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 Forum index » DIY Hardware and Software » Thomas Henry designs
The VCO-555
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ungleichklang



Joined: Dec 03, 2011
Posts: 84
Location: East-Belgium

PostPosted: Sat Jan 25, 2014 5:56 pm    Post subject: Reply with quote  Mark this post and the followings unread

jukingeo wrote:
Hello All,

Now for the VCO, the issue I am having with the MFOS design is that I feel it is overly complex and it seems there is a fairly long calibration process. Naturally I am wanting to look for something simpler and less complex, but nearly offers the same features as the MFOS design.

First of all welcome to EM .......
now... every VCO sounds a bit different depending on the components used, so you can not compare MFOS with the TH-555 by Fonik ....
You can use the TH-555 with all MFOS modules, so if you prefer to build those, go ahead ..
btw. there are even more complex VCOs than the MFOS-VCOs


jukingeo wrote:

After a quick search I came across this post on a 555 based VCO created by Thomas Henry. After reading through this thread, it seems that it is accepted that this is the arguably the best VCO out there currently. What I like it is that it uses quite less parts than the MFOS design, and a fellow in Germany is making boards for this. So I have a few questions:


jukingeo wrote:

1) Is this really the better picks of the VCO's out there and does it compare to the MFOS VCO or does this clearly blow the MFOS one away?

See above ... so actually the answer is ... NO

jukingeo wrote:

2) Is there someone here in the US that is distributing the boards?

These boards are not distributed ..... read back the posts and get on Fonik's list ....

jukingeo wrote:

3) One feature I liked on the variable skew LFO is the ability to adjust the waveform of the triangle wave to a saw or ramp wave and anywhere in between. Could this feature be added to the 555-VCO?

you can add what ever you like .... the PCB is designed as designed by TH ..

jukingeo wrote:

4) I would assume that changing out the timing cap could easily make this an LFO, correct?

If you want an LFO ... read this thread http://electro-music.com/forum/topic-55470.html

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elmegil



Joined: Mar 20, 2012
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PostPosted: Sat Jan 25, 2014 7:08 pm    Post subject: Reply with quote  Mark this post and the followings unread

It is worth noting that one measure to compare VCOs by is how well they track--how many octaves they stay in tune.

It's certainly only one measure, but on that score, I find the 555-VCO to be the best tracking of any of the analog ones I've built. I've only built the MFOS soundlab VCOs, but also el Cerrito (another TH design), X4046 (another TH design), and the Teezer (a through zero VCO by Ian Fritz).
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jukingeo



Joined: Oct 24, 2007
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PostPosted: Sat Jan 25, 2014 10:05 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ok, guys, fair enough.

Judging by your answers and what I read so far, I think I would be more happy with the 555 VCO than those from MFOS. So I put myself down for 3 555 VCO circuit boards. BUT for the LFO I am going to stick with the MFOS Variable Skew.

Thanx,

Geo

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jmcecil



Joined: May 11, 2013
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Location: Prattville, AL

PostPosted: Tue Jan 28, 2014 12:25 pm    Post subject: Reply with quote  Mark this post and the followings unread

I'm having a hard time translating the thermistor requirements to a datasheet. Will this one work?

Mouser: Vishay 2k Radial Thermistor
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mcop



Joined: Apr 27, 2012
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PostPosted: Tue Jan 28, 2014 3:57 pm    Post subject: Reply with quote  Mark this post and the followings unread

Try these: http://www.thonk.co.uk/shop/tempco-resistor-krl-bantry-3500ppm-x2/
or these: http://synthcube.com/cart/forums.html?route=product/product&path=74_18&product_id=147
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jmcecil



Joined: May 11, 2013
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PostPosted: Tue Jan 28, 2014 4:12 pm    Post subject: Reply with quote  Mark this post and the followings unread

mcop wrote:
Try these: http://www.thonk.co.uk/shop/tempco-resistor-krl-bantry-3500ppm-x2/
or these: http://synthcube.com/cart/forums.html?route=product/product&path=74_18&product_id=147

perfect, thank you... other than it's UK. But, Thonk has been good before.
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jmcecil



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PostPosted: Tue Jan 28, 2014 8:31 pm    Post subject: Reply with quote  Mark this post and the followings unread

damn, I tried to find them on synthcube but it kept taking me to a lesser tempco. I could find that one.
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mosheen



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PostPosted: Mon Feb 03, 2014 4:10 pm    Post subject: Reply with quote  Mark this post and the followings unread

Magic smoke carries them. http://www.magsmoke.com/tempco-resistors.asp
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andreschouhy



Joined: Mar 13, 2014
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Location: Buenos Aires, Argentina

PostPosted: Thu Mar 13, 2014 7:52 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi, i'm building 2 of these vco 555 modules. But I'm having troubles to get some components like the tempco (which, reading above, i'll be replacing with a fixed resistor until i get the tempco), but also some resistor values. So, my question is: Is it ok to replace the following resistors?
R9, R10 from 2k to 2.2k
R13 from 3k to 3.3k
R21, R22 from 20k to 22k
R26* from 300k to 330k (* this is not really R26, but the page 2 on the schematic presents a couple of resistors named R26 with different values)

