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Author Topic: OP Amp question  (Read 13302 times)

skynyrd

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Re: OP Amp question
« Reply #15 on: September 03, 2010, 10:19:30 PM »
Would R8 be the cause of the compression sound? It is right after the pregain pot and my line of thinking is it could be loading up so to speak. Or with it being 1K is it not big enough and it is overloading the second gain stage?
« Last Edit: September 03, 2010, 10:23:29 PM by skynyrd »

phatt

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Re: OP Amp question
« Reply #16 on: September 04, 2010, 02:23:52 AM »
Try a lower value for C3, 22uF/25V

Try 2.2uF instead.

It's a fine line between getting great OD but by then you loose the bottom end and your sound becomes tiny and lifeless.
Phil.


skynyrd

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Re: OP Amp question
« Reply #17 on: September 04, 2010, 10:55:22 AM »
Correct me if I have been given wrong info, but I was told the lower a capacitors value increases bass and rolls off more treble ?  Wouldn`t dropping from 22UF to 2.2 UF increase the bass at the input ? I don`t mean to question YOUR knowledge just trying to improve mine.

phatt

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Re: OP Amp question
« Reply #18 on: September 04, 2010, 07:42:35 PM »
Hi Skynyard,
LOL, Heck even God could be wrong on the internet and no one would notice. 0:) ;D

Here in lies the problem of one line answers to complex things.
The info was correct but only in one situation.

Lowering the value of A cap that is *in series* with
the AC signal cuts bass.

Raising the value of A cap that is *in parralell*
(i.e. across the input) with the AC signal will cut more
high frequency.

Both of these conditions refer to the AC part of a circuit and guess what???
Neither one will help in this situation because C3 is part of yet another thing in a circuit called DC condition.

It's probably better if one of the more teky ones here cover that part. I'll just confuse the issue.

Meantime just keep this little rule in your head;
To build a circuit you have to set the DC conditions of a circuit first so that the AC signal will pass through in the best possible way.
AC stuff is not so hard but DC is a little more complex,,well was for Me at least. :-[

Cheers, Phil.

skynyrd

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Re: OP Amp question
« Reply #19 on: September 04, 2010, 09:19:05 PM »
I have been finding out that the DC and AC circuits are confusing,,lol.  I know no one can come on here and type out a complete electronics theory course that a ying yang like me could pick up and run with,,lol. But I do appreciate everyone taking the time and the patience to answer my questions so I can understand what I am looking at a little better. I know i can`t take my old Mace and make it a high gain amp,,well i probably could but that would take more than I am capable of,,lol. But with the guidance all of you are helping me with I am getting it closer and closer to the sound I am looking for.

skynyrd

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Re: OP Amp question
« Reply #20 on: September 06, 2010, 06:30:40 AM »
Well I decided yesterday to really dig into this amp and see what I could do, first off the normal channel never has worked right and there was always a loud squeal when plugged into it. Had a tech tell me the norm jack was bad and went ahead and replaced it, squeal gone but the norm channel stayed on all the time. I could toggle the effects channel on and off but the norm stayed on so always figured there was a messed up switching chip in it or something. So I switched out R50 from a 33k to a 22K in reference to another forum member and put 2 LED`s in series on R11 per the same forum member and plugged her in and tried her, did not like the grungy sound the LED gave so pulled them and went back to norm. The 2 resistors I changed added a little more distortion but with the effects channel pre gain on 10 it was super bassy and compressed, on 9 it had a decent rhythm tone but the lead tone was still not edgy enough. The 2 channels on the amp are suppossed to run paralell to each other and you should be able to boost 1 channel over the other, not in this case. I don`t know why but I decided to put both channels pre gain on 10 and set the effects channel on 1 and started turning the normal channel up to see what happens, the more I turned it up the more the bassyness and compression went away. Then this sweet little crunch came out and a cool growl and tone the amp never had before emerged. So I played with the eq`s on each channeland kept raising the norm chan volume and it got better and better. So it appears the amp has been rewired with the channels in series like i wanted to do. It would have been nice if the previous owner had told me this and saved me and everyone else alot of headaches..lol.

skynyrd

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Re: OP Amp question
« Reply #21 on: September 10, 2010, 05:41:07 PM »
Ok, now that Mr. Fahey`s mods made a nice change he has peaked my interest, since I have the warm up out of the way whats the next step?

phatt

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Re: OP Amp question
« Reply #22 on: September 12, 2010, 09:47:24 AM »
Hi skynyrd,
 What happened to *super bassy and compressed* you mentioned?

Did that get sorted?
Phil.

skynyrd

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Re: OP Amp question
« Reply #23 on: September 12, 2010, 10:37:19 AM »
Hi skynyrd,
 What happened to *super bassy and compressed* you mentioned?

Did that get sorted?
Phil.

If I just use the effects channel alone with the pre gain on 10 its there,, backed off to 9 it opens up and get a better tone, with the channels being run in series like I am 99% sure it is, the normal channel feeds the effects channel. So that with the tone stoack mod I did to the norm channel is brighter and helps even out the effects channel. Now if I crank the effects channel up it will over power the norm and the bassyness returns, but for low volume like stage level being miked its a very even tone.

skynyrd

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Re: OP Amp question
« Reply #24 on: September 18, 2010, 08:16:23 PM »
Well i installed a bias pot and bumped the bias up to 41 mA`s, the tubes get decently warm and not overly hot. She sound alot more full and open now, she is shaping up nicely. The tubes were on a 17mA bias before, I read where the JJ Tesla 6L6GC can be biased to 60mA`s but doubt I will push them that far, will get a small fan to pot on the back of the amp to help keep any extra heat down.

skynyrd

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Re: OP Amp question
« Reply #25 on: October 02, 2010, 03:36:26 PM »
I swapped out the magnet on the bridge pick up on the Les Paul and WOW ! !  All of the compressed sound and mushy bottom end I had is gone. The pick up is a Duncan Custom and had a ceramic magnet in it, the guys on the duncan forums have been talking relentlessly about mag swapping so I figured since mags are cheaper than pups I would try it. I picked up a Alnico 4 mag off ebay for $5, took the pup apart and double checked to make sure I had the A4 going in just like the old mag and put her back together and heated the pup with a hair dryer for 20 mins to get the wax flowing and sealing everything back up. I plugged in and had the roundest fullest tone I have ever gotten out of that guitar and amp, I was in shock for about 10 min`s as all the less than likeable aspects of the tone were gone and an actual lovable tone replaced. The normal channel I left stock sounded so sweet and had the best Skynyrd tone the amp has produced, the Effects Channel I modded per Mr. Fahey had this sweet growl and really good distortion, the rythm sounds were so clear and articulate. I would have never figured that a ceramic magnet would make a change for the worst, my Peavey Heritage had an even worse compressed mushy sound and when i plugged into it with the new mag it was gone as well. If you have a Peavey amp with a solid state preamp and a pup with a ceramic magnet do yourself a favor and hit ebay and get a Alnico mag, its easy to swap and will make a HUGE difference in your sound and tone