Members clusterchord Posted April 10, 2007 Members Share Posted April 10, 2007 Also, I wonder whether replacing the electrolytic caps on all voice cards (and on the lower/upper control/cpu boards as well) with cheap taiwanese caps, would effect the sound in any way... I'm not touching any non-electrolytic cap ! i don't see why would you skimp here, if u already went thru the trouble of getting sucha beautiful n unique machine. use Panasonic Gold or at least Elna's, and have a sound sleep. they're just a tad more expensive, so its gonna come out a few bucks difference. and you can use those rated at 105C instead of 85C, no change in sound yet they will last longer. Link to comment Share on other sites More sharing options...
Members gilwe Posted April 10, 2007 Author Members Share Posted April 10, 2007 Yah, but will the Panasonic Gold's retain the original sound quality ? This is important as I'd like to go and recap all my vintage synths in the near future. Yah know, it's about time... I know Elna has special caps for audio application - is that correct ?... Link to comment Share on other sites More sharing options...
Members clusterchord Posted April 10, 2007 Members Share Posted April 10, 2007 hard to tell. however i think the change in sound i noticed was definetely due to replacing AGING caps that didnt work as supposed to anymore with compromised and unstable performance. NOT due to change of cap manufacturer. for one thing, it surely sounds better. on some machines the change is more obvious, on some less - depending on the state of original caps inside. so the "orignal sound" is not the original sound. you have use the time mahicne and hear your Trident back in 1981 then you'd know what the "orignal sound qulity" was, if you know what i mean. as Wes once hinted, these guys in late 70s/80s just used what was available and what was cheap enough, not some SPECIAL mojo capacitors. first i used no names, then Elnas, then Panasonics. i think its more about their value accuracy, as in capacity and/or tempreature dependance and also their dependability/durability. i intend to do my Jupiter and SH2 next. all Panasonic Golds. i did wonder if using some boutique capacitors (black magic) that are insanely epxensive, on power supply could yield some extra signal to noise.. guys use them on high end boutique preamps, eqs n stuff... i need to investigate this option as i could probably afford to buy a few of them needed for the power supply only. Wes, what do you think ? is this only BS, like "monster" cables, or there's something to it, and is it viable to use in an vinage synth, considering the high noise floor of circuits to begin with..? Link to comment Share on other sites More sharing options...
Members flattop Posted April 11, 2007 Members Share Posted April 11, 2007 My opinion is that a good quality cap is all that is needed in the power supply. Going Gold is probably overkill. You will have other issues to worry about if you are working in environments that are typically over 85 degrees C. What you are shooting for is stability. What I do suggest is not undershooting a spec. I almost always use 50V caps, especially on 15V lines. I might go 25V in places where a 50V is almost impossible to find, like many Oberheim products that use 10,000uf value caps on the 5V line. Again, this spec is for stability on the line. Even this value is probably a bit on the cautious side. Most instruments use somewhere between 3300uf and 6800uf on these lines. Of course, it isn't wise to place a 2200uf cap where a 4700uf should be used. Now, caps that are a direct part of the audio circuit are a different story. I am not talking about the typical 10uf support caps for the power supply. There are many caps used to create an audio voice and these caps need to be replaced with exact value, type, and tolerance as was originally spec'd. They should also be replaced at the same time. So, if you feel you need to replace your audio caps, do all your voices at the same time. This can be something that helps an ailing instrument, but is not as important as the PS. PS first. It is the root of all evil (and goodness) in an analog synth. Wes Taggart Analogics http://www.analogics.org/ Link to comment Share on other sites More sharing options...
Members WhinyLittleRunt Posted April 11, 2007 Members Share Posted April 11, 2007 So Wes, Is the output noise in the OB-8 related to capacitors? I know we discussed this once but I wasn't sure. Let me know cuz i think I'm gonna be sending you back the infamous synth to see if you can clear up the output noise issue (it's getting worse but tolerable if I don't close the filter too much) and possibly that voice that never worked right. Nice pics on your website BTW - I was just out at the grand canyon a few weeks ago and it was great Link to comment Share on other sites More sharing options...