Thank you very much
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aladan



Joined: Aug 13, 2011
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PostPosted: Thu Mar 13, 2014 8:16 pm    Post subject: Reply with quote  Mark this post and the followings unread

andreschouhy wrote:
Hi, i'm building 2 of these vco 555 modules. But I'm having troubles to get some components like the tempco (which, reading above, i'll be replacing with a fixed resistor until i get the tempco), but also some resistor values. So, my question is: Is it ok to replace the following resistors?
R9, R10 from 2k to 2.2k
R13 from 3k to 3.3k
R21, R22 from 20k to 22k
R26* from 300k to 330k (* this is not really R26, but the page 2 on the schematic presents a couple of resistors named R26 with different values)

Thank you very much


I don't know for sure, but you'll probably be 99% OK for testing out the board to see if it basically works. In most circuits there are very few resistors are all that critical (unless you're building scientific equipment!)

You can always make 2K resistors by soldering two 1K resistors in series; similarly 3K = 1.5K + 1.5K (or 1.2K + 1.8K, etc etc), 20K = 10K + 10K, 300K = 150K + 150K.

Cheers,
A.
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John.R.Strohm



Joined: Feb 09, 2014
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PostPosted: Fri Mar 14, 2014 6:24 am    Post subject: Reply with quote  Mark this post and the followings unread

Thomas's designs call out a PT-146 2K ohm +3300 ppm/degree C tempco.

The part is manufactured by Precision Resistor Company.

It is not a stocked standard part. They make them to order. For a US customer, there's a $50 setup charge. Minimum order is 10 parts. They get about $5/each, for quantity 10-99. Unit price declines slowly as order quantity increases. To make it simple: 10 parts will cost you US$100, plus shipping: $50 setup and $5/each x qty 10 = $50. Plus shipping. That's IF you're in the US.

I emailed them recently. The above is taken from the quote they gave me.

Music From Outer Space offers them for US$9/each.

Magic Smoke offers them for either US$3.50/each or US$1.90/each, depending on whether you look at their Tempco page or their Price List page. I emailed them a few weeks ago to inquire as to which was the correct price, but have not heard back, and I am VERY nervous about ordering from someone who isn't answering emails asking about pricing. (I have my doubts about those prices, as they are significantly below the manufacturer's price at even the highest quantity break.)
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andreschouhy



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PostPosted: Fri Mar 14, 2014 7:13 am    Post subject: Reply with quote  Mark this post and the followings unread

aladan wrote:
You can always make 2K resistors by soldering two 1K resistors in series; similarly 3K = 1.5K + 1.5K (or 1.2K + 1.8K, etc etc), 20K = 10K + 10K, 300K = 150K + 150K.

Yeah, I was thinking of making that move, a little less aesthetic, but anyway the pcb is not intended to be seen.
Thank you for the feedback.
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elmegil



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PostPosted: Fri Mar 14, 2014 7:34 am    Post subject: Reply with quote  Mark this post and the followings unread

Tim (Magic Smoke) has moved and had other chaos in his life right now. He's a solid guy--I've never had any parts NOT show up that I've ordered from him.

That said I understand your nervousness, and I would not be able to reassure you about how long it might take.

There are other sources of 2K tempcos out there though:

http://synthcube.com/cart/forums.html?route=product/product&path=74_18&product_id=205
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wackelpeter



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PostPosted: Sat Mar 15, 2014 1:20 am    Post subject: Reply with quote  Mark this post and the followings unread

I'm thinking of an substitution for 2k tempco when i'm doing this in the future...

Rene Schmitz has an article written about this over here:
http://www.schmitzbits.de/
it's that article: whats this tempco stuff...

and as he wrote it works and is much cheaper with nearly the same results in the "normal" temperature range... only at very low or very high temperatures the difference in range between tempco and the substitutes will raise...
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acidblue



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PostPosted: Mon Mar 17, 2014 9:19 pm    Post subject: Reply with quote  Mark this post and the followings unread

Excuse me but what exactly is the triangle on sheet 2 with pins 9 and 10???
Its right between the two R26's
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elmegil



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PostPosted: Mon Mar 17, 2014 10:10 pm    Post subject: Reply with quote  Mark this post and the followings unread

The LM13700 has a darlington buffer in it.

Here's the view on the datasheet...


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acidblue



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PostPosted: Tue Mar 18, 2014 9:12 am    Post subject: Reply with quote  Mark this post and the followings unread

I did not know that, thank you
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fonik



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PostPosted: Wed Mar 19, 2014 6:31 am    Post subject: Reply with quote  Mark this post and the followings unread

wackelpeter wrote:
I'm thinking of an substitution for 2k tempco when i'm doing this in the future...

Rene Schmitz has an article written about this over here:
http://www.schmitzbits.de/
it's that article: whats this tempco stuff...

and as he wrote it works and is much cheaper with nearly the same results in the "normal" temperature range... only at very low or very high temperatures the difference in range between tempco and the substitutes will raise...


interisting. i might try the NTC option in future. no big deal with existing PCBs actually:
Posted Image, might have been reduced in size. Click Image to view fullscreen.

i just made a graph from his data, which illustrates his findings. the usable range should be okay for center europe:

Posted Image, might have been reduced in size. Click Image to view fullscreen.

