Just me it seems. I think the soldering will put people off, I've done it but my eyes were crossed afterwards. The powerpad bit needs to be made easy for group buyers.
in PSU (317/337) I use 100uF Cadj (Nichicon VZ) and main cap is 6800uF Chemicon LXZ (+2 protection diodes) and 33uF Oscon + 100nf as decouplers - I am going to try both opa627 & OPA 1632 as buffer - still have hope no caps in signal path
going back to soldering - friend of mine have nice airheater 😀 so I asked him to do the job - these SMD parts makes me crazy...
going back to soldering - friend of mine have nice airheater 😀 so I asked him to do the job - these SMD parts makes me crazy...
Hold your horses...
It's playing.
Low volume, it's late, wife and kid are sleeping.
First impressions... this seams really special.
Exciting.
Everything seams very natural.
Widely separated, space, detail, smooth, dynamics, bass "slam" (I love this word😀 ).
Let it
-in, tomorrow I'll listen more carefuly.
It's very promising.
I'm writing this on the next room to my main system and the sound is invading me.
Excuse me, gotta go!
It's playing.
Low volume, it's late, wife and kid are sleeping.
First impressions... this seams really special.
Exciting.
Everything seams very natural.
Widely separated, space, detail, smooth, dynamics, bass "slam" (I love this word😀 ).
Let it
-in, tomorrow I'll listen more carefuly.It's very promising.
I'm writing this on the next room to my main system and the sound is invading me.
Excuse me, gotta go!
Ok, I have changed the design a bit, added Cadj but I choose 100 nF.
Partslist is also uploaded.
http://www.sjostromaudio.com/hifi_files/qrv/qrv07r0xls.zip
Partslist is also uploaded.
http://www.sjostromaudio.com/hifi_files/qrv/qrv07r0xls.zip
peranders said:
You should really make that bigger. Try 22µF. I'm searching for a test that shows the influence of different sized caps in the Cadj position, I'll post the link when/if I find it.
Here's the article: http://www.tnt-audio.com/clinica/regulators_noise2_e.html
SMD in this case have a great advantage - you can shorten feedback path which makes application much more stable... and SMD 0,1% low noise resistors are easy available even in Poland 🙂carlmart said:
After a day of -in, now I have around 10mv DC-offset before the output caps.
Now I'm considering removing the caps...
The sound is different from my OPA627+BUF634 pre, but I don't know if it's better.
Although very good, there's a certain "smoothness" to the sound that on some recordings seam to rob some of the immediacy in the midband.
The treble is very good, smooth but very detailed.
The testing conditions right now are not the ideal.
I have a test pot wich is a cheap carbon thing...
And i'm listening with the output caps, but I'm gonna test now without them.
I don't have caps in the signal path on my OPA627+BUF634 pre and it gives me 0.1~0.2mv DC-offset.😎
I'd like that this TPA6120 did the same thing...
-in, now I have around 10mv DC-offset before the output caps. Now I'm considering removing the caps...
The sound is different from my OPA627+BUF634 pre, but I don't know if it's better.
Although very good, there's a certain "smoothness" to the sound that on some recordings seam to rob some of the immediacy in the midband.
The treble is very good, smooth but very detailed.
The testing conditions right now are not the ideal.
I have a test pot wich is a cheap carbon thing...
And i'm listening with the output caps, but I'm gonna test now without them.
I don't have caps in the signal path on my OPA627+BUF634 pre and it gives me 0.1~0.2mv DC-offset.😎
I'd like that this TPA6120 did the same thing...
I have another question ( for good judging of sound is one day too little 😉 ) : Have you any control of this amp by high speed scope ? I am asking about stability, 'cos in dataseeet is many warnings about this .
.Pictures Please !!!!
Carlos,
I too would like to see a photo.
I've got one of these chips waiting to go, and would like to bread board a circuit to check it out as a preamp buffer like yourself.
If youve got any more tips on using this pesky beast i am all ears 🙂
For instance - how have you powered it ? - what caps you for bypass ? - how did you solder the pad ?
Sorry for so many questions 🙄
thanks
Dickie
Carlos,
I too would like to see a photo.
I've got one of these chips waiting to go, and would like to bread board a circuit to check it out as a preamp buffer like yourself.
If youve got any more tips on using this pesky beast i am all ears 🙂
For instance - how have you powered it ? - what caps you for bypass ? - how did you solder the pad ?
Sorry for so many questions 🙄
thanks
Dickie
I don't have a digital camera.
Let me finish the film of my holidays.😀
Anyway, one day is of course not enough.
That's why I won't scavenge my OPA627+BUF634 pre while I'm sure that I found a better thing.
I'm also going to test the AD815.
The TPA was made for headphones and for low impedances.
The datasheet is very vague in applications to drive high impedances (like a line preamp).
Anyway, I could "decode"😱 from the TI datasheet that for high impedances you need a 2k feedback resistor, or a little more.
Even for 600 ohm headphones they advice a 2k feedback resistor.
I used 2.2k, and I have a gain of 3.4x, more or less a standard pre, like my other one.
Now it's time to make a board for the AD815 and compare.
Let's see...
I like to prototype with veroboard before considering doing a PCB. Any mod that's necessary is easily done, like adding the output caps, wich I decided not to remove.
P-A, I must say that you must test this chip before offering a group buy of a PCB.
Let me finish the film of my holidays.😀
Anyway, one day is of course not enough.
That's why I won't scavenge my OPA627+BUF634 pre while I'm sure that I found a better thing.
I'm also going to test the AD815.
The TPA was made for headphones and for low impedances.
