Incoming project: HVM for Eurorack

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Synthbuilder
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Incoming project: HVM for Eurorack

Post by Synthbuilder » Thu Jun 27, 2019 7:05 am

It's a fixed filter bank with the same set of circuitry used in the bigger HVM modules.

http://www.oakleysound.com/hvm-e.htm

Pictures and full documentation to follow in the next few days.

Tony

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Post by Synthbuilder » Thu Jun 27, 2019 8:13 am

And here it is, up against its older 5U brother:

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Post by basicbasic » Tue Jul 09, 2019 11:07 pm

While i'm anxiously waiting on a few parts to finish this off I wanted to mention a couple of things:
1. Goddamn this is a lovely PCB to work on. Generous pads, clearly labelled. I normally do SMD somewhat begrudgingly but this is a pleasure.
2. Would it be possible to get some sketches of how to replicate/approximate the VP-3300 presets?

:sb:

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Post by Synthbuilder » Wed Jul 10, 2019 3:24 am

Thank you for the kind comments.
basicbasic wrote:Would it be possible to get some sketches of how to replicate/approximate the VP-330 presets?
At some point in the very near future I hope to finish the User Manual with these very details included in it.

In the mean time this may be of some help.

There were four tabs (presets) on the VP-330. They use different filter settings for all of them but one main difference is that two of them use an audio input that is an octave lower than the other two. The 8' setting is one octave lower than 4'. In the Eurorack version of the HVM it's not possible to use two different octave input signals and have a different setting for each since we only have one set of pots. Unless you have two HVMs that is...

The four tabs are Male 8' (lower), Male 8' (upper), Male 4' (lower) and Female 4' (Upper). The upper and lower refer to the upper and lower parts of the VP-330's keyboard - so you can have one sound on the top half and a different sound on the bottom half.

The Male 8' (lower) and the other two Male voices are quite similar with only a slight change to the operating frequency of the lowest frequency band filter. This was not replicated in the HVM as it was considered to be more useful to have a new 330Hz filter band instead. So don't use the 330Hz output if you want to replicate the sound of the VP330.

For Male 4' (lower) you need to have roughly the following settings (100% is the pot being set fully clockwise), all other pots set to their minimum except level which sets the output volume:

230Hz 30%
600Hz 100%
910Hz 100%
2800Hz 40%

For Male 8' (Upper)

230Hz 40%
600Hz 100%
910Hz 100%
2800Hz 40%

For Female 4':

600Hz 30%
910Hz 100%
1300Hz 80%
3300Hz 40%

All the values are somewhat approximate but seemed to compare well with original. The Male 8' (lower) is similar to the Male 4' (lower) but the original did use a slightly different frequency for its lowest filter so it's not quite possible to replicate this sound exactly.

Tony
Last edited by Synthbuilder on Sat Jul 13, 2019 10:58 am, edited 1 time in total.

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Post by basicbasic » Wed Jul 10, 2019 4:10 am

Hi Tony - thanks for that - exactly what I was hoping for. The remaining parts should arrive tomorrow and I can't wait try those settings out.

Cheers,
Jamie

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Post by Synthbuilder » Sat Jul 13, 2019 11:02 am

I just edited my post about 330's preset tabs. I have now had a chance to compare it to the 330's original preset sounds and updated my post with more accurate settings of the Euro module's pots accordingly.

Tony

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Post by basicbasic » Sun Jul 14, 2019 7:10 pm

Image

All done! Tayda were out of panel mount pots so I had to improvise. I think I prefer the smaller pots anyway for a module so dense. A colleague did the panel in faux-aluminium acrylic as the price for a proper one from FPE to Australia was eye-watering. It looks ok for what it is. I have a spare if anyone else on this side of the world wants it.

Sounds terrific! I was planning to mainly use it with a Roland RS-101 but i'm finding it sounds even better with my Minilogue.

As I mentioned, it was a very enjoyable build!

Image

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Post by Synthbuilder » Mon Jul 15, 2019 2:45 am

basicbasic wrote:All done!
Brilliant! Thanks for sharing the photos.
Tayda were out of panel mount pots so I had to improvise. I think I prefer the smaller pots anyway for a module so dense.
Actually, they do work rather well. The spacing is about as close as I would want to get with the 1900H clone knobs. But then everything feels so small when compared with my normal 5U stuff.
...as the price for a proper one from FPE to Australia was eye-watering.
Ah, that's interesting. It's pretty cheap here in the UK with panels delivered from Germany. I think it was about 30Euros. Maybe it's time I got some panels made and sold those with the boards.
it was a very enjoyable build!
That's really good to hear. Although I designed my first surface mount board in 1988 I haven't been making any for sale to the general public until a year or so ago.

Tony

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Post by basicbasic » Mon Jul 15, 2019 8:44 pm

Synthbuilder wrote:
...as the price for a proper one from FPE to Australia was eye-watering.
Ah, that's interesting. It's pretty cheap here in the UK with panels delivered from Germany. I think it was about 30Euros. Maybe it's time I got some panels made and sold those with the boards.
It worked out to be ~$100AUD to get one panel posted to Australia. From memory the postage may have been more expensive than the panel itself which is why I had to improvise.

Offering panels with the boards would be fabulous, even if they were made of PCB material like Nonlinearcircuits offers.

Thanks again!
Jamie

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Post by basicbasic » Tue Sep 17, 2019 7:33 pm

Just a quick note in case it helps others:

I added a bypass toggle switch to mine (I have a Roland RS-101 permanently patched into it) and there was a large difference in volume between the bypassed and effected signal.

After some experimenting I replaced the feedback resistor on the final op-amp stage (R8 - 22k) with a 220k* resistor so I could better match the levels.

*220k creates more gain that true unity with all bands at max, but in normal use with bands at differing values it seems to give a decent result in matching perceived volumes.

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Post by Synthbuilder » Wed Sep 18, 2019 3:05 am

basicbasic wrote:... there was a large difference in volume between the bypassed and effected signal.
This is true. It's a deliberate design choice for the modular version of the HVM as the expected signal levels in modular systems are greater than those coming from an RS-101. The old rack mounted HVM, which was originally designed for stand alone use, had both input and output level controls.

The 5V peak signal from a modular VCO can easily cause the HVM's output stage to clip with even just a few bands turned up at certain frequencies. One of the really annoying things about modern modular systems is their use of much higher than needed audio signals. I really wish Eurorack VCOs used 2V peak which would give us a lot more headroom before clipping starts, which in Euro is only 9.5V peak.

Tony

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Post by Synthbuilder » Thu Sep 19, 2019 2:46 am

basicbasic wrote:I replaced the feedback resistor on the final op-amp stage (R8 - 22k) with a 220k* resistor so I could better match the levels.
I had a further thought on this. Perhaps it would be better to increase the levels going into the filter bank as well as after. This way you will decrease any noise generated by the filter bank itself. In this case, changing R10 to 100K, and R8 to 47K might work better.

Tony

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Post by basicbasic » Thu Sep 19, 2019 7:39 pm

Hi Tony - thanks for that - i'll have a tinker :tu:

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