I've been fiddling lately with a TPA6120A2, and also with an AD815.
These two chips are current feedback.
I've been very satisfied with my OPA627+BUF634 for a long time, but I just thought... why not try something different?
I'm opening this thread but the designs are not finished yet, so this is work in progress.
Tests with the TPA are here, beginning at post #85:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=39180&perpage=10&pagenumber=9
Now I'm testing the AD815, and I may test one more CF chip.
I opened this thread because I feel that P-A's thread was going off-topic (sorry P-A) and it's also easyer to make a seach.
In the end I will listen to them all.😎
These two chips are current feedback.
I've been very satisfied with my OPA627+BUF634 for a long time, but I just thought... why not try something different?
I'm opening this thread but the designs are not finished yet, so this is work in progress.
Tests with the TPA are here, beginning at post #85:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=39180&perpage=10&pagenumber=9
Now I'm testing the AD815, and I may test one more CF chip.
I opened this thread because I feel that P-A's thread was going off-topic (sorry P-A) and it's also easyer to make a seach.
In the end I will listen to them all.😎
follow up...
Talking about using input and/or output signal trafos...
It is.
0mv.
I was testing and measuring, but didn't listen to it yet with much attention with/without the trafos at the input.
From the sounds I've heard coming out of this chip, let's say it's worth the trouble.😀
Yes.
That's what I don't want to use, an extra stage.
I'm trying to avoid that at "any" cost.
The wire is thin (of course), but the trafos are quite big, 2cm sq.
I've seen smaller...
Talking about using input and/or output signal trafos...
analog_sa said:
It is.
0mv.
analog_sa said:
I was testing and measuring, but didn't listen to it yet with much attention with/without the trafos at the input.
From the sounds I've heard coming out of this chip, let's say it's worth the trouble.😀
analog_sa said:
Yes.
analog_sa said:
That's what I don't want to use, an extra stage.
I'm trying to avoid that at "any" cost.
analog_sa said:
The wire is thin (of course), but the trafos are quite big, 2cm sq.
I've seen smaller...
News from this corner
Well... with signal trafos on the input it makes a buzing noise.
Bzzzzzzzzz...
With the trafos on the output, no problem.
It seams that analog_sa is right, the trafos don't work well with a pot before it.
Input caps it is.
0.47uf poly + 100k to ground.
There is ~400 mv DC on the output, so I used output caps.
This happens because I can't match input impedances.
I would need 200R ~ 220R from NI to ground and this attenuates the signal too much.
And I don't want to use an input stage.
I may try the signal trafos on the output instead of the caps, but for now I'm gonna let this thing
-in.
It's playin' now, but it's late, I can't crank up the volume.
Promising...
Well... with signal trafos on the input it makes a buzing noise.
Bzzzzzzzzz...
With the trafos on the output, no problem.
It seams that analog_sa is right, the trafos don't work well with a pot before it.
Input caps it is.
0.47uf poly + 100k to ground.
There is ~400 mv DC on the output, so I used output caps.
This happens because I can't match input impedances.
I would need 200R ~ 220R from NI to ground and this attenuates the signal too much.
And I don't want to use an input stage.
I may try the signal trafos on the output instead of the caps, but for now I'm gonna let this thing
-in.It's playin' now, but it's late, I can't crank up the volume.
Promising...
Bingo
I had an idea and now...
No DC-offset at the output, with direct output (no caps, no trafos).😎
I had an idea and now...
No DC-offset at the output, with direct output (no caps, no trafos).😎
WARNING WARNING THREAD HIJACK IN PROGRESS
Sorry Carlos but you do promote my 'public service' so I just thought that I would use your thread to advertise my new Gainclone pre amp on Decibel Dungeon. 😉
No rocket science, just some sound basic advice for newbies wishing to build a pre amp to go with their GC's.
HIJACK OVER
Sorry Carlos but you do promote my 'public service' so I just thought that I would use your thread to advertise my new Gainclone pre amp on Decibel Dungeon. 😉
No rocket science, just some sound basic advice for newbies wishing to build a pre amp to go with their GC's.
HIJACK OVER
Nice job, nice page, Nuuk.
You keep doing a great public service for the DIY community.
Oh, thanks for getting in, I was starting feelin' lonely in this thread.😀
You keep doing a great public service for the DIY community.
Oh, thanks for getting in, I was starting feelin' lonely in this thread.😀
I guessed that you were lonely Carlos when I saw that you were threatening to build a valve buffer in another thread! 😀
Nuuk said:
Nuuk there is a pic of a pot with in, out, 0V connections. I think the in and 0V connections are the wrong way around.
Jan Didden
Thanks Jan, I'll check it out. I did it all that rather quickly and I appreciate somebody more knowledgeable checking it over. 😉
(And I'm honoured to have such an educated audience! 😱 )
AD815
The "idea" I was talking about was to find a way to have no DC on the output, with direct output (no caps, anything).
It's in practice now.
I'm feeding (double-regulated) voltage to the non-inverting inputs, with independent multi-turn trimmers to null DC-offset.
Now... you have to grab me because I'm listening to music compulsively.
The "idea" I was talking about was to find a way to have no DC on the output, with direct output (no caps, anything).
It's in practice now.
I'm feeding (double-regulated) voltage to the non-inverting inputs, with independent multi-turn trimmers to null DC-offset.
Now... you have to grab me because I'm listening to music compulsively.
I removed the input caps too, because now I have no DC-offset on the input. Zero. Nill. Rien.
