Charlize 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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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.
 
BWRX said:
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.

BWRX said:
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.:xeye:

I'll leave the fancy stuff to you Brian.;)
 
No you explained it ok, my brain is just being lazy. I get it now.:eek:

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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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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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!
 
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.:smash:

:att'n:BE SAFE:att'n:

If you want to try this you need to check for any voltage potential between the source ground and the BIASCAP pin :att'n:BEFORE:att'n: 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.:(

5y7ba7a.jpg
 
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. :eek:

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.
 
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/folders/print/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
 
pmkap said:
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/folders/print/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.:smash:

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.:D

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

An externally hosted image should be here but it was not working when we last tested it.
 
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