Wow, that was a big relief!
im really glad that none of the values are that critical, since putting resistors in series is a pain, and it also spoils the neatness of working with a pcb.
thanks a lot Mr. White,
will be sure to post pictures when im done...
cheersm,
mymindinside
im really glad that none of the values are that critical, since putting resistors in series is a pain, and it also spoils the neatness of working with a pcb.
thanks a lot Mr. White,
will be sure to post pictures when im done...
cheersm,
mymindinside
That would be great! Have you already got your PCBs?
The reason I ask is just to see if the gerber and drill files seemed to be fine.
Cheers!
Russ
The reason I ask is just to see if the gerber and drill files seemed to be fine.
Cheers!
Russ
Hey all
well the boards arrived they are fine, eventually used the pdf s not the gerbers, the board house said that it would be a lot more expensive with gerbers. right now i paid 450 INR for two boards. i think thats a little more than $10.
will post pictures later am in a bit of a rush now.
populated the boards last night, and tested it out...i had some wierd problems where the offset kept rising slowly and didnt settle. and when i played music it went wild and kept changing randomly...i desoldered the trimpots and set roffset to 5k and rbias to 1k and soldered them back on. it was fine....dont know what was wrong earlier...
with rbias at around 1k the voltage across r1-r6 is around 20mv....is that okay? i havent moved it much from there yet, it is set around 25mv will listen to it like this for a while before increasing the bias....
i just wanted one clarification....
i have populated all the postions on the board including the optional caps. is the gain of the amp in this configuration 6db? while testing it did not seem as though there was any voltage gain... how high can i take the gain without overly loading the output stage?
thanks, and will post pictures of both the boards and of the completed project soon....
cheers,
mymindinside
well the boards arrived they are fine, eventually used the pdf s not the gerbers, the board house said that it would be a lot more expensive with gerbers. right now i paid 450 INR for two boards. i think thats a little more than $10.
will post pictures later am in a bit of a rush now.
populated the boards last night, and tested it out...i had some wierd problems where the offset kept rising slowly and didnt settle. and when i played music it went wild and kept changing randomly...i desoldered the trimpots and set roffset to 5k and rbias to 1k and soldered them back on. it was fine....dont know what was wrong earlier...
with rbias at around 1k the voltage across r1-r6 is around 20mv....is that okay? i havent moved it much from there yet, it is set around 25mv will listen to it like this for a while before increasing the bias....
i just wanted one clarification....
i have populated all the postions on the board including the optional caps. is the gain of the amp in this configuration 6db? while testing it did not seem as though there was any voltage gain... how high can i take the gain without overly loading the output stage?
thanks, and will post pictures of both the boards and of the completed project soon....
cheers,
mymindinside
Very likely you did not have the offset trimpot centered. You should be able to adjust the offset to zero.
20mv - 25mv bias is enough.
You should adjust the gain until it seems sufficient to you, if you get the amp clipping you know the gain is too high. How much gain you need to depends on your source. Also if you don't have the bias /offset correct the amp may be quiet for other reasons.
You don't need to remove RBIAS to test the resistance accross it. You can simply use your multimeter at the ends of the pot because the wiper is tied to one end.
Try getting output offset to zero.
Cheers!
Russ
20mv - 25mv bias is enough.
You should adjust the gain until it seems sufficient to you, if you get the amp clipping you know the gain is too high. How much gain you need to depends on your source. Also if you don't have the bias /offset correct the amp may be quiet for other reasons.
You don't need to remove RBIAS to test the resistance accross it. You can simply use your multimeter at the ends of the pot because the wiper is tied to one end.
Try getting output offset to zero.
Cheers!
Russ
Just a question of curiosity, could you replace the output stage with a single pair of BD139/140 without much loss? I am just curious as I am looking at this circuit for headphone amp use and wondered if the TO-126 device would be better especially if used at a fairly high bias.
jaycee said:
It should work just fine. You may want to increase R16 and R17 (say to 10ohms) if you don't seem to be getting enough bias through the output devices. But I would try the indicated values first.
Cheers!
Russ
Russ White said:
I have a sort of off-topic question for you, Russ. What software do you use to design and simulate this stuff? I'm new to most of this, but I'm following along fairly well. I think getting into some related software just might help with my understanding of things.
