8PAKAMP & 12PAKAMP KIT BUILD THREAD

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Re: 8PAKAMP KIT BUILD THREAD

Postby Joe Malone » Mon Apr 04, 2016 11:19 am

Joekkel wrote:i've posted some pics on facebook and have linked you on a picture, feel free to add the pics to the jlm-site. just two last questions :wink:

i have installed a 2A slowblow fuse. i think that's too low, because it occasionally blows up during start-up. what fuse-value would you recommend for a 300va-trafo? and is it normal, that the amp-heatsink is getting hot, even on low to no signal within an hour of use? i mean, i still can touch it without problems. i would guess around 50-60 degree celsius.

many regards, joachim


Cool thanks for taking the time. I will go check out the photos.

Transformer fuse size is more related to power on surge of the transformer type. But yes you are on the correct path.
Smallest slow blow fuse that doesn't blow after a few power ups is the best. So try 3A Slow blow and see how it goes.

Yes heatsink temp sounds correct as each amp has 50mA idle current so adds up to about the temp you mention so is not a problem.
Joe :-)
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DaveW
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Re: 8PAKAMP KIT BUILD THREAD

Postby DaveW » Sun Jun 25, 2017 3:20 pm

Hi Folks! I've been tasked with designing the audio playback system for a new 'interactive narrative experience' (kind of like an escape room). And have realised that the 8 and 12PAK kits would suit this purpose well, as dozens of discrete channels of audio will be needed for the multiple spaces. I do have a bit of experience with making kits and cables etc, but not a huge amount of electronics experience or knowledge otherwise. Currently my rough plan for the spaces is to do a permanent install of the amp kits in a wall mounted cabinet, rather than traditional rack mount enclosures.

My question relates to the best way to power the boards. Initially there will probably be 2 x 8PAK modules, and then as the extra spaces are built, another 2 x 12PAK will be added (possibly more as needs may change). I have noted that SMPS have been used for various multi-channel amps on JLM Audio's Instagram, and thought that might be the best way to approach this particular situation. Would 2 x 600W SMPS be enough to provide the +/- rails for the first two 8PAK boards? (So long as the outputs are floating?) I'm thinking there would be an economy of scale here where purchasing larger power supplies that can run multiple boards would be more cost effective, or perhaps power supplies that can be run in parallel? Also some of those channels will be bridged to run subs, so I gather a lower voltage output supply is required.

Any advice would be much appreciated! Cheers!

Dave.

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Re: 8PAKAMP KIT BUILD THREAD

Postby Joe Malone » Tue Aug 01, 2017 11:59 am

DaveW wrote:Hi Folks! I've been tasked with designing the audio playback system for a new 'interactive narrative experience' (kind of like an escape room). And have realised that the 8 and 12PAK kits would suit this purpose well, as dozens of discrete channels of audio will be needed for the multiple spaces. I do have a bit of experience with making kits and cables etc, but not a huge amount of electronics experience or knowledge otherwise. Currently my rough plan for the spaces is to do a permanent install of the amp kits in a wall mounted cabinet, rather than traditional rack mount enclosures.

My question relates to the best way to power the boards. Initially there will probably be 2 x 8PAK modules, and then as the extra spaces are built, another 2 x 12PAK will be added (possibly more as needs may change). I have noted that SMPS have been used for various multi-channel amps on JLM Audio's Instagram, and thought that might be the best way to approach this particular situation. Would 2 x 600W SMPS be enough to provide the +/- rails for the first two 8PAK boards? (So long as the outputs are floating?) I'm thinking there would be an economy of scale here where purchasing larger power supplies that can run multiple boards would be more cost effective, or perhaps power supplies that can be run in parallel? Also some of those channels will be bridged to run subs, so I gather a lower voltage output supply is required.

Any advice would be much appreciated! Cheers!

Dave.


HI Dave

Sorry didn't get notified by the forum about this post.

2 x 600w SMPS should run 2 x 8 pack and probably the 2 x 12pack if the system is only putting out burst of music and speech etc.

Let me know if you have any more questions.
Joe :-)

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cowneko
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Re: 8PAKAMP KIT BUILD THREAD

Postby cowneko » Thu Apr 26, 2018 6:54 pm

Hi everyone,

Before everything else let me introduce myself. I'm a french audio enthusiast, and i've been hooked by the DIY virus some years ago. Since then I've already build a large number of gears (Pass F5/M2/Aleph/B1, Tubelab SSE, 300B se, some lm3886 stereo amp, some AB amps, a shigaraki MKIII cd player and repaired quite a bit of vintage gears like Onkyo M504, Hitachi HMA8500MkII, Marantz PM-55, Sharp SM-511H) as well as some speaker designs.
Recently I've built SL LXmini speakers and I think I got here one of the finest speakers I've ever listened to.
Right now they are driven by a Hitachi HMA8500mkII on the woofers and a Quad405 clone on the Fullranges and as I plan to add the subs (LXmini+2) I wanted to build a multichannel amp to drive the whole thing (with at least 6 identical channels), I then tumbled upon the 8PAKAMP kit witch seems to fill the bill nicely.