Members urbanscallywag Posted April 11, 2007 Members Share Posted April 11, 2007 High quality electrolytics will rarely bring down power supply noise much, they have too high of an ESR. That's why you use ceramic or tantalum to suppress noise on the rails. Link to comment Share on other sites More sharing options...
Members gilwe Posted April 11, 2007 Author Members Share Posted April 11, 2007 but is not as important as the PS. PS first. It is the root of all evil (and goodness) in an analog synth. As for the Obbie, the P.S is now refurbished (both caps and diode bridges) - but what about the electrolytics placed on the voice boards for example ? Wouldn't leaving the older one create voltage problems in the future, making ti possible for precious CEMs to go bad ? Link to comment Share on other sites More sharing options...
Members flattop Posted April 11, 2007 Members Share Posted April 11, 2007 So Wes, Is the output noise in the OB-8 related to capacitors? I know we discussed this once but I wasn't sure. Let me know cuz i think I'm gonna be sending you back the infamous synth to see if you can clear up the output noise issue (it's getting worse but tolerable if I don't close the filter too much) and possibly that voice that never worked right. Nice pics on your website BTW - I was just out at the grand canyon a few weeks ago and it was great Anything is possible. Many times noise can be attributed to the environment that the instrument resides in also. I think at times, though I find them very cumbersome, that the big aluminum motherboard trays served nicely as shields in the X/Xa. Just got some Alaska pics up yesterday. Probably expand all the vacation pics in the next few weeks. My wife and I have been a bit neglectful. For some reason, customers expect me to work on their instruments vs. me putting up unrelated pics of our vacations. Who would have thought. Wes Taggart Analogics http://www.analogics.org/ No problem. Link to comment Share on other sites More sharing options...
Members gilwe Posted April 19, 2007 Author Members Share Posted April 19, 2007 I just got a new DIP switch and a set of toggle switches, and am going to work on the beast this weekend... While on it - I wonder if I should replace all other three regulators, just in case... Link to comment Share on other sites More sharing options...
Members flattop Posted April 19, 2007 Members Share Posted April 19, 2007 I just got a new DIP switch and a set of toggle switches, and am going to work on the beast this weekend... While on it - I wonder if I should replace all other three regulators, just in case... I find the big TO-3 regulators are probably way over spec'd and rarely fail. You may risk more by replacing than by just going with what is already working in this area. I generally never replaced these unless there is a failure. The big failure areas in the OB series PS's are the rectifiers. They should be WO4M's vs. the WO2M's that Oberheim used. If you can find heatsinks for the rectifiers, that wouldn't hurt either. The 5V especially runs very hot. Like branding iron hot. Wes TaggartAnalogicshttp://www.analogics.org/ Link to comment Share on other sites More sharing options...
Members gilwe Posted April 19, 2007 Author Members Share Posted April 19, 2007 Thanks, I've already replaced them so I'm set. Link to comment Share on other sites More sharing options...
Members flat earth Posted April 20, 2007 Members Share Posted April 20, 2007 Gil, check your PMs. http://cgi.ebay.co.uk/Oberheim-OBX-a-Voice-Board-Card_W0QQitemZ230119651270QQcategoryZ38071QQssPageNameZWDVWQQrdZ1QQcmdZViewItem Link to comment Share on other sites More sharing options...
Members gilwe Posted April 20, 2007 Author Members Share Posted April 20, 2007 Thanks falt !! Currently a problem on voice position #7 needs to be solved first to be able to use an 8th card. I think now I know why they took out one card in the first place Do you think I can get them cheaper than 200$ ? I wonder if I should get it any way... hmmm I think I should General Update - All leds and toggles work ok now, DIP has been replaced as well. Going on for the calibration procedure !! ... this thing is damn FAAAAT !!! Link to comment Share on other sites More sharing options...
