GDIY51X Headphone amplifier

[kante1603]

4 x1N4004 missing in the bom,sorry guys!

Udo.

 

[culteousness1]

Thanks guys for clearing things up.

Udo, I found the Stiftleisten in your BOM and was looking for its counterpart without luck.
But from Volker's picture it's clear that no header is needed.

Cheers,
Carsten

 

[[silent:arts]]

4 x1N4004 missing in the bom,sorry guys!

Everybody will have some 1N400X at home ...

 

[kante1603]

Everybody will have some 1N400X at home ...

Yep

 

[kante1603]

Hi,

have done the prototype an hour ago,hooked it up to a 51x rack.No smoke (exept of me having a cigarette).
Best news:Is passing audio-hoooorrray!
Some  things to mention:To my taste the input is too sensitive,it starts distorting too early,or this amp doesn´t like low-impedance phones (had 75 Ohms types connected,didn´t have higher ones around).
The clip led only lits up far beyond clipping starts,Volker told me already that a resistor might have to be changed.
Besides of that I picked up rf but that is definetely coming from my my unshielded extender cable,so no biggie here.
The Alps pot I built in seems to be a bit scratchy.
The very good news is that there´s no hum,pretty cool.
This beast uses only one module slot (so the xlr male must be changed,I plugged in a gender changer that I had handy).

So far so good,it´s just a very first prototype,not bad,even now a usefull tool to have in your rack.
Here´s a pic of it (no faceplate,hahaha....I received the parts this noon and had one L-bracket leftover from Volker,had to drill and file that first which has eaten most of time working on it).

Best regards,

Udo.

Addendum:Have it running with program (music) at a pretty high level since 2,5hrs now,that thing stays ultra-cool.

 

[[silent:arts]]

Udo, always fast like hell  8)

 

[kante1603]

Udo, always fast like hell  8)

No,excellent and easy to do pcbs as always,doing my second dual psu meanwhile,hahaha.....

Cheers,

Udo.

 

[[silent:arts]]

Some  things to mention:To my taste the input is too sensitive,it starts distorting too early,or this amp doesn´t like low-impedance phones (had 75 Ohms types connected,didn´t have higher ones around).

input is not critical. output stage is for mid to high impedance headphones.
did use the "mother-circuit" with some Beyerdynamik DT990PRO" and always thought it could need some more gain ...
however, with some Sennheisers I wouldn't go up past middle gain.

The clip led only lits up far beyond clipping starts,Volker told me already that a resistor might have to be changed.

yes. we will measure and adjust. might go the middle way with 200R. this is only one resistor, and it is on the daughter board.

Besides of that I picked up rf but that is definetely coming from my my unshielded extender cable,so no biggie here.

don't think the circuit or PCB design is the cause, but will have an eye on it.

The Alps pot I built in seems to be a bit scratchy.

well. it is a cheap one. however, it is the only dual 50k log pot you can get from any stock ...

so, at the end, it is working  8)
we will adjust the LED for sure.
all other issues - we have to see.

great work Udo, thank you very much!

 

[kante1603]

You're welcome Volker,

well check back with DT990PROs,I have them at work with both 200(250?) and 600 ohms impedance.
Mine here were a Sony MDR-7506 and an AKG-K280,both on the low side.

Best,

Udo.

 

[[silent:arts]]

Mine are 250R.

Fine. However, is it loud enough?

The original is for +/-35V, we only have +/-24V.

4 resistors (each channel) are not adjusted yet.

 

[kante1603]

Mine are 250R.

Fine. However, is it loud enough?

The original is for +/-35V, we only have +/-24V.

4 resistors (each channel) are not adjusted yet.

Can't tell by now,but seems so.Sadly it distorts too early on lowish phones.
Btw.,I should have read the original manual first,it's stated there that there is a "LV"-version on demand which is lower voltage but drives lower impedances.
This one has clearly a recommendation for 250 to 600 ohms,just for info.

CU,

Udo.

 

[[silent:arts]]

Yes. Now people, let us know your impedance ;-)

(or at least the one of your phones)

 

[rob_gould]

I've got  Sennheiser HD-25s which are only 75Ω I believe.  They're designed for volume rather than flat response, but I don't intend to use them for mixing, just as a way to monitor when recording.

Will these be OK with some changes in resistor values, or is it high impendance pro headphones only with this headphone amp?!

 

[culteousness1]

I've got  Sennheiser HD-25s which are only 75Ω I believe.

Well, I can beat that with my AKG K271. They are 55Ω.
Will test with them too.

BTW, had the prototypes in this morning. Thanks!
Sent some comments via Email.

Have to get all parts together now...

 

[[silent:arts]]

Looking forward to play with it this weekend.
I already know which resistors will be socketed to compare and measure different loads.

 

[kante1603]

Hi,me again,

so I picked up a DT990Pro (250 ohms version) from my work and plugged it in,all good now.Way better general behaviour,loud enough for me,clip led now comes closer to where it should start.Still too high so needs some resistor changing,but that should be it.
My ALPS pot is definetely a bad one (scratchy),must swap it out.
Found my rf issue during first rough testing:As said I ran an extension cable from one empty slot in my rack with the audio unshielded.I moved it a bit et voila,rf dissappeared.The cause was one of Brian´s TBDDs (Dimension-D Roland Chorus/Ensemble).
Remember this unit is based on LFO´s,clock-dividers,stuff like that,therefore carrying bazillions of high level clock signals.
That´s it so far,

best,

Udo.

 

[[silent:arts]]

Cool Udo.

I guess we will start with the original values converted to 24V.
We need and should find a compromise between 50Ω and 250Ω.

Is the ALPS potentiometer scratchy on both sides?

 

[kante1603]

Cool Udo.

I guess we will start with the original values converted to 24V.
We need and should find a compromise between 50Ω and 250Ω.

Is the ALPS potentiometer scratchy on both sides?

Hi Volker,

yes,seems to be alternating randomly,do you think we have a dc issue?
Besides of that,I already have used this RK09-type on another build,had to swap out 3 or 4 out of 24 on a passive mixer.
But I´m sure you can look for dc at your workshop,no?

Best,

Udo.

 

[[silent:arts]]

No I don't think - if it would be only on the right side I would.
(and for sure I will look for it)

OK, like in your experience bad quality.
Sad. Don't want to order custom potentiometers.

 

[kante1603]

No I don't think - if it would be only on the right side I would.
(and for sure I will look for it)

Seems to be more on the right side,but definetely is present on the left too.

OK, like in your experience bad quality.
Sad. Don't want to order custom potentiometers.

You mustn´t,one could buy some more of them-or chop the small pcb to give room for an ALPS Blue (RK27....).I know them as excellent pots,they exceed their specs by far and Left-Right matching is damn good.I know,they´re much more expensive,but the total cost of this build is so low that one might think about it....and they´re available!It was 50k,stereo,log.,right?
Here it is:
http://www.reichelt.de/6mm-Potis-stereo/RK27112-LOG50K/3/index.html?;ACTION=3;LA=2;ARTICLE=73834;GROUPID=3136;artnr=RK27112-LOG50K
Seeing a phones amp as an "audio microscope" I would gladly spend the money for a good pot,and around 12 Euros is not too much for it in my opinion.I did that before on an other phones amp and never had to look after it no more.

Just thinking.......

Udo.