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 Forum index » DIY Hardware and Software » Thomas Henry designs
The Thomas Henry Mega Percussive Synthesizer
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01012k7



Joined: Aug 31, 2013
Posts: 20
Location: England

PostPosted: Thu Apr 10, 2014 1:31 pm    Post subject: Reply with quote  Mark this post and the followings unread

Decided to build another MPS after some one giving me a board so its going into my euro rack so far here a few pictures


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P.S Installing a second power supply 15- ov 15+ for mps, Oakley little LFO,ETC
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jpjsenior



Joined: Jan 04, 2014
Posts: 3
Location: Bristol, UK

PostPosted: Thu Apr 17, 2014 3:30 pm    Post subject: Additional power inputs question
Subject description: MPS J12 and 19 unsure how to wire
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Hi there,

I'm about to embark on building a couple of these and I have a question about something I've not come across before that is a bit basic I think, but as it's concerned with something on the MPS boards I thought I would post it here.
Back on page 24 of this thread kkissinger has kindly made a list of the wiring on the board. It shows J11 as where the main power comes in from the power supply. J12 and J19 also are listed as bringing + and - V in. I'm unsure how this works. From looking briefly over the schematics I'm assuming these additional voltages would be 15v. Am I right in thinking that? Would there need to be separate connections from the PSU for these? Or are they something else and if so can anyone guide me towards some info on how to get everything set up power-wise? I have a +/-15V PSU with a distribution board assembled ready for this project. This issue is the only thing stopping me getting on with the soldering at present so any help would be much appreciated,

Thanks,
Jon
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elmegil



Joined: Mar 20, 2012
Posts: 1536
Location: Chicago
Audio files: 14

PostPosted: Thu Apr 17, 2014 4:59 pm    Post subject: Reply with quote  Mark this post and the followings unread

J11 is power in

J12 is power out to the various pots that need it.

Not sure what 19 was for, mine is in the basement and not convenient at the moment; I could check it out later if you need.
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jpjsenior



Joined: Jan 04, 2014
Posts: 3
Location: Bristol, UK

PostPosted: Fri Apr 18, 2014 8:17 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks man, that makes sense. Gonna spend a bit of time studying the schematic against the boards I reckon before getting started.
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qfactor



Joined: Jul 19, 2010
Posts: 5
Location: Singapore

PostPosted: Sat May 31, 2014 8:39 am    Post subject: Reply with quote  Mark this post and the followings unread

elmegil wrote:
J11 is power in

J12 is power out to the various pots that need it.

Not sure what 19 was for, mine is in the basement and not convenient at the moment; I could check it out later if you need.


I believe if you have version 107 PCB, there is no more J19,20 and 21, right?
So there's no need to hook those up.
My question is Similar to defog's on the use of +-12V instead of 15v. Do I need to change any resistor/cap values for this, or can I go ahead with everything unchanged?

Thankie!
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01012k7



Joined: Aug 31, 2013
Posts: 20
Location: England

PostPosted: Sat Jun 14, 2014 1:55 pm    Post subject: Reply with quote  Mark this post and the followings unread

I would like to take full credit for this project but I cannot my friend wired the thing up and got it working I did make the front panel and drill the holes and solder the parts on the board with I guess some errors Smile


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davebr



Joined: Jun 09, 2007
Posts: 193
Location: portland, or

PostPosted: Thu Nov 20, 2014 6:39 pm    Post subject: Mega Percussive Synthesizer Reply with quote  Mark this post and the followings unread

I just finished building a 2U MPS module. I was greatly influenced by sduck's design and tweaked it to fit my modular style. I bought the XR-2206 at Jameco and everything else at Mouser. I have photos and documentation on my MPS Module page http://modularsynthesis.com/electro-music/mps/th-mps.htm

Dave

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elmegil



Joined: Mar 20, 2012
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PostPosted: Thu Nov 20, 2014 10:13 pm    Post subject: Reply with quote  Mark this post and the followings unread

I'm curious about the reasons for the modifications you listed....
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davebr



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PostPosted: Sun Nov 23, 2014 10:04 pm    Post subject: Reply with quote  Mark this post and the followings unread

elmegil wrote:
I'm curious about the reasons for the modifications you listed....

I'm not sure who you are asking. If it is my modifications it is simply I bought a lot of 100K potentiometers so want to use them whenever possible. There were four 10Ks that were easy to change to 100K. The second mod is I didn't install the volume control but it is one half of the load on the output capacitor to bleed a charge off of it. I increased the load from 20K to 100K just because I wanted a higher DC resistance. The third mod is simply I wanted a manual trigger.

