seppoman Posted January 18, 2004 Report Posted January 18, 2004 Hi,I built my MidiBox SID with the PSU Optimized cirquit. Because I want to integrate an Alesis NanoVerb in the box, I now added pins directly behind the power plug where I can get the required 9V AC out. The audio out from my two SIDs leads to 6,3 mm "direct out" jacks which combine the signals via 10k resistors to a mono signal for the NanoVerb when nothing is plugged in.So I just connected everything and when I switched the box on the fuse of the PSU blew. I checked the "direct out board for errors or short cirquits - everything ok.I admit I don´t fully understand how the PSU Optimized cirquit gets 14 V from the two voltages. Could it be that with this cirquit it is not possible to get the 9V out at the same time? Without load (nothing connected) I measure all three voltages correctly. The Alesis works fine when everything else is disconnected. Also the output board makes no problems when connected to the synth. Power consumption can´t be the problem either - I measure DC 5V 650 mA, AC 9V 10 mA without the Alesis, and the Alesis needs about 250 mA.So what´s the reason for the blown fuse?Thanks,Seppoman Quote
TK. Posted January 18, 2004 Report Posted January 18, 2004 The ground connection is the problem, think about how the voltage regulation unit of the NanoVerb is built, and from where it gets its ground. Measure the NanoVerb ground against the SID ground, it must be between 5V and 14V, no? Once you connect both grounds together, you will shorten the PSU.I see now proper way to solve this with the optimized PSU circuit. How does the PSU of the NanoVerb looks like? Best Regards, Thorsten. Quote
seppoman Posted January 18, 2004 Author Report Posted January 18, 2004 Hi Thorsten,I made a schematic from the PSU section, I hope I got everything right:First I thought it would be possible to simply desolder the 7805 and connect the 5 V supply there, but there´s also negative voltage involved (named LSP2 in the schematic, Eagle didn´t want to rename this output...).About where to get ground from an AC voltage, I don´t know anything about. Perhaps you can tell from the schematic.Do you see any solution?Thanks,Seppoman Quote
doc Posted January 18, 2004 Report Posted January 18, 2004 Hi seppoman,I'm not quite sure about that but I think you need a another AC 9V Transformer to get a negative voltage. The ground would then be the middle connection of both transfrmers.I know two ways to get balanced voltage out of one transformer: 1.) With a OP. But then you get just half the voltage (+4.5V and -4.5V)2.) A symetric powersupply out of one transformer. I don't know the englsh word. In german it's called "Villard-Spannungsvervielfacher". It uses 4 Diodes and some caps to get (for example) + and - 19V/150mA out of one 8V transformer. The +/- 19V should not be so problematic because you can put your +/- 5V regualators after that. Never tested this circuit with a Microcontroller application. If your interested I publish the schematic tomorrow. ( Have to draw it first and publish it on some webspace first)I'm pretty sure there are several other ways on doing it. So just leave the question open to the other "midiboxers" .... :P Quote
seppoman Posted January 18, 2004 Author Report Posted January 18, 2004 Hi Doc,thanks for your reply :)The schematic above is not what I intend to build. I tried to show what happens in the NanoVerb behind the plug. It is driven by a normal AC wall wart. I hope the schematic shows all parts in the correct connection. After the +/-5 V points I don´t see anything that could influence the voltage anymore. But my electronics knowledge is limited...So I suppose I´d have to generate -5V in another way, rip everything shown above out and connect this -5V and the normal 5 V line to the cirquit?The last possibility would be putting another jack in the case and plugging in the normal wall wart of the alesis. But I´d like to avoid this - too many cables...Seppoman Quote
doc Posted January 18, 2004 Report Posted January 18, 2004 Oh sorry, seppoman......think I was quite too fast.I read a little more carefully next time. ;DThinking about your problem. And AFTER I understood it I may give the next advice. ...sorry.Till thenDoc Quote
seppoman Posted January 18, 2004 Author Report Posted January 18, 2004 Hi,whoops, I missed one important connection: The upper 9V AC connector is also directly connected to ground, so it´s no surprise one can get a short cirquit... But I still don´t know what to do about...Doc: No problem - I may misunderstand a lot more things than you here because of my limited knowledge ;)Seppoman Quote
