AMP HEAD Build Thread

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studiomollan
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Re: AMP HEAD Build Thread

Postby studiomollan » Tue Jan 22, 2013 7:26 pm

Hi!
I just ordered 5 kits to build a personal headphone mixer system for my studio. Similar to the one Kante built.
I will have 4 mono inputs with pan, 2 mono inputs without pan and 2 stereo inputs?
What value should i use for the gain setting resistors? Also the values for potentiometers, resistors in H-pads etc would be much appreciated!
Looking forward to this!
Here's what the mixers will look like.

Thanks!
/
Emil
photo qmix.JPG
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studiomollan
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Re: AMP HEAD Build Thread

Postby studiomollan » Tue Jan 22, 2013 9:31 pm

Could this cirquit work? Only the pan part without the input amp. It's unbalanced here but i figure it would work as a dual version with either a dual lin pot or a switch.
http://www.extremecircuits.net/2010/07/pan-pot.html

/
Emil

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Joe Malone
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Re: AMP HEAD Build Thread

Postby Joe Malone » Tue Feb 05, 2013 8:25 pm

studiomollan wrote:Could this cirquit work? Only the pan part without the input amp. It's unbalanced here but i figure it would work as a dual version with either a dual lin pot or a switch.
http://www.extremecircuits.net/2010/07/pan-pot.html

/
Emil

No need for such a complicated pan circuit.

I need to know the input levels you will be able to send this mixer to work out how to do this best in front of the MAP HEAD kit?

Will you always be driving with the HP mixer inputs balanced inputs than can really drive 600ohm?

Do you really need full panning or would Left, Centre, Right switch panning work?

Running more passive U pads and full passive panning in front of the U pad volume already on the AMP HEAD will take a bit working out for best performance.
Joe :-)
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studiomollan
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Re: AMP HEAD Build Thread

Postby studiomollan » Wed Feb 13, 2013 7:46 pm

Hi Joe!
I vill be using the outputs of either a Lynx aurora 16 or a digidesign 96i/o. Possibly from the bus putputs of my API desk but not very often.
Lynx info:
http://www.lynxstudio.com/nav/getFile.a ... roductfile
Digi info:
---
These are balanced, 1/4-inch TRS jacks for analog
audio output connections.
The 96i I/O analog outputs feature 24-bit digital-
to-analog converters. Output operating levels
are software-switchable between +4 dBu and
–10 dB(V) operating levels.
The 96i I/O is factory calibrated at +14 dB headroom,
yielding a maximum output level of
+18 dBu when in +4 dBu operating mode.
When set to –10 dB(V) operating mode, maximum
output level is +4 dBV.
Unbalanced connections are supported through
the use of standard 1/4-inch TRS mono phone
---

"Will you always be driving with the HP mixer inputs balanced inputs than can really drive 600ohm?" To be honest i'm not sure exactly what you mean but i guess you can figure it out from the info of the aurora/digidesign 96. I'm planning to use a cheap IC based splitter for the mixers. Can that cause impedance issues? It wont give the best sound quality for sure but for a que system I'm willing to trade price over a bit of a sound quality reduction.

If the panning cirquit is troublesome I'll rather scrap it and go for L-C-R switches instead. ¨'

I got the kits the other day and finished a LA500 kit yesterday. Looks great!
Thanks!
/
Emil

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HOW TO USE AMP HEAD TO MAKE 4 WIRE BRIDGED/BALANCED HP OUTS

Postby Joe Malone » Mon May 19, 2014 1:44 pm

I have been asked how to use the AMP HEAD to run 4 wire In Ear Monitors.

Easiest and best way is to run the Tip to + Left and Ring to + Right and wire - Left and - Right to 0v.
This will run them fine and very very loud with one AMP HEAD so be careful


But if you really must have them balanced/bridged use the circuit below.
The reason IEM are usually balanced/bridged is due to the low 3 to 9v battery voltage the IEM receiver is running on so it is needed to get loud levels.
This is not the case when using a AMP HEAD on +/-24v = 48v battery. But you could run the AMP HEAD on as low as 12v = +/-6v if needed.
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Joe :-)

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studiomollan
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Re: AMP HEAD Build Thread

Postby studiomollan » Sat Mar 07, 2015 12:32 am

Hi,
My intern is troubleshooting my que mix system built with the amp head. I've always had noise in them but figured it was caused by bad wiring. The noise is however there even if it is only connected PSU and Headphones. The psu is a JLM powerstation +/- 18v. Op is NE5532. They are quiet when using the original 1k gain resistor (RGr- RGl) but when used with a mixer in front, changing the gain resistors to 100 the noise comes up quite a bit. Hissin noise, no hum. Any way to get rid of this? There's nine channels in front of the Head Amp all using 10k resistors.
/
Emil

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Re: AMP HEAD Build Thread

Postby Joe Malone » Mon Mar 09, 2015 10:40 am

studiomollan wrote:Hi,
My intern is troubleshooting my que mix system built with the amp head. I've always had noise in them but figured it was caused by bad wiring. The noise is however there even if it is only connected PSU and Headphones. The psu is a JLM powerstation +/- 18v. Op is NE5532. They are quiet when using the original 1k gain resistor (RGr- RGl) but when used with a mixer in front, changing the gain resistors to 100 the noise comes up quite a bit. Hissin noise, no hum. Any way to get rid of this? There's nine channels in front of the Head Amp all using 10k resistors.
/
Emil


