AMP HEAD Build Thread

[Joe Malone]

WOW Udo looks great. That is one heavy duty headphone box

Thanks for the kind words

Let me know what info you need for the mixer version you mentioned.

[kante1603]

WOW Udo looks great. That is one heavy duty headphone box

Thanks for the kind words

Let me know what info you need for the mixer version you mentioned.

Thank you Joe,

i love this heavy duty stuff,although it´s small it´s heavy-weight tool.
And:"Mine goes to eleven"
I think I´ve got it right now,but still hesitating about how many inputs my little "satellites" will have (maybe 3-4,mixed of mono and stereo).
Anyway: Each should have additional inputs,built of full H-pads with Mono/Mute capabilities.This all connected to the pcbs main inputs to keep the mastervolume-pot (at the IDC or screwterminal,right?).
Just thinking about the input impedances:How low am I allowed to go?
I´m working on a small active linelevel-distributor,something like 4-6 times 1 input in maybe 4-8 (for putting on up to 4-8 satellites).

Hope this makes sense,

cheers,

Udo

[Joe Malone]

i love this heavy duty stuff,although it´s small it´s heavy-weight tool.
And:"Mine goes to eleven"
I think I´ve got it right now,but still hesitating about how many inputs my little "satellites" will have (maybe 3-4,mixed of mono and stereo).
Anyway: Each should have additional inputs,built of full H-pads with Mono/Mute capabilities.This all connected to the pcbs main inputs to keep the mastervolume-pot (at the IDC or screwterminal,right?).

Yes correct. Depending on number of inputs you may need to make the 2 1k gain setting resistors smaller in value to make up any lost gain.

Just thinking about the input impedances:How low am I allowed to go?
I´m working on a small active linelevel-distributor,something like 4-6 times 1 input in maybe 4-8 (for putting on up to 4-8 satellites)

Any normal solid state output can drive 2k load fine. So with the 20k input per channel that would mean 10 satellite headphone boxes without a problem.

[kante1603]

Hello Joe,

me again.
Have decided how to build my "satellites" now:

There will be 4 satellites for now (maybe later up to eight).
Each with 3 inputs in stereo with a mono switch.
Your board will be/have the master level control with mute switch.

So paralleling these satellites should not be a problem I think,but about the loss in gain:
Can you give me an approximate value for the gain setting resistors (or an equation)?

Will send you a schemtaic for one satellite-will you be so kind and look over it?

Thank you in advance,

Udo.

[Joe Malone]

Hello Joe,

me again.
Have decided how to build my "satellites" now:

There will be 4 satellites for now (maybe later up to eight).
Each with 3 inputs in stereo with a mono switch.
Your board will be/have the master level control with mute switch.

So paralleling these satellites should not be a problem I think,but about the loss in gain:
Can you give me an approximate value for the gain setting resistors (or an equation)?

Will send you a schemtaic for one satellite-will you be so kind and look over it?

Thank you in advance,

Udo.

The 3 input submix schematic you sent me will work fine. You do not need the 10uF caps on the sub mix H pads.

The sub mix will loss 20dB of signal level. So changing the 1k gain setting resistors to 100R will make up the 20dB and restore the amp head to the usual 15dB overall gain.

[kante1603]

The 3 input submix schematic you sent me will work fine. You do not need the 10uF caps on the sub mix H pads.

The sub mix will loss 20dB of signal level. So changing the 1k gain setting resistors to 100R will make up the 20dB and restore the amp head to the usual 15dB overall gain.

Hello Joe,

cool-this will be one of the smallest mixers ever
Thank you very much again,

best regards,

Udo.

[Joe Malone]

The 3 input submix schematic you sent me will work fine. You do not need the 10uF caps on the sub mix H pads.

The sub mix will loss 20dB of signal level. So changing the 1k gain setting resistors to 100R will make up the 20dB and restore the amp head to the usual 15dB overall gain.

Hello Joe,

cool-this will be one of the smallest mixers ever
Thank you very much again,

best regards,

Udo.

[kante1603]

Here it is-10cm (width) of pure mixing power!

Submixer.jpg

Udo (having a lot of fun).

[alistair]

Hi Joe,

I've got 2 amp head kits I've mounted together in a box. Previously I had only bothered to make one of them, and it was working perfectly, however I recently finished off the 2nd kit and attached them via a ribbon cable. I've had some problems since then-

First off one of the 100uf caps (C4) blew, which I replaced both units are now running audio again. However, the 2nd unit (the unit connected via ribbon cable) only plays audio out the right side, and the left side is silent.
On the original unit, which used to work perfectly, it now works ok for the first half of the dial, but on the second half, it has a very large hum on the right channel only, and near the top of the dial it oscillates and generates a very loud tone- again only on the right side.

Any ideas what might be happening?

