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LJM Audio

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#201
DIP version of the L15D REV3. TEST
 

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#202
ljm_ljm said:
In fact I have a design similar products.

But after testing his performance is not the L15D good, so I gave up.

I repeated the same reference design based on the IRAUDAMP7S.

But every time the failure of the test in all SMT less than the performance of L15D.

400K HZ PWM frequency. Inductors, capacitors, filters.

Waveform distortion. L15D DIP parts. Distortion is very small.

At present, I still have no way to using SMT instead of DIP.L15D version.
Click to expand...
Hisoka from HxH 🙂
 
#203
Hi LJM,

I have a pair of L15 which I've used it for a few months. Its power supply is a 33.6-0-33.6 Transformer with 10,000uF filter capacitor.

I'm wondering if I could further increase the Gain because as compared to my EL34 tube amp, its volume is softer which I have to crank up my PC's volume before it can match my tube amp.

Reading from the IRAUDAMPS7S data, its possible to adjust the value or R7 which is a 3.01K resistor. Is this the same for your L15?

If not, which resistor of what value is it responsible for its gain in the L15?

Thanks.
 
#206
Apologize if this is covered elsewhere, I couldn't find. I want to use a pair of L15D per side as bi-amp controlled by Minidsp unit. My old speakers were rated 60w max new. I'd like to avoid adding a pot, as I will have master volume in the dsp and can pad if necessary there too. If I supply a lower voltage..say +25 or so, will that limit the output to 50w peak? If so will L15D still work ok? The lowest distortion area of L15D is 5-35w, right where I want to run them.-Thanks
 
#207
This document is the basis for the LXXD designs from ljmljm (l15,l20,l25). He simplified the design(removed the over/under voltage protection), but the basic circuit is the same. Page 37 describes the differences between the suggested versions. The L15D is equivalent to the Amp7s-150, and you likely want something like the AMP7S-100, which you can get by changing the various resistors, to adjust the operating point of the amp. Unfortunately there are no schematic diagrams, of ljmljm's designs, so you have to figure out which resistors you need to change. Someone has identified the components numbers for the L25, but its a slightly different board layout, so you'll have to do it yourself (I was planning on doing it for the L15 myself, but havent had time yet).
 
#208
Maybe I'll be forced to use something else. I don't have the knowledge to do that modification. My focus is designing folded bass horn boxes with rear firing back loaded and tractrix front loaded for the woofers so they have a chance to keep up with the 811 horns without padding the horns. As these projects do, it evolved. Now into a bi-amping design using the Minidsp. I suppose I can build a generous equipment bay into the box and leave room to start out with a cheapy and then after it's going, maybe I'll figure a way to get something higher quality in there.
hanks for the response.
 
#210
Idefixes said:
I just finished to solder L15D LJM kit, will test it next few day

1204270907271246339775142.jpg


1204270907271246339775141.jpg


1204270907301246339775144.jpg


1204270907291246339775143.jpg


I swap all elko to Panasonic Fc and increase the 220µF to 390µF. I also soldered 220nF decoupling cap on 22µF and 10µF

Marc
Click to expand...

Is .22 UF can choose to use a larger capacity .22-68UF.

I have been using the Fujitsu OSCON capacitors. It is very good. I use 20V22UF.L15D, L15DX2 on.
 

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#211
chanfh said:
Hi LJM,

I have a pair of L15 which I've used it for a few months. Its power supply is a 33.6-0-33.6 Transformer with 10,000uF filter capacitor.

I'm wondering if I could further increase the Gain because as compared to my EL34 tube amp, its volume is softer which I have to crank up my PC's volume before it can match my tube amp.

Reading from the IRAUDAMPS7S data, its possible to adjust the value or R7 which is a 3.01K resistor. Is this the same for your L15?

If not, which resistor of what value is it responsible for its gain in the L15?

Thanks.
Click to expand...

The L15D amplification gain is about 36 times. About can increase the 120K resistor. Gain to improve.

I suggest to add a preamp can add an op amp gain.
 
#213
Hawaiiman said:
Apologize if this is covered elsewhere, I couldn't find. I want to use a pair of L15D per side as bi-amp controlled by Minidsp unit. My old speakers were rated 60w max new. I'd like to avoid adding a pot, as I will have master volume in the dsp and can pad if necessary there too. If I supply a lower voltage..say +25 or so, will that limit the output to 50w peak? If so will L15D still work ok? The lowest distortion area of L15D is 5-35w, right where I want to run them.-Thanks
Click to expand...

L15D can not be less than less than +-35V.
If you do need to +-25V I recommend using the TA2022??, LM4766??

Perhaps they are more simple.
 

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#214
ljm_ljm said:
The L15D amplification gain is about 36 times. About can increase the 120K resistor. Gain to improve.

I suggest to add a preamp can add an op amp gain.
Click to expand...

Thanks LJM. Currently I placed a TL072 preamp before the L15D using a non-inverting config. The set again is 2.5X only but I have a fairly loud hiss coming from the output. If the input of the preamp is not connected, it's gives out a audible hum at the output. Any idea why?

Thanks!😕
 
#215
chanfh said:
Thanks LJM. Currently I placed a TL072 preamp before the L15D using a non-inverting config. The set again is 2.5X only but I have a fairly loud hiss coming from the output. If the input of the preamp is not connected, it's gives out a audible hum at the output. Any idea why?

Thanks!😕
Click to expand...

Cancel the pre-amplifier. If there is no noise, the noise is generated by the pre-amp.

Preamplifier noise is likely to occur..

Or short circuit L15D signal input IN INGND. If there is no noise.

Description of noise generated by the input signal.
 
#216
Thanks LJM for the advice. Its working fine now.

I didn't need the preamp after all. My problem was I plugged into the wrong source where it has a 10K resistor across the line level. Now its working great with a 10000uf rectifier at a Vs of 46V.

It's a great amp board with very minimal heat.

Cheers!
 
#217
Can use this circuit level before the match
It can be a good and L15D L20 D and D match up

As four times as much amplification. Have a minimal noise value.


Won't hear.
 

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#218
I am planning to go for stereo L15d. I have 4 ohms speakers. Also have a pass b1 bueffer. I need to get a linear psu 50-0-50 volts DC right? Is there a recommended one. Would like to build one myself, not a module. Are 63 volt caps enough or do I need to go for more. What kind of trafo is a good option, ei, torroid or r core. I need speaker protection curcuitry. Do I need a soft start module also, any recommended ones? I will probably get these from fleabay. Most of these run on 12v right, will check anyway before getting the trafo etc.
 
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