Marsh headphone amp from Linear Audio

[sonidos]

@jackinnj

You close to giving a green light to distribute boards?

[Neutrality]

What about this.

Headphone ground return wire goes directly to audio ground and the left/right SGD are each connected to the audio ground through 10R//100nF.

The audio ground is then directly connectd to regulator/cap multiplier ground.

In my opinion this should be the best solution.

[RNMarsh]

BTW- I didnt use any 10 Ohm resistors in my headamp sample and have no grounding issues..... just follow the current loop (s) to see if they intersect one another...or share a common path. -RNM

[sonidos]

Yes, jackinnj introduced the idea in an addendum to your pcb.

One question that another member brought up several posts back. In the matching of pnp to npn, many have told me that it's a pipe dream to get matches that are very close. I know when I refurbed my Adcom 535 amp, I went the distance to match. Finding PNP to NPN matches was darn near impossible. NPN to NPN or PNP to PNP was a piece of cake...the trannies came from the same batch and all matched very closely.

I think the member who asked first said he planned to by 1000 of them, if IIRC.

How close were your matches?

[RNMarsh]

Originally Posted by sonidos

Yes, jackinnj introduced the idea in an addendum to your pcb.

One question that another member brought up several posts back. In the matching of pnp to npn, many have told me that it's a pipe dream to get matches that are very close. I know when I refurbed my Adcom 535 amp, I went the distance to match. Finding PNP to NPN matches was darn near impossible. NPN to NPN or PNP to PNP was a piece of cake...the trannies came from the same batch and all matched very closely.

I think the member who asked first said he planned to by 1000 of them, if IIRC.

How close were your matches?

It isnt obvious but I did spend about 2000 dollars on this project. A lot was trying different transistors for matching. I think you will find these particular transistors will Not take a 1000 to get a match. How close? 5% is what got for the results I published. The jFets - I bought 100 each and found 20 of each matched. Bipolar was easier because the one you will use are closer to being a good compliment in the first place. So, dont panic or worry how it will turn out... I have taken a lot of the cost and drudgery out of it for you (as much as my budget would tolerate, at least). -RNM

[sonidos]

Thanks for the additional details. I bought 8 pcs. of the p-fet and then started to think...that ain't gonna do it!

I did find the jfets at Futurelec for about 10 cents each. I bought about 40 of each, so I'm hoping to get in the neighborhood.

BJTs are all USA made, so that should do the trick and get good results.

[Unomas]

Originally Posted by RNMarsh

It isnt obvious but I did spend about 2000 dollars on this project. A lot was trying different transistors for matching. I think you will find these particular transistors will Not take a 1000 to get a match. How close? 5% is what got for the results I published. The jFets - I bought 100 each and found 20 of each matched. Bipolar was easier because the one you will use are closer to being a good compliment in the first place. So, dont panic or worry how it will turn out... I have taken a lot of the cost and drudgery out of it for you (as much as my budget would tolerate, at least). -RNM

Not so easy, I'm afraid!! I am the one that post before regarding the problems with MJE200/210. I bought 100 of each and NOT even one pair!

Now I will try with Onsemi (the other where Fairchild's). I will report later on the results. I hope (well better say PRAY) this time will have better luck...

Javier

[RNMarsh]

Originally Posted by Unomas

Not so easy, I'm afraid!! I am the one that post before regarding the problems with MJE200/210. I bought 100 of each and NOT even one pair!

Now I will try with Onsemi (the other where Fairchild's). I will report later on the results. I hope (well better say PRAY) this time will have better luck...

Javier

Well that must be frustrating! What tests are you matching for?? And, what brand and source did you use?

[Unomas]

Originally Posted by RNMarsh

Well that must be frustrating! What tests are you matching for?? And, what brand and source did you use?

Yes indeed, quite frustrating.
As I said in my previous post, I tested them using a Peak Atlas DCA55. They have perfectly equal Vbe, but Hfe was a whole different story:
- MJE200: From 140 to 170
- MJE210: From 210 to 225

I bought them from a reputable (well I think so...) source like Mouser and they are from a reputable manufacturer (again, I think so...) like Fairchild.
This time I will try with On Semiconductor. I will tell you later on the result.

Javier

[RNMarsh]

Originally Posted by Unomas

Yes indeed, quite frustrating.
As I said in my previous post, I tested them using a Peak Atlas DCA55. They have perfectly equal Vbe, but Hfe was a whole different story:
- MJE200: From 140 to 170
- MJE210: From 210 to 225

I bought them from a reputable (well I think so...) source like Mouser and they are from a reputable manufacturer (again, I think so...) like Fairchild.
This time I will try with On Semiconductor. I will tell you later on the result.

Javier

Good that the Vbe match as compliments. Isnt so important that the Hfe match as the configuration and the fact they are used as followers reduces the matter. use them. Match the fets and the to92 devices for Hfe and Vbe... did those test ok for you?