New preamp kit!

[tpryan]

The C84 is a high gain, low noise, low distortion microphone preamplifier intended for applications where the least amount of "color" is desired. The circuit is a combination of discrete and high quality integrated components, which provides terrific performance, lowers cost, and eases assembly. The signal path is transformerless and fully differential. Phantom voltage isolation is provided by 100uF low-esr electrolytics in parallel with 1uF film capacitors. The C84 can drive 600 ohm loads (and lower) with ease through the use of a pair of high current discrete buffers.

For some background info, have a look at:

An expensive preamp with very similar specifications.
Nice description of the buffer circuit.
Fred Forssell's JFET version and floating output buffer.

[Category 5]

Excellent! Looks like the smell of flux is soon to return!

Will you be using 604s for gain? Is it time to sell the HV-3 ? (The HV-3 has been getting used less frequently with the a12, n72, and j99's around!)

Shane

[ErikB]

How does the C84 compare/differ from the J99?

[tele_player]

Tim's description at the top of this thread is pretty clear about how C84 is different. The J99 has transformers, isn't fully differential, uses discrete opamps... and costs three times a much.

[ErikB]

Sorry, I typed that as I was heading out for work. I should have been more specific. What I meant was how do they differ in terms of "color." My impression was that the J99 is very clean, uncolored pre, similar the description of the C84. I'm going to buy a C84 kit in a month or two, but I'm just curious how the two compare sonically.

[Category 5]

The J99 is extremely quiet, free of distortion, has lots of gain, and has excellent bandwidth but it is not "free" of color.

It is pretty much as colored as can be without changing the source too much. That is, it is colored only enough to give a rich euphonic character to the source.

The C84 will likely be virtually devoid of ANY color. If it is like my Millennia then it will almost sound too clean compared to the other SCA preamps. This isn't a bad thing however. A lot of the time a source sounds so perfect on its own your goal is to capture JUST that sound without any change whatsoever (classical instruments such as strings come to mind, as does spanish classical guitar).

To be honest, I don;t use the Millennia much since bulding the SCA pres. I always have a sound in mind, and the SCA's are how I get it...yet I have been reluctant to get rid of the Millennia since it does come in handy when I just can't get what I'm looking for.

Maybe the C84 will take it's place and I can sell the Millennia. The HV-3 is excellent, but its' awfully expensive to have around for as much as I use it.

You might also want a completely colorless preamp when you are recording an unfamiliar source, and you want to be sure you don't commit to the wrong color.

The C84 doesn;t look all that exciting to me on paper, compared to the other designs...but that's only because I have grown so fond of transformers.

I notice the ferrite beads on the input. Doesn't teh Amek circuit claim this helps simulate transformer like sound?

Shane

[tele_player]

Those aren't ferrite beads - those are inductors used as a lowpass filter. (assuming you're referring to L3 on the schematic)

[Category 5]

Thanks for setting that straight. Now I don;t know why I thought they were ferrite beads. I guess because I saw them on the green pre schematic or something.

When can we see pictures Tim? I am starting to get anxious!

Shane

EDIT - Oh. It was on Fred Forsell's schematic that I saw the Ferrite beads. I guess Tim does not use these in his design.