Pitchfork pre-amplifier

[rsavas]

Good news and good luck on your testing.
Damn those film caps stick out, as being huge, really wonder if they are necessary, can be replaced by a little ecap, I guess your testing will determine necessity.

 

[jwilhelm]

I always use polypropylene or silver mica in direct audio signal whenever possible, but yes they are massive!

 

[Krisfr]

Looking Very Good, Good LUCK with the testing overall

 

[Carl_Huff]

That's a good looking layout Jeff! I am looking forward to hearing your impressions.

 

[jwilhelm]

All supplies are good. The input buffer is nice and stable with 15mV offset. The DAC buffer isn't very stable though. It falls off at 50kHz and clips at less than 1 volt.

 

[mlloyd1]

looks very nice!!!
good luck with the testing ...

mlloyd1

Almost ready to start testing supplies and buffers.

 

[fredlock]

Count me in for the group buy.

 

[jwilhelm]

Control hardware is working well as far as I've been able to test. I've been battling with software for most of the afternoon. I'm having issues with device addresses. Linux-works/Bryan has been a great help figuring things out so far.

 

[thimios]

Control hardware is working well as far as I've been able to test. I've been battling with software for most of the afternoon. I'm having issues with device addresses. Linux-works/Bryan has been a great help figuring things out so far.

Nice work!
What about final cost?

 

[jwilhelm]

I'm going to get a working version going before I figure out an accurate cost. I think it'll be around $400 with all options populated plus supplies and chassis.

 

[maouna]

is there a single layer pcb for pitchfork preamplifier?

 

[jwilhelm]

All the boards I've designed for it are double sided. Other than the linestage board, they are all going to be redesigned after a test unit is fully operational.

 

[yngvejos]

I'm putting together a line stage to use with a 25K (I have resistors to rebuild it to 10K if that will work better) r2r attenuator, I already have a dcb1 buffer in the box, but I'm not sure if there's space for both buffer and linestage.
Do you recommend to run the line stage before or after the attenuator? Are there any use for the buffer when running the linestage?

 

[jwilhelm]

The linestage is connected after the attenuator. There's no advantage to having the buffer with it.

 

[yngvejos]

Great! That was the answer I was hoping for I have another lcudino/d1 attenuator that I would like to put the buffer into.
I managed to populate the board ~50% with parts from my junkbox, the rest will arrive from mouser and digikey on tuesday or wednesday. Looking forward to try it.

 

[jwilhelm]

D1 should work well with it. I'm curious if there is going to be annoying clicking on volume changes though.

 

[yngvejos]

I don't expect any clicking. I have been running 2v sources through D1 into Honey Badger with 98dB sensitivity speakers earlier without any clicking through the speakers. I kind of like the mechanical clicking from the relays after getting used to it.

 

[yngvejos]

Just finished the linestage. I noticed that the heat sink on q9-10 17 and 18 gets very warm (to hot to touch) within 1 minute with power on.
Are my heatsink too small or is there something wrong?

 

[jwilhelm]

That heat sink should be bigger. It runs class A for headphones. Some adjustments can be done to drop the current if you are just going to use it as a buffer. You can replace one of those diodes with the reversed silkscreen on each channel with a 100 ohm resistor to drop the current.

 

[yngvejos]

I guess i should find some way to lead the heat to the chassis, I have no ventilation inside the case so I guess I will be in trouble when I put the lid on even with lower bias.
Will it affect the performance if I mount the transistors on the baseplate next to the board and connect them with wire?