Ensoniq SD-1 32 Clipping Noise

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rundgrenrules
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Ensoniq SD-1 32 Clipping Noise

Post by rundgrenrules » Fri Apr 16, 2021 1:13 am

Hello everyone, this is my first post!

Years ago I inherited an old Ensoniq SD-1 that used to belong to my uncle. He was a working musician who passed away coming home from a gig in '93 when I was very young. The SD-1 was his last purchase and it was certainly state of the art at the time. It was the first keyboard I learned to play on, but I had always assumed I didn't like the sound. That was before learning that I LOVE the sound of digital keys from this time period. Needless to say it has quite a bit of sentimental value.

I finally pulled it out, reglued some of the lifted face plate plastic, and re-capped both the power supply board and main board along with the battery.

I was hoping the re-cap would take care of some nagging clipping I am getting on certain sounds, but no dice. This sound doesn't seem to occur on every sound, but on the sounds it does it is quite apparent (at least to me). I have linked an MP3 sample of the sound on the preset it occurs most audibly:

https://soundcloud.com/user-314957032/e ... ise-sample

You can hear that the lower frequency / higher amplitude notes produce this clipping more than the higher notes.
Does anyone know what rabbit hole I can embark down to try and get this sound outta there?

Thanks all

blueknob
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Re: Ensoniq SD-1 32 Clipping Noise

Post by blueknob » Fri Apr 16, 2021 7:19 am

I have a SD-1, I kinda recognise that particular patch. I've had a listen to your audio clip and on my laptop it seems ok. Tell me what patch you are using, choose one from the ROM banks 0 - 1 as then I can find the exact same sound on mine.

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Re: Ensoniq SD-1 32 Clipping Noise

Post by rundgrenrules » Fri Apr 16, 2021 2:56 pm

Its on Page 1 of the factory presets and its called DEEP-TINES. I took the reverb that comes with the patch off for a better sample of the noise. If you have headphones you should be able to hear the clipping on my sample. Might not come through on a phone or laptop speakers.

Thank you!

blueknob
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Re: Ensoniq SD-1 32 Clipping Noise

Post by blueknob » Sat Apr 17, 2021 8:10 am

I've now given your audio clip a listen on better speakers and can hear the "fizz" you speak of. I have RM11- DEEP-TINES setup on my SD-1 which is at hand. Mine doesn't have any fizz so we need to investigate.

My suggestions are:
I've turned off the FX for each of the 4 parts DEEP-TINES uses, Select Voice - select a part, EPNO-HARD, then press Output twice to see Destination Buss = DRY

Then I switched off the 3 parts, "double click" the button (above/below) and that will put brackets around the part thus, (EPNO-HARD) those parts are now mute. It's also possible to Solo that part by triple clicking, but that is less predictable; *EPNO-HARD* is soloed. Give each part a close listen. Listen for fizz at any volume level, or fizz just on loud signal. Does it fizz on low volume signals?

Then it is worth trying sending each part to the Aux buss:
EPNO-HARD, the press Output twice to see Destination Buss = AUX, obviously this needs the rear panel audio connections changed over to Aux Output. Maybe better not to use headphones at this point, but could be useful later.

From what I recall, the SD-1 uses two TDA1471 DACs, (I forget the exact part number) - one for the main and another for the Aux output.

Maybe by experimenting with those it might be possible to get closer to the source of the problem. From what I remember the circuits after the DAC are the same, just normal circuits using good spec opamps. Ensoniq used good quality components.

If possible list on which Sounds/Instruments you hear this fizz.

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Re: Ensoniq SD-1 32 Clipping Noise

Post by rundgrenrules » Sun Apr 18, 2021 5:34 pm

OK I performed all of the tests you described to try and isolate the source of the clipping. Each voice was soloed and tested dry through the master outputs and then through the AUX outputs. Each voice displays the clipping, both EPNO SOFT and EPNO HARD.

I also did extensive testing to see which presets display the clipping. It seems the modeled acoustic piano sounds are by and large free of this clipping, but the tine presets and some of the warmer strings and brass obviously display this clipping. It could be that the clipping is present in some degree on all presets but due to the nature of some of the sounds it is much less obvious. Im not completely sure. Anyways, here are the presets that I can most audibly detect the clipping:

INTERNAL BANK:
SQUARE PAD
DEEP TINES
QUARTET
CELLO
CHICAGO
JAZZ GUITAR
NU-BEL
808

RM BANK:
ZIRCONIUM
WONDERS
NEW PLANET
DANGEROUS
FUNKY CLAV
WARM TINES
METAL TINES
BIG PIANO
CLASSIC PIANO
WOOD FLUTE
FRENCHORN
TOP BRASS
SYNTH HORNS
SMAK BASS
BEBOP BASS
SYNTHBASS
REEL STEEL
SPANISH GUITAR

I wonder if tracing down some replacement DAC or op-amps would be worth it to try? I wish they had used sockets on these chips, would have been easier to pop a new one in....

