8PAKAMP & 12PAKAMP KIT BUILD THREAD

[Joekkel]

hi there,

i've just ordered an 8pakamp-kit. i would like the amps to run 3 pairs of speakers. there's only going to be one stereo-input. i would like to select, which output is active (switching through speakers while mixing music) . so my questions:

can i easily add an "output/amp-selector" by wiring the 2 xlr-ins to a 4 pole 3 position switch, and from there on to the corresponding inputs of the amp, without having nasty clicks when selecting amps?

amp 5&6 and 7&8 are going to be bridged. input-connection is clear (+input to amp1 +in and amp2 -in. -input to amp1 -in and amp2 +in). is the order of the volume-trim crucial? or can i wire the inputs like this and leave the 10-trimpot away?: xlr-in--->3way-amp-selector--->alps volume-poti--->pcb-input-pads. this would save some wiring...

the 300v 2x18v-transformer has 4 output-cables: A0v, A18v, B0v, B18v. should i make a center-tab out of the middle-two cables (A18v and B0v), which goes to the pcb 0v and chassis? and then connect the outer-two cables (A0v and B18v) to the rectifier?

thx

[Joe Malone]

hi there,

i've just ordered an 8pakamp-kit. i would like the amps to run 3 pairs of speakers. there's only going to be one stereo-input. i would like to select, which output is active (switching through speakers while mixing music) . so my questions:

can i easily add an "output/amp-selector" by wiring the 2 xlr-ins to a 4 pole 3 position switch, and from there on to the corresponding inputs of the amp, without having nasty clicks when selecting amps?

Yes as long as the outputs have no dc on them it will switch fine. If outputs are floating with no 0v reference then adding 10k resistors to 0v would fix this. But just try switch with nothing first.

amp 5&6 and 7&8 are going to be bridged. input-connection is clear (+input to amp1 +in and amp2 -in. -input to amp1 -in and amp2 +in). is the order of the volume-trim crucial? or can i wire the inputs like this and leave the 10-trimpot away?: xlr-in--->3way-amp-selector--->alps volume-poti--->pcb-input-pads. this would save some wiring...

Yes you can do that when leaving out the trims or if you want a level control for that bridged amp send the input to one amp and wire the outside legs of the trim pot position to the other channel trimpot position in reverse. Only one trim pot or pot is needed then to adjust both amps as one.

the 300v 2x18v-transformer has 4 output-cables: A0v, A18v, B0v, B18v. should i make a center-tab out of the middle-two cables (A18v and B0v), which goes to the pcb 0v and chassis? and then connect the outer-two cables (A0v and B18v) to the rectifier?

thx

Yes correct

[Joekkel]

thx joe!

Yes as long as the outputs have no dc on them it will switch fine. If outputs are floating with no 0v reference then adding 10k resistors to 0v would fix this. But just try switch with nothing first.

are you here talking about connecting signal-ground to chassis-ground with a 10k resistor? input3 on pcb would be signal-ground so to speak, no?

[Joe Malone]

thx joe!

Yes as long as the outputs have no dc on them it will switch fine. If outputs are floating with no 0v reference then adding 10k resistors to 0v would fix this. But just try switch with nothing first.

are you here talking about connecting signal-ground to chassis-ground with a 10k resistor? input3 on pcb would be signal-ground so to speak, no?

No 0v and in pin 1 xlr etc should all connect. The 10k can be needed between your preamp +/-out and 0v as some outputs these days are caps with no discharge resistor after to pull to ground. Basically do nothing and if you have clicking let me know.

[Joekkel]

will do so, thx!

is this the right way to bridge the amps? this would also help me to understand the insert-point of the volume/trim-pot.

am i right to think, the yellow labeled pads are connected? so my grounding of the whole input-section would be: from the two light-blue, in the middle-of-the-pcb-laying-ground-pads to chassis-ground, and from the xlr pin1's to chassis ground, right?

[Joe Malone]

will do so, thx!

is this the right way to bridge the amps? this would also help me to understand the insert-point of the volume/trim-pot.

Yes if you cross link at the trim pot then only a single pot is needed to adjust the bridged amp. And only one input in is also needed for both amps.

am i right to think, the yellow labeled pads are connected? so my grounding of the whole input-section would be: from the two light-blue, in the middle-of-the-pcb-laying-ground-pads to chassis-ground, and from the xlr pin1's to chassis ground, right?

