QRV-08 Building and test

[galouche]

Hi, I'm waiting for some coponents wich are missing but as soon I receive it I'll give my impression about this baby :)

  I've built 6 jsr 03 at differents voltages and I was impressed by the noise floor so I hope this headphones amp will be on the same quality  :-).

  I have a complete symmetrical system so perhaps will I do a second one to use them symmetricaly ...
As I can't find the good EI transfo here in belgium, I've choose a torroid one wich'll be separeted by an aluminium case.



Thanks Peranders for your kindness and your answers to all my mail  :wink:

[peranders]

Looks very good so far.

[galouche]

Not so good ... one condensator was touching a litle small pad ... and tow pad of a zener weren't soldered ...  :-D

I can't give my impression about it because I hear a very small sound behind my preamp ... farnell have sent me 1uF condensators instead of 100 n but when I put wima 100 nF instead of those 1uF the result is the same ... I'm gonna try to find if I've made a mistake whit the coponents placement ... I've had several doubts about it in the amp part of the pcb ...

[peranders]

The DC servo should have 100 nF to create the right speed but nothing stops you have a slower servo. The input cap could be 1 uF the type should be good. What kind of type did you get?

[galouche]

For the moment I've put wima mkp 100 nF just to test. it's the same thing on the two channels a very very little sound ... regulator part is okay, the problem must be in amp part ... I think about a placement mistake ? I'm verifying it because I was having a doubt for two coponents if I remember well ...

[peranders]

If the supply voltage is OK, you should check the DC levels and idle currents. Don't for get to have a input coupling cap and also trim the bias current at the input.

[galouche]

I've tested everything ...  :? :-D

  I have 13.88 on each amp entry so I think it's ok  for the regul.

  A 560R resistor was dead on the left channel ... but it's not the problem .... When I test the input bias I see no current at all in this circuit ... ?

[peranders]

R3 is extremely important. This resistor sets the bias for the whole amp. Assume this: Vbe = 0.65 V, Hfe = >10000
All transistors should have 0.6-0.7 V in Vbe, if not something is wrong.

[galouche]

I've tested all the vbe this afternoon and all the resistor, all the voltages points ... I'm gonna do a simulation to help ...thanks for helping ... the problem is on each channel so I don't thing about aparticular prob except a wrong coponent ( farnell has made two mistake in this command ) or a wrong coponent placement ( I've tried to see on your pictures but it's hard ...  :-D ).

[galouche]

I've made a simulation and I find the same values ... Tomorrow I'll look with a cd player at the input and a oscilloscope at the output ... very curious ...

[galouche]

With the oscilloscope I've seen immediatly the problem ... the 220pF input condensater for the rf filter was down and all the signal was going to the ground ...  :-)that's for the left channel, I'm gonna searche for the right channel but ... ouah ... the sound on my left ear is really good ...

[peranders]

When you are 100% finished you'll notice that this headphone amp is not mainstream.

[galouche]

My english is not perfect at all, I dont understant mainstream.

  The right channel has the same problem ... the input rf condensater was out too ... :?  I've heard this baby with my AKG k-701 and a the output of my professionnal sound card on the computer ( I've not finished yet the cd pro2 cd player with pcm1794 DAC ).

  I don't know how to describe what I hear as I'm a new audiophile but as a professionnal musician working in studio I can say I'm near of what I'm used to ear in studio on the recorder ... it's the best sound I've ever eared in a headphone  :-)

  Thanks for this baby ... very cool :) I solder since 20 years but I've killed one resistor, two condensator and one transistor ... :D what a shame

  I can give my impression of this baby on my french forum now ... :)

[peranders]

Mainstream = average, not particulary cool but not "uncool" either.

I'm rather as you even in my native language. I don't have the nice words for decribing small things in sound impressions. I'll guess we'll agree, the QRV08 is a masterpiece of mine. This is my "objective" opinion and I'm glad you'll think the same. A very important thing is the power supply which certainly not is mainstream, a quadruple 40 MHz ultra low noise super regulator.

[galouche]

What I'm looking for is the neutral sound and this headphones amp is really neutral ... without being chirurgical ... It has its place behind my cd pro2 ...

  Indeed it doesn't need a preamp ...

  I have to find another problem ...T26 and T26 have 3 V as VBE on the right channel ... I was suspecting it because of little disturb on this channel ...