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Ross/Dynacomp adjustment question

Started by Govmnt_Lacky, August 17, 2010, 10:42:08 AM

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Govmnt_Lacky

August 17, 2010, 10:42:08 AM
I built the Dynacomp w/Ross mod from the Tonepad layout. I fired it up and I get sound from both the bypass and effect however, I am not knowledgable enough to know what "sound" to look or listen for when adjusting the trimmer. Can someone explain what I should be looking for during the adjustment or, better yet, let me know where to find a test signal procedure like the BOSS pedals? I know that when the trimmer gets near the extremes it kinda gets distorted however, everything in-between just sounds like normal guitar sound. I do not have a well trained ear  :icon_redface: so I sometimes need a little help with these things!
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Govmnt_Lacky

#1
August 17, 2010, 03:46:46 PM
Any ideas?
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ppatchmods

#2
August 17, 2010, 05:01:09 PM
i used 2 1k resistors instead of the trim and it sounds great.

i've read that some people adjust the trim until the volume is at it's highest with the least amount of noise. never had to do it though.
When your life is over, will any of this STUFF really matter?

JDoyle

#3
August 20, 2010, 04:26:17 PM
To adjust trim: plug in guitar and output of comp to amp. Turn on amp. Turn up guitar volume. Note noise. Turn trim until the noise is at it's LOUDEST. You want the gain to be as high as possible when there is no signal present - making the noise likewise as loud as possible. You don't get something for nothing. This point will be somewhere near the middle, allowing the use of two 1k resistors get the circuit running. However, the bias 'window' for a bare differential pair such as that on the input of the CA3080 is less than a diode drop, so with even basic tolerences the 'sweet spot' may not be found with two 1k resistors - add in the unavoidable mismatch in Vbe of the input pair of transistors and even perfectly matched resistors will miss the 'sweet spot'.

I suggest a multi-turn trim and adjusting the bias as outlined above. Use your ears - a misbiased 3080 in this circuit doesn't sound good.

Regards,

Jay Doyle 

Govmnt_Lacky

#4
August 21, 2010, 09:24:15 AM
Thanks JDoyle.... I will try that this weekend and post back! :icon_biggrin:
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'

fretzburner

#5
January 21, 2011, 08:29:06 AM
Quote from: JDoyle on August 20, 2010, 04:26:17 PM
To adjust trim: plug in guitar and output of comp to amp. Turn on amp. Turn up guitar volume. Note noise. Turn trim until the noise is at it's LOUDEST. You want the gain to be as high as possible when there is no signal present - making the noise likewise as loud as possible. You don't get something for nothing. This point will be somewhere near the middle, allowing the use of two 1k resistors get the circuit running. However, the bias 'window' for a bare differential pair such as that on the input of the CA3080 is less than a diode drop, so with even basic tolerences the 'sweet spot' may not be found with two 1k resistors - add in the unavoidable mismatch in Vbe of the input pair of transistors and even perfectly matched resistors will miss the 'sweet spot'.

I suggest a multi-turn trim and adjusting the bias as outlined above. Use your ears - a misbiased 3080 in this circuit doesn't sound good.

Regards,

Jay Doyle 

What about the knobs settings? what should be the output and sensitivity settings during trimmer adjustment Mr.Jay Doyle?I am asking this because my 80's dynacomp output is not unity gain when sens set to minimum while output set to maximum.

ayayay!

#6
January 21, 2011, 09:14:59 AM
I could have sworn I posted on this thread when it was first started, but apparently not...  Anyway, my method:

Turn the sustain/sensitivity all the way up, and volume will need be set pretty low.  Then just start adjusting the 2k trimmer.  At both extremes you will probably have NO signal whatsoever, but you should have a narrow sweet spot near the middle that provides the cleanest headroom. 

You'll find if you don't have the sustain knob all the way up, the trimmer works all the way through it's travel.  So the method above seems to be the best way I've found to set it. 
The people who work for a living are now outnumbered by those who vote for a living.

R.G.

#7
January 21, 2011, 11:49:42 AM
Seriously folks, put in two 1K resistors. Only go to the trimmer if you have a specific gripes about the sound that results.

Seriously.
R.G.

In response to the questions in the forum - PCB Layout for Musical Effects is available from The Book Patch. Search "PCB Layout" and it ought to appear.

JDoyle

#8
January 21, 2011, 12:00:22 PM
Quote from: R.G. on January 21, 2011, 11:49:42 AM
Seriously folks, put in two 1K resistors. Only go to the trimmer if you have a specific gripes about the sound that results.

Seriously.

I respectfully disagree. Someone building it for the first time and using two 1k resistors has no idea if there is anything to gripe about.

But to each his own.

Regards,

Jay Doyle

R.G.

#9
January 21, 2011, 01:46:38 PM
Quote from: JDoyle on January 21, 2011, 12:00:22 PM
I respectfully disagree. Someone building it for the first time and using two 1k resistors has no idea if there is anything to gripe about.
That's OK. I can agree to disagree.

I have a history on that particular circuit running to a number of thousands of copies. The older CA3080s were fairly crude, and needed the trimmer. The later LM3080 was better, and the majority of them did not need it. Even newer OTAs are even better, and frankly have no need of it at all unless they're defective. People with the experience of only the CA3080s will see the trimmer as critical. LM3080 users will think the sound can be improved with tinkering, and it can for a fraction of LM3080s. The trimmer is essentially useless for the 3280, 5517, and 13600, at least in my experience.
R.G.

In response to the questions in the forum - PCB Layout for Musical Effects is available from The Book Patch. Search "PCB Layout" and it ought to appear.

fretzburner

#10
January 21, 2011, 05:46:12 PM
this is original used dynacomp,maybe the former owner of this replaced the ic because it has LM3080 and this model is 80's.Maybe don't have to adjust the trimmer,i'm just curious why the output is not so loud.my output knob always on the 6 to 10max position to obtain slightly louder than bypassed sound depending on the sens knob settings.

zombiwoof

#11
January 22, 2011, 04:35:32 PM
Quote from: fretzburner on January 21, 2011, 05:46:12 PM
this is original used dynacomp,maybe the former owner of this replaced the ic because it has LM3080 and this model is 80's.Maybe don't have to adjust the trimmer,i'm just curious why the output is not so loud.my output knob always on the 6 to 10max position to obtain slightly louder than bypassed sound depending on the sens knob settings.

Is the LM3080 the DIP version?.   That's probably an early Dunlop DynaComp you have, I have one and it uses the DIP version of the 3080, not the metal can CA version.

Al

fretzburner

#12
January 22, 2011, 09:51:18 PM
yes it is DIP version and i noticed that it performs gain reduction when played loud but on the other side it does'nt amplify when played soft.in short will not sustain almost same as bypassed regarding sustain.but even out the over all volume when large signal is fed like strumming hard.
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