I need a new preamp, and I want to to build a DIY preamp like Mike Freda did. Have collected parts like output transformers from Edcor, tubes...Trying to buy the HLMP-6000 LED, for the ccs, but it is difficult to obtain. Are there any equivalents to the HLMP-6000? Data for the LED are 1,6v and 10 mA. Kan I use any other LED, but with the same data?
Any red LED should do, though the dynamic impedeance can vary a bit, having a small effect on gain. That number is available from DigiKey, $1.45 each in small quantites. A bit steep with postage unless you're ordering other parts.
The project has stopped. I'm not sure if I should go for ccs, or just put in drop resistors/chokes...I have so many tube amplifiers lying around, so I'm selling a bit away. Selling the amplifiers for what the iron cost a few years ago, but they are difficult to get rid of... Better to store them in a warehouse, then I can try later... Can post a picture of what it looks like....
So I'm putting this 5670 single stage pre amplifier together. Making decisions on OTL or not.
I'm trying to figure out the cost/performance benefits of an OTL option. It looks like your going through a coupling cap regardless if you omit the OT.
The Aleph J power amp has an input zΩ of 252K per First Watt documentation. So this pre amp in an OT configuration with an zΩ of 15K provides a ratio of 10:1
And if you go without the OT, do you have to increase the size of the cap to say100uF?
Metal foil caps of that size present no cost savings! None! How does that affect the roll off towards DC?
Unlike headphones, we definitely want to roll off below 20hz here. Maybe I'm missing something fundamental (as is normally the case)?
Freda 5670 preamp drawing circa 2022:
I'm comparing to the crack circuit, if redone as a simple 12AU7 single stage. Why was 100uF the choice vs 1uF here? Was this to bring down the output impedance for headphones?
My Schiit Vali 2 appears to be output capacitor coupled at 470uF at its line level out. How is this value selected?
Two stage Crack circuit without CCS:
I'm trying to figure out the cost/performance benefits of an OTL option. It looks like your going through a coupling cap regardless if you omit the OT.
The Aleph J power amp has an input zΩ of 252K per First Watt documentation. So this pre amp in an OT configuration with an zΩ of 15K provides a ratio of 10:1
And if you go without the OT, do you have to increase the size of the cap to say100uF?
Metal foil caps of that size present no cost savings! None! How does that affect the roll off towards DC?
Unlike headphones, we definitely want to roll off below 20hz here. Maybe I'm missing something fundamental (as is normally the case)?
Freda 5670 preamp drawing circa 2022:
I'm comparing to the crack circuit, if redone as a simple 12AU7 single stage. Why was 100uF the choice vs 1uF here? Was this to bring down the output impedance for headphones?
My Schiit Vali 2 appears to be output capacitor coupled at 470uF at its line level out. How is this value selected?
Two stage Crack circuit without CCS: