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The Objective2 (O2) Headphone Amp DIY Project
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Old 11th December 2018, 08:24 AM   #5411
Mooly is offline Mooly  United Kingdom
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The Objective2 (O2) Headphone Amp DIY Project
We've covered this many times. You can use any red LED by fitting a trimmer in place of R9 to set the appropriate low voltage battery cut-off point.
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Old 11th December 2018, 03:42 PM   #5412
MaverickPT is offline MaverickPT  Portugal
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Originally Posted by Mooly View Post
We've covered this many times. You can use any red LED by fitting a trimmer in place of R9 to set the appropriate low voltage battery cut-off point.
If I want to use it as desktop only I can then just place a "random" Led and forego the trimmer right?
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Old 11th December 2018, 06:45 PM   #5413
Mooly is offline Mooly  United Kingdom
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The Objective2 (O2) Headphone Amp DIY Project
Yes, you can do that. Just make sure you do fit something in its place though because the circuit may not work correctly with either leaving the LED out or shorting it out. It certainly doesn't in simulation anyway.

And if you are never using batteries then the easiest way is just to link the two FET's out and not fit any of the comparator circuitry components at all.
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Old 14th January 2019, 01:15 AM   #5414
Thommy Eggers is offline Thommy Eggers
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Hi sirs
just completed my first build on the Objective2 O2, all works fantastic, thank you for your work on this.


my question


how could i connect my balanced xlr outputs to the inputs of the amp in an uncomplicated manner


BR


Thommy Eggers
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Old 14th January 2019, 07:22 PM   #5415
sgrossklass is offline sgrossklass  Germany
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That depends on what you consider "uncomplicated". Do you mind warming up the soldering iron again or do you insist on something prebuilt?

XLR outputs are not all created alike, and you will need different kinds of adapter cables depending on what you have. (This applies to any device with unbalanced input, not just the O2.)

There are two possible cable pinouts:
a) XLR pin 2 = signal, pin 1 = ground
b) XLR pin 2 = signal, pin 3 = ground, possibly 1 and 3 tied together as well

Ground-referenced output stages require type (a) and will not work with (b).
Floating or servo-balanced output stages require (b), they will not work with (a).
Merely impedance-balanced output stages (= single-ended output stages souped up with some passives to get balanced output impedance) will work with both types. These are usually found on gear towards the budget side of things (compact mixers, the Behringer 2496 series, budget audio interfaces, ...).

I would consider going from female XLR to e.g. RCA with Actually Decent Coax(R), then use/make a short 2x RCA to stereo 3.5 mm adapter with some thinner shielded audio cabling. I have even used abominations like 1-piece 2x RCA to 1/4" and 1/4" to 3.5 mm adapters plugged together, but it really is not ideal in terms of leverage and potentially pots a lot of stress on the poor input jack.

I imagine designing a balanced input board wouldn't be that hard either, assuming it can still be squeezed into the case complete with 2x 1/4 TRS inputs (people have fitted RCAs, and those jacks aren't too different in size; XLR might be possible but I wouldn't be getting my hopes up too far right now). It kind of depends on what sort of performance standards you want to apply. A 1-opamp circuit with e.g. a gain of -6 dB would probably work perfectly fine in practice, it's just that the rest of the O2 performs to rather high standards (well, arguably the input stage is needlessly low noise even). I might look into it if there is any kind of demand.

Last edited by sgrossklass; 14th January 2019 at 07:39 PM.
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Old 14th January 2019, 11:41 PM   #5416
Thommy Eggers is offline Thommy Eggers
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Quote:
Originally Posted by sgrossklass View Post
That depends on what you consider "uncomplicated". Do you mind warming up the soldering iron again or do you insist on something prebuilt?

XLR outputs are not all created alike, and you will need different kinds of adapter cables depending on what you have. (This applies to any device with unbalanced input, not just the O2.)

There are two possible cable pinouts:
a) XLR pin 2 = signal, pin 1 = ground
b) XLR pin 2 = signal, pin 3 = ground, possibly 1 and 3 tied together as well

Ground-referenced output stages require type (a) and will not work with (b).
Floating or servo-balanced output stages require (b), they will not work with (a).
Merely impedance-balanced output stages (= single-ended output stages souped up with some passives to get balanced output impedance) will work with both types. These are usually found on gear towards the budget side of things (compact mixers, the Behringer 2496 series, budget audio interfaces, ...).

I would consider going from female XLR to e.g. RCA with Actually Decent Coax(R), then use/make a short 2x RCA to stereo 3.5 mm adapter with some thinner shielded audio cabling. I have even used abominations like 1-piece 2x RCA to 1/4" and 1/4" to 3.5 mm adapters plugged together, but it really is not ideal in terms of leverage and potentially pots a lot of stress on the poor input jack.

I imagine designing a balanced input board wouldn't be that hard either, assuming it can still be squeezed into the case complete with 2x 1/4 TRS inputs (people have fitted RCAs, and those jacks aren't too different in size; XLR might be possible but I wouldn't be getting my hopes up too far right now). It kind of depends on what sort of performance standards you want to apply. A 1-opamp circuit with e.g. a gain of -6 dB would probably work perfectly fine in practice, it's just that the rest of the O2 performs to rather high standards (well, arguably the input stage is needlessly low noise even). I might look into it if there is any kind of demand.
Thanks for your reply


i am connecting my Yamaha CL3 Digital mixer outputs (balanced xlr) to the input of O2

i built six of these O2 for my recording studio setup in order to give each musician their own seperate listening. I just want to make shure i use the proper connection not to loose quality.


im thinking that since the O2 has unbalanced input there is nothing else to do but connecting with two cables xlr to rca with the xlr pin 1 ground, pin 2 hot, and pin 3 cold gong to rca shield - 1 and cold, and rca pin to hot. thereby loosing six db signal but how else could it be done?


BR...T
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Old 17th January 2019, 03:08 PM   #5417
sgrossklass is offline sgrossklass  Germany
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Originally Posted by Thommy Eggers View Post
i am connecting my Yamaha CL3 Digital mixer outputs (balanced xlr) to the input of O2
Oh, that's a Big One. The outputs are called OMNI OUT, with nominal output of +4 dBu und maximum of +24 dBu. The block diagram shows two amplifier triangles with + und - symbols on pins 2 and 3... I am guessing this is a ground-referenced output.
Quote:
Originally Posted by Thommy Eggers View Post
im thinking that since the O2 has unbalanced input there is nothing else to do but connecting with two cables xlr to rca with the xlr pin 1 ground, pin 2 hot, and pin 3 cold gong to rca shield - 1 and cold, and rca pin to hot. thereby loosing six db signal but how else could it be done?
I'd also give the (a) cable a shot first. XLR pin 3 should remain unconnected (unless you can't seem to get much of any signal out at all).

Losing some signal amplitude would be the least of my worries here, you'd still have up to +18 dBu to work with either way. I hope you built your O2s with a minimum gain of 1X, 'cause you're going to need that setting. I think the gain stage should clip at a hair over +18 dBu then. Depending on headphones used, running into volume pot imbalance at low settings might be more of a problem...
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Old 17th January 2019, 11:03 PM   #5418
Thommy Eggers is offline Thommy Eggers
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Thanks, most kindly
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Old 17th January 2019, 11:14 PM   #5419
Thommy Eggers is offline Thommy Eggers
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Hi all geniuses


My mixer, Yamaha Cl3 additionally has digital output (AES/EBU)


Does anyone possibly know how to change the ODAC so that it could recieve that signal as opposed to the present usb port/optical input.


That would be awsome.


BR...T
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