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Re: JLM 60Watt Power AMP Kit

Posted: Sun Feb 08, 2015 2:10 pm
by trenchrecordings
what size transformer can i get away with bare minimum ? Thinking i might just use this for a bench / test tone speaker.... and listening to tunes while soldering. Also specs on a woofer/tweeter on the cheap ? I'll upgrade it down the road

-Dave

Re: JLM 60Watt Power AMP Kit

Posted: Mon Feb 09, 2015 12:10 am
by trenchrecordings
How about a 18v wall wart plug if I can find one laying around?

Re: JLM 60Watt Power AMP Kit

Posted: Mon Feb 09, 2015 10:46 am
by Joe Malone
trenchrecordings wrote:How about a 18v wall wart plug if I can find one laying around?


You could use an 18vac wall wart with 2 diodes to make +/-25vdc. The wall wart VA or wattage would limit the max amp wattage but for normal listening level that would be fine.

You could use a 12vac wall wart with 2 diodes as well.

Re: JLM 60Watt Power AMP Kit

Posted: Mon Feb 09, 2015 1:08 pm
by trenchrecordings
Ok great. Thanks for the info Joe !

I dug up these wall warts from my junk pile.

Input 120V AC 60Hz - Output 12V AC 1000mA
Input 110/117VAC 15W - Output 16V AC 500mA
Input 100-240V 50/60Hz max 700mA 50VA - Output 12V DC switching 2A

What would be the best choice ? the DC switching supply is DC already so no diodes needed ?

Re: JLM 60Watt Power AMP Kit

Posted: Mon Feb 09, 2015 1:58 pm
by Joe Malone
trenchrecordings wrote:Ok great. Thanks for the info Joe !

I dug up these wall warts from my junk pile.

Input 120V AC 60Hz - Output 12V AC 1000mA
Input 110/117VAC 15W - Output 16V AC 500mA
Input 100-240V 50/60Hz max 700mA 50VA - Output 12V DC switching 2A

What would be the best choice ? the DC switching supply is DC already so no diodes needed ?


You need AC as you are going to make +/-V with 2 diodes so the 12vac 1A one should be best.

One wire from the AC plug pack goes to 0v

The other wire from AC plug pack goes to Cathode of 1st diode going with Anode going to -V and also Anode of 2nd diode with Cathode going to +V

Re: JLM 60Watt Power AMP Kit

Posted: Tue Feb 10, 2015 12:22 pm
by trenchrecordings

Re: JLM 60Watt Power AMP Kit

Posted: Tue Feb 10, 2015 12:48 pm
by Joe Malone
trenchrecordings wrote:speaker hums and doesn't pass sound. Can you post a drawing of the diodes ?

https://www.dropbox.com/s/0o0cs9tm0zb8ism/2015-02-09%2021.40.30.jpg?dl=0
https://www.dropbox.com/s/6hitb7ct6jiy8vm/2015-02-09%2021.42.11.jpg?dl=0


Diodes in your photo wrong way around. Swap them over between +V and -V and it will work.

Below is the first post image but with one winding shown only. You will need a wire link where switch is shown for the mute to be disabled so you get sound.

Image

Re: JLM 60Watt Power AMP Kit

Posted: Tue Feb 10, 2015 1:08 pm
by trenchrecordings
works great. thanks Joe. Amazing response time by the way!

Re: JLM 60Watt Power AMP Kit

Posted: Tue Feb 10, 2015 1:19 pm
by Joe Malone
trenchrecordings wrote:works great. thanks Joe. Amazing response time by the way!


Cool. Great to hear you got it working. Also make sure it does have a heatsink as it draws 50mA at idle so needs a Diecast box or heatsink to not overheat or it will go into protect mode.

Re: JLM 60Watt Power AMP Kit

Posted: Sat Jul 02, 2016 2:13 pm
by msmithers
Hi,

I used the AMP kit board to build a 2nd order high pass at about 60 Hz around the LM3886. The LTSpice simulation schematic is shown below. (Not shown are all the power supply, mute circuit and LED components which I did use on the circuit board as is.) R3 represents a speaker 8 ohm load. The simulated frequency response looks good and the in-band voltage gain is 20.8 dB.

The problem is that the circuit is "motorboating." I have a rectified 25-0-25 Vdc coming in (from a 300VA toroid w Joe's bridge rectifier) and I'm seeing the speaker output square-wave oscillate between -25 and 25 VDC at about 1Hz.

