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 Forum index » DIY Hardware and Software » YuSynth
Need help with YU-Synth Arp 4072 VCF
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ericcoleridge



Joined: Jan 16, 2007
Posts: 885
Location: NYC

PostPosted: Tue Mar 25, 2008 1:02 pm    Post subject: Need help with YU-Synth Arp 4072 VCF
Subject description: Anyone know Pin-out of 2SA798? Their orientation in this layout?
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The datasheet I have for the 2SA798 is in japanese, and its hard to tell from which orientation the pins are numbered.

I'm just rtying to figure out which way they fit into the YU-Synth Arp 4072 VCF PCB pattern:

http://yusynth.net/Modular/EN/ARPVCF/index.html
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numbernone



Joined: Aug 16, 2006
Posts: 477
Location: new york city

PostPosted: Tue Mar 25, 2008 1:35 pm    Post subject: Reply with quote  Mark this post and the followings unread

I spent many hours tearing out my hair figuring out the pins for this thing. But I did get it right eventually.

Lemme see, this is gonna be a very UNprofessional description.

The center pin (#3) is the center lead in the schematic item for the 2sa798. The OUTSIDE pins (#1 and #5) are the ones in the center of each transistor(I forget if this is E B or C!!! The part the arrow is pointing at), then the middle 2 (#2 and #4) are the outside leads on the schematic.

Jeez did that make any sense??? anyhow this is the way I used it for the 8038 osc, and it works!! I figured it out by tracing the signal thru that filter, let us know how it is cuz I have a pile of these trannies.
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guitarfool



Joined: Feb 26, 2007
Posts: 156
Location: Maryland
Audio files: 8

PostPosted: Tue Mar 25, 2008 1:55 pm    Post subject: Reply with quote  Mark this post and the followings unread

If you have the same type of package (5 pin inline, I don't recall the "T" number) it shouldn't matter. The center pin is the common emitter, and the outside pins (1 & 5) are the collectors. If you put it in "backwards", you'd just be swapping the transistors. However, I've been known to be wrong Embarassed

I just acquired a crapload of these and was planning on building a couple of those myself. I have 2 of the EFM PCB 4072 filters (with the mods that Yves did) on dotcom panels in my system already, but I think they would sound better with Yves' board layout and the matching in the 2sa798.
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ericcoleridge



Joined: Jan 16, 2007
Posts: 885
Location: NYC

PostPosted: Tue Mar 25, 2008 2:36 pm    Post subject: Reply with quote  Mark this post and the followings unread

guitarfool wrote:
The center pin is the common emitter, and the outside pins (1 & 5) are the collectors. If you put it in "backwards", you'd just be swapping the transistors.


This makes sense. It must be why there is no mention of orientation in any of the documentation. I was thinking, yu-synth is always so thorough, how could he have forgot to include this detail?? It must be that it doesn't matter.


guitarfool wrote:

I have 2 of the EFM PCB 4072 filters (with the mods that Yves did) on dotcom panels in my system already, but I think they would sound better with Yves' board layout and the matching in the 2sa798.


Hmm, does this mean they don't sound that great?

Last edited by ericcoleridge on Wed Mar 26, 2008 2:22 pm; edited 1 time in total
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guitarfool



Joined: Feb 26, 2007
Posts: 156
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Audio files: 8

PostPosted: Tue Mar 25, 2008 4:36 pm    Post subject: Reply with quote  Mark this post and the followings unread

ericcoleridge wrote:
Hmm, does this mean they don't sound that great?


No, they sound pretty good, I just can't stop building modules Shocked

The cardboard box visible at the bottom is another 22-space dotcom cabinet I just got via UPS today Very Happy


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Etaoin



Joined: Jun 30, 2005
Posts: 760
Location: Utrecht, NL

PostPosted: Tue Mar 25, 2008 11:11 pm    Post subject: Reply with quote  Mark this post and the followings unread

guitarfool wrote:
I have 2 of the EFM PCB 4072 filters (with the mods that Yves did)


There was a problem with those mods as well. I send Yves a correction some years ago which he acknowledged but never put online I think.

Check the red line on the modded board here: http://www.dompselaar.org/VCF7tracks.jpg
You'll notice it starts at U1 pin 1, goes through CE and EC of two transistors and ends up at pin2 of U1, which is a different opamp. Should have been either pins 1 and 6 or pins 2 and 3.

I redrew the whole PCB and found the sound decent enough. Here's a sample with the wrong caps still in: http://www.casia.org/modular/efmvcf7.mp3 (560pF ceramic caps instead of decent 470pF ones).

