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Old 10th August 2007, 08:42 PM   #1
dweekie is offline dweekie  United States
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Default Charlize 2

New Charlize is out, version 2. The input caps have been removed, so the 2.4vdc bias must have been taken care of somehow. I wonder how much improvement comes from this change. It will definitely save some money on nice caps.....

http://www.diyparadise.com/charlize2.html
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Old 10th August 2007, 09:12 PM   #2
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It's the same DC coupling tweak that has been discussed here before; nothing new. I have done it to a few Tripath amps.

You simply connect your source ground to the BIASCAP pin of the chip instead of the analog ground. This requires you to isolate the source ground and the power supply ground and Yeo does state that in the description.
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Old 10th August 2007, 09:41 PM   #3
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That sure isn't the best or most reliable way of getting rid of the coupling caps... but it is the cheapest!
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Old 10th August 2007, 09:44 PM   #4
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Brian, would it be possible to power the chip with a +/-2.5v supply by connecting the supply ground to the BIASCAP pin? Could the 100nf cap then be taken out so the new BIASCAP ground can be connected to the supply ground?
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Old 10th August 2007, 09:55 PM   #5
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We don't know how the 2.5V bias is generated inside the chip. Most likely it is just a voltage divider with equivalent resistors, and if that's the case you could safely use a +/-2.5V supply with the ground connected to the biascap pin.

But if you're going to the trouble of making a separate +/- supply you could up the voltage to +/-12V and DC couple the source to an instrumentation amp whose output is referenced to the 2.5V bias. The inamp will also allow you to use balanced or unbalanced sources.
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Old 10th August 2007, 10:04 PM   #6
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Quote:
Originally posted by BWRX
We don't know how the 2.5V bias is generated inside the chip. Most likely it is just a voltage divider with equivalent resistors, and if that's the case you could safely use a +/-2.5V supply with the ground connected to the biascap pin.
I think I'm going to try this. I will cheat and use 2.5V regulators instead of adjustables.

Quote:
Originally posted by BWRX
But if you're going to the trouble of making a separate +/- supply you could up the voltage to +/-12V and DC couple the source to an instrumentation amp whose output is referenced to the 2.5V bias. The inamp will also allow you to use balanced or unbalanced sources.
Say waaaah.

I'll leave the fancy stuff to you Brian.
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Old 10th August 2007, 10:05 PM   #7
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I'll draw up a schematic later. It's actually very simple, I just made it sound worse than it is.
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Old 10th August 2007, 10:10 PM   #8
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No you explained it ok, my brain is just being lazy. I get it now.

I was planning on making a +/-12v supply for a buffer I am going to add anyway.

If I only have single ended inputs, would an instrumentation amp be worth the effort? If I did use one, would there be no point of trying a +/-2.5v supply?

EDIT: Nevermind about the 2.5v supply. Now that I think about what I was hoping to accomplish, it won't work. The negative of the supply is permanantly attached to the analog ground, so if the 100nf cap is removed there will still be a DC offset plus the fact it would short the negative supply to ground.
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Old 10th August 2007, 10:58 PM   #9
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The inamp will be worth it regardless of your source considering that you'll remove coupling caps from the signal path. But if you have a single ended source and are happy with the sound as it there's certainly not much reason to try this! If you use the inamp there is no need to use the +/-2.5V as well.

If you are going to try the +/-2.5V rails do it on an amp you wouldn't mind losing and with a dummy load or test speaker, just in case anything crazy happens. And don't forget to make sure this supply is floating.

If you're going to try the inamp you'll want to tie the ground of the inamp supply to the ground of the Tripath circuit.

One other thing... If the 2.5V bias is indeed derived from a simple voltage divider, it may be advantageous to use a unity gain buffer for the biascap voltage so you have a nice low impedance output driving the reference of the inamp.
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Old 10th August 2007, 11:13 PM   #10
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Na, forget about the 2.5v supply idea.

I have some OPA1632 I can try this with. Is this what you mean for a reference voltage buffer?

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Old 11th August 2007, 04:51 AM   #11
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Well it's funny about Charlize losing her cap. I've been working on the same thing, but with transformers. Brian and I have discussed this a bit off list.

You have to be very, very careful when you leave out the caps. Using the Bias Cap as the ground reference is clever, but it needs attention. If you have a DC offset circuit like the Trends, it screws up things. (Charlize does not have one).

Anywho, it can be done and is a clever idea - you just have to be careful about it. The circuit I'm working on will not have the grounding and power supply problems of the prevoius capless circuits. Wish me luck!
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Old 11th August 2007, 02:39 PM   #12
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I was thinking about trying transformers, but with the cost of a decent transformer at around $70 each; I lost interest pretty fast.
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Old 11th August 2007, 04:50 PM   #13
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It should also be mentioned that anyone who has the original Charlize does not need to buy v2 to be able to DC couple.

