idle?
I'm hoping to run one amp on two 6'5" 8Ohm woofers (d'appolito) in an active setup using double output transistors. If it fails, maybe I have to go with one amp per woofer.
The LJM 12-2 was not similar to the MX50SE in sound, so that's why I want to try some mods to the MX50.
I'm now trying to double the output transistors (toshibas as mentioned before) using 4x0,27 Ohm emitter resistors (per amp) I had 'in the bin'. I tried simulating this on in LTspice using the model from this thread, but I have not used Spice since school, and that was abt 20 years ago..(I remember I had to add components to the network via text commands!) It seems to work from what I can see but maybe I'm doing it all wrong.. My gut feeling is that it should work, and they will just share the currents. Ok, maybe not 50/50, since they are not well matched, but should be 'ok'. Should I worry about load on the drivers? Added capacitive load on drivers? Or is it too low to be a concern? Stability of the amp?
What do you think? Will it work? Would I have to change some resistors too? I'm new to modifying amps in this way, so advice is welcome.
I modified one and powered it up with a lab supply. Seemed fine, no oscillations (no load, no input signal).
A bit funny on the 'turn on' when I adjusted idle current. One transistor would turn on before the other, and Idle currents through the paralleled transistors was not equal (Vbe & hfe diff?). I guess it would even out as current goes up and they are more in the linear working range. However I could not verify this since I have no heat sink right now. How critical is it to get both paralleled transistors to get past the 'knee' and pass current at idle?
I'm hoping to run one amp on two 6'5" 8Ohm woofers (d'appolito) in an active setup using double output transistors. If it fails, maybe I have to go with one amp per woofer.
The LJM 12-2 was not similar to the MX50SE in sound, so that's why I want to try some mods to the MX50.
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IMO, for bass I prefer the MX50SE with an easy load, because it sounds more 'dynamic' and tight/correct all the way down to low frequencies (nice drums and bass on rock music). For some reason I find the 12-2 somewhat 'sloppy' in the low frequencies (bass guitar does not sound as realistic and dynamic, same for kick drum etc). This is for 8Ohm load with some pretty easy to drive 8" & 6,5" speakers. When the load is 4ohms the difference is minimal.
For mid and treble the L12-2 sounds nicer, especially on 4ohms load. IMO the MX50SE had a more 'black background' in mid and treble, but also sound a bit harsh/grainy somehow. This is with KEC transistors, with Toshiba SA1962/5242 or with the (fake?) Sankens, they sound better in mid/treble, but background seemed not as 'black'. Actually the first thought that came to mind with the sankens was 'this sounds like an expensive amp' 🙂
I recently installed the boards with sanken transistors in a 'half-gutted' integrated amp (still using pre amp), where the PS caps are maybe 2x6800uF, and bass ok, but not as good, so capacitance seems to make a difference. All other tests have been with really big Philips PS caps, around 2x0,5F and +-37VDC.
I tried 0,08ohm emitter resistors on the L12-2 as an experiment (LJM some time commented that these could probably be removed), but got some harsh treble(oscillations?), and i did not hear the bass improve. Only idea (long shot) I have for the bass on them now is to try bigger capacitors for the small signal supply (RC filtered). I will definitely go back to 0,15ohm emitter resistors. Maybe try a lower supply voltage and really high bias..
As you see, this is all subjective.. I wish I could add some science to it, but not at the moment.
All tested at normal listening levels, not full power..
About the parallel output transistors earlier (2 pairs), it made them sound a little smoother, and a little bit better for 4ohms, but till not the same as one one pair with 8ohms. So I went back on that, and plan to use one amp per woofer.
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On all these boards I tried to replace the electrolytic capacitors(DC) in the feedback circuit with non polar ones (as recommended in amp books), but can't say I could hear a difference.
Same goes for the input cap on the L12-2, I tried a 6,8uF Metal film Polyester, but could not tell the difference.. Hmm, thinking about that, I actually think I did it at the same time as I replaced the emitter resistors.. not so smart!
Same goes for the input cap on the L12-2, I tried a 6,8uF Metal film Polyester, but could not tell the difference.. Hmm, thinking about that, I actually think I did it at the same time as I replaced the emitter resistors.. not so smart!
thanks for the detailed description🙂 Maybe bi-amping would give you the best of both worlds? The good think about these amps is you can build a power supply, and buy some modules to compare without spending too much.