Members gilwe Posted April 25, 2007 Author Members Share Posted April 25, 2007 Hey flattop, interesting news - While going into the calibration procedure I found that the instrument has lost all of the patches. Last time I programmed it was about a week ago and haven't powered it up since then. Now the memory is reset. It happened a few times before but I didn't take it too seriously as I disassembled the boards every now and then and thought this was the reason why the memory got lost.... I read your post about the Juno 60 losing its memory the other day, and I assume the Obbie has got a similar problem ? This is most likely an issue with the power up circuitry. Most instruments with memory need to delay parts of the power supply to allow certain areas (like memory) to become stable before booting up the rest of the digital part of the instrument. This circuitry can sometimes fail, causing the instrument to quickly turn off and then on again, resetting the memory yo the boot up condition (--). I'm not sure I quite understood what you meant... Is that a P.S fault ? I just refurbished it... Another reason I thought of could be that I used a regular CR2032 coin cell battery instead of the stock ER3/3.6v .... or that the only difference is the CR2032 will last for a shorter time ?... UPDATE - I checked the voltage which is going to the Memory section and it's +4.5v instead of the required +5v... any thoughts ? (+5v rail is 5.1v) Link to comment Share on other sites More sharing options...
Members flattop Posted April 25, 2007 Members Share Posted April 25, 2007 Diode D9 is probably doing a drop down on the Mem line. 4.5 Volts is fine there. Does the battery still check good? Many instruments with memory have a power up circuit to make sure that all the important digital stuff has stable power before turning them loose. Is the battery in a holder? Though some here use them, I never do. Also, make sure C5 is good. Wes TaggartAnalogicshttp://www.analogics.org/ Link to comment Share on other sites More sharing options...
Members gilwe Posted April 28, 2007 Author Members Share Posted April 28, 2007 Hey Wes, so what you're saying is hard-solder the battery and replace the diode and cap ? What and where is the power up circuit ? I can check this out once I know how to target it Link to comment Share on other sites More sharing options...
Members flattop Posted April 28, 2007 Members Share Posted April 28, 2007 My opinion is if you have about 4.5 volts with the power on at the point you have indicated, that would be ok. Diode D9 would probably knock it down about that much. You need to check the battery. Is it below 2.8 volts? Watch the battery voltage when you have the power on and when you have the power off. If the battery voltage slowly drops when the power is off, either the battery can't handle the load or there is something on the line draining it. I'll need to dig up the schematic. Wes TaggartAnalogicshttp://www.analogics.org/ Link to comment Share on other sites More sharing options...
Members gilwe Posted April 29, 2007 Author Members Share Posted April 29, 2007 Problem, 2.88v tested when power off 2.2v-2.58v (changes from test to test) when power on When placing a fresh battery then in both cases I get 3.3v (same 4.5v at diode point) What does this indicate....? Link to comment Share on other sites More sharing options...
Members flattop Posted April 30, 2007 Members Share Posted April 30, 2007 Problem, 2.88v tested when power off 2.2v-2.58v (changes from test to test) when power on When placing a fresh battery then in both cases I get 3.3v (same 4.5v at diode point) What does this indicate....? 2.88 is way low. You need to determine why it is that low. Can the battery handle the draw? Is there something slowly draining the line to ground, drawing the battery down? Was the battery not that good to begin with? The battery you put in really only has about 1/8th the capacity of what was spec'd. First things first may warrant replacing with a 2/3A lithium to eliminate the first question. After replacing, you need to monitor the battery voltage after you turn the unit off. If it very slowly decreases, you have a problem. Your battery should keep a very consistent voltage. Also, it would seem that the voltage should not go down when the power is on, if you have provided the numbers above accurately. Again, you need to monitor the voltage every hour or so to witness any undesired trends. Wes Taggart Analogics http://www.analogics.org/ Link to comment Share on other sites More sharing options...