Dave
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elmegil



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PostPosted: Sun Nov 23, 2014 10:56 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yes, I was asking you Smile. Some of us have had issues with low output levels, even on the "Synth" level output, and I was curious if anything you modified was perhaps to address that. Obviously not Smile

Thanks Dave!
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01012k7



Joined: Aug 31, 2013
Posts: 20
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PostPosted: Mon Nov 24, 2014 1:27 am    Post subject: Re: Mega Percussive Synthesizer Reply with quote  Mark this post and the followings unread

davebr wrote:
I just finished building a 2U MPS module. I was greatly influenced by sduck's design and tweaked it to fit my modular style. I bought the XR-2206 at Jameco and everything else at Mouser. I have photos and documentation on my MPS Module page http://modularsynthesis.com/electro-music/mps/th-mps.htm

Dave

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looks bigger then 2u looks like full rack which is it 5u ?? you done a great job . I could be wrong on the XR-2206 I got a military spec part as some the other version have a problem which I been told its down to 15v they run better on 12v but then I could be wrong my friend wired the mps and the other one up I just made the boards which is the easy part.
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01012k7



Joined: Aug 31, 2013
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PostPosted: Mon Nov 24, 2014 1:33 am    Post subject: Reply with quote  Mark this post and the followings unread

My stand alone version runs of the mains


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davebr



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PostPosted: Mon Nov 24, 2014 2:16 am    Post subject: Re: Mega Percussive Synthesizer Reply with quote  Mark this post and the followings unread

01012k7 wrote:
looks bigger then 2u looks like full rack which is it 5u ?? you done a great job . I could be wrong on the XR-2206 I got a military spec part as some the other version have a problem which I been told its down to 15v they run better on 12v but then I could be wrong my friend wired the mps and the other one up I just made the boards which is the easy part.

It is a 5U (height) module, but a 2U wide.

Dave
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davebr



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PostPosted: Mon Nov 24, 2014 2:19 am    Post subject: Reply with quote  Mark this post and the followings unread

elmegil wrote:
Yes, I was asking you Smile. Some of us have had issues with low output levels, even on the "Synth" level output, and I was curious if anything you modified was perhaps to address that. Obviously not Smile

Thanks Dave!

I've noticed I can change the output volume by adjusting the trigger sensitivity. At least to me it sound quieter until eventually it stops triggering. I've found that I really need to leave the trigger sensitivity near 0. I haven't gone through the circuit but it is possible that a narrow output pulse from the comparator could not be fully operating the subsequent circuits. Are all three outputs quiet? From the scope images on my web page the Impact looks like +/-2.2V waveform, shell looks like +/-1.1V waveform although with the ring mod on it is up to +/-2.2V, and noise looks like just over +/-1V waveform.

Dave
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elmegil



Joined: Mar 20, 2012
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PostPosted: Mon Nov 24, 2014 7:41 am    Post subject: Reply with quote  Mark this post and the followings unread

davebr wrote:

I've noticed I can change the output volume by adjusting the trigger sensitivity. At least to me it sound quieter until eventually it stops triggering. I've found that I really need to leave the trigger sensitivity near 0. I haven't gone through the circuit but it is possible that a narrow output pulse from the comparator could not be fully operating the subsequent circuits. Are all three outputs quiet? From the scope images on my web page the Impact looks like +/-2.2V waveform, shell looks like +/-1.1V waveform although with the ring mod on it is up to +/-2.2V, and noise looks like just over +/-1V waveform.
Dave


I'll have to check that, I don't know if I tried that. If I recall correctly, the biggest volume problem was with the shell.

Also: I'd *swear* that Thomas' description on Birth of a Synth says that the Synth level outputs are supposed to be 10Vpp. If I expect them to be closer to line level I wouldn't be so surprised Smile

Not the best time for me to be going and double checking that though...
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davebr



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PostPosted: Tue Nov 25, 2014 12:56 am    Post subject: Reply with quote  Mark this post and the followings unread

elmegil wrote:
davebr wrote:

I've noticed I can change the output volume by adjusting the trigger sensitivity. At least to me it sound quieter until eventually it stops triggering. I've found that I really need to leave the trigger sensitivity near 0. I haven't gone through the circuit but it is possible that a narrow output pulse from the comparator could not be fully operating the subsequent circuits. Are all three outputs quiet? From the scope images on my web page the Impact looks like +/-2.2V waveform, shell looks like +/-1.1V waveform although with the ring mod on it is up to +/-2.2V, and noise looks like just over +/-1V waveform.
Dave


I'll have to check that, I don't know if I tried that. If I recall correctly, the biggest volume problem was with the shell.

Also: I'd *swear* that Thomas' description on Birth of a Synth says that the Synth level outputs are supposed to be 10Vpp. If I expect them to be closer to line level I wouldn't be so surprised Smile

Not the best time for me to be going and double checking that though...

I updated my web page at http://modularsynthesis.com/electro-music/mps/th-mps.htm with scope images of the levels through each of the three sections. I measured at the source, at the VCA, and at the output. The issue is you are summing three sources, so if you want to keep the output at 10V pk-pk you need to keep the individual sections less than that so they add to 10V pk-pk. The Locked feature makes it easy to measure the levels. Impact is the largest at 4.3V pk-pk, Shell is lower at 2.7V pk-pk and noise is the lowest at 1.3V pk-pk. The overall output with all section at max is 8V pk-pk. Remember, these are measured so there will be some variation between builds.

