907. Schematic ...faults ?

System 55 • System 35 • Model 15
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Rarecomponentadsr
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907. Schematic ...faults ?

Post by Rarecomponentadsr » Tue Oct 13, 2020 12:42 pm

I know there are one of two schematic errors in the 914 ..mainly resistors.

Does anyone have any knowledge of any errors in the 907 schematic?

My cloned 907 with inductors has been in use for a couple of years but Ive never been totally satisfied with it.
I cut the R43 which attenuates the signal to ground which woke up the output considerably but the description of adding padders and also no value resistors (to tune) are a little vague.

Also, regarding tuning, is it feasible to tune by ear using a modern clone such as the Behringer 914 as comparison ?

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MRNUTTY
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Re: 907. Schematic ...faults ?

Post by MRNUTTY » Wed Oct 14, 2020 7:49 am

Rarecomponentadsr wrote: Tue Oct 13, 2020 12:42 pm I know there are one of two schematic errors in the 914 ..mainly resistors.

Does anyone have any knowledge of any errors in the 907 schematic?

My cloned 907 with inductors has been in use for a couple of years but Ive never been totally satisfied with it.
I cut the R43 which attenuates the signal to ground which woke up the output considerably but the description of adding padders and also no value resistors (to tune) are a little vague.

Also, regarding tuning, is it feasible to tune by ear using a modern clone such as the Behringer 914 as comparison ?
Do you mind providing a pointer to these 914 faults? I would like to check it out as I go through the Behringer 914. What I have so far is - replace the pots. Lol :-)

Found this schematic with annotation that sounds like what you're talking about http://analoguerealities.com/wp-content ... -notes.pdf
VoyagerEB, Minitaur, LittlePhattyII, 4xSlimPhatty, Sub37, MF[2x101,2x102,103,104M,105,105B,105M,2x107,108M], 3xCP251, XV351, MP201;
System 55 and Minimoog clones, personally modified to bring them closer to OG spec(s).

Rarecomponentadsr
Posts: 99
Joined: Mon Aug 24, 2015 5:08 pm
Location: Derbyshire England

Re: 907. Schematic ...faults ?

Post by Rarecomponentadsr » Wed Oct 14, 2020 5:15 pm

Yes...that’s the main source of schematic error / additions.

However, the author specifies that a lot of these changes are assumptions and guess work as well some serious work he has put in.

I have collected quite a few images of the interiors of 907 and 914 but
working out what component is what is immensely difficult.

So far no mention of any known 907 schematic errors anywhere.

I have built Yu Synths 914 clone and to my ears this is an excellent clone.
But how close the original I simply don’t know.

I have some rough recordings I made of a very dirty genuine Moog 914 but they are random samples.

I too am awaiting delivery of the Behringer 55 914 and hope to use it as a “tuning “ master for my 907 as Behringer state it’s as close to the original as possible. Close inspection and samples from an original 907 would be extremely helpful.

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MRNUTTY
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Re: 907. Schematic ...faults ?

Post by MRNUTTY » Wed Oct 14, 2020 11:06 pm

I have two Behringer 914's. The are RC designs with passing similarity to Norlin service manual - the canonical first reference I guess.

That being said, the only issue I have with it are the potentiometer's. It sounds like an SMT RC Design should sound. I haven't checked the individual CF's, but there's about a 6db drop when it's wide open, about what the spec says. Once I get the circuits fleshed out - the fun can begin. I always wondered what installing chokes would do for one of these cheapies. They're cheap enough to burn on experiments alone!

I'll check the CF's tomorrow. Got a long list of fixes and stuff to check on this kit; knobs to change, switches to install, good stuff. Wish the panel finish was a bit thicker.
VoyagerEB, Minitaur, LittlePhattyII, 4xSlimPhatty, Sub37, MF[2x101,2x102,103,104M,105,105B,105M,2x107,108M], 3xCP251, XV351, MP201;
System 55 and Minimoog clones, personally modified to bring them closer to OG spec(s).

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MRNUTTY
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Re: 907. Schematic ...faults ?

Post by MRNUTTY » Thu Oct 15, 2020 11:48 am

Here's the CF's for the one I just modified. I'lll check my other one out later too for you. Measurements are in Hertz.
625B3D88-0183-42D8-8C1F-D9E2B1EF7775.jpeg
VoyagerEB, Minitaur, LittlePhattyII, 4xSlimPhatty, Sub37, MF[2x101,2x102,103,104M,105,105B,105M,2x107,108M], 3xCP251, XV351, MP201;
System 55 and Minimoog clones, personally modified to bring them closer to OG spec(s).

Rarecomponentadsr
Posts: 99
Joined: Mon Aug 24, 2015 5:08 pm
Location: Derbyshire England

Re: 907. Schematic ...faults ?

Post by Rarecomponentadsr » Fri Oct 16, 2020 6:04 am

Thanks for posting this

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MRNUTTY
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Re: 907. Schematic ...faults ?

Post by MRNUTTY » Sat Oct 17, 2020 10:33 am

Rarecomponentadsr wrote: Fri Oct 16, 2020 6:04 am Thanks for posting this
If you need a 2nd measurement, I have another I haven't modified yet that I can take measurements from as well.
VoyagerEB, Minitaur, LittlePhattyII, 4xSlimPhatty, Sub37, MF[2x101,2x102,103,104M,105,105B,105M,2x107,108M], 3xCP251, XV351, MP201;
System 55 and Minimoog clones, personally modified to bring them closer to OG spec(s).

Rarecomponentadsr
Posts: 99
Joined: Mon Aug 24, 2015 5:08 pm
Location: Derbyshire England

Re: 907. Schematic ...faults ?

Post by Rarecomponentadsr » Sat Oct 17, 2020 6:09 pm

The Behringer 914 came yesterday and I’ve done some quick ear tests.

Initial conclusion is that my 907 High Pass section is not functioning correctly as compared to the Behringer.
However it seems that the low pass and band pass sections are not that far off.
Shortly I’ll take the 907 out and try some of the modifications suggested on the 914 schematic “update “ and compare frequencies of the band pass sections as well as fixing the High Pass which at the moment is totally lacking in top end.

I note the weak output of the Behringer 914 and wonder if it is in keeping with the original Moog 914 ?

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MRNUTTY
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Re: 907. Schematic ...faults ?

Post by MRNUTTY » Sat Oct 17, 2020 6:59 pm

The level difference really isn't all that much I think It's only 6db down and a CP mixer will boost that easy. I'm working with a mixed Mutable and Behringer System 55 module set. The headroom is less on the behringer stuff, but it doesn't really take much gain staging to get good results.

The 914 is better if you replace all the pots with ALHPA brand.
VoyagerEB, Minitaur, LittlePhattyII, 4xSlimPhatty, Sub37, MF[2x101,2x102,103,104M,105,105B,105M,2x107,108M], 3xCP251, XV351, MP201;
System 55 and Minimoog clones, personally modified to bring them closer to OG spec(s).

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