I'm not trying to take sales away from Yeo, but I don't see the need for a new board just to switch the connection of one wire.

BE SAFE

If you want to try this you need to check for any voltage potential between the source ground and the BIASCAP pin BEFORE you connect the source. If there is any voltage between these two points you have done something wrong. I would first check to see if the source groung and power supply ground are truely isolated.

Brian,

Is it possible to use OPA1632 to DC couple the input for a single ended application? I have been trying some simulations and I can only get it to work properly with a balanced input.

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Old 11th August 2007, 05:53 PM   #14
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Ok, I think it will work this way. A benefit of doing it this way would be the ability to add a switch to change between which output to use.... a phase switch. Or, it could be used with a chip like the TA2020 to be able to bridge and DC couple.

Please tell me if I'm completely off course with this.

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Old 12th August 2007, 12:03 AM   #15
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It's true you can run the little darling san input cap, costs nothing and as many people have said the best sounding cap is no cap.
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Old 12th August 2007, 01:03 AM   #16
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ahem, ahem.

this little tweak of removing the input cap is just one of the many we have incorporated into the new charlize.

sorry, we are not keaned to disclossing more. we are sick of all those copy-and-paster guys out there.



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Old 12th August 2007, 01:19 AM   #17
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Use a THS4131 fully differential chip, for your buffer/pre and set the 2.5 v bias with its Vocm pin....
http://focus.ti.com/docs/prod/folder...t/ths4131.html
with a dpst swith/relay you've got a phase invert control, or with a non balanced bridge Tripath chip, you can use 2 and you're set for balanced bridged operation

Heck, without much effort you could repurpose the board from TwistedPear
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Old 12th August 2007, 02:13 AM   #18
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Quote:
Originally posted by pmkap
Use a THS4131 fully differential chip, for your buffer/pre and set the 2.5 v bias with its Vocm pin....
http://focus.ti.com/docs/prod/folder...t/ths4131.html
with a dpst swith/relay you've got a phase invert control, or with a non balanced bridge Tripath chip, you can use 2 and you're set for balanced bridged operation
Hellooooooo helloooooo hellooooo helloooo...........

Sorry, I thought I heard an echo.

THS4131 and OPA1632 are basically the same chip.

I'm in the process of making the layout for the above circuit. Then I will have a DC coupled T-amp with zero DC offset and a phase switch.

Here is a pic of a DC offset adjust board I just made for an AMP32.

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Old 12th August 2007, 04:24 AM   #19
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theAnonymous1,

Yes, you're correct. I didn't look at the post with the OPA134 carefully enough to see it connected to a label 'OPA1632 Vocm'. I hadn't realized that the OPA1632 had that feature.
Sorry.....
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Old 12th August 2007, 06:19 AM   #20
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Quote:
Originally posted by theAnonymous1
Is it possible to use OPA1632 to DC couple the input for a single ended application?
It is possible but the OPA1632 is not an instrumentation amp (inamp for short). The method I described is best done using an inamp. Something like TI's INA128 http://focus.ti.com/docs/prod/folders/print/ina128.html would probably work well.
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Old 12th August 2007, 02:48 PM   #21
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Quote:
Originally posted by BWRX
It is possible but the OPA1632 is not an instrumentation amp (inamp for short). The method I described is best done using an inamp. Something like TI's INA128 http://focus.ti.com/docs/prod/folders/print/ina128.html would probably work well.
I realise the OPA1632 isn't an instrumentation amp, but will the circuit I posted work? I sure hope so because I already made a layout.

I already have some OPA and not any INA, so I might as well give it a go.
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Old 12th August 2007, 03:23 PM   #22
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It will work because you can set the common mode output voltage to the bias voltage of the Tripath input stage. The input impedance will be low if you ground one of the input resistors for use with a single ended input, and you may benefit from using a buffer between the source and the other input resistor. You could make the OPA134 an OPA2134 and now use both opamps. I would also add the option to use a resistive load between the differential outputs.
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Old 12th August 2007, 04:11 PM   #23
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Quote:
Originally posted by BWRX
I would also add the option to use a resistive load between the differential outputs.
Between the two outputs, or from the outputs to ground? What value should the load be?
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Old 12th August 2007, 04:58 PM   #24
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Between the two outputs. A value in the 5k to 10k range would be good.
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Old 16th August 2007, 11:11 PM   #25
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I was just about to etch some boards when an idea popped into my head. In the pic above I made a DC trim board, but is it possible to add one to the dc coupling/buffer circuit instead? I would like to kill two birds with one stone if possible.

Something like this......

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