LJM Web Page
ljm_ljm
What is your real home page.
http://www.ljmaudio.net/ sends to ljmaudio.net. This dominio is for sale
ljm_ljm
What is your real home page.
http://www.ljmaudio.net/ sends to ljmaudio.net. This dominio is for sale
L7 first impressions
My lab supply is only +/-30V so all my tests were at that rather low supply voltage. What surprised me is that amp runs dead cold at that voltage meaning that fixed resistors combination result in underbiased condition and output works almost in pure B class. What surprised me more is that even underbiased this amp sounds neutral which probably is the result of excellent input CFP stage. Mosfet outputs usually sound bright when underbiased, which I like, but not this amp. It's ideal for use with brighter sounding preamp or tone control preamp or PC preamp with EQ, or brighter sounding loudspeakers.
My lab supply is only +/-30V so all my tests were at that rather low supply voltage. What surprised me is that amp runs dead cold at that voltage meaning that fixed resistors combination result in underbiased condition and output works almost in pure B class. What surprised me more is that even underbiased this amp sounds neutral which probably is the result of excellent input CFP stage. Mosfet outputs usually sound bright when underbiased, which I like, but not this amp. It's ideal for use with brighter sounding preamp or tone control preamp or PC preamp with EQ, or brighter sounding loudspeakers.
Attachments
ivan,
Were you using a linear PSU, or SMPS when doing these tests? Have you done any further testing with higher voltages yet? I'm also wondering what size heat sinks would be required if running at +-56VDC?
I just completed assembling the modules without the output devices attached, as they need to be properly fitted to the end packaging and enclosure I select - based on power output of course.
I've used LJMs Class D modules before (L20) and thought they sounded okay. But I understand the L7 should sound 'better'?
My diy lab supply is linear. Based on comments of other builders +-56VDC is too high for this amp. Output stage would probably survive high power at this voltage but it seems that VAS and driver stages are not happy with this high voltage. For high power you need at least 500gm heatsink per channel.
Better sound? It depends on the taste of user. I expected brighter sound but at the end got wonderfully balanced, linear and neutral sound.
Better sound? It depends on the taste of user. I expected brighter sound but at the end got wonderfully balanced, linear and neutral sound.
I don't have appropriate transformer yet but plan to use one with 25-30V secondaries so that supply voltage after smoothing is somewhere between 35 and 45VDC. There will be more power than with 30VDC but still on the safe side. After all this is only one pair of output transistors, and although they are specified for 20Amps, that rating is for switching PSU duties, not for linear applications.
LJM L12 finished amplifier variations
Hello All:
I seem to have jumped in on this thread late.
I have followed this thread the last few days with keen interest.
My current setup consists of Solstice Floor Standers (Jeff Bagby Design/Kit from Parts Express), which has been converted to an Active Crossover Setup.
The speakers consists of Tweeter: Morel CAT 308 1 1/8" 8ohms and
Woofers: Two x Morel TiCW 638nD 6" Woofers.
I am currently driving my active setup via:
Tweeter: TP-22 Topping Amp
2 x Woofers: AKITIKA GT-101 Amp
My DIY skills are mediocre, although the Solstice Speakers and AKITIKA GT-101 Amp are DIY Kits.
I have browsed through various stores on AliExpress and have worked out that it may be easier for me to purchase a Finished L12-2 Amplifier rather than getting the modules/chasis/transformer etc.
My questions to my fellow DIYAUDIO Mates here are:
1) For my Solstice Speakers which are converted to an Active Crossover setup, would there be much discernible audible difference to driving them with 2 L12-2 Amplifiers, 1 L12-2 to the Tweeters and 1 L12-2 to 2 x Woofers.
Compared to 3 L12-2 Amps, 1 L12-2 to the Tweeters and 2 L12-2 to 2 woofers.
Specs of the Solstice are here:
Solstice MLTL Reference Tower Speaker Kit
2) For the L12-2 Finished Amplifier, there seems to be 2 versions.
Can anyone help me identify the difference?
L12 HIFI -
L20.5 -
Answers from anyone will be very much appreciated.