The datasheet is very vague in applications to drive high impedances (like a line preamp).
Anyway, I could "decode"😱 from the TI datasheet that for high impedances you need a 2k feedback resistor, or a little more.
Even for 600 ohm headphones they advice a 2k feedback resistor.
I used 2.2k, and I have a gain of 3.4x, more or less a standard pre, like my other one.
Now it's time to make a board for the AD815 and compare.
Let's see...
I like to prototype with veroboard before considering doing a PCB. Any mod that's necessary is easily done, like adding the output caps, wich I decided not to remove. P-A, I must say that you must test this chip before offering a group buy of a PCB.
I discovered why I have around 10mv DC-offset on the output.
My test pot is 10k.
What's more, DC varied with the position of the pot (louder=more DC).
Reading the TI appnote slou169 posted here by P-A, it is making sense now.
Please read the topic 4.4 - Input bias voltage, at page 24 to 25.
4k is low as an input impedance, I need more.
What's more, without an input buffer, wich I don't want to use, it will affect the log pot.
I'm thinking on a solution without adding an input buffer.
Maby an input cap, followed by a resistor to ground.
In the end, with low DC (let's say below 10mv) I will remove the output caps.
My test pot is 10k.
What's more, DC varied with the position of the pot (louder=more DC).
Reading the TI appnote slou169 posted here by P-A, it is making sense now.
Please read the topic 4.4 - Input bias voltage, at page 24 to 25.
4k is low as an input impedance, I need more.
What's more, without an input buffer, wich I don't want to use, it will affect the log pot.
I'm thinking on a solution without adding an input buffer.
Maby an input cap, followed by a resistor to ground.
In the end, with low DC (let's say below 10mv) I will remove the output caps.
Tricky chip
Mmmm...
I had 10~12mv on the output, with the pot at minimum position.
On the max, it went to more than 100mv.
I've put caps on the output, and no DC.
But I had some DC on the input, wich was affecting the pot too.
Yes, this chip has DC on the input.
Testing caps on the input and 2.2k resistors to ground after them, I could remove DC on the input, but on the output it got a little higher.
The position of the pot doesn't change DC on the output now.
I went as low as 620 ohms😱 , and now I have around 18mv DC on the output.
It works fine.
I will remove the output caps.
The input caps are 68uf/16v Philips electrolythics, that I'm gonna bypass with some good 100nf Siemens film caps I have here.
Btw, I'm sure that the PCB on the appnote, with those components, has DC on the output (and not small), and on the input...
If this chip needs an input buffer I'll just forget it.
If it delivers after solving all the issues, it will still have to prove that it sounds better than my OPA627+BUF634 pre.
Mmmm...
I had 10~12mv on the output, with the pot at minimum position.
On the max, it went to more than 100mv.
I've put caps on the output, and no DC.
But I had some DC on the input, wich was affecting the pot too.
Yes, this chip has DC on the input.
Testing caps on the input and 2.2k resistors to ground after them, I could remove DC on the input, but on the output it got a little higher.
The position of the pot doesn't change DC on the output now.
I went as low as 620 ohms😱 , and now I have around 18mv DC on the output.
It works fine.
I will remove the output caps.
The input caps are 68uf/16v Philips electrolythics, that I'm gonna bypass with some good 100nf Siemens film caps I have here.
Btw, I'm sure that the PCB on the appnote, with those components, has DC on the output (and not small), and on the input...
If this chip needs an input buffer I'll just forget it.
If it delivers after solving all the issues, it will still have to prove that it sounds better than my OPA627+BUF634 pre.
Done
It's on the -in stage.
I'm gonna take a break for a few days, enjoy some music, laugh reading some audio magazines
...
Let's see how this sounds in the end.
? 
?
It's on the
-in stage.I'm gonna take a break for a few days, enjoy some music, laugh reading some audio magazines
...Let's see how this sounds in the end.
? ? Yes, I just received a confirmation.
TI's evaluation module has more DC on the inputs and outputs than I have.
And that's with a gain of 2, while I have a gain of 3.4.
DC changes with the position of the pot, although with a 50k pot the change is smaller.
I have my sources.😀
I've solved these issues on my pre, let's see how it goes.
TI's evaluation module has more DC on the inputs and outputs than I have.
And that's with a gain of 2, while I have a gain of 3.4.
DC changes with the position of the pot, although with a 50k pot the change is smaller.
I have my sources.😀
I've solved these issues on my pre, let's see how it goes.
It shouild be connected to a zero ohm source to have no DC output voltage. The 4.02 K ohm resistors are only there to limit the DC offset when the source is disconnected or turned off. I connected it directly to a soundcard output and used the computer volume control and had only a couple mV DC output voltage. Sounds best with +/- 15V power.
ok - my app works 🙂 - I know you like to see poor soldering 8)
here it is the pic:
no caps in signal path, output offset -0,1mV and +0,3mV
two 627 as input buffers
plays great - I am not real audiomaniac but it was just worth the job
here it is the pic:
An externally hosted image should be here but it was not working when we last tested it.
no caps in signal path, output offset -0,1mV and +0,3mV
two 627 as input buffers
plays great - I am not real audiomaniac but it was just worth the job
Good job and the soldering doesn't look so bad.
I think have made the right decision to include a buffer because of the large input bias currents of the TPA6120. With this bufer you can connect any source without having problems with offset voltage.
What supplyvoltage do you use? How hot does the IC get?
I think have made the right decision to include a buffer because of the large input bias currents of the TPA6120. With this bufer you can connect any source without having problems with offset voltage.
What supplyvoltage do you use? How hot does the IC get?
- Status
- Not open for further replies.