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DIY DIY amp club V2, Post your DIY amp here

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empire23
post Jan 31 2009, 01:59 PM

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QUOTE(LittleGhost @ Jan 31 2009, 01:29 PM)
Not necessarily.

Read the recent review from Majkel? He ranked the AD797 better than the OPAs from Audio-GD.

HDAMs are kinda limited in some area due to space constrains. You cant lay additional parts for it. The AD797 is also an improved folded cascode topology which gives it insanely low distortion. (tip: the extra transistor on the floating mirror biggrin.gif) If you want to beat that you'll have to lay the entire amplifier circuit down instead and use as much performance enhancing designs as possible.
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I just read the data sheet.

Reminds me so much of the LM4562. Both are BJT inputs, have great performance and voltage range, but are really b****es to work with.
LittleGhost
post Jan 31 2009, 02:58 PM

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Not only that. The AD797 hates driving capacitive loads too. Fortunately I'll be using a buffer along with it so it's not really an issue lol.

Just pray that it's not as worse as the AD8397. I don't want to use ferrite beads on mein signal.
ccschua
post Feb 1 2009, 06:41 PM

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I wonder if anyone has AD797 x 4 for loan and test. it looks promising to be used for IV conversion and then buffer output of the TDA 1541a
empire23
post Feb 1 2009, 06:51 PM

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QUOTE(ccschua @ Feb 1 2009, 06:41 PM)
I wonder if anyone has AD797 x 4 for loan and test. it looks promising to be used for IV conversion and then buffer output of the TDA 1541a
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They don't seem too good for that kind of work man. Just my 2 cents.

A buffer should always be one tough basket that'll drive anything under the blue sky. Buffers are also Unity gain, and unstable amps at unity gain are well....unstable tongue.gif

Try this http://www.national.com/ds/LM/LME49600.pdf
LittleGhost
post Feb 1 2009, 10:26 PM

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Empire23 is right. It hates driving capacitive loads like I've mentioned earlier. Adding output resistances will counter it but you kinda mess up the whole idea of a buffer (low Zo)

The AD797 is not cost effective. How about giving Amb's Jisbos a try? It's one of the best buffers around.




ccschua
post Feb 1 2009, 10:33 PM

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Well this is my output stage of the TDA1541A. I will implement the DEM reclocking using 352kHz (i.e. remove C19 and add the 352kHz positive and inverting clock as in diyaudio to remove the intermodulation cause by the DA conversion.)

I dont like this output stage as it sounds rather resistricted. further I dont see the recommendation by AD being implemented in this output stage.

Qustion : What is global feedback. Does this output stage have global feedback?

Qujestion 2 : The first 2 NE5534 is IV conversion right? The second is buffering right ?

user posted image

This post has been edited by ccschua: Feb 1 2009, 10:34 PM
LittleGhost
post Feb 1 2009, 10:38 PM

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The AD797 is a beast. I doubt the schematic's AD797 is properly implemented.

AD797 requires a lot of effort to tame it down and to sound good.

Q1: yes it does have global feedback. Global feedback generally means the loop encompasses the entire signal path. Feedback point is taken from the end of the output.

Q2:Schematic doesnt show the NE5534
empire23
post Feb 1 2009, 10:57 PM

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QUOTE(ccschua @ Feb 1 2009, 10:33 PM)
Well this is my output stage of the TDA1541A. I will implement the DEM reclocking using 352kHz (i.e. remove C19 and add the 352kHz positive and inverting clock as in diyaudio to remove the intermodulation cause by the DA conversion.)

I dont like this output stage as it sounds rather resistricted. further I dont see the recommendation by AD being implemented in this output stage.

Qustion : What is global feedback. Does this output stage have global feedback?

Qujestion 2 : The first 2 NE5534 is IV conversion right? The second is buffering right ?

user posted image
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Before you go further. That's a shitload of voltage on the opamp supply rails man tongue.gif

If you ask me, when it comes to DACs, follow what the datasheet says. Because to sell the DACs the Manufacturer has to spec them at high performance levels, and to do that they need very specific circuits, which they almost always include in the Dsheet. The only thing i recommend you tweak aside from simple component replacement (eg; replacing the buffer amp with a dB or JISBOS straight) would be to change the DAC select settings.

Oh yeah, i see DC offset removal caps in the signal path. DO NOT WANT.
ccschua
post Feb 2 2009, 12:00 AM

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QUOTE(LittleGhost @ Feb 1 2009, 10:38 PM)
The AD797 is a beast. I doubt the schematic's AD797 is properly implemented.

AD797 requires a lot of effort to tame it down and to sound good.

Q1: yes it does have global feedback. Global feedback generally means the loop encompasses the entire signal path. Feedback point is taken from the end of the output.

