Using HA-5002 instead of LME49600 on THE WIRE - diyAudio
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Old 13th March 2012, 01:43 PM   #1
Mickey is offline Mickey  China
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Default Using HA-5002 instead of LME49600 on THE WIRE

Since I have some Instersil HA-5002 buffers left I want to use 8 - 16 (bridge-parallell) on THE WIRE BAL-BAL instead of 4 x LME49600. My main concern is DC offset, HA-5002 has 20 mV, is it possible to get rid of it? By the way I have 60 Ohm KOSS KSC35, 120 Ohm custom IEM, 120 Ohm AKG K501, 600 Ohm AKG K240DF, 600 Ohm AKG K240M headphones, how to calculate Rf value so I can have the right gain ratio for each of them? I will install a rotary switch to change gain.
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Old 14th March 2012, 01:32 PM   #2
qusp is offline qusp  Australia
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are you going to make your own pcb? tbh this proposal sounds like a stability nightmare
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Old 14th March 2012, 04:53 PM   #3
Mickey is offline Mickey  China
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I have to, there is no PCB left, good news is 3 to 4 layer PCB is not a problem for factories around here, will cost $$$ though. I have been reading about PPA v1.1 which used paralleled HA-5002 buffers for output, what worked for PPL shall work for Mickey, I hope. If (IF, does not mean I really can) I can eliminate DC offset on the buffers, stuff components as close as possible, optimize the layout for shortest signal path, will it still be a nightmare? Any idea how to calculate Rf value for different headphones? I will switch only when the amp is off.
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Old 3rd April 2012, 01:27 AM   #4
Mickey is offline Mickey  China
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Default Will this work?

Please help this n00b
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Old 3rd April 2012, 02:14 AM   #5
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Originally Posted by Mickey View Post
My main concern is DC offset, HA-5002 has 20 mV, is it possible to get rid of it?
Based on looking at the BAL->SE WIRE circuit (I couldn't find the BAL->BAL version)...

Because the buffer will be within a feedback loop with an opamp the output offset will be controlled by the opamp's input offset voltage, input offset current and input bias current. If you stick to using 4 and forget trying to parallel them then the output offset should be no worse than that of THE WIRE
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Old 5th April 2012, 09:08 AM   #6
Mickey is offline Mickey  China
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but buffers in parallel can lower the distortion, lower output current for each buffer and make the 5002s harder to kill if i insist then DC servos are a must right? seems like tl074 is just for such situation stupidness continues, if i use 4 buffers in parallel shall i change the 330F caps to 1500F or higher and use 4x PSU as well? @counter culture, THE WIRE schematic is right here, please see page 3 for BAL-BAL.
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Old 6th April 2012, 09:15 AM   #7
qusp is offline qusp  Australia
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I think you should stop calling it the wire. the only similarity is you are using the opa1632 and a buffer of some sort somewhere, there are numbers of other amps dating back years that used the opa1632 and a buffer and they werent called the wire.

Last edited by qusp; 6th April 2012 at 09:18 AM.
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Old 7th April 2012, 12:20 AM   #8
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Mickey,

I'm not sure this will work well.

First you could have some issues with both inputs and outputs. You have to watch the outputs on the 5002's and while I use them often (hard to beat for the price on Ebay) over the LME49600, etc. you have to address the input bias and make sure the outputs don't oscillate which can happen if the load impedance is to high.
These guys are made to drive loads and they do it well but be careful how you set them up.

I'm using a new bias scheme over the 5002 project now and you can see it in the May issue of aX next month where I used the 5002's driven by THS4631's.
Jan Didden pointed out the 4631's to me and I think they work well driving the 5002's especially if you want to inject some gain into the circuit. I still like the 5002's on outputs though.

I would try it with 100 ohms into ONE 5002 , not 4 to see what it looks like before I started multiplying the 5002's. Also what value are you using for the current limit on the 5002's?
There's a specific formula for that- see the data sheet.


Best,
Rob

Last edited by robaroni; 7th April 2012 at 12:27 AM.
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Old 9th April 2012, 06:27 AM   #9
Mickey is offline Mickey  China
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I think you should stop calling it the wire. the only similarity is you are using the opa1632 and a buffer of some sort somewhere, there are numbers of other amps dating back years that used the opa1632 and a buffer and they werent called the wire.
sorry, i will call it THE PIPE from now on
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Old 9th April 2012, 12:25 PM   #10
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sorry, i will call it THE PIPE from now on
Good one!

One more thing, to keep the outputs from conflicting with each other when you use parallel arrangements it's best to put a small resistor on each output leg of your buffers. I used .5 ohms on the the 5002 amp.

Rob
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