Thanks!
Scott
DipTrace has a much better component editor, easier/more intuitive interface... just better overall really.
Yes I use DipTrace. I had used Eagle for quite a while, but finally got tired of its limitations and clunky interface.
DipTrace is much better in terms of usability and certainly is more cost effective. No software is perfect, but I get much more efficiency from DipTrace and that's important when time is an issue.
I highly recommend it.
DipTrace is much better in terms of usability and certainly is more cost effective. No software is perfect, but I get much more efficiency from DipTrace and that's important when time is an issue.
I highly recommend it.
Hi
Well i finished the amp, and it now lives in a nice wooden case..
im using a 10k pot at the input...
the problem however is, that the dc offset changes when i change the position of the volume knob....
this is a big problem., as the offset goes quite high. and when the pot is turned to the fullest extent,i.e. loudest volume, the offset goes wild and goes into 100+ mv on the positive adn negative side, it keeps going like this and does not settle. if i reduce the volume to 70%, the offset goes down to 5 mv or so,.. the problem is clearly audible in only one channel, the right one, and i hear distortion....its mostly noticeable in the low bass....and i can hear it only on the bass notes...
Can i solve the problem by putting a DC blocking cap at the input...im not sure if this would solve the problem. if it would help what would be the best place to put it? before or after the input resistor. Rin. also to calculate the corner freq would one use the value of Rz?
Thanks guys.
mymindinside
Well i finished the amp, and it now lives in a nice wooden case..
im using a 10k pot at the input...
the problem however is, that the dc offset changes when i change the position of the volume knob....
this is a big problem., as the offset goes quite high. and when the pot is turned to the fullest extent,i.e. loudest volume, the offset goes wild and goes into 100+ mv on the positive adn negative side, it keeps going like this and does not settle. if i reduce the volume to 70%, the offset goes down to 5 mv or so,.. the problem is clearly audible in only one channel, the right one, and i hear distortion....its mostly noticeable in the low bass....and i can hear it only on the bass notes...
Can i solve the problem by putting a DC blocking cap at the input...im not sure if this would solve the problem. if it would help what would be the best place to put it? before or after the input resistor. Rin. also to calculate the corner freq would one use the value of Rz?
Thanks guys.
mymindinside
Is there DC from your source?
I am thinking the there is some issue with Roffset (pot).
What happens when you remove it?
The offset should not be very high even with no pot there.
If you want to use a DC blocking cap at the input just use Rz to calculate the corner frequency. With 47K Rz , 10uf or so should work great. Even 4.7uf would be fine.
Cheers!
Russ
I am thinking the there is some issue with Roffset (pot).
What happens when you remove it?
The offset should not be very high even with no pot there.
If you want to use a DC blocking cap at the input just use Rz to calculate the corner frequency. With 47K Rz , 10uf or so should work great. Even 4.7uf would be fine.
Cheers!
Russ
Thanks,
will add the cap andpost my results,
do you think that the offset is the cause of the distortion?
cheers,
mymindinside
will add the cap andpost my results,
do you think that the offset is the cause of the distortion?
cheers,
mymindinside
mymindinside said:
It definitely could be, especially if offset nulling pot is bad. There are also lot of other potential problems. Including one or more bad or very mismatched Qs.
Cheers!
Russ
Mr White !
Can you sand me by E mail schematic and/or pcb for source selector with relais.
I know isn't thema, but!
I saw somewhere in the forum.
Thanks in advance.
linkxp@sezampro.yu
Regards zeoN_Rider
Can you sand me by E mail schematic and/or pcb for source selector with relais.
I know isn't thema, but!
I saw somewhere in the forum.
Thanks in advance.
linkxp@sezampro.yu
Regards zeoN_Rider
Has anyone tried running these as balanced? Im thinking of whipping four together to use in a preamp with the darwin switches. Do they produce a heat because Im planning on stacking them two and two?
Hello,
Yes, the amps can be bridged without issue.
The heat produced will depend on the bias. At the recommended bias levels the heat won't be enough to prevent stacking.
Cheers!
Russ
Yes, the amps can be bridged without issue.
The heat produced will depend on the bias. At the recommended bias levels the heat won't be enough to prevent stacking.
Cheers!
Russ