[dgardner]

Quote:

Originally Posted by Pars /img/forum/go_quote.gif Current consumption for the Dynalo if I remember right is around 100mA per channel. I would plan on perhaps 200mA per.

About 150ma per rail is typical.

 

[jcx]

While it depends on your music and listening preferences I think the voltage swing doesn't give really adequate dynamic peak headroom for HD-600 or other 300 Ohm can - it was designed as a Grado 32 Ohm amp when run single-ended

Glimore also hints that this can be made with a balanced output stage; balanced drive would be better for the Senns with this amp - as mentioned in Glimore's original article, now aka "dynamid"

dual mono balanced would be a possibility but would use 2x the rare jfets and PCB

you could also rework the bias (change resistor values) and use a higher Vsupply (maybe +/-24V?) to better match the Senns - with the same PCB single-ended

the max Vsupply is still a little limited by the input JFET's Vds - cascoding them moves up to dynahi topology

http://www.djgardner.com/headphone/gilmore/

 

[breizheau]

Thx.
I spoke with my friend yesterday, the other crazy guy who follows me in this adventure, and i told him : i planned to build 2 amp but if i build only one with balanced output ? My CDplayer is a good quality (NAIM) and maybe it could be another challenge.

What do you think ? What do i have to modify/change ?
For the transformer, does a 50VA 2X15 fit ? If this one is good i really need a 2U enclosure !

And for a balanced version, i would take a deep enclosure to separate the PSU and the amps part.....

 

[00940]

Quote:

Originally Posted by jcx /img/forum/go_quote.gif While it depends on your music and listening preferences I think the voltage swing doesn't give really adequate dynamic peak headroom for HD-600 or other 300 Ohm can - it was designed as a Grado 32 Ohm amp when run single-ended you could also rework the bias (change resistor values) and use a higher Vsupply (maybe +/-24V?) to better match the Senns - with the same PCB single-ended the max Vsupply is still a little limited by the input JFET's Vds - cascoding them moves up to dynahi topology

I agree but careful if you raise the rails: the servo opamp runs from those rails. The opa604 will accept up to +/-24v.

What I'm currently doing for my own Dynalo is to raise the front end voltage to +/-21V or so, while keeping the output stage at +/-15V. It starts clipping above 7.5Vrms, which provides 280mWrms @300r. The hd600 max input power is 200mW.

 

[jcx]

good catch and rec on op amp at higher Vsupply - a little board hacking could add dropping zeners or even shunt reg



the amp is simple enough that point-to-point vero/perfboard/protoboard build isn't much challenge if you only want one amp - just look at Gilmore's build

that would allow the balanced output option too - remember you would have to rewire the headphone for balanced connection but the the Dynalo is single ended input so the source wouldn't need to be balanced

the pwr xfmr specs look OK, for dedicated Senn use you could even just leave off 1 or 2 paralleled output pairs to cut power drain
I'd stop at standard 3-pin reg - Gilmore's pwr op amp power supply is a little over the top

 

[NelsonVandal]

Could someone please show a simplified schematic with the complete wiring for balanced bridge operation. Values for feedback resistors etc. What happens with the input impedance?

 

[jcx]

HeadWize - Project: A Pure Class A Dynamic Headphone Amplifier by Kevin Gilmore
fig 1 + fig 2

the extra "VAS" and output stage connects to the other side of input diff pair collector Rs, recieving opposite phase drive

with no global feedback there is no change of input Z despite the output stage change


I see Gilmore claims this can work with just manual offset trim when using hi Z cans

 

[NelsonVandal]

Quote:

Originally Posted by jcx /img/forum/go_quote.gif HeadWize - Project: A Pure Class A Dynamic Headphone Amplifier by Kevin Gilmore fig 1 + fig 2 the extra "VAS" and output stage connects to the other side of input diff pair collector Rs, recieving opposite phase drive with no global feedback there is no change of input Z despite the output stage change

So the negative signal is quite different from the positive. Higher output impedance, lower damping factor, higher distortion with a totally different harmonic spectrum.

 

[NelsonVandal]

I forgot to ask, does it sound better balanced bridge than single end?

 

[breizheau]

I rode somewhere that the balanced version is good but not enough comparing with the single end to do it.

 

[breizheau]

So, what to think about the higher voltage ?

What to change on the PSU board ?

 

[jcx]

Quote:

Originally Posted by NelsonVandal /img/forum/go_quote.gif So the negative signal is quite different from the positive. Higher output impedance, lower damping factor, higher distortion with a totally different harmonic spectrum.

you could easliy add 2 more R for feedback from the added output giving a fully balanced amp with the slight disadvantage of 2KOhm input Z instead of single ended amp's high Z input that can be directly attached to the Vol pot


for single ended use just for Hi Z cans I would use +/-24 V, 200mA regulated supply and change the 510 and 3.3K resistors for ~10mA per pair output bias and 1.5x more V gain ~= 500 and 5K in my quick sim (and you could just leave 1 output transistor pair empty to save some current) - also bumping up the feedback R to ~15K Ohms might be a better match to the Hi Z cans (I assumed the diff pair ccs run at ~ 2mA each per Gilmore's text - you need the right LED or change the emitter R value for that current with the LED Vf you end up with)

rather than using the OPA604 at its absolute max V rating I would simply connect the DC_adj to the centertap of a 50K Ohm pot connected across the supply V - the op amp pads on the pcb would be handily located for this change

300 Ohm cans should be less sensitve to DC offset and I'd bet a manual trim, maybe repeated in a year would be fine

 

[NelsonVandal]

Quote:

Originally Posted by jcx /img/forum/go_quote.gif you could easliy add 2 more R for feedback from the added output giving a fully balanced amp with the slight disadvantage of 2KOhm input Z instead of single ended amp's high Z input that can be directly attached to the Vol pot

... and a buffer between the pot and input?

 

[breizheau]

I am totally lost !

 

[digger945]

Quote:

Originally Posted by breizheau /img/forum/go_quote.gif I am totally lost !

Hang in there friend

It took me a lot of reading and questions to even commit to the Dynahi.