anbello said:
I am thinking your kooka is fine.
It sounds pretty normal, as mine does the same thing.
Dead silent, but you will get a very slight click on volume change up of the very top of the PGAs range, as you say in the 90-100% range. There is no such thing as "perfect" zero crossing. As even though the signal may be at zer there is still a switching machanism that still must occur, that s what you are hearing. As a test, just to be sure the zero sense pin is being driven you can run a 1K resistor from +5V to pin #1 of the PGA (ZCEN) but as I just tested this, I can tell you there will be no difference.
You have found the weak spot of virtually all digipots/vol controllers.
Actually a lot of stepped attenuators also can have similar behaviour.
Happy listening!
Cheers!
Russ
Thanks for your words Russ, now i think there is nothing wrong in my kooka
but i fear i have found another weak spot of digipots:
for some defined postions in the volume on the top of the PGA range the click noise becomes continuous. I think that in these (hard to find) position of the volume the PGA switch between two consecutive gain states. If this is true i think it is possible to correct via software: change the pga gain state only when you see two consecutive change of the value read from ADC in the same direction, a sort of software isteresis.
Ciao
Andrea
but i fear i have found another weak spot of digipots:
for some defined postions in the volume on the top of the PGA range the click noise becomes continuous. I think that in these (hard to find) position of the volume the PGA switch between two consecutive gain states. If this is true i think it is possible to correct via software: change the pga gain state only when you see two consecutive change of the value read from ADC in the same direction, a sort of software isteresis.
Ciao
Andrea
tilt said:
The AD8610 and other such JFET-input opamps are fairly easy to implement and swap around. However, the AD8397 is a bipolar-input opamp which, generally speaking, requires the circuit to be tailored to the opamp. With an AD8397 you will run into relatively large DC offset. Furthermore, the AD8397 tends to oscillate easily, from what I can remember.
Good opamp, from what I've heard, but not a candidate for this particular circuit.
Member
Joined 2003
Picture Show
Thanks to Tony D for selling me his parts.
Here's some pics of what I have done. I think I should tidy up the input/output wires a bit. It's not completely done yet, I have to take it back to my buddy's shop to drill the hole for the fuse holder the correct size. I noticed the "zero crossing" noise very audibly when I powered it up for the first time. So much so that I thought there was something wrong. After I played a couple songs, the noise lowered significantly. It is still there, but at a quiet and quite acceptable level. It was an odd phenomenon, since I hadn't touched the preamp at all to do anything to reduce noise levels.
Everything on the PCB is stock from Twisted Pear, except the transformer is my own. It is a larger XF, and has better regulation. It definately sounds wery nice, I can't say that I can tell a difference between this preamp and the Freebird, I would have to switch back and forth quickly to determine any differences. I do like the idea of the volume pot being out of the signal path. After many years of use the volume knob will not be scratchy. Enjoy the pics!
Thanks to Tony D for selling me his parts.
Here's some pics of what I have done. I think I should tidy up the input/output wires a bit. It's not completely done yet, I have to take it back to my buddy's shop to drill the hole for the fuse holder the correct size. I noticed the "zero crossing" noise very audibly when I powered it up for the first time. So much so that I thought there was something wrong. After I played a couple songs, the noise lowered significantly. It is still there, but at a quiet and quite acceptable level. It was an odd phenomenon, since I hadn't touched the preamp at all to do anything to reduce noise levels.
Everything on the PCB is stock from Twisted Pear, except the transformer is my own. It is a larger XF, and has better regulation. It definately sounds wery nice, I can't say that I can tell a difference between this preamp and the Freebird, I would have to switch back and forth quickly to determine any differences. I do like the idea of the volume pot being out of the signal path. After many years of use the volume knob will not be scratchy. Enjoy the pics!
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.
Nice job puting that thing together, you asked a lot of good questions and I hope you get a lot out of the project.
Member
Joined 2003
Thanks for you kind words.
Tilt, you would have to ask Tony D. I bought the case from him in this thread. There are no manufacturer's marking whatsoever on it.
Tilt, you would have to ask Tony D. I bought the case from him in this thread. There are no manufacturer's marking whatsoever on it.
Member
Joined 2003
Slight problem
Where I live it is very cold and dry, so it is not uncommon for me to get an electrostatic zap when I touch some grounded metal like the chassis of my preamp. I know in the pics there is no earth ground connected but it is connected to the chassis now. Anyways, I've experienced twice now that when I get a zap from the chassis, there is no sound anymore. A bit scary at first, but I turn the preamp off then back on and it is working again.
