It is currently Fri Nov 24, 2017 6:56 pm




Post new topic Reply to topic  [ 5 posts ] 
 A cpl questions about 27xx LFO 
Author Message

Joined: Wed Sep 25, 2013 10:31 pm
Posts: 56
Post A cpl questions about 27xx LFO
1. What kind of waveform does this LFO use? Sine or triangle? And if it's a triangle LFO, would I be able to say route the symmetry trimmer to the front and use that to change the triangle to rising/falling ramp?

2. Which components affect the depth and rate of the LFO and what would you suggest to replace those with to get a much faster/slower speed and more depth? And any suggestions on replacing the rotary speed switch with a continuous pot for setting the coarse speed without jumping to predefined values?

3. I have another LFO with some issues - the oscillation often ceases when I switch between speeds, or it barely oscillates, or the oscillation slowly picks up. Am I correct to assume that some capacitors that set the speed are bad and need to be replaced or is there more behind it?

Thanks ahead for your help :D


Fri Feb 14, 2014 12:37 pm
Profile
User avatar

Joined: Sun Nov 09, 2008 2:49 pm
Posts: 726
Post Re: A cpl questions about 27xx LFO
The 2720-5 (4750) Control Oscillator / Noise Source kit assembly manual is posted in this area:

viewtopic.php?f=6&t=177

Notice the front cover describes the output as sinusoidal. It is such a simple circuit that to add and change for the features you're after, you might as well start anew.

The power supply voltage being the specified 18V is important (within a volt or so) and check to see if the transistors Q1 and Q2 have been replaced with substitutes. If so, the biasing might not be optimized for them -- it might take some resistor changes to get things balanced out right.

_________________
Scott Lee
scott@paia.com


Fri Feb 14, 2014 5:29 pm
Profile

Joined: Wed Jan 01, 2014 1:36 pm
Posts: 61
Location: Toronto
Post Re: A cpl questions about 27xx LFO
I am working on a simple but usefull LFO. I hoipe to have it ready in a week or so (subject to getting my oscillators in tune)

Bill


Fri Feb 14, 2014 7:30 pm
Profile

Joined: Wed Sep 25, 2013 10:31 pm
Posts: 56
Post Re: A cpl questions about 27xx LFO
There is a simple LFO schematic flying around the web somewhere. If I remember correctly, it puts out a triangle and a squarewave, and it utilizes a quad op-amp and just a handful of rc components. I'll have to look around and find it again. It's very simple and low parts count. I'll post a link to it if I find it again.


Fri Feb 14, 2014 9:36 pm
Profile

Joined: Wed Sep 25, 2013 10:31 pm
Posts: 56
Post Re: A cpl questions about 27xx LFO
Ok, this is not the same circuit I was talking about but this one is even simpler and uses one dual op-amp, 10 parts total if you count in the biasing circuit. I haven't tried this though, so don't ask me about it's performance.

http://www.experimentalistsanonymous.co ... %20LFO.gif

PS: If I'm not mistaken, you could ditch the biasing circuit and use the Paia's -9V rail directly which would probably increase the depth/power of the LFO, but also decreases the parts count by 3 (unless you need to use some capacitors for conditioning)


Fri Feb 14, 2014 9:49 pm
Profile
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 5 posts ] 


Who is online

Users browsing this forum: No registered users and 5 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB © phpBB Group.
Theme designed by Vjacheslav Trushkin , adapted for PAIA by Illumimedia Design Studios
Not able to open ./cache/data_global.php