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Old 4th May 2006, 06:34 PM   #611
KOHTOPA is offline KOHTOPA  Europe
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Here are some thoughts just in case if somebody else will also
decide to add USB remote control to this preamp.

There are two possible implementations/configurations:
1) USB remote only
2) USB remote + pot

In case 1) you could still use pot just for reference. So that
when preamp starts PIC could read that pot and set volume
according to that value. You could adjust it up to your taste.
It would be used just for initial volume and pot could have very
small size and could be placed on PCB. When you start using
remote it could start from that reference value.

Case 2) is more complicated because there are two
different sources which can regulate volume. Whenever preamp
starts it could use pot for initial value. Then remote could work
the same way as described above. When you change volume
by pot the value should smoothly change to the pot's current position.

There are several PICs which can handle USB:
18F2455 (28 pins DIP and surface mounted, 24K memory),
18F2550 (28 pins DIP and surface mounted, 32K memory),
18F4455 (40 pins DIP and 44 pins surface mounted, 24K memory),
18F4550 (40 pins DIP and 44 pins surface mounted, 32K memory)

USB in these chips works with interrupts as well as ADCs.
So there is no need to poll ADC for reading pot position.
Firmware for handling USB protocol is available at Microchip
site.

You just need to know all codes/numbers corresponding to
the buttons of your remote. Here are these numbers for
Griffin's AirClick remote control:
http://www.griffintechnology.com/products/airclick/

Button released - 0
Play - 1
Volume Up - 2
Volume Down - 4
Next - 8
Previous - 16

You will need only Volume Up/Down and button released
to control preamp. So you start changing volume whenever
you receive 1 or 2 and stop changing volume whenever you
receive 0.

For different types of remotes there could be either a set of
jumpers (1) which could be used for selection of the particular
remote with known codes or there could be software only
solution (2) when you have firmware with a list of codes for
just one particular remote. In case (1) PIC could read jumpers
during startup and use codes map corresponding to that
jumper position.

Hope this helps
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Old 4th May 2006, 06:40 PM   #612
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This is the chip I was experimenting with. Basically it's a PIC 16Fxx with RC5 codes preprogrammed. Very simple to impliment. I used a TI quad H-Bridge chip (I can't remember the number right now). from there, driving the pot up and down and even toggling the power is super simple from any Sony remote.
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Old 4th May 2006, 09:08 PM   #613
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Thanks Russ,
"Try 2 4.7K resistors to get the voltage down by half."
...where can I exactly change resistors with 4.7K resistors ?

Thanks again.
Alessandro.
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Old 4th May 2006, 09:13 PM   #614
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Quote:
Originally posted by magnum_1
Thanks Russ,
"Try 2 4.7K resistors to get the voltage down by half."
...where can I exactly change resistors with 4.7K resistors ?

Thanks again.
Alessandro.

Th would be new resistors. You would put one from JACK_IN to GND and another from JACK_IN to PCB_IN. You would need 4 resistors to do both channels.

You may even want to decrease the signal by more than half. a 2.2K resistor to GND may be even better than the 4.7K.
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Old 5th May 2006, 01:55 AM   #615
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Default Change Request for DRV134 / SSM2142 driver

Hey Russ. Sorry for showing up so late for this party.

Any chance you could tweak the layout to use the BB DRV134 (or, the AD SSM2142 which is also pin compatible).

I actually need fully balanced drive capability - to drive cables and an input transformer. The balanced audio drivers can also be used to drive single ended.
However, we'd have to modify your code to digitally compensate -6dB of gain
to make up for the added +6dB of gain for the SSM chips.

Since the Attenuator chips has 0VDC Vout for 0Vin, there is no worry about DC
offset. Should be a nice direct DC coupling between the attenuator and the driver.

-- Jim
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Old 5th May 2006, 02:01 AM   #616
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Default Re: Change Request for DRV134 / SSM2142 driver

Quote:
Originally posted by jrdmedford
Hey Russ. Sorry for showing up so late for this party.

Any chance you could tweak the layout to use the BB DRV134 (or, the AD SSM2142 which is also pin compatible).

I actually need fully balanced drive capability - to drive cables and an input transformer. The balanced audio drivers can also be used to drive single ended.
However, we'd have to modify your code to digitally compensate -6dB of gain
to make up for the added +6dB of gain for the SSM chips.

Since the Attenuator chips has 0VDC Vout for 0Vin, there is no worry about DC
offset. Should be a nice direct DC coupling between the attenuator and the driver.

-- Jim
Everyone always welcome at the party.

Wow that sounds like an interesting proposition, but it probably qualifies as a new design. Definite food for thought.

If you need SE in and Balanced out in the near term you might consider a XBOSOZ witha Joshua Tree at the output.

The Twisted XBOSOZ can convert SE into balanced and I would say a fair bit better than he DRV134.

Cheers!
Russ
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Old 5th May 2006, 03:12 AM   #617
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Default no DRV134, no problem

Thats cool. I'll stick to a breadboard approach... Although the BOSOZ looks
hard-***, I have other constraints. Here's the transplant candidate:

http://www.jr.com/JRProductPage.proc...eed.GMI+PA7000

For $99, the sheet metal quality is actually very nice... It has XLR outs as well
as a pair of SE RCA outs. All ins are RCA. The point being for $99 you
rip out all the guts and replace it with something more hardcore. i.e. it
becomes an organ donor to a far more worthy cause.

It has a PSU built it, which can also be ripped to the guts.

The reason I was interested in your board is the ADC/PIC sampling of pot to
derive the digital attentuator level. I'd like to use the shitty pot that is on the product, which might be shitty for a linelevel signal, but perfect to feed the A/DC.

Further, the chassis invites other hacks - like a DIY headphone amp (there's a
jack), a DIY MIC amp (there's another jack), and, of course a nice phono stage.

See where I'm going with my change request ? I'm all about hijacking
that sheet metal work, the connectors and the panel controls.

-- Jim
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Old 5th May 2006, 11:22 AM   #618
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Jim, that sounds like a great plan, you could still use the kooka. Just protoboard a DRV134 circuit in front of it. You could then probably omit the input buffer on the kooka.

You would simply have one kooka/drv combo per channel. A dual gang linear pot would control them both nicely.

Cheers!
Russ
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Old 5th May 2006, 01:07 PM   #619
maxw is offline maxw  United Kingdom
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FYI the DRV134 adds 6dB gain
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Old 5th May 2006, 01:16 PM   #620
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Quote:
Originally posted by maxw
FYI the DRV134 adds 6dB gain

Yes, that is why I would be much more inclined to use something like the OPA1632, which not only has much better specs, it is easy to implement. I said DRV134 because it had been mentioned previously.

Cheers!
Russ
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