Q2:Schematic doesnt show the NE5534
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Q1 : Oops. That's not what I want. But the global feedback is the easiest to implement. I wonder if people say no global feedback with with proper selection of filters, they are talking about multiple order of filter, perhaps 3rd to 6 order. (why is feedback adding so much odd order harmonix )

Q2. the triangle is the NE5534 single output. It can be directly replaced with AD797. What is recommended in AD797 is this.

user posted image

DC blocking capacitors in the output is unavoidable as this DAC1541A is output DC coupled.

Isnt that almost always current output DAC such as TDA 1541 uses the IV as first stage and then follow by Buffering for isolation?

This post has been edited by ccschua: Feb 2 2009, 12:11 AM
LittleGhost
post Feb 2 2009, 08:31 AM

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Feedback is a good thing. But too much is bad. The feedback factor on opamps are generally high due to the very high open loop gain and the not so flat/linear open loop gain/bandwidth.


Another way to counter this is to use jung multiloop so you push the distortions due to feedback out of the audio spectrum.


EDIT: Yes, the TDA is dc coupled. Caps however can be added in between stages for better effect. If the AD797 is stable, you can put a small high quality film cap between the DAC and the buffer instead to get more efficiency and signal quality. Since the input Z of the opamp is high, you don't need an electrolytic.

This post has been edited by LittleGhost: Feb 2 2009, 08:33 AM
ccschua
post Feb 4 2009, 08:17 PM

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Wau. that sound to chim to me.

The circuit i given is from JAPAN TDA1541a circuit mass produced in Hong Kong. So the cmponent values are basically tested for use with those opamp. If I were to place the dc blocking cap between IV and LP stage, that will involve changing the values of the RC circuit righte.
empire23
post Feb 6 2009, 08:00 PM

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Hay Guis. Just got my SumR trannies. Doesn't come with the pottery case because i felt it didn't look cool enough.

Now due to my pocket being blown to bits by the recession, casing the B22 PSUs will have to wait. Sadly.

The extra tranny is for a S11 powering an M^3 so i figured 20 VA should hold the fort as these trannies are underrated.

user posted image


Added on February 7, 2009, 8:46 pmI just found 4 JISBOS Boards. Anyone want me to try and populate em? Board only. Casing will cost alot extra.

This post has been edited by empire23: Feb 7 2009, 08:46 PM
ccschua
post Feb 8 2009, 12:03 PM

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hi diy amp community,

how about some FET cyclotron, the atom smasher. no. the amp..

http://www.passdiy.com/pdf/Build%20The%20A...0Circlotron.pdf
jazzy939
post Feb 8 2009, 01:24 PM

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SUM R toroids, are they any good?

ccschua, interesting stuff that Circlotron.. you getting one? wink.gif

empire23
post Feb 8 2009, 02:01 PM

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QUOTE(ccschua @ Feb 8 2009, 12:03 PM)
hi diy amp community,

how about some FET cyclotron, the atom smasher. no. the amp..

http://www.passdiy.com/pdf/Build%20The%20A...0Circlotron.pdf
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Topology seems very old and a tad bit too simple when compared to topologies like the Firstwatt F series and the Beta24.

Anyways, i'mma looking for self tapping M3 screws for my FETs. Finished the S22 PSU, waiting on the cases for now.
empire23
post Feb 8 2009, 06:16 PM

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I'm 2 Blackgate Caps short of having a full B22 balanced blackgated. Using my old stocks that i had left over.

Can anyone help me hit up Octave electronics for some 470uF 50v and 100uF 50v blackgates? I'll pay for everything including a hefty dinner brows.gif
ccschua
post Feb 8 2009, 06:33 PM

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aiyo. I have that in silmic II for 470uF / 50V.
empire23
post Feb 8 2009, 06:36 PM

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QUOTE(ccschua @ Feb 8 2009, 06:33 PM)
aiyo. I have that in silmic II for 470uF / 50V.
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I got tons of silmic IIs, always buy in bags of 200s.

I wan blackgates for bling factor, not because of performance brows.gif

And i beh tahan there are 6 caps and yet i need 8. So might as well buy 10.
ccschua
post Feb 8 2009, 10:08 PM

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someone at diyaudio is coming with some findings on the issue blackgate being out of production. there will come a time blackgate will end up like dinasours and new species is on the horizon. can catch the story at diyaudio.
jazzy939
post Feb 8 2009, 10:33 PM

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Thanks for the info, I have read the postings...

Time to 'stock up' then? tongue.gif

But personally, I don't use much BGs in my work...

QUOTE(ccschua @ Feb 8 2009, 10:08 PM)
someone at diyaudio is coming with some findings on the issue blackgate being out of production. there will come a time blackgate will end up like dinasours and new species is on the horizon. can catch the story at diyaudio.
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