KG Balanced Dynahi build discussion thread

[Aive]

I got my pcb from birgir/spritzer. Cheap and fast shipping totally worth it.

[spritzer]

I have a few dozen of them.  The same PCB also takes the TKD 4cp-601 or even the 2cp.  Ditto on the dual gang RK27. 

[G600]

You have an email, then !

Thank you fellas.

[Aive]

Hmm, I seem to notice some grain/etch on certain tracks - any ideas? I really need to get a CRO to see what distortion I've got, maybe I've biased it wrong...

[cetoole]

Certain tracks have grain/etch?

[Aive]

Yeh I tend to notice grain/etchiness on certain tracks in the treble region - will need to do a comparative test with my GS-X MK2. Maybe I haven't biased it effectively resulting in additional distortion...

[luvdunhill]

What is the output impedance of your source?

[kevin gilmore]

and what is the voltage level. If its way high, then you definitely

want to cut the gain of the headphone amp. some cut the balanced

gain to 6.

[Aive]

My DAC specs says output impedance of 10 ohms and voltage of 5V. Should I reduce the gain?

[mypasswordis]

5V what? Peak to peak, peak, or RMS?

[kevin gilmore]

you should reduce the gain

[Aive]

I'll be using a 10K balanced volume control. Balanced gain will be 10 by changing R52, R56 to 50K and C1, C3 to 5 pf.

Would this be appropriate KG? Is there a calculation for gain and frequency response?

Edit: if I change the resistors to lower gain do I also have to change the caps? Thought the roll off frequency is fixed based on cap size...

I'm not sure if it's 5V RMS or PP it doesn't say on the DAC's website :/

Edited September 25, 2014 by Aive

[kevin gilmore]

50k resistors and 5pf give a balanced gain of 14db

which should be fine.

[Aive]

Hey KG, thanks for the response. If I just want to halve the gain do I use 100k resistors? What would be the associated capacitance values?

 

Thanks

 

Edit: ordering bits in OZ is a pain in the ass so I'm including a few component options in my list...

 

Edit2: Man this compensation capacitor theory is voodoo, been trying to learn about it all night - most optimal solutions = get a CRO and wave form generator and trial >< dayum. I should've stolen one from my uni days :/ Will be getting a rigol next year though, gonna be so handy for this diy goodness.

Edited September 26, 2014 by Aive

[kevin gilmore]

actually ltspice is your friend. But its a bit of work. You can just overcompensate a bit,

but then you won't be able to hear 150khz.

[Aive]

lol, think I can stick with 2 pf caps for half gain?

[Aive]

I really can't get over how good the bass is with this amp, don't feel the same love on my GS-X although the treble is smoother on it. Ended up ordering a Rigol 1054Z DSO for more tweaking pleasure

 

Ppl looking for a DSO/CRO should look into this relatively new unit from Rigol. Can option hack it to unlock upgrades too... New Rigol DS1054Z oscilloscope

[Aive]

Hey Kevin, do you think it's practical to drop the gain to 2 (balanced gain of 4) by changing R52/R56 to 10 k? Do you know what would be the associated capacitor values if this is practical?

 

 

[kevin gilmore]

20pf for that.  Supersymmetry is guaranteed unity gain, so no issues with any amount of gain.

but gain of 2 unbalanced is as low as you can go with the topology.

 

but unless you have a very high voltage source, what you could end up doing is clipping the source

and essentially putting very nice square waves into your headphones.

Edited October 4, 2014 by kevin gilmore

[Aive]

Thanks Kevin, might avoid a gain of 2 then... 

 

Dumb question, you previously posted some capacitor values for a gain of 11 (55 k feedback resistor) - I'm assuming we want as much bandwidth as possible through the amp, so 3 pf would be the recommended value here? 

 

 

5pf is 3db down at 278Khz

3pf is 3db down at 500khz

 

I think gain of 11 is where I'll start with my tuning...

Edited October 4, 2014 by Aive

[G600]

I have some fine (silly) questions for you gentlemen 

 

I'm at the point of first power on. I'm OK with the biasing method.

What's the most efficient method, biasing with the pot or with shorting resistors ?

Shorting resistor = 1K between I- and Gnd, and another between I+ and Gnd ?

Pot to minimum setting = full clockwise ?

 

Is there any need of a switch or a soft start between PS and Dynahi ?

 

What if the source brigs a few mV of DC offset ?

 

Thank you.

[kevin gilmore]

just the volume knob set to zero is sufficient.

 

the servo will get rid of a few mv of input offset.

however as you turn the volume knob you will

hear some "whooshing" depending on how much

input dc.

[G600]

Thank you !

[Aive]

Hey G600, what size compensation capacitor (in feedback circuit) did you end up with for your 55 kohm feedback resistors for 11 gain? 3 pf or 5 pf?

[G600]

I chose 5pF.