Aunt Corey's preamp questions

[Kent Rould]

Hi,
First, I'm a newbie. This will be my first DIY project (other than building speaker cable, interconnects, powercords).

I am planning on building Aunt Corey's Homemade Buffered Passive Preamp. I'm hoping some of you will be able to answer some of the detail questions I have and maybe look at my circuit layout. Here is the link to the article:

http://stereophile.com/amplificationreviews/54/

1. The Avel Lindberg transformer spec'ed is now a torriod. Does this change anything in the circuit. Is there anything I need to watch out for (placement, hum, etc.)?

2. For dual regulation, do I double up on the caps C1 and C8? This would bring the total 4700uf caps to four.

3. For the bypass, what kind of 470uf/35v and 1uf/50v caps should I use?

I have already aquired the BUF03AJ-883 milspec buffers (www.americanmicrosemi.com)

[SY]

The advantage of the toroid is the reduction in field; its placement is less critical than with an E-I or similar construction. The disadvantage is that the primary and secondary are more tightly coupled at high frequencies, so you have to pay more attention to getting rid of line noise.

You can probably get by without doubling up the raw supply caps, though a real purist would insist on duplicating everything, including the rectifiers and transformers. Personally, I wouldn't bother- the regulators will do a fine job of keeping the channels isolated and the BUF-03 has great power supply rejection.

[analog_sa]

I have already aquired the BUF03AJ-883 milspec buffers

Ha, those things ain't cheap. What's the point of using sand if you can get real tubes for the same price

Seriously, are they way better than the 634?

[markp]

Originally posted by analog_sa


Ha, those things ain't cheap. What's the point of using sand if you can get real tubes for the same price

Seriously, are they way better than the 634?

I think the BUF03s are way better than the 634s. The 03s are bias in class A internally too.

[CharleyW]

That transformer was always a toroid (I think).

[Kent Rould]

Hi again. Thanks to all who replied. I'm ordering parts from Micheal Percy Audio and have some parts questions.

1. c4-7 anc11-14 .01uf/100v film type (these parallel with the rectifiers), can I use Reliable Capacitor .01uf/200v polystyrene and tin foil types?

2. c15-18 470uf/35v (power supply bypass), can I use 470uf/50v Nichicon "KZ"?

3. c19-22 1uf/50v (power supply bypass), can I use a Nichicon non-polarized "ES" or should I use a Black Gate polarized ($2.65 ea)?

4. Corey discusses upgrading the rectifiers to MUR-810, Michael Percy has 8a/600v Fairchild "Freds". Is this a good substitute?

5. Would a TDK conductive plastic pot be a good choice (for now anyway, if it all works I might upgrade later)?

Why did I choose this project (the topic of some replies)? I have not found a preamp I liked or could afford. My pure passive volume control has some deficiencies I think the buffered design will address. It is a "proven" design. And if I don't like it I can use it as a headphone amp. Not to mention, I have always been interested in the peices and parts. This is a reasonable start in getting my hands dirty (or burnt with a soldering iron)

[eLarson]

Originally posted by Kent Rould
Hi again. Thanks to all who replied. I'm ordering parts from Micheal Percy Audio and have some parts questions.

1. c4-7 anc11-14 .01uf/100v film type (these parallel with the rectifiers), can I use Reliable Capacitor .01uf/200v polystyrene and tin foil types?

- If you are going to use the FREDs of part 4, I'd save the polystyrene film&foils for something else. You probably could use them, but I'm not sure you'd need them there.

2. c15-18 470uf/35v (power supply bypass), can I use 470uf/50v Nichicon "KZ"?

- By all means.

3. c19-22 1uf/50v (power supply bypass), can I use a Nichicon non-polarized "ES" or should I use a Black Gate polarized ($2.65 ea)?

- Polarized are fine as power supply reservoir caps. As long as the voltage rating is high enough, go ahead and use the BGs.

4. Corey discusses upgrading the rectifiers to MUR-810, Michael Percy has 8a/600v Fairchild "Freds". Is this a good substitute?

- Yup. I would go for it.

5. Would a TDK conductive plastic pot be a good choice (for now anyway, if it all works I might upgrade later)?

- I don't see why it wouldn't work for you. Is it a Log-taper pot that you have in mind?

[Kent Rould]

Thank you so much for the reply. I'm now very confident about this project. I was planning on an audio taper pot. Is a log taper preferable over an audio taper pot?

[eLarson]

Originally posted by Kent Rould
Thank you so much for the reply. I'm now very confident about this project. I was planning on an audio taper pot. Is a log taper preferable over an audio taper pot?

No, it is the same.

If that is what you have, you are going to be in fine shape, I think. You may decide to switch to a discrete volume control for the sake of repeatable volume settings, but I'd start building with what you've got.

Erik