Hello All:
I seem to have jumped in on this thread late.
I have followed this thread the last few days with keen interest.
My current setup consists of Solstice Floor Standers (Jeff Bagby Design/Kit from Parts Express), which has been converted to an Active Crossover Setup.
The speakers consists of Tweeter: Morel CAT 308 1 1/8" 8ohms and
Woofers: Two x Morel TiCW 638nD 6" Woofers.
I am currently driving my active setup via:
Tweeter: TP-22 Topping Amp
2 x Woofers: AKITIKA GT-101 Amp
My DIY skills are mediocre, although the Solstice Speakers and AKITIKA GT-101 Amp are DIY Kits.
I have browsed through various stores on AliExpress and have worked out that it may be easier for me to purchase a Finished L12-2 Amplifier rather than getting the modules/chasis/transformer etc.
My questions to my fellow DIYAUDIO Mates here are:
1) For my Solstice Speakers which are converted to an Active Crossover setup, would there be much discernible audible difference to driving them with 2 L12-2 Amplifiers, 1 L12-2 to the Tweeters and 1 L12-2 to 2 x Woofers.
Compared to 3 L12-2 Amps, 1 L12-2 to the Tweeters and 2 L12-2 to 2 woofers.
Specs of the Solstice are here:
Solstice MLTL Reference Tower Speaker Kit
2) For the L12-2 Finished Amplifier, there seems to be 2 versions.
Can anyone help me identify the difference?
L12 HIFI -
L20.5 -
Answers from anyone will be very much appreciated.
Hi all
I have to change the (not very good and, now dead) amp board on my step father's Marantz PM50.
the supply is dc +/- 47v and i would like to use an LJM class A/B or D design.
If any one have tried some of these boards, can you tell me sound wise which one is the best to you between MX50X2, L20SE or L15d-pro ?
Max power doesn't really mater, SQ is the most important thing in that perticular case.
what are the last revision (or best transistors) of these boards please ?
Best regards.
t-minik
I have to change the (not very good and, now dead) amp board on my step father's Marantz PM50.
the supply is dc +/- 47v and i would like to use an LJM class A/B or D design.
If any one have tried some of these boards, can you tell me sound wise which one is the best to you between MX50X2, L20SE or L15d-pro ?
Max power doesn't really mater, SQ is the most important thing in that perticular case.
what are the last revision (or best transistors) of these boards please ?
Best regards.
t-minik
LJM claims that you can use many different output transistors including 1943/5200 but you should check stability with the scope after replacement.
No. + and - 50VDC is correct. It's the high end, but doable. That's rectified and filtered voltage rails.I'm thinking of buying the L7 but what really stands out to me is the voltage... is that in +/- added together or actually +50V and -50V? not possible right??
Oh that explains it. I forgot it was DC not AC
is beyond +/-29VAC safe for it? i read comments saying beyond 29 they will blow up but not sure if it still maintains or i need to look for a 250v FET which will probably be harder to drive due to increased input capacitance
Hi ljm,
I follow your product like a while (L15D, etc) and I just ordered two L20.5 to compare with my Class D JLE-800S (IRS2092 by Jlester on diyaudio) with the same SMPS (+-55v).
The winner come to my new realisation (8 channels HiEnd HomeTheater/Hifi amp)
I wan't to know if the gain at 31 is too loud for me which component I can't change to lowering it around 27 times ? (18 is too low)
Another thing, the capacitor side left to the analog entry is the link capacitor , i can remove it if my preamp haven't any offset ?
Best Regards.
I follow your product like a while (L15D, etc) and I just ordered two L20.5 to compare with my Class D JLE-800S (IRS2092 by Jlester on diyaudio) with the same SMPS (+-55v).
The winner come to my new realisation (8 channels HiEnd HomeTheater/Hifi amp)
I wan't to know if the gain at 31 is too loud for me which component I can't change to lowering it around 27 times ? (18 is too low)
Another thing, the capacitor side left to the analog entry is the link capacitor , i can remove it if my preamp haven't any offset ?
Best Regards.