Now for the questions/problems/trouble ;)

I am planning a full unbalanced build (so -6db of gain) and since I need a gain of at least 27 I will have to change the gain somehow, so here is what I've done:

-Built the board with kit parts except for R11 witch has 220R instead of 1K (+12db of gain)
-Chips mounted below the board and fixed to a huge Heatsink.
-I use 300VA 2x24V trafo (a little less than 300VA for instance but it's for test purpose, will use a proper 500VA 2x24V for final build)
-I'm using two 200V 25A bridges for pos and neg rails (outputs wired backward on the negative rail bridge)

The wiring is made as follow:

-one return to starground from on of the ground terminal in the middle of the board (currently it's taken from on of the speaker return but will be changed for final assembly)
-return for each bridges to starground
-Mains earth to starground
-Speaker return to starground (may be soldered directly to the board in the final assembly)

-RCA hot to +in (pin 2)
-RCA cold to -in (pin1)
-Board shield (pin3) to ground (on board)

Now for the problems:

If a signal is present on the input (music or sin from a generator) or if the input is shorted, everything works fine, but if there are no input or an input without signal, the output give 28V AC, speakers do not like that at all :(

I'm surely doing something wrong with input wiring but Before trying every possible combinations I prefer to ask for your enlightenment.

Also, It seems like shorting R1 and R4 and installing a fixed 10K res in place of the trimmer is a cleanest way of getting back 12db of gain, but as my board is already populated I don't know where are R3 and R4, can you show me on a board picture?

Image
Image
Image
Image

EDIT:

I made some changes:

I Changed R3&R4 for pieces of wire, replaced R11 for a 1K res, and put a 10k res in place of the trimmer, and that for all channels.
I relocated the pcb ground return to the terminal witch is between filter caps.
I wired the speaker return directly to the PCB (next to the speaker output terminal)
I wired the rca hot to +in (Pin 2) and rca cold to -in (Pin 3) no bridge from pin3 to ground

I wired the two 24V secondaries of my transformer in parallel (2x24V 130va became 1x24V 260VA) so to only use one 25A 200V bridge.

Voltages after bridge are +-35,4 VDC.

Now for the measurments:

I use a Shanling M2s DAP connected to the two wired channels (channels 1 and 3) with a jack to 2x RCA cable (common ground)

-With no connections at all on both rcas I got 0V AC and 10mV DC offset on each speaker outputs.

-With one RCA connected (but not connected to the DAP) on channel 1, I got 0,1V AC and 10mV DC offset on each speaker outputs.

-With two RCA connected (but not connected to the DAP) on channel 1 and 3, I got 8vAC witch collapse abruptly to 0v AC after less than a minute, and 200mV DC offset witch rise abruptly to -4,15v DC after less than a minute. This is exactly the same when the DAP is connected and music signal is playing (except AC voltage is on range with the music signal)

Same behavior whenever pin 3 is bridged to ground or not

Somethings weird here

Image
Image
Image

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Re: 8PAKAMP KIT BUILD THREAD

Postby Joe Malone » Tue May 01, 2018 11:25 am

Ok I hope you mean you wired the 2 x 24vac in series (Not parellel) to make 48v centre tapped ?? So the centre tap goes to 0v and the outside connections go to ACs on the bridge?? Make sure the phase of the 2 winding going to 0v are 180 degrees different to each other.

Please show a photo of the how thew power supply is wired at the moment with one bridge so I can check it over.
Joe :-)

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cowneko
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Re: 8PAKAMP KIT BUILD THREAD

Postby cowneko » Thu May 03, 2018 6:23 am

Well, seems like I wired then in parallel..... I've redone the wiring in serie and I don't have the voltage sag anymore, nor any DC offset on output, my bad. Thanks for pointing out my mistake.

However I still have the problem of AC voltage on output until actual music signal is played. With my dap connected on RCA input (without music signal) when powering on the amp I get 17 V AC on output witch goes done to 9,4V AC in few seconds (problematic), It goes straight to the mV zone as soon as music signal is played and this with and without Pin3 shorted to Ground.

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Re: 8PAKAMP KIT BUILD THREAD

Postby Joe Malone » Thu May 03, 2018 2:03 pm

cowneko wrote:Well, seems like I wired then in parallel..... I've redone the wiring in serie and I don't have the voltage sag anymore, nor any DC offset on output, my bad. Thanks for pointing out my mistake.

However I still have the problem of AC voltage on output until actual music signal is played. With my dap connected on RCA input (without music signal) when powering on the amp I get 17 V AC on output witch goes done to 9,4V AC in few seconds (problematic), It goes straight to the mV zone as soon as music signal is played and this with and without Pin3 shorted to Ground.


If the DAP is made to drive headphones then make sure it has at least 33R to 100R resistor mounted directly across the back of the RCA socket to give the DAP the signal a load is connected.