If you want to increase any of the section levels, just decrease the corresponding mixer resistor R90, R91, or R92. These set the gain at the mixer and 200K sets the gain to 1/2. 100K will set the gain to unity (so it will increase the gain of that section by 2X). If you wanted all at equal output then you could adjust the resistors accordingly but the mix seems about right to me.

If you want to keep the mix then simply increase R77. If you increase it to 200K then the output levels will all double.

Dave
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elmegil



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PostPosted: Tue Nov 25, 2014 7:26 am    Post subject: Reply with quote  Mark this post and the followings unread

Thank you very much; I will have to go drag my MPS upstairs and compare....
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davebr



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PostPosted: Tue Nov 25, 2014 12:14 pm    Post subject: Reply with quote  Mark this post and the followings unread

elmegil wrote:
Thank you very much; I will have to go drag my MPS upstairs and compare....

Remember also that if the ring modulator depth is set low then the ring modulator balance affects the shell level output. On mine full CW is louder than full CCW. I put an explanation of that on my site also. I eventually changed the gain of Shell by increasing it 4X and Noise by 2X. Details are on my web page.

I also found that the Impact envelope decay was erratic and added a 51 pF capacitor across R94. The trigger comparator was glitching quite badly and this settled it down. All changes are documented in my Modifications section.

Dave
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elmegil



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PostPosted: Tue Nov 25, 2014 12:50 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yah, I had noted the effects of the ring mod when I was looking at this before.... That explanation helps too though, thank you again.
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elmegil



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PostPosted: Tue Nov 25, 2014 10:28 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks Dave!

While I had noticed that the ring mod affected the shell volume I don't think I fully understood the trigger sensitivity or the ring mod behavior. I may also have the trigger sensitivity pot wired backwards.

With the notes you gave me here, I was able to get quite serviceable volumes out of my MPS. I'm pretty sure I always set the balance full CCW, but I could see on my scope I definitely get a higher signal with it full CW.

I do think the relative levels are still off a bit, so I think I will make the same R90/R91 changes you have noted on your website, but thank you very much for helping me figure out what I was (apparently; been many months now since I had last messed with it) doing wrong.
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elmegil



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PostPosted: Tue Nov 25, 2014 11:34 pm    Post subject: Reply with quote  Mark this post and the followings unread

The bugbrand mps_connections_v1.pdf on page 8 and reposted on page 19 as well as this diagram which was made from that source:

http://electro-music.com/forum/phpbb-files/mps_layout_111.jpg

All appear to have things wired such that rotating the sensitivity pot CW makes it *more*sensitive. While that makes sense from a certain perspective, I'm accustomed to setting trigger sensitivities the other way, where the lowest threshold (and threfore highest sensitivity) is with the pot full CCW.

I think that's another contributor to my confusion about levels. I'd set that full CCW expecting to get the best trigger sensitivity when in fact I was doing the opposite.
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davebr



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PostPosted: Sat Nov 29, 2014 11:46 pm    Post subject: Reply with quote  Mark this post and the followings unread

elmegil wrote:
The bugbrand mps_connections_v1.pdf on page 8 and reposted on page 19 as well as this diagram which was made from that source:

http://electro-music.com/forum/phpbb-files/mps_layout_111.jpg

All appear to have things wired such that rotating the sensitivity pot CW makes it *more*sensitive. While that makes sense from a certain perspective, I'm accustomed to setting trigger sensitivities the other way, where the lowest threshold (and threfore highest sensitivity) is with the pot full CCW.

I think that's another contributor to my confusion about levels. I'd set that full CCW expecting to get the best trigger sensitivity when in fact I was doing the opposite.

You will note that on my page I have the wiring diagram for Sensitivity reversed so the most sensitive setting is CCW. I also changed the nomenclature to Trigger Level since that is what it is. CCW corresponds to 0V and CW corresponds to +5V so it is more intuitive that CCW is the more sensitive setting.

Dave
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davebr



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PostPosted: Sat Nov 29, 2014 11:57 pm    Post subject: Reply with quote  Mark this post and the followings unread

elmegil wrote:
Thanks Dave!

With the notes you gave me here, I was able to get quite serviceable volumes out of my MPS. I'm pretty sure I always set the balance full CCW, but I could see on my scope I definitely get a higher signal with it full CW.

Note that the ring mod balance is asymmetric. R89 sets the output with no audio signal to +7.5V, or the Vcc/2 point. R49 shifts the output of the op-amp by +2.7V / -4.5V so one end of the potentiometer should be louder. The specification calls out for Vcc/2 +/-4V which would be 3.5V to 11.5V. This setup ranges from 3V to 10.2V (if I did the math right). The modulation voltage of course adds to this.

Dave
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