HELP ME REBUILD MY OBXA

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snod_donkey
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Re: HELP ME REBUILD MY OBXA

Post by snod_donkey » Wed Nov 16, 2011 2:02 pm

Tants are also used in many other parts of circuits as stated

The reason they are used is they are a far Superior capacitor than electrolytic due to the way they work.
I am fixing a vintage synth today which has a couple of faulty tants and they are on the charge discharge circuit for the "AD" attack and decay filter envelope. If i put a electrolytic in its place it will change how it works... it will still work but a little different

I would always replace like for like to make sure it works as designed. There is always arguments about tant and electrolytic caps but remember there was a reason the tant was fitted in the first place. Simply buy a brand new modern tant to replace any and stay away from old stock that have been on the shelf for years

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Re: HELP ME REBUILD MY OBXA

Post by madtheory » Wed Nov 16, 2011 6:32 pm

snod_donkey wrote:I would always replace like for like to make sure it works as designed.
Agreed. Problem is it's so fashionable to assume that newer= better. Sometimes that crappy 741 is exactly the right part, "upgrading" it should be done with the utmost care.

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Re: HELP ME REBUILD MY OBXA

Post by Steve Jones » Wed Nov 16, 2011 9:25 pm

madtheory wrote:
synthparts wrote:Also any 30 year old tantalum caps should be replaced as they short out the power rails when they die.
Not all tants are connected to a power rail! Stop propogating myths.
Many are though, and their general failure mode is short circuit.
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Re: HELP ME REBUILD MY OBXA

Post by synthparts » Thu Nov 17, 2011 8:26 am

Yeah I'm sure Steve and I have repaired more synths with shorted power rails caused by dead tantalum caps than madtheory's even seen.
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Re: HELP ME REBUILD MY OBXA

Post by madtheory » Thu Nov 17, 2011 9:54 am

The problem is you were effectively advising someone to replace tants willy nilly, and he doesn't even know what they are. You made a sweeping and unqualified generalisation that, in this context, would lead to expensive damage.

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Re: HELP ME REBUILD MY OBXA

Post by synthparts » Thu Nov 17, 2011 2:31 pm

I said they should be replaced I didn't say he should do it... Electrolytics I would agree don't really need to be replaced unless there is excess AC ripple or they are leaking. Tantalums which are used in lots of vintage synths as bypass caps across the power rails fail in a catastrophic manner and there is no warning. That is NOT a myth.
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Re: HELP ME REBUILD MY OBXA

Post by madtheory » Thu Nov 17, 2011 5:32 pm

Fair enough. I thought your original post was ambiguous.

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Re: HELP ME REBUILD MY OBXA

Post by Skiroy » Thu Jan 05, 2012 6:54 pm

Okay guys. It has been a while since I have been home so I am back on the OBXA. I have 6 voices at this point. I strated with 4. The Obxa in the video here has 8.


A good example of the sound that made me want to buy this is at 0:25 secs. He said its just a stock preset. This thing sounds freaking amazingly awesome. But mine sounds nothing like this. Why? Mine is no where near as bright and full sounding. He told me in the demo he used only a little bit of delay and reverb from a Lexicon MPX. But that shouldnt matter that much.

Is it that he has 2 more voices? He said that at 0:25 secs he is only playing 6 notes so my 6 voices should sound exactly the same.

There is a filter section on each voice right? So its unlikely that my caps are causing it to sound dull on every card right?

I really love the sound in his demo but Im feeling defeated and like I wasted alot of money right now. I dont want to give up so can someone help?


I attached a Mp3 of a quick terribly played example of how mine sounds right now. I tune the voice cards but still have to get around to the Mod,filter and tracking calibration.


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Re: HELP ME REBUILD MY OBXA

Post by madtheory » Thu Jan 05, 2012 8:47 pm

It sounds like the second oscillator is not there.

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Re: HELP ME REBUILD MY OBXA

Post by sequentialsoftshock » Thu Jan 05, 2012 10:13 pm

You don't know s**t about synthesizers, do you? I'd suggest taking it to a repair person to fix whatever you may have messed up... Did you buy it in poor condition??
bonne chance

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Re: HELP ME REBUILD MY OBXA

Post by Skiroy » Fri Jan 06, 2012 3:50 pm

I dont know s**t about synths but I bought it as all working condition supposedly. The only thing I did was tune the cards so I dont see what I messed up. Doesnt each card have 2 oscillators? How could they all not work on every card?

Who is a good tech? I live in Panama city FL. What should I expect to pay to get this thing serviced, if nothing is broken?

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Re: HELP ME REBUILD MY OBXA

Post by Skiroy » Sun Jan 08, 2012 4:48 am

Bump

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Re: HELP ME REBUILD MY OBXA

Post by sequentialsoftshock » Sun Jan 08, 2012 4:55 am

Wasn't trying to be a d**k btw. If you don't have an issue sending it to Atlanta, I know a really fantastic tech. He actually services some famous dudes OBxA...
bonne chance

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Re: HELP ME REBUILD MY OBXA

Post by Skiroy » Sun Jan 08, 2012 10:25 pm

I am at a crossroads now to see if I should even keep it. Are you familiar enough with these to tell me if mine sounds broken or it just need calibration? Do you think the 2nd Oscillator is not working because when I turn the 2nd Oscillator knob I hear it change frequencies.

And I dont have a problem with sending it to Atlanta but it is going to depend on if it is broken or not and how broken?And if I am going to need to add 2 more voice cards to get it to sound like the sample in the video. That another $700.00 plus shipping to ATl is going to be $150.00 - $200.00. Then if it is broken it going several more hundred for parts and labor. I am already $2750.00 into this thing. $4000.00 is just not in my price range right now.

If someone can ensure me that 6 voice cards is what I need for the sound I want and that 8 voice cards are only relevant for bigger chords or in unison mode,which the examples I point to in the video are 6 note chords, and also that my OBXA sounds like it needs calibration vs repair, then I will send it to ATL.

Give me the contact info to the guy in ATL if you could man. He is probably the guy I need to really speak to.

Thankx

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Re: HELP ME REBUILD MY OBXA

Post by madtheory » Sun Jan 08, 2012 10:34 pm

The sound you're after does not require more polyphony (i.e. more cards) as long as you don't play more than 6 notes, unless it's a layered sound in which case you can't play more that 3 notes. So more voice cards does not really affect the size of the sound, even if it's a layered one.

I doubt it's a problem with the voice cards, given that it really does sound like only one oscillator is sounding. That's unlikely to happen on all 6 cards, unless there's some crazy bad failure on an OBXa that no one has ever mentioned. But that's a pretty big problem, it would be internet lore by now! ;)

I've never played an OBXa (just an OB-8) but this is fairly basic stuff. How much are these things worth? And how much is that sound worth to you?

So ya you're right, talk to the tech.

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