I nulled DC-offset on the output without a pot, just the input resistors to ground.
But...
DC at the output varies with the position of the pot.
Whith my settings now it changes from ~ -30mv to around +40mv at max volume.
At a little pass mid-volume there's 0mv.
There's a little issue.
In a scale from 1 to 10 as volume setting, from 9.5 to 10 there's a jump in DC to around 400mv.
As I use input caps on my power amp and on any amp I make, there's no problem for me. Also, I would be mad to listen to music at this volume.😀
I may consider using two outputs on the pre: one with caps, the other one without.
It would be easy for me to use input and output coupling caps.
But this chip deserves all the attention, all the efford.
The AD815 is used on the best preamp I've ever heard: the Jeff Rowland Coherence.
I had to try it.
My way.
It seamps the the JR uses input and output signal trafos, although I don't know exactly the circuit they use.
Fiddling with current-feedback op-amps is not easy, and these are made for video applications, not audio.
This has been a challenge for me.
But it pays, definitelly.
I was getting bored to just use VF 8-pin op-amps.
I'm now gonna le it-in for some days and listen to some music.
Carol Kidd on HDCD is playin' on my room right now.
Gotta go, she's calling me!😎
I nulled DC-offset on the output without a pot, just the input resistors to ground.
But...
DC at the output varies with the position of the pot.
Whith my settings now it changes from ~ -30mv to around +40mv at max volume.
At a little pass mid-volume there's 0mv.
There's a little issue.
In a scale from 1 to 10 as volume setting, from 9.5 to 10 there's a jump in DC to around 400mv.
As I use input caps on my power amp and on any amp I make, there's no problem for me. Also, I would be mad to listen to music at this volume.😀
I may consider using two outputs on the pre: one with caps, the other one without.
It would be easy for me to use input and output coupling caps.
But this chip deserves all the attention, all the efford.
The AD815 is used on the best preamp I've ever heard: the Jeff Rowland Coherence.
I had to try it.
My way.
It seamps the the JR uses input and output signal trafos, although I don't know exactly the circuit they use.
Fiddling with current-feedback op-amps is not easy, and these are made for video applications, not audio.
This has been a challenge for me.
But it pays, definitelly.
I was getting bored to just use VF 8-pin op-amps.
I'm now gonna le it
-in for some days and listen to some music.Carol Kidd on HDCD is playin' on my room right now.
Gotta go, she's calling me!😎
Anyone know where can I get BUF634T from Online shop? I am from Malaysia. And I can't find this component from Farnell. RS show the price each is USD800++. I am not sure this BUF634T cost that price!!!
sorry for the previous post... I was looking at the wrong item and giving the wrong info...
I got the actual info and correct part from RS, it is around USD11 per piece.
I got the actual info and correct part from RS, it is around USD11 per piece.
Well Carlos Filipe, don't leave us all hanging in the air. Which revs your motor more - the TPA or the AD - and how do they compare to your OPA627/BUF634 setup?
I am thinking about using OPA1632's to give me a differential input into the TPA so as to make best use of its CMR capabilities, but I am a bit inexperienced so perhaps I will try a simpler design first. (The OPA1632 also looks like a bit of a cranky beast)
Anyone had any experience along these lines yet?
I am thinking about using OPA1632's to give me a differential input into the TPA so as to make best use of its CMR capabilities, but I am a bit inexperienced so perhaps I will try a simpler design first. (The OPA1632 also looks like a bit of a cranky beast)
Anyone had any experience along these lines yet?
hihopes said:
I thought this thread didn't have much interest?
Most of the posts is me talking alone...
😀
Ladies and gentlemen, the winner:
AD815
carlosfm said:
I thought this thread didn't have much interest?
Most of the posts is me talking alone...
😀
Nah, there's an awful lot of us out here lurking in the shadows, my friend.
Ladies and gentlemen, the winner:
AD815
Let's here what made you change favorites.
Are you using the Alpha mini-pots that Joe Ras suggested in that other thread?
darkmoebius said:
I tested them, yes.
My intention is to make a new pre, new case, new board, and use an Alpha pot.
Meanwhile, I opened my OPA627+BUF637 pre, made some internal changes and changed the OPA+BUF board for the AD815 board.
Volume pot on my pre is a 20k log. Alps Blue.
The AD815 is better, but not night and day.
The main difference is in the treble.
Gorgeous.
"Round", not the smallest hint of "splash", very very detailed.
That sort of detail that a drummer could recognize a Zildjan cymbal.😱
The TPA6120 is very good, but ultimately a little too smooth and laid back for my taste.
So, here's my conclusion:
1. AD815
2. OPA627+BUF634
3. TPA6120
Any of these makes a very good pre. But the AD815 is in another league of it's own.
Like the Jeff Rowland Coherence.
I can' wait to hear your impressions regardig the Alps vs. Alphas.
Sold!!! I played drums as a teen. I've always wanted a system that could recreate the shimmer and decay of a light brush stroke across the ridges on the top of a cymbal. It's right up there with the deep woody resonance of a cello as my favorite tones.The AD815 is better, but not night and day.
The main difference is in the treble.
Gorgeous.
"Round", not the smallest hint of "splash", very very detailed.
That sort of detail that a drummer could recognize a Zildjan cymbal.😱
This may sound like an "amateur hour" question, but will there be a need for the buffer once you use the AD815 pre?But the AD815 is in another league of it's own.
Like the Jeff Rowland Coherence.
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