Zen headphone amp problem

I have build the zen headphone amp as descriped by Marcello Pellerano URL

One channel works nice and is adjustable as described, but the other channel I can only adjust the R12 drop to 300mv and lower.

I have made it P2P, so I have checked and rechecked and I can't find any errors or at least any difference between the 2 channels.

Right now I am listening to the amp and I can't tell any difference between the 2 chanels, but it bugs me that my multimeter tells me that something is wrong.

Any suggestions what to check?
 
Flemming J P said:
I have build the zen headphone amp as descriped by Marcello Pellerano URL

One channel works nice and is adjustable as described, but the other channel I can only adjust the R12 drop to 300mv and lower.

I have made it P2P, so I have checked and rechecked and I can't find any errors or at least any difference between the 2 channels.

Right now I am listening to the amp and I can't tell any difference between the 2 chanels, but it bugs me that my multimeter tells me that something is wrong.

Any suggestions what to check?


are mosfets OK?


are they matched ?

if they are OK,and not matched , then increase R4 on that channel
 
I remade both channels. One of the works perfectly... again, but the other acts up.

Testing with 1khz tone, there is no gain (input and output is more or less the same) and a bit hiss. After 5 minutes warm up, I got the following measurements.

Any clues?
 

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steenoe

Member
2004-03-23 10:43 am
Flemming J P said:
I remade both channels. One of the works perfectly... again, but the other acts up.

Testing with 1khz tone, there is no gain (input and output is more or less the same) and a bit hiss. After 5 minutes warm up, I got the following measurements.

Any clues?

Nope, but some of the Q's has to be blamed! What I say now, wont be in accordance with your question:::::The Zen-headphoneamp gave headaches for several builders allready. It doesnt even sound that good on a pair of headphones. Sorry for telling you..... I made a few other headphoneamps to compare, and the Zen didnt turn out to be too good!!! Sorry again... Having build a few great headphone amps, the Zen is not to aim for...This is my latest HP-amp......::::


Steen:)
 

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Flemming J P said:
Now that is just plain unfair, you couldn't leave me in the dark thinking I had the best.

I have 10 other IRF610, and if I am lucky at least 2 of them works.

What amp would you recommend then? Currently using grado RS2 but will switch to Shure SE530 (too much noise at work).


well - you almost have there Aleph J

you can build HP one ;

or search for EUVL's LU Jfet based cascode HP amp , maybe is just that what Steen described with his bluuuuuuurrrrrrrrr pic ;)
 

steenoe

Member
2004-03-23 10:43 am
Darn, I searched.... I am sure it was EUVL's schematic, but Grey started the thread with some other objective in mind..... Who ever can come up with the right thread???????
I even had some handmade boards from EUVL.....real goldnuggets
indeed.....


Me:)
 
Tried changing Q1 and Q2 a few times, and it looks like I have killed all of my IRF610's.

>20~25W to dissipate

That rules out a small sweet headphone amp/buffer and this is just to big.

>well - you almost have there Aleph

half way, but it isn't working, so what is the change of me getting that thing to work ;)

I can almost complete a simple "paint by numbers" project, so my options are rather limited.
 
Hello JP,
I'm very sorry to hear you have problems with this amp.
As far I know, a lot of them (more than 2 hundreds (!), at least those who wrote me directly to share opinions and so) are running well.
Anyway, if you have problem, you can send me to my email address (or post in DIY Audio space) photos and DC voltage values for both channels: I will do my best to help you. In the worst case, you can send me the amplifier, you will have to pay both the shippings, nothing more: I've done this with only one (very kind) person, who fitted two electrolytics with wrong polarity. Of course you must not be in a great hurry! :)
As for the sound, everyone is free to think what he wants, but take care that in audio world too compatibility is very important: this amp has been designed for Grado stuff, and with these I (and a lot of people too) like it very much.
With other HP the sound may not be as good and a bit dark.

Marcello
 

RoboMan

Member
2006-07-20 11:35 pm
Flemming J P said:
I remade both channels. One of the works perfectly... again, but the other acts up.

Testing with 1khz tone, there is no gain (input and output is more or less the same) and a bit hiss. After 5 minutes warm up, I got the following measurements.

Any clues?

Don't really understand what the problem is as you've already got (from your attached image) 0.53v across R12 and 0.7v across R10, and you can adjust the bias, I suppose your circuit is working properly.

One or both R12 and R10 may be off from the labeled value, otherwise they should have the same voltage drop since they are connected in series.

Bias is mainly determined by the value of R10. You should choose R10 according to the max. bias you need while R16 is disconnected. Then use R16 and R4 to lower the bias.

R10 = 0.7V/Max. Bias

Hope this will help.
 
My main problem was dead mosfets. I have managed to kill of 6 mosfets.

Now I have a ground loop issue, but I think it is cause be my temporary test power supply.

But at least I learned something from it: make sure to disconnect the amp from everything, especially the computer before you begin soldering.
 
One problem fixed and 2 other appears.

I made my dual mono power supply with CRC, 10.000uf 5.6 ohm 3.300 uf.

The headphones I plan to use with this amp is my grado rs2 and shure se530.

First problem: The amp plays too loud, how can I reduce the gain?

Second problem:
With grados I can only hear a slight hum, but with the shures there is power supply hum and a hiss, both a bit too loud for my taste. Any clues how I can get it lower?