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 Forum index » DIY Hardware and Software » YuSynth
YuSynth Minimoog Documentation
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camelneck



Joined: Sep 27, 2008
Posts: 68
Location: KY (USA)

PostPosted: Thu May 28, 2009 11:28 pm    Post subject: YuSynth Minimoog Documentation Reply with quote  Mark this post and the followings unread

I just wanted to let everyone know that I found an error in the Minimoog documentation posted on YuSynth's website. Both the schematic and the BOM have Pot "P4" (Frequency Cutoff pot) listed as a 10K linear pot. However, YuSynth's wiring diagram shows a 50K Linear pot wired as the Frequency Cutoff pot.

Since the original Minimoog schematics show the value of this pot to be 10K (as well as YuSynth's BOM & schematic) I'm sure that 10K linear is the correct value. (Unfortunately, I discovered this mistake a little too late though. I referenced the wiring diagram when I went to order my pots so I ordered 2 50K Lin instead of 1 50K Lin and 1 10K Lin.)

I'm also sure that many people who have bought the Bridechamber PCB have spotted the discrepancy involving the 4 ladder capacitor values. They are marked as 22nF on the PCB, while YuSynth's documentation calls for 47nF. However, what makes this matter even more confusing is that neither of these values agree with the official Minimoog schematics, which calls for 4 68 nF capacitors. (Shouldn't a clone use the original capacitor values?)

Although I'm sure the filter can be adjusted to work with all 3 values, I'm curious as to why there are all these discrepancies? Is it due to the fact that different transistors are used?

If so, I might rebuild mine with the original TIS97 transistors. BTW, why weren't the original TIS97 transistors used since they can still be easily and cheaply obtained?
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yusynth



Joined: Nov 24, 2005
Posts: 1233
Location: France

PostPosted: Fri May 29, 2009 5:28 am    Post subject: Re: YuSynth Minimoog Documentation Reply with quote  Mark this post and the followings unread

camelneck wrote:
I just wanted to let everyone know that I found an error in the Minimoog documentation posted on YuSynth's website. Both the schematic and the BOM have Pot "P4" (Frequency Cutoff pot) listed as a 10K linear pot. However, YuSynth's wiring diagram shows a 50K Linear pot wired as the Frequency Cutoff pot.

This has very little impact on how the filter behaves. Still I will correct the inconsistency on my site.

camelneck wrote:

I'm also sure that many people who have bought the Bridechamber PCB have spotted the discrepancy involving the 4 ladder capacitor values. They are marked as 22nF on the PCB, while YuSynth's documentation calls for 47nF. However, what makes this matter even more confusing is that neither of these values agree with the official Minimoog schematics, which calls for 4 68 nF capacitors. (Shouldn't a clone use the original capacitor values?)

Although I'm sure the filter can be adjusted to work with all 3 values, I'm curious as to why there are all these discrepancies? Is it due to the fact that different transistors are used?

If so, I might rebuild mine with the original TIS97 transistors. BTW, why weren't the original TIS97 transistors used since they can still be easily and cheaply obtained?


The values of the caps actually depends on the brand of transistors in the ladder and considering that you use TIS97 then 67nF is better suited. But for BC547C as in my redesign of the minimoog filter (OK let's not calling it a clone ! it's not a clone anyway) 47nF was giving the best result, as I compared the sound with that of my Minimoog from 1973.

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camelneck



Joined: Sep 27, 2008
Posts: 68
Location: KY (USA)

PostPosted: Fri May 29, 2009 12:25 pm    Post subject: Re: YuSynth Minimoog Documentation Reply with quote  Mark this post and the followings unread

yusynth wrote:
This has very little impact on how the filter behaves. Still I will correct the inconsistency on my site.


I agree that it should have little impact on how this VCF behaves as far as its specs are concerned. Although increasing the resistance of the Frequency Cutoff pot would effectively lower Fc, the value of Fc when the pot resistance is 10K should already be very close to the low end of the audio spectrum (20 Hz). Therefore, increasing the pot resistance above 10K would have little or no effect on the audio output.