Send me a hand drawing of the passive front end circuit with values you are using so I can computer simulate it. You shouldn't have to increase the gain up so much that you need 100R.
Joe :-)

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studiomollan
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Re: AMP HEAD Build Thread

Postby studiomollan » Tue Mar 10, 2015 10:31 pm

Hi Joe,
This is a drawing i got from a fellow forum member. I know you've been in contact with him as well. My mixer has two stereo inputs and 5 mono inputs. The mono inputs has a L-C-R an switch but thats totally passive and doesn't load anything. Electronically identical to the stereo inputs in the picture. the resistors to the right is the input of the AMP Head. It also points out the changing of the gain setting resistor to 100r. (I left out the AMp head Schematic as i know you don't want that out.
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studiomollan
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Re: AMP HEAD Build Thread

Postby studiomollan » Tue Mar 10, 2015 10:34 pm

It just struck me that maybe I'm not getting enough level out to the mixers? Ill try to crank that up and get back to you but please run the simulation if possible. I think that it's actually a recommendation to replace the gain setting R with 100r when using the AMP Head with a passive mixer in front. I think i read that earlier in this thread?

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Re: AMP HEAD Build Thread

Postby Joe Malone » Wed Mar 11, 2015 11:47 am

studiomollan wrote:It just struck me that maybe I'm not getting enough level out to the mixers? Ill try to crank that up and get back to you but please run the simulation if possible. I think that it's actually a recommendation to replace the gain setting R with 100r when using the AMP Head with a passive mixer in front. I think i read that earlier in this thread?


OK first thing have you made R1L R1R R2L R2R on AMP HEAD all 0ohm links instead of 10k? As they should be 0ohm links as you already have them in your passive mix circuit already.

Set your D/A to highest output. And change 100R back to 1k. And let me know if you need it to be louder still.
Joe :-)

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TWM
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Re: AMP HEAD Build Thread

Postby TWM » Mon Mar 30, 2015 9:30 pm

Hi Joe.

I built a couple of these with OPA 2604 running at +/- 24 from a linear PSU
The op amps seem to be running really hot, too hot to touch comfortably. Should these be that hot?
I don't think they are oscillating out of hearing range but is there a way to check easily?
I don't have the schematic [I bought just the PCBs] it would be helpful to have that to look at.

Thanks Joe

Peter
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Re: AMP HEAD Build Thread

Postby Joe Malone » Tue Mar 31, 2015 11:24 am

TWM wrote:Hi Joe.

I built a couple of these with OPA 2604 running at +/- 24 from a linear PSU
The op amps seem to be running really hot, too hot to touch comfortably. Should these be that hot?

Yes they do run very hot as they have 48v across them

I don't think they are oscillating out of hearing range but is there a way to check easily?

You can just look at the output with a scope but usually the AMP HEAD will not oscillate at all due to the way we do the gain.
It is very wide band amplifier which mean sometimes you can get mobile radio interference which can be heard in the headphones but in a metal case this will not usually happen.
The kit has 4 x 220pF ceramic cap (for limiting bandwidth to 50khz by adding under PCB across R7 and R8. Only used if you have mobile or radio transmitter interference)
Joe :-)

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Technologyworks
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Re: AMP HEAD Build Thread

Postby Technologyworks » Tue Mar 31, 2015 6:45 pm

Thanks Joe.

Cant see anything unusual on the output, I just wasn't expecting them to be so hot. I probably wouldn't have mounted them one above the other, side by side might have been better.
These have a gain of about 5 times is that correct? If I input say 2v peak to peak 1KHz I see about 10v p-p output at max output

Thanks

Peter

studiomollan
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Re: AMP HEAD Build Thread

Postby studiomollan » Wed Apr 01, 2015 12:40 am

Joe Malone wrote:
studiomollan wrote:It just struck me that maybe I'm not getting enough level out to the mixers? Ill try to crank that up and get back to you but please run the simulation if possible. I think that it's actually a recommendation to replace the gain setting R with 100r when using the AMP Head with a passive mixer in front. I think i read that earlier in this thread?


OK first thing have you made R1L R1R R2L R2R on AMP HEAD all 0ohm links instead of 10k? As they should be 0ohm links as you already have them in your passive mix circuit already.

Set your D/A to highest output. And change 100R back to 1k. And let me know if you need it to be louder still.


I did all the correction and it made a huge improvement. They are now quiet and have lots of gain.
However I did an analog session last week and when using the desk/tape the output from the amps could be a little louder. Do you have any suggestions Joe?
/
Emil

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Re: AMP HEAD Build Thread

Postby Joe Malone » Wed Apr 01, 2015 11:15 am

studiomollan wrote:
Joe Malone wrote:
studiomollan wrote:It just struck me that maybe I'm not getting enough level out to the mixers? Ill try to crank that up and get back to you but please run the simulation if possible. I think that it's actually a recommendation to replace the gain setting R with 100r when using the AMP Head with a passive mixer in front. I think i read that earlier in this thread?


OK first thing have you made R1L R1R R2L R2R on AMP HEAD all 0ohm links instead of 10k? As they should be 0ohm links as you already have them in your passive mix circuit already.

Set your D/A to highest output. And change 100R back to 1k. And let me know if you need it to be louder still.


I did all the correction and it made a huge improvement. They are now quiet and have lots of gain.
However I did an analog session last week and when using the desk/tape the output from the amps could be a little louder. Do you have any suggestions Joe?
/
Emil


Is the 1k now back to 1k? How many more dB do you think you need? Was the desk out unbalanced ?
Joe :-)

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