Members Aanalogaddict Posted April 30, 2007 Members Share Posted April 30, 2007 See it this way; if you have to shell out $1000 to make it work flawlessly, you still pay less than the going price..! That's a beautiful synth. Link to comment Share on other sites More sharing options...
Members gilwe Posted April 30, 2007 Author Members Share Posted April 30, 2007 Hey Analog, thanks, but you missed the whole thread Wes, you are right, the higher voltage is when power is ON, and the lower is when OFF. I got 2.9/2.5 today. Anyway, just a thought - the battery which was there once I got the unit looked as if it wasn't original, and was empty, so there IS a chance that something is draining it down though I can't really be sure.... The CR2032 I used was fresh when I put it in, few weeks ago. As for the battery to be used - how about a CR2450 ? It is a 600ma Lithium, will that be ok ? Link to comment Share on other sites More sharing options...
Members gilwe Posted April 30, 2007 Author Members Share Posted April 30, 2007 Good news ! I decided to replace D9 and C5 like you said, but what I really suspected was C4 actually. The one they used is (of course) the same tanatalum 6.8uf .... (schematics says "0.68uf" btw). Nasty tantalums... as I already had two blown tantalums in this machine, I went and replaced this one as well ! It might be the diode but I tend to believe is was the tantalum, does this make any sense ? Guess what ? 2.9v when ON 2.9v when OFF (4.58v at diode point) Same, used CR2032 battery... I think I need to replace them all 6.8uf tantalum in this particular machine... Link to comment Share on other sites More sharing options...
Members flattop Posted April 30, 2007 Members Share Posted April 30, 2007 Good news ! I decided to replace D9 and C5 like you said, but what I really suspected was C4 actually. The one they used is (of course) the same tanatalum 6.8uf .... (schematics says "0.68uf" btw). Nasty tantalums... as I already had two blown tantalums in this machine, I went and replaced this one as well ! It might be the diode but I tend to believe is was the tantalum, does this make any sense ? Guess what ? 2.9v when ON 2.9v when OFF (4.58v at diode point) Same, used CR2032 battery... I think I need to replace them all 6.8uf tantalum in this particular machine... Well, if you were losing voltage that quickly on the replaced battery, something was/is drawing it down. Wes Taggart Analogics http://www.analogics.org/ Link to comment Share on other sites More sharing options...
Members gilwe Posted May 3, 2007 Author Members Share Posted May 3, 2007 For all those who are following this thread - I'm now behind the tuning procedure and the battery issue seems to be solved as well (same CR2032 btw). However, as the unit finally in working condition, new issues show themselves. I now realize that the Amplifier ("Volume") Attack doesn't work for the upper voice boards, and so the Pulse Width section (it behaves just as if the Attack was at minimum position and the OSC1/OSC2 switches on the PW section are always OFF). Another issue is the Depth contol on the Mod board which is never flat, so I guess it's a pot issue. Third one is at one of the voice cards which always sound thinner (no low end) than the other voice cards in the system and voice position #7 which gets distorted after some while - but I don't care too much about this because currently I only have 7 cards anyway.... BTW, I notices that when using Split mode, the system won't pass over the missing card like it does when in normal mode, and there will be always one voice not heard for the upper preset... interesting.... (slot #7 is disabled in DIP switch) Cheers evertybody, and particular huge thanks for flattop for his help !! (and as always, I'd be glad to hear ideas as for the remaining issues ) Link to comment Share on other sites More sharing options...
Members flattop Posted May 3, 2007 Members Share Posted May 3, 2007 When you have symptoms which are common to a motherboard tray, you will need to look at connection issues or something in the common analog section, like one of the sample and hold circuits for the memory and panel parameters. Wes TaggartAnalogicshttp://www.analogics.org/ Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.