AT-PEQ3 anyone?

[mlloyd1]

i see these have been discontinued, so if you find one, you can pick them up cheap. i just wanted to know what's inside, since i haven't seen any pictures anywhere else. so, here you go. enjoy ...

and, no, i haven't listened to it yet. first, a couple of things have to go immediately ... like those 220pF cartridge loading caps.



mlloyd1
oops, sorry about the picture size for the first one. i wanted that one big since i knew that's the one you all wanted to see.
works best to click and save to hard drive before viewing ...

[h_a]

Hi,

thanks for posting photos of front+back - when time permits, I'll have a look at backengineering it.

Hannes

[mlloyd1]

i asked for a schematic - yeah, yeah, i know, i'm being lazy.
:-)
i'll let you know if i actually get something in response.
i wonder why folks make the power rails so low in these little preamps?
using higher supply voltages seems a quick and easy way to get some headroom benefits and improved distortion specs for starters.
i'm surprised nobody here posted anything about modifying one - especially since I've noticed it got a little positive buzz in stereophile not long ago. seems a prime candidate for mods - provides a nice little case, uses through-hole parts and uses an opamp that many people would love to change out.
:-)

mlloyd1

[h_a]

using higher supply voltages

Well, there are not so many nice high voltage opamps out there

And distortion is usually not much of a problem for opamps anyway.

Still - a schematic would be fun!

Hannes

[mlloyd1]

wow, ask and ye shal receive, as they say ...

enjoy,
mlloyd1

Originally Posted by mlloyd1

i asked for a schematic - yeah, yeah, i know, i'm being lazy.
:-)
i'll let you know if i actually get something in response
....
mlloyd1

[h_a]

Hi,

thanks for the schematic!

Actually, quite different from what I expected.

AC-coupled with single supply, non-inverting single stage with active RIAA; the japanese bipolars are only used as 2nd regulating stage after the IC-regs.

Hannes

[Bonsai]

I took a look at the schematic. Dissapointing to say the least.

Single ended, running off a low supply voltage (fully agree with your observation MLloyd1) to save just a few pennies. A split rail supply would have avoided all the shenannigans around the half rail reference circuitry, and they could have dropped the transistors (or better still, used them for an output stage buffer, enclosed in the overall feedback loop).

Another concern is the rather high resistor values used for the feedback netowork. If they had used lower value resistors (which would of course require larger RIAA equalization caps) this pre-amp could have been a lot quieter.

One good thing about this RIAA of course is that it is fully active, which means the best possible overload characteristics. That said, you could also argue that they can get away with a lower supply rail as a result . . .

However, I would have done it a bit differently . . .

[Fasterdamnit]

Thought i would resurrect a post- I set up a turntable in the living room which is primarily TV/AV room. The distance required a 10 foot cable to the Pioneer Elite VSX-39TX. Using the onboard phono stage rolled the highs off a bit. I had PEQ3 on a shelf so decided to use it as a line level source. Replaced the cheap electrolytics, put in a socket and rolled some op amps. Currently have LME49990 SMD singles on an adapter. Beat the LM4562 with same detail but not as harsh. Soundstage is wider, better bass with great attack. For a bargain basement pre, $15 in parts made a big improvement.

[mlloyd1]

Fasterdamnit:

thanks for sharing your results. i'm curious; it looks like you did not make any changes to optimize the preamp loading to your cartridge?

also, does your ground terminal work well? mine didn't because of the paint. i changed the screw after sanding the paint off around the hole.

mlloyd1

[Fasterdamnit]

Originally Posted by mlloyd1

Fasterdamnit:

thanks for sharing your results. i'm curious; it looks like you did not make any changes to optimize the preamp loading to your cartridge?

also, does your ground terminal work well? mine didn't because of the paint. i changed the screw after sanding the paint off around the hole.

mlloyd1

Hi, ML. I just clipped one leg of the 220pf input caps. Yes, I removed paint around the ground lug. I am looking into swapping in a 24Vdc supply. I think I have one buried in the junk box. I need to see what the regulator is rated.