On the other hand, It seems to me that if you were to substitute a 50K pot for the original 10K pot, the effective range of the pot would be 1/5 of a rotation. (Since the maximum rotation for most pots are 300 degrees, 1/5 of a rotation is equal to 60 degrees or the distance between 8 and 10 on a scale from 1 to 10.)

Thus, with a 50K pot you would be able to sweep the filter over the entire audio range with just 1/5 of the pot's rotation, while the other 4/5 of the pot's rotation would have no effect on the audio output. (It would just be one huge dead band.) Therefore, this 50K pot substitution has reduced the overall resolution of the Frequency Cutoff control by 80% compared to the way it was before the substitution with a 10K pot.

Although it might not effect the filter's overall specs or what the listener hears, choosing the correct pot (with maximum resolution and no dead band) certainly maximizes the way the filter behaves as far as the musician is concerned and consequently his/her performance.
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yusynth



Joined: Nov 24, 2005
Posts: 1233
Location: France

PostPosted: Sat May 30, 2009 1:54 am    Post subject: Re: YuSynth Minimoog Documentation Reply with quote  Mark this post and the followings unread

camelneck wrote:
yusynth wrote:
This has very little impact on how the filter behaves. Still I will correct the inconsistency on my site.


I agree that it should have little impact on how this VCF behaves as far as its specs are concerned. Although increasing the resistance of the Frequency Cutoff pot would effectively lower Fc, the value of Fc when the pot resistance is 10K should already be very close to the low end of the audio spectrum (20 Hz). Therefore, increasing the pot resistance above 10K would have little or no effect on the audio output.

On the other hand, It seems to me that if you were to substitute a 50K pot for the original 10K pot, the effective range of the pot would be 1/5 of a rotation. (Since the maximum rotation for most pots are 300 degrees, 1/5 of a rotation is equal to 60 degrees or the distance between 8 and 10 on a scale from 1 to 10.)

Thus, with a 50K pot you would be able to sweep the filter over the entire audio range with just 1/5 of the pot's rotation, while the other 4/5 of the pot's rotation would have no effect on the audio output. (It would just be one huge dead band.) Therefore, this 50K pot substitution has reduced the overall resolution of the Frequency Cutoff control by 80% compared to the way it was before the substitution with a 10K pot.

Although it might not effect the filter's overall specs or what the listener hears, choosing the correct pot (with maximum resolution and no dead band) certainly maximizes the way the filter behaves as far as the musician is concerned and consequently his/her performance.


Hi Camelneck

You're wrong on that one, you are missing a point about how the CUT-OFF of the filter works. It is voltage controlled and the CUT OFF pot is a voltage divider connected between the +15V rail (through a very very small resistor with respect to that of the pot) and ground.
As such the voltage at lug is directly proportionnal to the position of the pot wiper and neglecting the 680 resistor we can write
Vw = Vr . (Rw / Rp) with Vw the voltage at the wiper lug, Vr the voltage between the CW lug and CCW lug, Rw the resistor between the wiper lug and the CCW lug (ground) and Rp the total resistor of the pot.
Therefore either with a 10K and 50K pot at the fourth of the wiper run you'll get the fourth of the voltage (and consequently frequency) range, at half-run you'll get half of the voltage range, at three-quarter of the run you'll get three-quarter of the voltage range. And here the change between 10K and 50K has really very low impact, no dead band as you feared.

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yusynth



Joined: Nov 24, 2005
Posts: 1233
Location: France

PostPosted: Sat May 30, 2009 11:37 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi Camelneck,

I have corrected the wiring diagram on my site. The silk-screening will be corrected on the next Bridechamber PCB run.

By the way do you enjoy the sound of this filter ?

Cheers

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Last edited by yusynth on Tue Jun 16, 2009 9:59 am; edited 1 time in total
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camelneck



Joined: Sep 27, 2008
Posts: 68
Location: KY (USA)

PostPosted: Tue Jun 16, 2009 9:16 am    Post subject: Reply with quote  Mark this post and the followings unread

>>I have corrected the wiring diagram on my site. The silk-screening will be corrected on the next Bridechamber PCB run.