Any help would be most appreciated. I haven't done much analog work, let alone analog with an amp chip. (I'm a DSP guy. :-) )

jlm_amp_kit_2nd_HPF_motorboating.png

Re: JLM 60Watt Power AMP Kit

Posted: Sun Jul 03, 2016 3:41 pm
by msmithers
So after some transient simulation and more reading about the LM3886 and stability, I mod'd the board to do the HPF as a passive 2nd order on the input. The gain reduction at DC in the feedback path makes the final response a little steeper than 2nd order. All good. :-)

jlm_amp_kit_2nd_HPF_ok2.png

Re: JLM 60Watt Power AMP Kit

Posted: Mon Jul 04, 2016 11:59 am
by Joe Malone
msmithers wrote:So after some transient simulation and more reading about the LM3886 and stability, I mod'd the board to do the HPF as a passive 2nd order on the input. The gain reduction at DC in the feedback path makes the final response a little steeper than 2nd order. All good. :-)


HI Michael
Yes if you get motorboating removing DC gain from the opamp will usually work. The normal balanced split negative feedback circuit on the AMP PCB doesn't need this for stability at all. But once you convert back to the normal unbalanced circuit you will need it usually just to reduce the output dc offset to the speaker.

Also if you calc C4 value properly to can use it as a extra 6dB per octave roll off making a total of 18dB per octave HPF

Re: JLM 60Watt Power AMP Kit

Posted: Tue Jul 05, 2016 1:19 pm
by msmithers
Thanks Joe. Yep, I see some of C4's extra roll-off in the simulation.

I realised by changing from the 2nd order Sallen-Key HPF to the passive 2nd order, I've lost the ability to have high Q on the HPF. (I.e. I have 2 real poles rather than complex poles.) Do you have any suggestions for making the original circuit stable? Or it an inherent problem with the LM3886 versus a regular unity-gain-stable op amp?

Joe Malone wrote:
msmithers wrote:So after some transient simulation and more reading about the LM3886 and stability, I mod'd the board to do the HPF as a passive 2nd order on the input. The gain reduction at DC in the feedback path makes the final response a little steeper than 2nd order. All good. :-)


HI Michael
Yes if you get motorboating removing DC gain from the opamp will usually work. The normal balanced split negative feedback circuit on the AMP PCB doesn't need this for stability at all. But once you convert back to the normal unbalanced circuit you will need it usually just to reduce the output dc offset to the speaker.

Also if you calc C4 value properly to can use it as a extra 6dB per octave roll off making a total of 18dB per octave HPF

Re: JLM 60Watt Power AMP Kit

Posted: Mon Aug 15, 2016 11:52 am
by Mattsoniclab
Hi everyone. It's interesting reading through the build thread and seeing what people are making :)

I'm about to pull the trigger on one of these and just have a couple of questions first. I'll be using it to build my own version of an auratone. A mono reference speaker, but hopefully with a better sound than the auratone! I'll be using a single paper cone speaker, with some sort of passive mono summing device which I imagine I also need to construct.

> what is the maximum rated wattage that I should be looking for in a speaker? I have a Tannoy mercury mx2 which I might pull apart for the driver. :)
> I obviously need a power supply, does JLM have a reccomended power supply? or can this just be any old common AC 25v adapter?
> is there anything else that I should be purchasing from JLM to make this project work, ie, any crucial parts that need to be added to my shopping cart?

Thanks!
Matt

Re: JLM 60Watt Power AMP Kit

Posted: Wed Aug 17, 2016 9:54 am
by Joe Malone
Mattsoniclab wrote:Hi everyone. It's interesting reading through the build thread and seeing what people are making :)

I'm about to pull the trigger on one of these and just have a couple of questions first. I'll be using it to build my own version of an auratone. A mono reference speaker, but hopefully with a better sound than the auratone! I'll be using a single paper cone speaker, with some sort of passive mono summing device which I imagine I also need to construct.

> what is the maximum rated wattage that I should be looking for in a speaker? I have a Tannoy mercury mx2 which I might pull apart for the driver. :)
> I obviously need a power supply, does JLM have a recommended power supply? or can this just be any old common AC 25v adapter?
> is there anything else that I should be purchasing from JLM to make this project work, ie, any crucial parts that need to be added to my shopping cart?

Thanks!
Matt


Wattage markings on a speakers mean little. A 4 to 5 inch full range of any watts will work for a auratone clone.
Best is just a 2 x 25vac 80VA transformer for full power.

But for this project a 2 x 15vac 30VA transformer would drop the wattage and size down and still be heaps of power for the speaker.

JLM order
1 x 60w amp kit
1 x 25A bridge rectifier
1 x world power kit with 2 x 15vac 30VA transformer (or get local transformer to save shipping cost)

You will just need a case, heatsink and in and out termianls to finish. Use a diecast box as it would work as a case and heatsink.