G is chassis pin from XLR so goes to nothing on the PCB. As there is no chassis connection to anything on the PCB. This should be done in your power wiring. All pin1 and 0v are connected on the ground plane of the PCB.

Basically mains ground to chassis bolt with both 0v wires from power transformer and 0v wire from here to one or two of the center large pad holes between the 2 large caps in the middle of the PCB.

Make sure any speaker 0v for non bridged amps comes from pad next to out pad of that amp.

[Joekkel]

thx joe!

Basically mains ground to chassis bolt with both 0v wires from power transformer and 0v wire from here to one or two of the center large pad holes between the 2 large caps in the middle of the PCB.

so both 18v secondaries to the rectifier?

then my post above was wrong:

the 300v 2x18v-transformer has 4 output-cables: A0v, A18v, B0v, B18v. should i make a center-tab out of the middle-two cables (A18v and B0v), which goes to the pcb 0v and chassis? and then connect the outer-two cables (A0v and B18v) to the rectifier?

Yes correct

had this suggestion from the 60w amp build thread.

this gonna be my wiring. is there going to be a problem, if i run the balanced signal without the shield? i will twist the wirepairs. or does my idea mess with the whole starground-thing? if so, i would switch signal+shield in a 2deck-switch to the pcb-inputs and wire the level-pot as intended by you.

[Joe Malone]

thx joe!

Basically mains ground to chassis bolt with both 0v wires from power transformer and 0v wire from here to one or two of the center large pad holes between the 2 large caps in the middle of the PCB.

so both 18v secondaries to the rectifier?

then my post above was wrong:

the 300v 2x18v-transformer has 4 output-cables: A0v, A18v, B0v, B18v. should i make a center-tab out of the middle-two cables (A18v and B0v), which goes to the pcb 0v and chassis? and then connect the outer-two cables (A0v and B18v) to the rectifier?

Yes correct

had this suggestion from the 60w amp build thread.

this gonna be my wiring. is there going to be a problem, if i run the balanced signal without the shield? i will twist the wirepairs. or does my idea mess with the whole starground-thing? if so, i would switch signal+shield in a 2deck-switch to the pcb-inputs and wire the level-pot as intended by you.

I will draw it all out for you so you can see it clearly. The volume control idea the way you have drawn it will short out the output of your preamp.

How much level difference will you need between your different speakers? As the 1k resistor on the 8pakamp PCB can be changed to be 5k trim so each amp can be set to different gain.

[Joekkel]

wooops, where is it shorting? with no schematic at hand, i guessed that input-pads 2 and 3 are linked to the trimpot-pads 1 and 2&3, as i can bridge the amps on the trimpod-pads.

i'm fine by having different volume-pot-settings between the amp-pairs to have the speakers play at the same level. but out of curiosity: my auratones are about 6dB louder than my mains on the same amp-lvl-setting.

[Joe Malone]

wooops, where is it shorting? with no schematic at hand, i guessed that input-pads 2 and 3 are linked to the trimpot-pads 1 and 2&3, as i can bridge the amps on the trimpod-pads.

i'm fine by having different volume-pot-settings between the amp-pairs to have the speakers play at the same level. but out of curiosity: my auratones are about 6dB louder than my mains on the same amp-lvl-setting.

When you turn the pot fully counter clock wise in your drawing the pot shorts red and blue out of phase inputs together making a dead short across the XLR input. This is all before you get to the PCB.

See attached on how to wire so input pad on the 8pakamp is used and shared for bridged amps. The pot can be the trim pot on the PCB or wired out to a normal pot or stereo pot if 2 bridged or single amps need to be controlled as stereo.

[Joekkel]

could it be, that the + and - speaker-connections are reversed in your drawing?

[Joe Malone]

could it be, that the + and - speaker-connections are reversed in your drawing?

Yes you are correct as I wired to the end amp in phase it is the positive output. So is reversed to the + - shown

[Joekkel]

hey joe, it's working perfectly, no clicks when i switch, no noise, just plain, clear gain! thanks a lot for your support

[Joe Malone]

hey joe, it's working perfectly, no clicks when i switch, no noise, just plain, clear gain! thanks a lot for your support

Cool great to hear

Did you got the gains set ok to match the different speakers?

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[Joekkel]

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

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