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DIY: Summer Projects

solderdude

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He is correct in the sense that you probably don't need that much power.

Alternatively you could run a single board on +/- 17V (there are ways to do this) but that won't bring much more power, but at least slightly more than Atom.
You would have to ditch the 9V batteries and use another transformer.

Bridging it requires some modifications and isn't the wisest move when you want to power anything lower than 50 Ohm or so.

As mentioned running the Butte on +/-24V may be a better idea but in this case you would have to mount small heatsinks on the OPA's.
 
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Silou

Silou

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The goal is to build an amplifier that features a symmetrical output, because I never owned one (besides the Loxjie P20 for a few days). I want to buy a planar headphone like the HE5, HE500 or Audeze LCD-2 in the future and I do not want to make the decision based on whether my amp can drive the headphone or not. As you mentioned the bridged O2 is probably not the best approach, because low impedance headphones need current and wattage rather than voltage.
The most important thing is to have fun building the amp and learning something about the parts used to build the amp.

The Butte PCB alone would cost me 42€. Looks interesting but as I mentioned, I am not very interested in a single ended amplifier since I already own an excellent one.

BTW: I am very grateful to you, because you are the only one that answers my questions and helped me so far. I posted the same thread in a german forum, but no one answered me for one week so I deleted the thread and posted it here.
 

solderdude

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If balanced is the goal then the O2 is suited but requires quite a few modifications to the PCB but not impossible to do.

I suspect that's why NwAvGuy mentioned to not go balanced.
It is quite possible to make a balanced amp with those PCB's.
If you don't want super high power you could even make it battery fed as well.

I can tell you what needs changing and how to connect it... step by step.

THIS is probably cheaper though, but less tinkering fun.

And just to be shure... you want single ended (RCA) in and balanced out ?
 
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Silou

Silou

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I would like to use both single ended and balanced input if that is doable. Does it even make sense to use single ended input and balanced output? How do we obtain two different grounds for L and R?

I really look forward to the project. I will order the parts in the next days so they will arrive once I am back from vacation. Do you know what I need besides the PCB and Stock parts yet?
 

solderdude

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That will be a lot harder to make using 2 O2 boards.
You would also need another potmeter (4 gang)
single ended in and balanced out is quite do-able.
Balanced in would only be beneficial when you are bothered by ground loops or had really long wires on the amps input.

4 x 2.2k resistors and 4x 100pF capacitors (NP0/C0G ceramic)
 

solderdude

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What gains do you want ?
Remember that the total gain is +6dB (2x) because of the balanced operation.
I can calculate which other resistors you would need.
You can also fit a 6.3mm socket as the amp can be used single ended AND balanced.
Single ended the gain is 6dB (2x) lower than when used balanced.
 
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Silou

Silou

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OK than we can stick with only single ended in. I only own single ended DACs anyway.
I do not know if it is better to feed the amp directly by the Tone Board or use the Atom as a preamp to get a louder input. The Gain would differ, but I do not know how much Vrms the Atom would output at full volume in low Gain. Best Gains with a 2Vrms source are probably 1X and either 7X or 8.5X. If the Atom is not used as a preamp, it would be nice to have an untouched signal output so I can feed the Atom with the same DAC just like the Stax amps have.

Edit: I did the same mistake again. 1X and 3X or 4X (or 5X? 3dB headroom mentioned by nwavguy)

Edit2: Atoms Low Gain is 1X so is there even a voltage increase?
 
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solderdude

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I see no need to put 2 quite similar amps in series.
I would connect the tone board directly and adjust the volume digitally.
You won't be needing 'full blast' as that would overload all your headphones.
1x gain and (secretly 2x gain) and 3x (6x) will be enough.
Besides, when it doesn't work for you (usable volpot range) then you can always change the gain numbers.

the 1x gain for atom is to ensure the input stage does not clip with high output voltage DAC's and to get a usable volpot range when using sensitive IEM's
 
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Silou

Silou

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OK no preamp and 1X, 3X than. Which Kind of power switch do I need to power off both boards? I am also not quite sure how the filter selection is going to work yet. I have to split the signal into four signals and than use a four way switch to select the desired filtered signal, but that means I need two four way switches. Is there a better way to do it? With an extra LED for every filter design I would need four poles and four steps for the second switch and three poles and four steps for the first switch.
 

solderdude

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You can use 1 4-way switch but when balanced do not have a LED indicator possibility as you need to switch 4 wires for balanced stereo.
This has 3 positions so 1 unfiltered and 2 filtered outputs.

Switches exist with multiple decks (expensive).
When you have at least 5 decks you can have 12 positions (or less) and LED indication.
There are also 6 position switches. In this case 3 decks is enough.
 
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Silou

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Do I really need to switch the two grounds aswell? I thought I could just connect them to the socket since the ground is always the same.
 

solderdude

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Thinking about this.. :facepalm: you could directly connect the negative wires to the output socket... freeing 2 contacts which can be used for the LED :).
You only need to switch the positive wires as that's where the filter will be in.
There are no grounds in balanced headphone outputs. The negative terminals carry a signal.
So 3 filter positions and 1 'normal' position unless you use a second switch to bypass the filter selector in which case you can select 4 filters (using a 3x 4-position switch)
 
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Silou

Silou

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So I have to wire L+, R+ and LED+, LED- to the input of the switch and the filters aswell as the LEDs to the output of the switch. That way I will have to use a switch with 16 combinations and wire four wires (three filters and one unfiltered signal) to L+ and four wires to R+ at the same time. My thought was to use a second switch that works the other way around with four inputs and one output that is wired to the output socket. If it works with one switch that is even better. Please correct me if I am wrong because I am still a bit confused. I can not think straight because it is so hot here in Italy at the moment o_O
 

solderdude

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You switch only the + side of the LED so 3 contacts is enough = 4 positions.

This works with 1 switch (12 pole, 3 center contacts and 4 positions)
 
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Silou

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Can I use this buttons for Power and Gain?
Power
Gain
Is the Power button connected to both boards and the gain button only connected to the negative board?
 

solderdude

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The gain and power button must be a dual change-over switch (so must have 6 contacts and must be locking in both positions)
Both switches do not comply to that.
 
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Silou

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So I think I got the locking part,(on/off instead of (on) /(off)) but I am still trying to figure out how many poles the switch needs.

1 Pole = 2 Contacts
3 Pole = 6 Contacts or is it not related?

The Power switch is on/off and the Gain one is on/on?
 

solderdude

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the gain switch has 2 (Change Over) CO switches.
Such a switch is often called DPDT (Dual Pole, Dual Throw) or DPCO or 2PDT.
It thus has 2 switches in it.
It has 6 contacts.

The Power switch also has 2 contacts but does not need to be change over.
So a DPST (Dual Pole Single Throw) can be used as well as the same switch used for the gain switch DPDT.
 
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Silou

Silou

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I ordered the PCBs, the power supply and the O2 parts today. I was looking for a nice power switch at Conrad, but they are quite expensive though :D
 
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