Thomas Henry's 8038 VCO stripboard layout

[para]

i figured i'd start a new thread for this.

so i made a nice little compact stripboard layout for Mr. Henry's 8038 VCO. there a few things that need to be mentioned. first he said this is only for us to experiment with so keep it on the board. the image link is to a hidden section of my website so i can easily update it if need be, and there it will stay unless of course Mr. Henry asks me to take it down.


Quote: "Try this on for size. This is something I came up with in a book I wrote three years ago but haven't published yet. I used the AD821 because I had one, but feel free to try another matched pair.

This is for Forum users to play with only. Obviously, don't do anything commercial with it without permission, and please don't Web-publish this anywhere, but provide links back to this message.

Note the unusual power supply connections.

Thomas Henry "



so far its been said that you can use an AD821, a 2sa798 or a pair of matched PNP's such as 2n3906's. on the board i used the 2n3906's but if i did it correctly you can drop in a 2sa798 with no changes ( fingers crossed X ). i couldn't find a datasheet for either the AD821 or the 2sa798, so i'm not sure of that. if someone could let me know that would be great. also does anyone know of another PNP pair that will work?

* make sure that the R3 tempco and the transistor pair are all touching! hard to show in the board, this is why the layout is a little odd.

Scott Stites posted a link to some available 2SA798's here: http://www.electronicsurplus.com/commerce/catalog/product.jsp?product_id=76173&czuid=1074043777995



* notice the three jumpers to the 072. they can be made under the board. i just wanted to make sure you noticed them. also the jumper across pin 7 and 8 of the 8038 is just to remind you not to cut the trace there.


all the filter caps are 10uf and 0.001uf and labeled C-F but i added those myself so it would be nice if someone could confirm those are alright with the odd power scheme Mr. Henry used.


* notice there is plenty of ground space for adding all the pot and jack ground connections. i hate when people make beautiful PCB’s but don’t add any extra ground connections for all the off board components so you end up with an ugly mess. hint! hint!


more of Mr. Henry's notes "One possible mod: try an LF442 for the op-amps. I think they are more stable than the TL072 in expo converters. You can probably reduce the feedback cap at the same time, perhaps to 100pF. Make sure your layout is clean around that area.

About the negative supply: I did this to turn the response around. It works for both linear and expo VCO's with this chip."

* notice the LF442 will drop in and replace the 072 without any changes as well.


i assume you could add a switch to change out C3 the 0.22uf mylar ? cap and switch between AC and DC for the linear FM input. i like having this on the SN-voice.

i wonder if it would be easy to add a sync input to this? any idea's?


i guess i should also point out that this is untested. i should be able to get to it in a couple days. but i spent a lot of time going over this so i'm pretty confident in it.

and thank you Mr. Henry for letting us play with this!!!!


--DUAL- 2n3906 version--







--SINGLE- 2SA798 version--










reference thread
http://electro-music.com/forum/topic-13823.html&postorder=asc

[para]

looks like C1-C4 should all be mylar or poly maybe right?

[Mikmo]

For the 2sa798 transistor pair :

datasheet (kind off ) :

http://www.datasheets.org.uk/Databooks/download.php?code=&q=100&p=42

And if you are in europe Senso from vintage planet has them for euro 1.75
http://www.vintageplanet.nl/index.html

vintage planet is a VERY cool place to look fo anything retro synth related.

[para]

thanks mikmo i checked there already but no pinout, i'm pretty sure its right though. both emitters should be on the center pin right?

i'm in the central states unfortunately, but vintageplanet.com does have some very useful stock. i’ll be restoring a polysix soon and they’re the only place i've found with the led buttons i need. hopefully they will ship the u.s.


steven

[etaoin]

As to the 2SA798 pinout; check Yusynth's ARP VCF, he uses six of them in the filter:
http://www.yusynth.net/Modular/EN/ARPVCF/index.html

[Mikmo]

I'm quite sure Vintage planet will ship to the states, Senso who is running it is a really nice guy, and frequent poster on the Synth DIY mailing list

[para]

thanks Etaoin, that helped a lot. by tracing out that 4072 board it looks like my assumption was wrong. the base's are on the outside - pin 1 and 5, and pin 2 and 4 are the collector. i'll have to work that out when i get a second. i guess if anyone is trying to do this with a 2SA798 now and they will be leaving the leads long anyway, they can just swap pin 1 and 2 with each other and the same with 4 and 5.


good to know Mikmo thanks. now i just have to buy enough stuff to make the shipping cost worth it

[v-un-v]

[para]

i updated the post above and did two different layouts. one for the 2SA798 and one for the dual PNP's

[Senso]

[fluxmonkey]

has anybody built and confirmed this layout?

bbob

[Snaper]

Have somebody the original schematics?
Would like to check the elkos value.

[elmegil]

This appears likely to be the VCO schematic from Thomas' book "The VCO Chip Cookbook". This is available from Lulu.com, though I'm not sure what their international availability might be.

Assuming I've understood correctly and by "elkos" you mean the Electrolytic Capacitors, C5 is 4.7uF, but I have no idea what the several "C-F" caps (of different types even) are supposed to be.

[Snaper]

Thanks Elmegil,

Found the schem. over the net...

http://www.birthofasynth.com/Thomas_Henry/Pages/8038.html

Still don't know that is layout confirmed to work?

[elmegil]

I looked at that but I don't believe it's the same schematic because

1) "audio generator" vs "VCO" -- Thomas is pretty precise in his language

2) the schematic on birthofasynth uses a TL074, and uses all 4 op amps, not a TL072.

[Snaper]

[kalda341]

I stupidly started building this, using the components from TH-8038 on his site, before realizing it must be wrong. Does anyone know where the schematic for this layout is?
Thanks!

[elmegil]