By the wat do you enjoy the sound of this filter ?<<

Hi Yves,
Thanks so much for everything. (I was on vacation June 1 - June 13 so that is one of the reasons for this delayed response to your question.)

Anyway, I finally completed the panel wiring on my Minimoog VCF last night and got a chance to test the filter using my Moog Voyager. I opened the VCF all the way on my Moog Voyager and ran the output of the Voyager through the YuSynth Minimoog VCF. Since I also have the analog output break-out box for my Moog Voyager, I was also able to route LFO and Envelope Generator CV outputs from the Voyager to the VCF. (So I basically had a Moog Voyager with a Model D filter although the filter was wired after the VCA instead of before it.)

Although I still need to adjust all the trimpots (I only tweaked the resonance trim so the filter would self-oscillate when the Resonance pot was set on 85%), I was really impressed with the sound of the filter as it was. Although the sound of the Voyager is very similar to the Minimoog, I have never been able to duplicate certain Minimoog Model D sounds, such as its brass sounds, quite to my satisfaction. Well, that was until last night ... . Thanks to your filter, I can now get those killer Model D brass sounds out of my Voyager.

I also tried to emulate some other Model D sounds and I must say that this VCF really "rocks". I'm sure I will like it more once the all the trimmers tweaked properly and I get more familiar with it.

(Although this VCF may sound more like the Model D than the Voyager's VCF this should not be interpretted as a "knock" against the Voyager's more flexible dual filter design. The Voyager's dual filter design is much more flexible and allows one to produce a much wider assortment of sounds than was ever possible on the Model D.)

Also, thanks for the refresher course on "pot dividers". Although I've been an EE for 23 years, I haven't done a whole lot of circuit analysis since I graduated from the university and it was a little embarrassing when I realized that I had overlooked one of the fundamentals. However, asking questions is a big part of the learning process.

Finally, I hope you didn't feel like I was "attacking" your documentation for mentioning the typo regarding the 10K pot. I've read and studied the documentation for most all of your modules posted on your website and I think you do an outstanding job on your project documentation. I certainly wish every PCB Designer held himself to the same standards regarding their documentation.

Again, the filter sounds wonderful and thanks for all of your help!

CN
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yusynth



Joined: Nov 24, 2005
Posts: 1233
Location: France

PostPosted: Tue Jun 16, 2009 10:08 am    Post subject: Reply with quote  Mark this post and the followings unread

camelneck wrote:
Although I still need to adjust all the trimpots (I only tweaked the resonance trim so the filter would self-oscillate when the Resonance pot was set on 85%), I was really impressed with the sound of the filter as it was. Although the sound of the Voyager is very similar to the Minimoog, I have never been able to duplicate certain Minimoog Model D sounds, such as its brass sounds, quite to my satisfaction. Well, that was until last night ... . Thanks to your filter, I can now get those killer Model D brass sounds out of my Voyager.

When I developed this filter I had my Minimoog D sitting beside my workshop and I run comparisons between the true one and mine and I could not hear a significant difference. I am glad you are happy with it ! This is what SDIY is all about : building a circuit and be happy with the sound it produces Smile

Quote:
Also, thanks for the refresher course on "pot dividers". Although I've been an EE for 23 years, I haven't done a whole lot of circuit analysis since I graduated from the university and it was a little embarrassing when I realized that I had overlooked one of the fundamentals. However, asking questions is a big part of the learning process.

Finally, I hope you didn't feel like I was "attacking" your documentation for mentioning the typo regarding the 10K pot. I've read and studied the documentation for most all of your modules posted on your website and I think you do an outstanding job on your project documentation. I certainly wish every PCB Designer held himself to the same standards regarding their documentation.

No it's alright, as a matter of fact I appreciate that people let me know about typos or discrepancies in the content of my documentation, it helps me improve it.
Wink

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