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Old 29th January 2012, 04:24 PM   #11
DDB is online now DDB  United States
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Should anyone be considering a build of the HP339 oscillator clone as referenced in post #3 at Modifications: Heathkit IG-18 Audio Generator, Newark has only 42 pieces of the HA3-2625 IC in stock @ 5.92 ea. After they are gone part probably will no longer be available. INTERSIL|HA3-2625-5|IC, OP-AMP, 100MHZ, 35V/s, DIP | Newark.com The HA2625 has some unique characteristics and it is unknown whether a newer chip can replace it. I have some of these but am holding off building it until I see what Dick Moore has in mind for his IG18 #3 mod. IG-18 #3
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Old 30th January 2012, 12:33 AM   #12
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Originally Posted by DDB View Post
Should anyone be considering a build of the HP339 oscillator clone as referenced in post #3 at Modifications: Heathkit IG-18 Audio Generator, Newark has only 42 pieces of the HA3-2625 IC in stock @ 5.92 ea. After they are gone part probably will no longer be available. INTERSIL|HA3-2625-5|IC, OP-AMP, 100MHZ, 35V/s, DIP | Newark.com The HA2625 has some unique characteristics and it is unknown whether a newer chip can replace it. I have some of these but am holding off building it until I see what Dick Moore has in mind for his IG18 #3 mod. IG-18 #3

Do you have any idea what the approximate cost of parts would be less the Heathkit? Rough estimate.

This looks like a project I could do. Thanks for sharing.
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Old 30th January 2012, 01:56 AM   #13
DDB is online now DDB  United States
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A very rough guess might be $80-90 if you need to buy everything. The switch is the most expensive part @ about $23.00 from Mouser. The large frequency caps also tend to be expensive for good film. It will be a bit more if you decide to build a pc board, a group buy might be nice. I believe this one is an improvement in distortion over the design you first listed. The Cordell design as shown on Dick Moore's page is also a top notch performer but perhaps a little more difficult to build.
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Old 1st February 2012, 12:59 AM   #14
Pingrs is offline Pingrs  United Kingdom
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Originally Posted by dennismiller55 View Post
I am looking to add a low distortion audio sig gen to my bench. I have been watching eBay for good deals. Any worth bidding soon rise above my budget.

Anyway, I starting looking into a DIY Signal Generator. My research turned this up. Low-distortion Audio-range Oscillator

Anyone ever build this? Sounds good but is it? There is no build tips or PCB layout. Just a diagram and parts list.

This author has a book of all his circuit designs but comes at a steep price. However, my local library has a copy and I will pick it up sometime this week.
I too liked the simplicity of this. Here's my pcb layout. I mounted + / - 15V regs on the pcb.

Brian.
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Old 1st February 2012, 09:30 AM   #15
PChi is offline PChi  United Kingdom
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That PCB is an impressive bit of work Brian. I am in the middle of laying out a PCB for an alternative design and appreciate the amount of work it takes. If I get it all working on the PCB I will post it here.
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Old 2nd February 2012, 08:05 PM   #16
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I wonder if the distortion would be lower with something like the LME49740? I'm interested in a PCB if anyone is offering.
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Old 2nd February 2012, 09:35 PM   #17
coluke is offline coluke  Italy
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Originally Posted by dirkwright View Post
I wonder if the distortion would be lower with something like the LME49740?
I think the answer is definitely... no. The distortion products you see in the spectrum I've posted are mainly (or entirely) due to the peak detector, whose time constant is zero - no filtering at all means very low settling time (which is good), buy the price you have to pay is that all the harmonics produced by the full wave rectifier are injected in the level control loop, i.e. in the output signal. In order to lower the output THD you have to set up an integrating loop - maybe you can try the one from the JLH's original design:
JLHWB.PNG
it's a Wien Bridge ring-topology (in order to get rid of the opamp common-mode THD), and the amplitude control loop is based on a canonical peak-detector/integrator chain (whose time constant you'll have the to tailor in order to suite your needs - ie freq range and output amplitude).

L.
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Old 2nd February 2012, 09:39 PM   #18
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Thanks. I don't understand all of this, so I'll just leave it at that. I can stuff a PCB though....
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Old 2nd February 2012, 10:34 PM   #19
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Originally Posted by Speedskater View Post
That one looks worth building, in figure 47. There's an error in the text. Figure 47 appears to be the one with 0.0003% distortion, not figure 48.
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Old 2nd February 2012, 11:16 PM   #20
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Originally Posted by dirkwright View Post
Thanks. I don't understand all of this, so I'll just leave it at that. I can stuff a PCB though....
I kind of feel this way too. I can stuff a board. There are so many different ways to approach this. But I am learning. I have read everyone's response to my opening post. I opened every link and read what I could. I googled these different approaches and found more info to study.

They all have merit, but DDB's post on the modified Heathkit is the one I understand. Mainly because I can visualize the end product that will sit on my bench.

So this is route I am leaning towards.

Thanks everyone for your responses.
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