[Joe Malone]

Hi Joe,

I've got 2 amp head kits I've mounted together in a box. Previously I had only bothered to make one of them, and it was working perfectly, however I recently finished off the 2nd kit and attached them via a ribbon cable. I've had some problems since then-

Ok did you test them separately first to make sure each worked properly first? Always the best idea.

First off one of the 100uf caps (C4) blew, which I replaced both units are now running audio again.

OK cap would have to be in backwards to blow. Or a dead short on the opposite rail if you are running zeners and a 36v SMPS rail but this would have blow the same 100uF cap on both AMP HEAD kits.

However, the 2nd unit (the unit connected via ribbon cable) only plays audio out the right side, and the left side is silent.

Sounds like a ribbon cable with a short in i or one end reversed maybe. Or opamp in backwards or blown when 100uF cap blew.

On the original unit, which used to work perfectly, it now works ok for the first half of the dial, but on the second half, it has a very large hum on the right channel only, and near the top of the dial it oscillates and generates a very loud tone- again only on the right side.[/quote]

What power supply are you using?
Are you using zeners on the AMP HEAD PCBs?
Are the voltage rails correct now on each PCB?
Do both AMP HEAD kits work wired direct in on the terminals separately?

[alistair]

Hi Joe,

Sorry for the delay in reply, I was super busy and haven't had time to open up the unit and fiddle around.

Yes, I tested both amp heads separately and they worked fine before installing together with ribbon cable.

Definitely all caps are in the right way round (negative leads facing towards output jack/volume knob as marked on PCB).

I've replaced all NE5532P opamps, with no change whatsoever. The 2nd board (connected via ribbon cable) has blown the same cap again, and is exhibiting exactly the same behavior (only one channel working). For reference, the cap it is blowing is the 100uF cap closer to the volume pot side of the board.
Furthermore, the 1st board (connected directly to input jacks and power supply) is now playing sound on the Right channel even with the volume knob rolled all the way off. Once the volume knob is bumped up a touch, but still less than halfway it operates normally. Above halfway it's still oscillating and showing strange behaviour.
I've replaced all opamps on this board, and also removed the ribbon cable so it is operating separately from the other amp. No change whatsoever.

For reference, I'm using your 48v SMPS (turned down to about 38v), and 2x 15v 1watt zeners per board. Negative and positive seem to be showing +/-18.25v going out of PS/into the PCB.

[alistair]

Hi Joe-

Just an update- issues with the 1st channel seem to have been related to a faulty input jack. I've replaced this and all seems ok on that channel now, fingers crossed. Explains why replacing other parts wasn't helping!
Still yet to solve the 2nd channel, but I'll keep trying.

Just to eliminate other things, should the ribbon cable remain straight or should it twist? Eg, should the end of the cable marked with the black line go out of pin 1 and into pin 1, or out of pin 1 and into pin 10?

[Joe Malone]

Hi Joe-

Just an update- issues with the 1st channel seem to have been related to a faulty input jack. I've replaced this and all seems ok on that channel now, fingers crossed. Explains why replacing other parts wasn't helping!
Still yet to solve the 2nd channel, but I'll keep trying.

Just to eliminate other things, should the ribbon cable remain straight or should it twist? Eg, should the end of the cable marked with the black line go out of pin 1 and into pin 1, or out of pin 1 and into pin 10?

Like I mentioned before test each AMP HEAD kit seperately with direct wiring to XLR/TRS and power with no ribbon cable. When both work ok then you can hard wire into one and jump power and audio to the next by using a 10pin ribbon with pin 1 stripe going to pin 1 stripe (Do not reverse one end as it will short out everything). If you want to only share power and not audio then strip off the 2 outside pairs of wires so only the center 6 wires in the ribbon cable are left.

[mike_s]

Hi,
I have a 200ma 48v DC unregulated wall wart, that actually measures 61volts. Give or take a bit depending on mains supply variation I guess. Would that be ok as is, or would you recommend regulating it to 48v? Is there any problem with what I am guessing is a diode bridge and a couple of caps in the wall wart, and regulating inside my amp head case? Should I add some more filtering too?
Cheers,
Mike

[Joe Malone]

Hi,
I have a 200ma 48v DC unregulated wall wart, that actually measures 61volts. Give or take a bit depending on mains supply variation I guess. Would that be ok as is, or would you recommend regulating it to 48v? Is there any problem with what I am guessing is a diode bridge and a couple of caps in the wall wart, and regulating inside my amp head case? Should I add some more filtering too?
Cheers,
Mike

The AMP HEAD would need the 2 PCB zeners to be 24vdc 5w types with the zeners legs left long (zener 10mm or so above pcb) to be able to pull the unregulated plug pack done to 48v. So would make a lot of heat and still may have hum/buzz problems due to the unregulated 48v. So not really recommended but since you have it you could try it if you have 2 x 24v 5w zeners.