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

[kevin]

Hmm.. how about I just finish it up and ship it out.. TODAY???

Obviously this doesn't do it justice, but I will tell you I am tempted to send you MINE and keep this one, LOL. Nah I wouldn't do that to ya, Kev. Anywhoo... so I figured out where the issue was... the old saying "walks like a duck, talks like a duck, must BE a duck" applied - Damn if those standoffs were not LOOSE, and those provide the main chassis ground to the power supply!

I knew I wasn't nuts... this pre DID sound good a few posts back, so it was likely that the ground contact was "just" enough.. but then when it broke contact, that's where the buzz came back.

I will tighten the shit out of 'em when I get it back together tonight, then after a few hours of listening OFF IT GOES!!

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No wonder .... All I could here was noise... That thing sounded terrible... You will never get all that noise out of that thing Jer !!!! .... Wait a min.... Was that the music ?????? LMAO !!!!!!! You mean its supposed to sound like that ???? OK... So now all I gotta do is change the CD ..... I THINK I CAN HANDLE THAT JER !!!!!!

 

[jbeckva]

No wonder .... All I could here was noise... That thing sounded terrible... You will never get all that noise out of that thing Jer !!!! .... Wait a min.... Was that the music ?????? LMAO !!!!!!! You mean its supposed to sound like that ???? OK... So now all I gotta do is change the CD ..... I THINK I CAN HANDLE THAT JER !!!!!!

Ooops.. did I need to put on some Lawrence Welk for ya?? Maybe some errr.. Elvis??

 

[jbeckva]

Ok, sent you the bulletin, Joe. Let me know what you think... remember I am using the LME49740's instead of the TL074's they specify, if it makes a diff?

Also hmm... doesn't that make the buffer amp have an increase in gain? Just thinking... my own may already have it (gotta look), as it sure seems "hotter" than other preamps I have tried out.

 

[jbeckva]

Great stuff! Thank You.

Things just keep getting better here all the time!

Took your idea and expanded a lil bit on it. Great suggestion!

Here's your forum... which also is nestled up in a whole new DIY section.. We're still moving threads and reorgin' a lil, but it's a work in progress..

http://forums.phxaudiotape.com/forumdisplay.php/72-Cool-circuits-and-other-DIY-gadgets

 

[NavLinear]

Ooops.. did I need to put on some Lawrence Welk for ya?? Maybe some errr.. Elvis??

I think Kev wants to hear some Steely Dan - or is that Manly Man?

 

[Gepetto]

Ok, sent you the bulletin, Joe. Let me know what you think... remember I am using the LME49740's instead of the TL074's they specify, if it makes a diff?

Also hmm... doesn't that make the buffer amp have an increase in gain? Just thinking... my own may already have it (gotta look), as it sure seems "hotter" than other preamps I have tried out.

Jer any time you attenuate signals followed by more amplification to compensate for that attenuation you introduce opportunities for noise.

 

[jbeckva]

Jer any time you attenuate signals followed by more amplification to compensate for that attenuation you introduce opportunities for noise.

Ok and how does that help me with this? Should I just do what the bulletin says, or would you happen to have a better combination?

 

[Gepetto]

Ok and how does that help me with this? Should I just do what the bulletin says, or would you happen to have a better combination?

Yeah give me some time on it Jer, Will be back later tonight.

 

[Gepetto]

Yeah give me some time on it Jer, Will be back later tonight.

Question: Do you ever plan on using the Mono/Stereo switch in Mono mode?

 

[jbeckva]

Question: Do you ever plan on using the Mono/Stereo switch in Mono mode?

I'd say more thank likely no.

 

[Gepetto]

I'd say more thank likely no.

Well then:

C242 from 0.22uF to 0.33uF or greater, non polar
R260 from 1M to 100K
R257 from 100 to 0
C241 from 33p to 180p
R250 from 20K to 100
R258 from 20K to 16.5K

All resistors from carbon film to metal film

The same applies for the 100 series of parts too Jer. I just listed the 200 series channel.

 

[jbeckva]

Well then:

C242 from 0.22uF to 0.33uF or greater, non polar
R260 from 1M to 100K
R257 from 100 to 0
C241 from 33p to 180p
R250 from 20K to 100
R258 from 20K to 16.5K

All resistors from carbon film to metal film

The same applies for the 100 series of parts too Jer. I just listed the 200 series channel.

Ahh, I can see why you asked about the mono switch (going from 20K to 100 on R250/150). Leave R156/256 at 1.1K?

 

[Gepetto]

Ahh, I can see why you asked about the mono switch (going from 20K to 100 on R250/150). Leave R156/256 at 1.1K?

Unless I mentioned it specifically, leave as is except change to metal film (lower noise)

 

[jbeckva]

Unless I mentioned it specifically, leave as is except change to metal film (lower noise)

Just making sure you know I have the 1.1K right now (I have not done the mod from the bulletin, which would change it to 1.8K instead).

For C142/242 (coupling from the volume control to the non inverting input)... should that be a "fancy" dayton/solen/jantzen kind of cap or is a standard wima/etc family ok there?

 

[Gepetto]

Just making sure you know I have the 1.1K right now (I have not done the mod from the bulletin, which would change it to 1.8K instead).

For C142/242 (coupling from the volume control to the non inverting input)... should that be a "fancy" dayton/solen/jantzen kind of cap or is a standard wima/etc family ok there?

It does not get any fancier than Wima Jer. Those are the best caps on the planet...

 

[jbeckva]

Ok, order done n sent... We'll see how it goes! Ordered the above and any other resistor in the main buffer amp circuit. If it does "good" we can look at the tone control circuits next...

Thanks so much, Joe! I want Kev to do cartwheels when he hears this.. hehe.

 

[kevin]

Ok, order done n sent... We'll see how it goes! Ordered the above and any other resistor in the main buffer amp circuit. If it does "good" we can look at the tone control circuits next...

Thanks so much, Joe! I want Kev to do cartwheels when he hears this.. hehe.

Now why would you want to fall flat on my ass ????

 

[Gepetto]

Ok, order done n sent... We'll see how it goes! Ordered the above and any other resistor in the main buffer amp circuit. If it does "good" we can look at the tone control circuits next...

Thanks so much, Joe! I want Kev to do cartwheels when he hears this.. hehe.

That should move it in the right direction Jer. There may be other contributors within the pre that are contributors that we can tackle one at a time.

Getting rid of that megohm input impedance into that amp will go a fair distance to your goal.

 

[jbeckva]

That should move it in the right direction Jer. There may be other contributors within the pre that are contributors that we can tackle one at a time.

Getting rid of that megohm input impedance into that amp will go a fair distance to your goal.

Thanks again. Hey... by chance have you figured out what the overall gain would be? Would it be less or more than it is now?

 

[Gepetto]

Thanks again. Hey... by chance have you figured out what the overall gain would be? Would it be less or more than it is now?

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.