What can I do to stop this. The electrostatic discharge is audible in my speakers. Would placing a large resistor like a 5MOhm between the chassis and earth ground help? I have checked that the chassis is not connected to the circuit in any way. The ground on the RCA's is completely isolated.
Thanks.
Where I live it is very cold and dry, so it is not uncommon for me to get an electrostatic zap when I touch some grounded metal like the chassis of my preamp. I know in the pics there is no earth ground connected but it is connected to the chassis now. Anyways, I've experienced twice now that when I get a zap from the chassis, there is no sound anymore. A bit scary at first, but I turn the preamp off then back on and it is working again.
What can I do to stop this. The electrostatic discharge is audible in my speakers. Would placing a large resistor like a 5MOhm between the chassis and earth ground help? I have checked that the chassis is not connected to the circuit in any way. The ground on the RCA's is completely isolated.
Thanks.
Wow, that is funky. Try this the next time it happens, instead of turning the pre off and back on just turn the volume pot a bit.
If that helps than what I suspect is the the ADC is getting confused by the static spike. You may need to groud the body of the pot, or isolate it, I am not sure which.
Cheers!
Russ
If that helps than what I suspect is the the ADC is getting confused by the static spike. You may need to groud the body of the pot, or isolate it, I am not sure which.
Cheers!
Russ
adding phono
I'm somewhat of a noob as far as preamps go, but not to soldering. I was wondering how would I go about adding a phono preamp like Elliott Sound's project P06 P06 or Hagtech's Bugle to the kookaburra?
Would it be something like this: RCA phono inputs>phono preamp board>into rotary switch> rotary switch out to kookaburra?like it shows in the project 88 wiring diagram
Could they be powered off of the transformer used for the Kookaburra?
If not, how would I hook up the seperate phono preamp power supply?
Thank you for any and all help.
I'm somewhat of a noob as far as preamps go, but not to soldering. I was wondering how would I go about adding a phono preamp like Elliott Sound's project P06 P06 or Hagtech's Bugle to the kookaburra?
Would it be something like this: RCA phono inputs>phono preamp board>into rotary switch> rotary switch out to kookaburra?like it shows in the project 88 wiring diagram
Could they be powered off of the transformer used for the Kookaburra?
If not, how would I hook up the seperate phono preamp power supply?
Thank you for any and all help.
I don't see any reason why something like the P06 could not be easily be added in front of the Kookaburra. I have never tried it, but I can't see any obvious issues, Go for it.
Some day I may get around to desning a phono stage, but for now just about any phono stage with a low(or even relatively high if you use the input buffer) output impedance should work fine as input into the kooka.
Cheers,
Russ
Some day I may get around to desning a phono stage, but for now just about any phono stage with a low(or even relatively high if you use the input buffer) output impedance should work fine as input into the kooka.
Cheers,
Russ
Russ White said:I don't see any reason why something like the P06 could not be easily be added in front of the Kookaburra. I have never tried it, but I can't see any obvious issues, Go for it.
Some day I may get around to desning a phono stage, but for now just about any phono stage with a low(or even relatively high if you use the input buffer) output impedance should work fine as input into the kooka.
Cheers,
Russ
Thank you for your quick reply. Being new to preamps I am unfamiliar with power supplies. Would I run the phono off of the transformer or would I use the seperate power supply designed for it?
I looked at the VSPS page and the next batch of boards will be for sale this summer. I'm thinking about making my preamp with phono sooner than that.
As for the Elliott Sound Project 06 phono preamp would I just use the Project 05a power supply Project 05a page and connect it to the trafo (7VA) sold with the kookaburra kit?
Or the other options I am considering are..... running the Hagtech Bugle off of batteries or the Dantimax Phono 1 phono preamp kit.
Dantimax Phono 1 page. The Dantimax phono preamp has a power supply on it.
Once again, thanks for all your help
As for the Elliott Sound Project 06 phono preamp would I just use the Project 05a power supply Project 05a page and connect it to the trafo (7VA) sold with the kookaburra kit?
Or the other options I am considering are..... running the Hagtech Bugle off of batteries or the Dantimax Phono 1 phono preamp kit.
Dantimax Phono 1 page. The Dantimax phono preamp has a power supply on it.
Once again, thanks for all your help
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