Digitally controlled preamp/headphone amp

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#202
bender460 said:
One little thing I noticed about the pre is the range of the pot from minimal volume to max is very small, like a 1/4 turn. Could it be specific to my application?
Click to expand...


It is possible your power amp has very high gain. The preamp goes from -95.5db to +31.5db in .5db steps. You could do a couple thing to get more pot travel.

1) Reduce your power amp gain, this will actually probably give you a better sounding amp as a bonus. 🙂

2) add a 500ohm resistor in series with the pot wiper. This will lower the maximum voltage getting to the ADC. Ick I don't like this option at all.

Cheers!
Russ
 
#203
package arrived in very good condition

Perfect guys!

A beautifull job again.

Packaging is perfect. Board looks perfect.

As component sourcing in small volumes is a pain in the... over here this really helps me to build the things I really want.

Great, thanks

earsandeyes
 
#204
size of the footprint of the source selector

I need to do some planning.

What is the approximate footprint (dimensions) of the source selector part that you are working on?

Would be nice to know so I can start to design/source a nice house for the whole thing as a preamp.

regards,
earsandeyes
 
#210
I have added an preorder page to the web site for the Kookaburra boards and kits.

PCB: $12
Kit (including PCB): $60
Transformer: $14

The kit, as usual, contains everything you need to stuff the board, the 5K pot, as well as hardware, such as standoffs, screws, heatsinks for the vregs, thermal pads, etc.

The transformer is a tiny 7VA torroid that will power both the pre and source selector (when available) simultaneously.

Changes to the kit from the beta are as follows:
- Kit now includes both input and output buffers (beta was just the output)
- Op amps are now BurrBrown OPA2227's (SOIC) (beta has a single AD8620)

As always: questions@twistedpearaudio.com

I'll be updating the site more in the next few days.
 
#214
Evilsizer said:
What was the reason for switching to the BB opamp?
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The main reason was to keep the kits affordable, as the AD8620 are about three times the price. The OPA2227 is a very solid audio opamp, and is used in a lot of great gear. It provides more than enough bandwidth, and sounds excellent. So it is a solid choice. Certainly one could order samples of the AD8620 and use them instead if you like. 🙂

Cheers!
Russ
 
#215
Russ White said:



The main reason was to keep the kits affordable, as the AD8620 are about three times the price. The OPA2227 is a very solid audio opamp, and is used in a lot of great gear. It provides more than enough bandwidth, and sounds excellent. So it is a solid choice. Certainly one could order samples of the AD8620 and use them instead if you like. 🙂

Cheers!
Russ
Click to expand...

THe ad8620 is a drop in replacement if one choses to use it?
 
#219
This is a preamp that uses a digitally controlled Burr Brown volume control.

There is no pot in the signal path, which is a very good thing, the pot in the circuit sends variable voltage to an ADC on a microcontroller which in turn adjusts the volume on the PGA2311.

There is an input buffer to help high output impedance input sources, and an output buffer to help low impedance output devices like headphones and inverting gainclones.

The audio signal is always analog, and never converted to digital in any way.

Cheers!
Russ
 
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