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yusynth



Joined: Nov 24, 2005
Posts: 1214
Location: France

PostPosted: Wed Mar 26, 2008 1:37 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi

The 2SA798 has a palindrome pinout therefore you can install it either ways,
the pinout is B1 C1 E C2 B2.

Concerning the EFM mods I removed these from my site long ago because I thought Tom Gamble would have corrected his pcb design and therefore this was no longer useful and also because I was designing my own yusynth ARP filter...

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Last edited by yusynth on Tue Jan 06, 2009 6:42 am; edited 1 time in total
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ericcoleridge



Joined: Jan 16, 2007
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Location: NYC

PostPosted: Thu Mar 27, 2008 12:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for the help; I got my 4072 up and running, and I think it sounds pretty darn good. I had an Odyssey with a 4075 filter at one time, and there is something about this filter that sounds familiar: when the cutoff is very low, the sound not only gets darker, but sounds like it is moving further away, or deeper into a closet. This was always how I described the filter on the Odyssey, and I can hear it on this filter as well. To each his own, right?

Theres one thing that sounds a little strange to me though (and I hope I haven't discredited my ears with that description above); There seems to be a strange slope thing happening around the middle of the cutoff pot. It sounds like one peak/slope is going down while another is rising-- and right at that point it sounds like there are two seperated cutoff slopes, like two filters moving at once. It also creates a little dip in the middle of the pot travel. Is this a weird artifact of something I did wrong when assembling this filter?
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yusynth



Joined: Nov 24, 2005
Posts: 1214
Location: France

PostPosted: Thu Mar 27, 2008 12:47 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi Eric

Did you install all the straps ? There are 8 of them, and at least four of them are involved with a given pole of the filter, if one strap is missing it could make a pole not behaving...

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ericcoleridge



Joined: Jan 16, 2007
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PostPosted: Thu Mar 27, 2008 8:27 pm    Post subject: Reply with quote  Mark this post and the followings unread

yusson wrote:
Hi Eric

Did you install all the straps ? There are 8 of them, and at least four of them are involved with a given pole of the filter, if one strap is missing it could make a pole not behaving...


I did put them all in, but maybe they aren't soldered in properly. I'll double check. Thanks!
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Luka



Joined: Jun 29, 2007
Posts: 1002
Location: Melb.

PostPosted: Mon Nov 17, 2008 4:41 pm    Post subject: Reply with quote  Mark this post and the followings unread

hi peeps
the ever long quest to work out bugs in my backlog is continueing
2 fixed so far 2 modules to go!

im getting strange behaviour with my arp 4072
i think the cv is having some quirks

first the symptoms

with no cv inputs, 10v square wave being fed through with audio input #1 not attenuated
i get no signal
when i turn up the resonance i get signal, maximum signal pass through is when resonance is 5/10, more than that and it drops away again
frequency responce is not functioning

i measure a 2.3v offset on the output and no signal (unless when resonance is up to 5, and i get the 2.3v offset and the signal)

my cv lines at the juntion before the Q6 is trimmed to 0v when no cv input
however the cv sum at the output of Q6 running to the input of all the 2sa798 in the poles is about -7v.
in fact when i sweep the frequency pot is ranged from -7.12 to -6.98

this was a clean etch and clean build so im wondering where my error is.
ive swapped tl074 to no effect and ive checked over my traces.
perhaps these symptoms can help someone point me in the right direction

thanks

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yusynth



Joined: Nov 24, 2005
Posts: 1214
Location: France

PostPosted: Tue Nov 18, 2008 12:53 am    Post subject: Reply with quote  Mark this post and the followings unread

Luka wrote:

my cv lines at the juntion before the Q6 is trimmed to 0v when no cv input
however the cv sum at the output of Q6 running to the input of all the 2sa798 in the poles is about -7v.
in fact when i sweep the frequency pot is ranged from -7.12 to -6.98

These values don't seem wrong, the fact that you have negative values at the emitters of the the 2SA798 is not surprising because the LM3900 are fed with a negative supply.
I will do some measurements tonight to give you clues.

Luka wrote:
this was a clean etch and clean build so im wondering where my error is.

You're entitled to think so but did you have it double-checked by somebody else than you ? We are all blind to our own mistakes Wink Please PM me photos of the PCB (track and component sides).

Also did you check for micro shortcuts between tracks ? I experienced a few time this problem with PCBs that looked cleanly etched but were not behaving, in fact there was a hardly visible short-cut between tracks that I eventually detected by checking with a continuity tester.