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wackelpeter



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PostPosted: Wed Mar 19, 2014 9:27 am    Post subject: Reply with quote  Mark this post and the followings unread

fonik wrote:
i just made a graph from his data, which illustrates his findings. the usable range should be okay for center europe:


i guess it wouldn't be a great idea to move with an modular into the Amazon rain forrest and playing there... not only because of the higher temperatures as i might think the immense air humidity wouldn't be so fine for the parts within... Razz

i've just ordered some of the otherwise mentioned Philips temperature sensors (KTY81.... 1k & 2K for ca. 0,50 Euro each)... maybe they'll fit in as well when i'm building that VCO...

But at first i have to wait for my traco PSU's or should find an Transformator with 2 x18V AC Outputs...
The one i have actually has 2 24V Outs and that is a bit too much Input for the 7915 & 7815 so the output voltage sinks very fast to only +/-13 V on my PSU...

btw. Mathias do you have any PCB's form one of your previous projects left, that you don't need for yourself? Would maybe re-think my building intentions and switch from stripboard to pcb...
In terms of payment and sending that should be easy to arrange as i'm from Germany too...
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fonik



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PostPosted: Thu Mar 20, 2014 2:30 am    Post subject: Reply with quote  Mark this post and the followings unread

wackelpeter wrote:
i've just ordered some of the otherwise mentioned Philips temperature sensors (KTY81.... 1k & 2K for ca. 0,50 Euro each)... maybe they'll fit in as well when i'm building that VCO...

i've ordered the NTCs (0.36 EUR/ea at tante angelika), however, i don"t know when i will build another VCO...


BTW i currently don't have any spare PCBs. nevertheless, i will do another 555-VCO run later this year. and i am working on quite a few project to come, alas, i don't have as much time as i used to, so i got veeeery slow.

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fonik



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PostPosted: Thu Mar 20, 2014 4:53 am    Post subject: Reply with quote  Mark this post and the followings unread

wackelpeter wrote:
i've just ordered some of the otherwise mentioned Philips temperature sensors (KTY81.... 1k & 2K for ca. 0,50 Euro each)... maybe they'll fit in as well when i'm building that VCO...

how did you select them?

i have a hard time figuring it out how to convert the 3300 parts-per-million / Celsius to the typ. resistance table from the datasheet.

in the datasheet they list different typical resistances at given temp, depending on the type (KTY81 -1xx).
however, there also is a graph showing one general sensor resistance as function of ambient temperature.

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wackelpeter



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PostPosted: Thu Mar 20, 2014 8:29 am    Post subject: Reply with quote  Mark this post and the followings unread

better do not ask how i select them... to be moderate i would call it intuitive... Razz surely have no idea which i should select so i took 2 different 1k and 2 different 2k sensors...
as René said they should be in series with a normal resistor reaching the value of the tempco... i'm not sure if it works, so i can only try it myself...
at least i have spent 2 Euros to experience that it doesn't work as supposed for me...
then i still have the NTC method to try...


hm... as you didn't have any pcb's left i see myself soldering and drilling stripboards my whole life.... Wink but no worries about that...
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jukingeo



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PostPosted: Mon Apr 07, 2014 4:55 pm    Post subject: Obtaining tempcos and matched transistors for VCO's Reply with quote  Mark this post and the followings unread

Hello All,

Ok, so I bit the bullet and bought 3 PCB's from Fonik to build 3 of these 555-VCO's. For the most part getting the parts isn't too difficult, but it seems the hardest part to get are the matched transistors and the special Tempco resistor.

I don't have as much test gear as I used to and I don't think I am going to be building a bunch of voltage tracking VCOs, so it seems like the easy way (but not the cheapest) is to buy the transistor set and Tempco that Ray offers on his MFOS site. The trouble is that the transistors are 3904's and not 3906's. The Temco is also different being a 3300 and not a 3500. So I am curious if I can use these transistors and Tempco or is this something that has to be exact. If it has to be exact, then were can I source the Tempco and matched transistors necessary to build the VCOs.

Thank You,

Geo

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mcop



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PostPosted: Mon Apr 07, 2014 10:26 pm    Post subject: Reply with quote  Mark this post and the followings unread

You'll need matched 2N3906's as they're PNP rather than 2N3904's which are NPN.
Ian Fritz's method for matching them is fairly easy and does the job perfectly. There's a thread about it over at Muff's : http://www.muffwiggler.com/forum/topic-81990-0.html&postdays=0&postorder=asc&highlight=

You can get the exact tempco's from either Synthcube in the US or Thonk in the UK although I think others have been successful with 3300ppm tempco's.
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Thomas_Henry



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PostPosted: Tue Apr 08, 2014 9:32 am    Post subject: Reply with quote  Mark this post and the followings unread

If you check the exponential relationship, you'll see that 3300 is a better fit. I only used 3500 because that's what I had. Either will work acceptably, though.
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