Opa660 I/V

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#82
OPA660 I/V for Tda1545

Thanks T,

I think I may have blown my TDA1545 - when I connect an I/V resistor directly to output I get little voltage accross it also?

Have two TDA chips on order will follow your stepwise plan for the next one

Thanks

JOhn
 
#83
Help

When I connect a multiturn pot to ground (acting as I/V resistor) on output of TDA1545 pin I get 4.5V accross it only when I set pot to 17K - this represents about 0.26mA output. I have 11K & 11K resistors on Vref pin as per max dynamic swing in TDA1545 datasheet.

Is my TDA1545 chip busted or is ther another issue?

Another question - why is input resistor to Vref set to 33K on Thorsten's post on battery supply & I/V to TDA1545?
 

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#84
Re: Help

Konnichiwa,

jkeny said:
Is my TDA1545 chip busted or is ther another issue?
Click to expand...

Hard to say. Clearly something is out for lunch.

jkeny said:
Another question - why is input resistor to Vref set to 33K on Thorsten's post on battery supply & I/V to TDA1545?
Click to expand...

Not sure nI track you. I normally (for years) have suggested the 1545 with 11K+11K reference res's....

Sayonara
 
#85
OPA660 I/V for TDA1545

Kuei,
I tried pot as I/V and get 3V accross 7K whith no connections to OPA660 - when connected TDA1545 output and Vref to OPA this goes down to 0.4V?

Does this mean DAC output needs injection current of 2mA as per TDA1541?

John
 
#86
Re: OPA660 I/V for TDA1545

Konnichiwa,

jkeny said:
I tried pot as I/V and get 3V accross 7K whith no connections to OPA660 - when connected TDA1545 output and Vref to OPA this goes down to 0.4V?
Click to expand...

Something is wrong. You need to check your wiring and the Chip. Even my understanding of how the Output current is build up is wrong, your results suggest a fundamental problem.

The resistors between +V and the Ref pin are 2 X 11k? Then the absolute minimum output current should be 1mA for digital silence. You have much less than that.

jkeny said:
Does this mean DAC output needs injection current of 2mA as per TDA1541?
Click to expand...

No.

Sayonara
 
#87
OPA660 Probs

Thanks Kuei for your patience

I will be away on hols for two weeks so won't get to work on it 'till I'm back, at which point I should have new TDA1545s to test with

I'm sure I have wired it up correctly but will wait until then and approach with a fresh mind

John
 
#88
Kuei,

I'm setting up an upgrade for an Onkyo DX607 which is a nice built CD player that has a Sigma Delta DAC which will be replaced by a AD1865N-K DAC chip.

This AD chip has a +-1mA current output, reading the data sheet it appears that the signal from it is centered at 0 mA but I can't be sure.

My idea has been to make an outboard I/V using the OPA660 and would like to hear your suggestion on how to modify the values of the circuit to be compliant with the new operating conditions.

In the other hand, related to this same CDP and modification it has been suggested by Haly on the AD1865N-K Project thread that using D flipflops through the connections between DF and DAC would be a good idea to reduce jitter plus also the use of ISO150 isolators will reduce RF from the DF. What would be your opinion an suggestion on these?
 
#89
apassgear said:
Kuei,

In the other hand, related to this same CDP and modification it has been suggested by Haly on the AD1865N-K Project thread that using D flipflops through the connections between DF and DAC would be a good idea to reduce jitter plus also the use of ISO150 isolators will reduce RF from the DF. What would be your opinion an suggestion on these?
Click to expand...

Go for the reclocking (join the club) but forget about the optocouplers, what do they bring ?

regards
 
#91
Konnichiwa,

apassgear said:
This AD chip has a +-1mA current output, reading the data sheet it appears that the signal from it is centered at 0 mA but I can't be sure.

My idea has been to make an outboard I/V using the OPA660 and would like to hear your suggestion on how to modify the values of the circuit to be compliant with the new operating conditions.
Click to expand...

Assuming that you are right, simply remove the "bias" circuit that removes the offset on the TDA1541 and double the I/V resistor in value. Done.

apassgear said:
In the other hand, related to this same CDP and modification it has been suggested by Haly on the AD1865N-K Project thread that using D flipflops through the connections between DF and DAC would be a good idea to reduce jitter
Click to expand...

Good idea.

apassgear said:
plus also the use of ISO150 isolators will reduce RF from the DF.
Click to expand...

Potentially good. It is equally good, but without jitter penalty (if using opto couples re-clock AFTER the OC's) are fully galvanically separate supplies for the DAC and that using very low leakage transformers in both Digital and DAC section (meaning no noise on ground and current loops closed locally).

Sayonara
 
#93
Kuei Yang Wang said:
Konnichiwa,

Assuming that you are right, simply remove the "bias" circuit that removes the offset on the TDA1541 and double the I/V resistor in value. Done.
Click to expand...


Not sure that there is no offset from the DAC so I think I'll leave some space on the PCB in case current injection is needed.

Or someone can say about output current offset from the AD1865?
 
#94
Coming back to the TDA1541 + OPA660.

After discussing the the drift of some other I/V on the AD1865N-K Project thread with Kello and P. Daniel I started monitoring these on the output of the OPA660 and found that with the lid on the CDP I had not more than 3 mv of variation so decided to get rid of the output caps.

The results were as expected, a great improvment of dynamics and resolution with improved bass openness and low level transients.

Now there is a more solid soundstage and details such as palpable tricks from lips and tongue done by singers...

I have a G. Tent clock that is waiting to be tested on this CDP and will report on the added benefits as soon as implemented.

I'm getting close to that objective of no cap on the signal path except for those of the PSU. The only remaining caps are on the output of the line amp, they will be replaced also with trafos in the near future.
 
#95
AD844 or OPA660

Hello,.... I am totally new here......and wondering....🙂
If I dont remember wrongly I have been warned (read) in the past about using BurrBrown OP-Amp's (i am aware this is not an ordinary OP-Amp...) as audio amplifiers, as they used to have good data, but not so good sound....but I dont remember where I read this....

Analog Devices on the other hand have an outstanding reputation making great sounding OP-Amps.....

Have anyone had the opportunity to listen to them both in the same environment ??

I am thinking about uppgrading my old DCD-2560 with new I/V stages (AD844 ?), and Elso Kwak's clock7.
This player have 4psc. of AD1862 DAC's (Balanced!?), and i was thinking about building 4 I/V stages trying to get a "perfect" balanced output from my CDP.
(the player have no balanced output today...)

Is this possible?
Have anyone of u tried this (on Denon (2560)) before??

P
 
#99
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