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Luka



Joined: Jun 29, 2007
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PostPosted: Tue Nov 18, 2008 4:08 am    Post subject: Reply with quote  Mark this post and the followings unread

ill have some photos tomorrow yusson, i just have to wait for my housemate to come home so i can use his iphone
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problemchild
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yusynth



Joined: Nov 24, 2005
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Location: France

PostPosted: Tue Nov 18, 2008 11:54 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi

As promised I measured the voltage at the collector of Q6 on my ARP 4072 clone and as expected the voltage varies from -7V to -6.9V when tweaking the frequency knob from minimum to maximum. Therefore the voltages you measured are as expected.

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Luka



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PostPosted: Tue Nov 18, 2008 3:19 pm    Post subject: Reply with quote  Mark this post and the followings unread

that is great news
thanks yusson

ill take some more readings at the output summing sections around the poles

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yusynth



Joined: Nov 24, 2005
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PostPosted: Sun Nov 23, 2008 3:00 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi Luka

Here are some checks that you can do with a scope.
In the figure below, four measurements points are shown, they correspond to the output of each filtering pole (output pin of the Norton amp stages).

All the measurements will be done with a square signal with a frequency around 800Hz with an amplitude of 8Vpp.


ARP-test-points.jpg
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Test points A,B,C,D : they correspond to the output pins of the Norton amp stages (pins 4,5,9,10 of LM3900)
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yusynth



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PostPosted: Sun Nov 23, 2008 3:08 am    Post subject: Reply with quote  Mark this post and the followings unread

Now setting the resonance pot to min (fully counter-clockwise) and the frequency pot to max (fully clockwise) this is what yould get (DC mode of the scope) : the upper trace is the input signal and the lower trace is what you get at the measurement point A,B,C,D. Normally, you should get a slightly trapezoidal square signal with a 5Vpp amplitude with an DC offset of -7.5V


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yusynth



Joined: Nov 24, 2005
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PostPosted: Sun Nov 23, 2008 3:14 am    Post subject: Reply with quote  Mark this post and the followings unread

Now setting the frequency pot to mid-range (12 o'clock), this is what yout get at the different poles : A) rising and falling log ramps B) roughly triangular signal C) triangle with smoothed peaks D) nearly sinewave.
The amplitude diminishes between the each poles and the amplitude of the last pole is roughly 3Vpp balanced around -7.5V. Because the signal is small if your scope is DC mode, these can be observed using the AC mode.

OK check these and let me know what you actually obtain at the four measurement points.

Cheers

Yves


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Luka



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PostPosted: Sun Nov 23, 2008 3:16 am    Post subject: Reply with quote  Mark this post and the followings unread

thanks!
i'll check over it now

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Luka



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PostPosted: Sun Nov 23, 2008 3:56 am    Post subject: Reply with quote  Mark this post and the followings unread

with res at 0

A - no square wave, -0.72v offset
B - no sqaure wace, -14v offset
C - same as B
D - no square wave, -7v offset

same result with res at 5


i have signal up until the 100k resistor coming out of the first summing amp
i might try change that resistor and see if it is just blown

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yusynth



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PostPosted: Sun Nov 23, 2008 4:02 am    Post subject: Reply with quote  Mark this post and the followings unread

Why do you mention resonance here ?
The series of measurements concern the frequency pot not the resonance pot that should be left to 0 in all cases.
Did you use the frequency pot at 10 (fully clockwise) ?

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Luka



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PostPosted: Sun Nov 23, 2008 4:10 am    Post subject: Reply with quote  Mark this post and the followings unread

sorry i quickly read through and though you mentioned changing resonance
yes frequency at 10


i just changed that resistor and it did nothing
i still cannot see any signal past the 100k leading to Q1


sweeping the freq knob from 0 to 10 does nothing at every pole
perhaps my lm3900 is out?

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yusynth



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PostPosted: Sun Nov 23, 2008 4:16 am    Post subject: Reply with quote  Mark this post and the followings unread

Luka wrote:
sweeping the freq knob from 0 to 10 does nothing at every pole
perhaps my lm3900 is out?


Yes I think so... Crying or Very sad

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Luka



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PostPosted: Sun Nov 23, 2008 4:18 am    Post subject: Reply with quote  Mark this post and the followings unread

ahh well then that is GREAT!
i hope it is that easy!!

unfortunately i dont have any spare
but ill get one tomorrow and have a check

thank for your time and effort yves

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problemchild
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Luka



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PostPosted: Sun Nov 23, 2008 4:23 am    Post subject: Reply with quote  Mark this post and the followings unread

hey what do you know!

checked over my spare parts and found an lm3900 deep in a bag
chucked it in and it worked no probs

woot!!

this filter sounds amazing

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