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Old 17th April 2013, 02:14 PM   #7131
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Has anyone gotten a sense of how much run time is needed on the Tibi Shiga before things are fully "burned in"?
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Old 17th April 2013, 02:27 PM   #7132
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Quote:
Originally Posted by tvicol View Post
The display was adjusted for the source I sent to you. If you have used separate power supply, than the LCD bias was changed. I suggest you to power the LCD from a separate PS, trough a 5K-10K potentiometer.
A linear multiturn is recommended.
As the LCD is multiplexed, you need to adjust LC78601 pin 40 potential trough pot cursor.
One pot leg at +5V one at GND and middle (cursor) to LC78601 pin 40.
LCD working voltage is 4.8V. Try to get around this potential.
This will allow you to adjust contrast as you like.

Regards,
Tibi
Tibi, I need a better explanation for this. Are you saying that I need to get 4.8V at LC78601 pin 40, or at the input to the LCD board?

Or is all of the above only if I was using a different supply for the LCD?

Is there a point on either the backside of the PCB (where the chips are) or on the LCD board where I can measure this bias voltage? I mean a point other than the chip itself. I don't trust myself with the probes I have to touch any of the leads on that chip. I'm afraid of shorting to another pin.

Is it the bias voltage that determines the optimum "angle of view" for the LCD segments?
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Old 17th April 2013, 02:54 PM   #7133
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By the way, the pdf of LC78601 suggests a minimum Vout of 0,9V at 12mA. Is there a chance we are killing too much signal with the 12db attenuator?
Especially when dropping its input impedance to 50R? Could we have a bigger voltage drop in the line than anticipated? The pdf does not specify that 12mA is the max rating, only a rough 300mW max dissipation for the entire chip and a 50mA max drain IDD for the Vin pins.

The 12mA make sense for the 0,9V (pdf minimum high Vout) for 75R input impedance (ohm s law).
If the Vout is actually closer to 2V, then for 75R we would draw around 26mA
and for 50R ~50mA which is pretty close to the max power drain of the chip IDD. So is it possible to have voltage drop below the 0,5V that we want?

Last edited by dimkasta; 17th April 2013 at 03:17 PM.
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Old 17th April 2013, 09:45 PM   #7134
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I have replaced the L-pad with a T-pad attenuator with 75R in and 75R out impedances....

Values are 45R series, 40R shunt, 45R series, again made out of resistance wire wrapped around pieces of wenge and then sealed in raw beeswax.

OK... This transport is just redonkulous...
The change was... WOW!!!!

The biggest problem for me till now was that mids had no clarity. More polite ones like violins were okish, but snare drums for example felt a bit... muted? A bit plastic? Now I can hear them nice and fast and sharp...
Echoes and other spacial sounds are also spooky now... snare drum, piano, guitar, everything now seems to reverb in the room.... amazing...

Although sometimes highs seem a bit overly rough, but at this point, I tend to believe that this is probably because of the PRP resistors on the output of my DCB1, or the rather fresh FT3 output caps...
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Old 18th April 2013, 02:11 AM   #7135
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Quote:
Originally Posted by tonyptony View Post
Tibi, I need a better explanation for this. Are you saying that I need to get 4.8V at LC78601 pin 40, or at the input to the LCD board?

Or is all of the above only if I was using a different supply for the LCD?

Is there a point on either the backside of the PCB (where the chips are) or on the LCD board where I can measure this bias voltage? I mean a point other than the chip itself. I don't trust myself with the probes I have to touch any of the leads on that chip. I'm afraid of shorting to another pin.

Is it the bias voltage that determines the optimum "angle of view" for the LCD segments?
Ah, I found that nice little test pad for Pin 40 on the chip side of the board. It reads 4.89V.
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Old 18th April 2013, 11:20 AM   #7136
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Quote:
Originally Posted by dimkasta View Post
By the way, the pdf of LC78601 suggests a minimum Vout of 0,9V at 12mA. Is there a chance we are killing too much signal with the 12db attenuator?
Especially when dropping its input impedance to 50R? Could we have a bigger voltage drop in the line than anticipated? The pdf does not specify that 12mA is the max rating, only a rough 300mW max dissipation for the entire chip and a 50mA max drain IDD for the Vin pins.

The 12mA make sense for the 0,9V (pdf minimum high Vout) for 75R input impedance (ohm s law).
If the Vout is actually closer to 2V, then for 75R we would draw around 26mA
and for 50R ~50mA which is pretty close to the max power drain of the chip IDD. So is it possible to have voltage drop below the 0,5V that we want?
Fran's experiments with attenuators suggest that it might be desirable to actually have more attenuation than the commonly accepted 12dB. He ended up favouring 25dB and 0.25V output level - although this may be too low to work perfectly with some DACs.
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Old 18th April 2013, 11:40 AM   #7137
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Yeah I guess the signal V level performance is pretty much DAC dependent... It s a trial/error situation specific to everyone's rig. By the way, I would expect average DMMs to "average" voltages in the DC setting, so I would expect the actual signal to be higher than its reading...
I ll try to get a proper reading with my scope to verify this.

My main concern was about the 50R in the input of the attenuator and how it might affect the ability of the chip to provide adequate square under a load twice as hard and the possibility of extra reflections because of the mismatch in the transmission line, especially if the attenuator is not close to the board and close to an RCA socket.

Last edited by dimkasta; 18th April 2013 at 11:42 AM.
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Old 19th April 2013, 12:37 AM   #7138
angcl is offline angcl  Singapore
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Originally Posted by apoopoo999 View Post
great we just need 7 more people to join us.
I am interested ,any chance to order ? am i too late ?
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Old 19th April 2013, 01:36 AM   #7139
syklab is offline syklab  Hong Kong
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Anyone had experience in using dc-dc buck converter with a high switching frequency to power digital circuit for audio? I am thinking of using the TPS5405 to provide a regulated 5V for powering the shigaclone.
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Old 19th April 2013, 02:16 AM   #7140
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Originally Posted by angcl View Post
I am interested ,any chance to order ? am i too late ?
apoopoo999, are you still looking into this?
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