Yes to both 🙂
I also tried the MX50x2 and NAP250mod. Did not like the 250mod much, MX50x2 was ok, kind of a 'rock 'n roll' amp, wanted to crank up the volume on that one. It might sound 'sweeter' with some other output transistors. Come to think of it, so might the 250mod.
I run active XO and plan to use 4xMX50SE for the midbass, and looking at class a alternatives for the tweeters. Still have to figure something out for the subwoofers. Maybe L20.5, but they are a bit expensive just to buy and try.
I have tried some alternatives for the subwoofers before, but have not been entirely happy with any of them: Behringer Inuke (class D), Yamaha PA amp, Tule hifi amp. I liked the bass from the Thule best of these, and it is modified with some enormous PS caps..
I have a gut feeling that class D should do it with a really 'rigid' PS.. I suspect the Inuke to be a bit flimsy in that department.
I also tried the MX50x2 and NAP250mod. Did not like the 250mod much, MX50x2 was ok, kind of a 'rock 'n roll' amp, wanted to crank up the volume on that one. It might sound 'sweeter' with some other output transistors. Come to think of it, so might the 250mod.
I run active XO and plan to use 4xMX50SE for the midbass, and looking at class a alternatives for the tweeters. Still have to figure something out for the subwoofers. Maybe L20.5, but they are a bit expensive just to buy and try.
I have tried some alternatives for the subwoofers before, but have not been entirely happy with any of them: Behringer Inuke (class D), Yamaha PA amp, Tule hifi amp. I liked the bass from the Thule best of these, and it is modified with some enormous PS caps..
I have a gut feeling that class D should do it with a really 'rigid' PS.. I suspect the Inuke to be a bit flimsy in that department.
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balanced amps for subwoofer may work, use a couple of the cheaper modules and double the power with reduced rails. Class D may be the right way for subwoofer, but I think the important thing is that all the amps have the same sensitivity or you use attenuation for the different amps so as they match.
I have played around with these boards a lot since I like the sound, so I thought I would share for those interested.
Recently I have been experimenting with high bias and measuring distortion spectrum and distortion vs power. I'm now running a pair at +-30VDC and Iq set to 0,45A. This improved them further, so now the mid and treble is really to my linking. It does require some proper heat sinks, but definitely worth it.
This is with 8ohm speakers, and the amp version with the big Sanken transistors. I have tried some other tweaks too, with bipolar decoupling cap for the feedback, and some paralleled decoupling caps for the supply, but the greatest (the only one I could clearly hear) improvement has been the higher Iq.
I'm actually amazed what I'm hearing from a pair of old Mission speakers with these amps. Cheap and simple, but sound great!
Recently I have been experimenting with high bias and measuring distortion spectrum and distortion vs power. I'm now running a pair at +-30VDC and Iq set to 0,45A. This improved them further, so now the mid and treble is really to my linking. It does require some proper heat sinks, but definitely worth it.
This is with 8ohm speakers, and the amp version with the big Sanken transistors. I have tried some other tweaks too, with bipolar decoupling cap for the feedback, and some paralleled decoupling caps for the supply, but the greatest (the only one I could clearly hear) improvement has been the higher Iq.
I'm actually amazed what I'm hearing from a pair of old Mission speakers with these amps. Cheap and simple, but sound great!
Hi Rallyfinnen, can you explain what's the aim with such a high iq?
Does it mean the amp stay longer in class A state?
Mine runs on 30mA iq (sanken too) and I'm very happy with for now.
Thanks a lot.
Does it mean the amp stay longer in class A state?
Mine runs on 30mA iq (sanken too) and I'm very happy with for now.
Thanks a lot.
With 450mA Iq the amp works in ClassA up to several watts, which means that at usual home listening levels amp operates as ClassA amplifier all the time. The subjective speed and clarity is better and the sound is relaxed and fluid, something that ClassAB amps can not provide. But you need very big heatsinks.
Yes, significant improvements in measured distortion, especially at lower output levels.
I could try to use terms as depth and sound stage, -or just say I think it sounds better in mids and treble 🙂
You could try to cool it with a temporary fan just to listen if you think it sounds better. However, I would recommend a relatively low supply voltage to keep the heat down.
I could try to use terms as depth and sound stage, -or just say I think it sounds better in mids and treble 🙂
You could try to cool it with a temporary fan just to listen if you think it sounds better. However, I would recommend a relatively low supply voltage to keep the heat down.
Can you explain why? I think 15W/device should not be any problem (0,5Ax30V), as long as the cooling is ok? They have pretty good surface area to transfer the heat to the heat sink too.