If this doesn't fix the problem then you may also need to add a 100R in series with each wire going to the + and - inputs on the 8PAKAMP as they share a common - point.
Joe :-)

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cowneko
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Re: 8PAKAMP KIT BUILD THREAD

Postby cowneko » Fri May 04, 2018 7:57 am

Seems like it works ;)

I put 47R res across each rcas and no more AC voltage on output when no signal present :) no thump on startup or shutdown, clean sound.....cool
Does the presence of those res modifies the input sensitivity in anyway or/and does it change the frequency response?

I still had a strange behavior, since one of the channels seems to mute after a while, have to investigate on this

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Re: 8PAKAMP KIT BUILD THREAD

Postby Joe Malone » Tue May 15, 2018 10:00 pm

cowneko wrote:Seems like it works ;)

I put 47R res across each rcas and no more AC voltage on output when no signal present :) no thump on startup or shutdown, clean sound.....cool
Does the presence of those res modifies the input sensitivity in anyway or/and does it change the frequency response?

I still had a strange behavior, since one of the channels seems to mute after a while, have to investigate on this


The 47R load doesn't change the frequency response of the amp or sensitivity but depends on the mp3 player which R value will give the lowest THD distortion. Values will usually be between 33R to 300R
Joe :-)

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cowneko
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Re: 8PAKAMP KIT BUILD THREAD

Postby cowneko » Mon May 21, 2018 8:58 pm

Thanks a lot Joe for all your advises ;)

Now the amp is working plenty good with the LXMini, the only remaining thing is that the gain is quite low (although I shorted R3 and R4 and installed a fixed 10K res in place of the trimpot).
Shall I reduce R11 to something like 470R to get more gain?

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Re: 8PAKAMP KIT BUILD THREAD

Postby Joe Malone » Tue May 22, 2018 9:51 am

cowneko wrote:Thanks a lot Joe for all your advises ;)

Now the amp is working plenty good with the LXMini, the only remaining thing is that the gain is quite low (although I shorted R3 and R4 and installed a fixed 10K res in place of the trimpot).
Shall I reduce R11 to something like 470R to get more gain?


Yes increase gain by reducing R11 1k to smaller values to get the gain you need.
Joe :-)

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cowneko
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Re: 8PAKAMP KIT BUILD THREAD

Postby cowneko » Mon May 28, 2018 2:17 am

Well Amp finished and boxed ;)

Image

Image
You may notice that a channel misses a 1000uf cap, it's because I fried one chip when doing tests (a bit of solder stuck between pins)... :oops:

The amp sounds pretty good but I definitely misses some output power, I think one lm3886 with a 35V DC rails gives something like 40W under 8ohm but the lxmini requires a bit more than that.
I may use the board in bridged mode (as I really need no more than 4 channels) in order to get more power. I understand that I must have 24V DC on rails (so a 2x18VAC transformer) and link two amps
Image
Is this the right way?
Also, In this configuration I only need one fixed 10K res in place of the trimmer per couple of amps, right?

How much power shall I get under 8ohm in bridged mode?

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Re: 8PAKAMP KIT BUILD THREAD

Postby Joe Malone » Tue May 29, 2018 2:16 pm

cowneko wrote:Well Amp finished and boxed ;)


Build looks good :-)

The amp sounds pretty good but I definitely misses some output power, I think one lm3886 with a 35V DC rails gives something like 40W under 8ohm but the lxmini requires a bit more than that.


With +/-35vdc power is 68watts into 8ohm load. +/-25v Bridged 140watts into 8 ohm load

I may use the board in bridged mode (as I really need no more than 4 channels) in order to get more power. I understand that I must have 24V DC on rails (so a 2x18VAC transformer) and link two amps


Correct but you can try it on +/-35vdc as depending on length of audio peaks and heat as to if the protection will cut in and make the audio sound bad earlier than expected. But first check you are getting the amp to actually clip and it is not the mp3 player clipping first before the amp gets to full power. You should be able to get a +/-31vdc clipped waveform out of the amp into a 8ohm load.

Image
Is this the right way?

yes

Also, In this configuration I only need one fixed 10K res in place of the trimmer per couple of amps, right?

No reason to remove the 10k as the load is already 47R to 100R by the load resistor. So just send input to +in on one amp and -in pn the other amp to bridge and connect unused inputs to 0v.

How much power shall I get under 8ohm in bridged mode?

Bridged 120w to 140watts into 8 ohm load with +/-35v depending on heat and current portection cutting in. Lowering the power rails limits the heat and lowers the current so protection comes in later.
Joe :-)

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Re: 8PAKAMP KIT BUILD THREAD

Postby cowneko » Tue May 29, 2018 4:49 pm

Image

So like this?

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Re: 8PAKAMP KIT BUILD THREAD

Postby Joe Malone » Tue May 29, 2018 6:40 pm

cowneko wrote:Image

So like this?


Yes that will work. Just make sure you prove the mp3 player can drive the amp into clipping as 70W is loud and 140w is only 6dB louder.
Joe :-)

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