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Re: Ensoniq SD-1 32 Clipping Noise

Post by blueknob » Sun Apr 18, 2021 8:58 pm

hmm.. :? some interesting results there! I shall have to ponder my crystal ball. Maybe wait up on swapping chips the TDA chips are sought after by Hi-Fi nuts (there's some chinese fakes too). I need to dig out some circuits to check if there are two TDA chips, one for Main and Aux outputs. I remember they are serial data in, possibly muxed stereo output... need a cct. :geek:

After a quick look around in VSE:
Mr R is "the man" - here's the Service Manual viewtopic.php?f=5&t=31971&start=60#p781027 - yeh see page 18, this is the exact document we need. (pushes a beer over to Mr R in thanks) See top of page 20 :o that will be a component fix.

Having a quick read of the Service Manual, it might be possible to do a "reset" - worth doing, I think it deletes the sequencer OS, it can be reinstalled later, comes on a floppy anyway. OmniFlop (see Mr R)
The VFX schematic only has one stereo pair out and a different DAC to the TDA as used in other Ensoniq kit. I wonder what the circuit is for the SD-1, need to look inside for the TDA chips or some other DAC.

I'm just thinking, how about giving us a photo of the circuit board so we can try and identify the DAC. If the "charge pump" is faulty, it's gonna be difficult finding it without a circuit. It would be good if someone has already fixed this to help us out. A charge pump is no big deal, designed them myself, it's a matter of finding it in the SD-1.

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Re: Ensoniq SD-1 32 Clipping Noise

Post by rundgrenrules » Mon Apr 19, 2021 6:41 pm

It is interesting that the service manual seems to point to the charge pump specifically for this type of issue. I did do a factory reset (no change in the issue) and I have the latest sequencer OS coming in the mail. I haven't used the sequencer yet so no rush there.

I will pop the synth back open and take a picture soon!

blueknob
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Re: Ensoniq SD-1 32 Clipping Noise

Post by blueknob » Mon Apr 19, 2021 8:07 pm

*more beer gets sent to Mr R* just found on his website the circuit for the SD-1 (thanks) and there I see two TDA1541A DACs. I'm familiar with these boys, if the power rails are in good order, should be ok.

I can't see a (singular) charge pump circuit, doesn't jump out at me but... I wonder about the mute, Q10 on sheet 2. I'd have to have a poke around that chap. C69 33uF needs a looking at. This type of circuit can go a bit wonky.

Hmm.. the DACs have a row of capacitors C79-C85 & C109-C115 100nF now those do handle charge. It would mean both DACs suffer from the same problem, maybe a bad batch of capacitors? Or maybe unbeknowngly wrong types fitted.
I'd have two options, open up my SD-1 and see what type of caps are fitted (square white ones I remember :lol: ) and look at the data sheet for the exact spec. They are easy enough to exchange if done carefully.
Maybe a closeup of the DAC and the caps might give clues. The caps are usually all lined up in a row aside the TDA chip. They won't look bad, but I can compare.

These would be my first swapsies. :D

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Re: Ensoniq SD-1 32 Clipping Noise

Post by rundgrenrules » Tue Apr 20, 2021 3:21 am

Here are the pictures!

You can see the picture of the power board there is a little scorching near the power transistors on the board. Don't know if that matters, but its there. I couldn't upload the images no matter how much I reduced the size, so I had to upload them elsewhere. C69 is a brand new electrolytic along with all the other main board and PSU board electrolytics.

https://ibb.co/SN96C39
https://ibb.co/mGsvpsv
https://ibb.co/pKg2T8g
https://ibb.co/BZyHnYB

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Re: Ensoniq SD-1 32 Clipping Noise

Post by blueknob » Tue Apr 20, 2021 6:56 am

Thanks, those are very good photos. Ah.. not the white square ones but the blobs on a stick. For me now it's one of those moments in time, decisions. As much as it seems unlikely the blobs can cause this find of fault, I have no other explanation. There might be someone else, Mr R maybe who is familiar with these boards who is able to pass comment.
It's never a good idea to just swap parts without being really sure, if this board was mine, the capacitors are easy enough to swap causing minimal damage to the PCB. So I'd get the data sheet look for the spec for the caps, get the spec for the blobs, compare and buy some in, take time and swap 'em. Obviously do one DAC see if that fixes the prob.

The power supply by the voltage regulators do tend to get a little fried and burnt. It's a matter of checking and rebuilding any weak joints/tracks/traces. Ensoniq were good at manufacture as these photos show.

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Re: Ensoniq SD-1 32 Clipping Noise

Post by rundgrenrules » Wed Apr 21, 2021 2:52 pm

I COULD go in and replace these caps, but man oh man....these PCBs are a bit eager to let a pad come off in the replacement process. I have a good desoldering station and am very careful, but in replacing all the electrolytics I had to scrape some solder mask off and manually bridge several caps due to lifted pads.

Based off of what you’re saying, it seems unlikely to me that BOTH DACs would display the exact type of clipping anyways. The issue has to be coming from somewhere upstream, like the charge pump. Do we know what the charge pump feeds? I would like to try to isolate those charge pump components for checking.

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Re: Ensoniq SD-1 32 Clipping Noise

Post by rundgrenrules » Thu Apr 22, 2021 9:04 pm

Alternatively, does anyone know of a good tech who works on Ensoniq synths? I'd hate to spend the money to ship and repair but I'd really like to get this noise cleaned up!

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