Kev's "Cobble Together a Good 3000 PL Preamp" thread...

[jbeckva]

Nominally the same. The elimination of attenuation increases gain. The change from 20K to 16.5K in the R feedback compensates for that and reduces the downstream amplification.

Any time you can decrease amp gain, you reduce amplified noise.

Hmmm... that last axiom has me thinking. I just switched back to my 3000. In comparison (difficult without a quick A/B switch, but anyway) I think my 3000 is a little bit quieter. Why - because for that one I dialed the regulators in for 16 volts. Kev's I had originally did 16 volts as well, but until I figured out that it was that zener for the output relay that needed to be swapped I bumped it to 17 (hoping the extra volt would be enough to kick K13 over).

I wonder if now I should knock Kev's down to 15.. I'm thinking that as you get closer to the max supply rating, the tradeoff is noticeable...

 

[jbeckva]

It's the Phoenix Pre!

Yup back from the ashes (reg boards crashed n burned). Blank here is the start of a new board and circuit using LM317/337 reg IC's. Damn after using the Dremel as a saw it frickin' STEEENKS in here LMBO.

 

[laatsch55]

Now that's gonna be trick...

 

[laatsch55]

Nominally the same. The elimination of attenuation increases gain. The change from 20K to 16.5K in the R feedback compensates for that and reduces the downstream amplification.

Any time you can decrease amp gain, you reduce amplified noise.

yep, let the big un do it, it's got no noise....

 

[kevin]

I have faith Jerry !!!! It's going to be perfect THIS time !!!!

 

[jbeckva]

I have faith Jerry !!!! It's going to be perfect THIS time !!!!

Take a look at this stuff... Circuit design ala Joe on a notepad (and not a puter.. a paper notepad LOL)...

I'll bring it up on a variac tomorrow... I like the results.. heheh

 

[laatsch55]

F*&^%$ Joe man....nice work Jer, regulated supplies....

 

[jbeckva]

F*&^%$ Joe man....nice work Jer, regulated supplies....

Man hope it works.

I figure I can put 100 ohms across each rail to test it out.. that would be nominally 150 mA. I'm comfortable with that!

 

[laatsch55]

Should be enough to blow every op-amp there!!

 

[jbeckva]

Should be enough to blow every op-amp there!!

The main preamp board remains UNPLUGGED until I see plus or minus fifteen @ 150mA, on the gnats-ass.. heheh.

 

[laatsch55]

LMOAO!!

 

[jbeckva]

Actually.. 16 volts mo bettah...

15 is just a little too low for the leds on the front.. very dim. 16 is about right...

(yup, it works... buah ha ha ha ha.....)

Gotta get the amps back in and see now....

 

[jbeckva]

Listening... aaahhhhh...

Now THAT's how a pre should sound IMHO!!

I went with 15.5 volts. It's also as quiet as a damn mouse... hell yeah.

BUT...

I really should stand the positive regulator off and attach it to the PS cage for effective heat dispersion. Damn thing bout burnt me finger.. Yeah, needs a pad, a nut and a bolt...

Heck the negative regulator too if I am going thru the trouble on the positive one..

FWUCK... AWESOME... (did I say that? yeah man.. Shponglin... Hallucinogen'in.... yeah buddy... )

<iframe width="640" height="360" src="//www.youtube.com/embed/s_cZxB5dEWA?feature=player_detailpage" frameborder="0" allowfullscreen></iframe>

 

[laatsch55]

well that dragon has been slayed...

 

[jbeckva]

well that dragon has been slayed...

Just about LOL... going to give those reg ic's air conditionin.. heh

 

[laatsch55]

What are they dissipating?

 

[Gepetto]

What are they dissipating?

Put a power dropping resistor between the bridge positive and negative output and your filter caps Jer. It is a trick I use often. It also reduces the noise floor in applications where you do not need a lot of power. It is better to get rid of the heat in a power resistor than in a semiconductor.

 

[jbeckva]

Put a power dropping resistor between the bridge positive and negative output and your filter caps Jer. It is a trick I use often. It also reduces the noise floor in applications where you do not need a lot of power. It is better to get rid of the heat in a power resistor than in a semiconductor.

What size and wattage do you recommend? Heck tho I already put in the order for four TO-220 mounting kits (note four.. I am going to build another for my own 3000! - Ordered another batch of parts to build one more)

Sounds reallly good

 

[kevin]

Well.... Jerry, Does this mean ya got it ???? This Pre reminds me of the P-500 I sent Mark... Bout drove him crazy... But he got it !!!!

 

[jbeckva]

Well.... Jerry, Does this mean ya got it ???? This Pre reminds me of the P-500 I sent Mark... Bout drove him crazy... But he got it !!!!

Pretty much, Kev. The one thing left is to make sure the regulator chips can dissipate the heat over time, so plan is to anchor them on the chassis and run wires from the leads to the new circuit board. Might get the hardware needed by this weekend, not sure.

But it sounds goooood...