doc Posted January 18, 2004 Report Posted January 18, 2004 Hi Seppoman,back again (after thinking 'bout ...)Your NanoVerb needs +/- 5V, as you said. It genarates these voltages with a virtual ground over C1. When connecting the SID and the NanoVerb you get a short circuit (perhaps) over the audio ground. Don't have a solution for it (except a extra transformer - but that isn't what you want to hear 8)).Perhaps someone else ?doc Quote
seppoman Posted January 18, 2004 Author Report Posted January 18, 2004 Hi,Don't have a solution for it (except a extra transformer - but that isn't what you want to hear  8)).docRight :)BTW: I exchanged the schematic to avoid confusion. So the displayed version is correct.Seppoman Quote
doc Posted January 18, 2004 Report Posted January 18, 2004 Hi seppoman,seems that we write at the same time, so I didn't get your upper Ground connection. AND. As you mentioned, my knowledge is either far from "profi". But when two with no knowledge do something together - It will work ! (hopefully) :-/doc Quote
d2k Posted January 19, 2004 Report Posted January 19, 2004 speaking of this optimised sid psu circuit - does anyone know any tricks to get 24V from it as well as? I'm trying a discreet jfet gain stage for the audio out that requires this voltage...taDan Quote
pay_c Posted January 19, 2004 Report Posted January 19, 2004 For 24 Volts: Nope, not without a DC/DC Converter or something like that. TK got the max out (5V + 9V = 14V). And those things (for the needed Power) are dammit expensive... For that ground to ground problem: Could be solved by using a 1:1 transformer (its 9V *AC*). Just put it in between the PSU 9V AC and the Nanoverb. Makes a galvanic disconnection - no shorts possible anymore! Only prob: Could bring in a big amount of hum, if not properly covered... :PUsing one PSU for two seperated things is always kinda prob.... :-/Anyhow: Greetz ;D Quote
seppoman Posted January 19, 2004 Author Report Posted January 19, 2004 Hi pay_c,I searched at Reichelt, Buerklin, Conrad and found that these 1:1 trafos cost at least 30 Euros and are not that small. Do you know a source for a suitable transformer which is cheap and not too big?Or could an "audio transformer" (NF-Uebertrager) between SID and NanoVerb be a solution? If yes, would it also be a 1:1 model and what about impendances? I´ve got an old one here in my collection which is 1:1 and has about 5 Ohm resistance on both sides. Is this one suitable and are there other measures necessary (e.g. resistors)?Seppoman Quote
doc Posted January 19, 2004 Report Posted January 19, 2004 Hi Seppoman,it's me again... so be warned :-/I don't think you can use a 1:1 NF audio transformer with 5 Ohm. Think about the current. You remember R=U/I ?If I'm right (and thats not sure at all) you get a current of 1.8 A (I=U/R -> 9V/5 Ohm). I'm pretty sure your audio transformer won't manage that. doc Quote
seppoman Posted January 19, 2004 Author Report Posted January 19, 2004 Hi doc,no, I meant if I can solve the problem if I put the NF transformer between SID audio out and NanoVerb audio in, and if yes, do I need to add other parts because of some impendance issues.Seppoman Quote
doc Posted January 20, 2004 Report Posted January 20, 2004 there must be something special... I always get you wrong ! - damned....In the NF line you can connect the 1:1 audio transformer. You need a good one there and the impendance should be higher than yours. Don't know the exact value. Just test it ! - If there is a impendance problem you'll hear it. (and before saying something stupid again... I go to bed now!. Â ;))doc Quote
d2k Posted January 20, 2004 Report Posted January 20, 2004 I'm just wondering - if using all 8580's u only need 9VDC right so there's noneed to tie the gnd to +5 for +14V. Instead just wire from after the 7809. Can all psu parts on each SID module be removed then? They can right? - or should the 2200uF caps be left on - or should i use a bigger cap before the 7809 on the main psu circuit?CheersDan Quote
seppoman Posted January 22, 2004 Author Report Posted January 22, 2004 Hi,I just tested the mentioned 1:1 audio transformer. As expected it doesn´t work at all, probably because of the 10k resistors on my "output board" (parallel wiring of the SID outs) vs. the 5 Ohm resistance of the transformer. I didn´t connect the transformer directly to a SID out because I´m anxious to blow something. Does anyone know which impendance/resistance/1:-relation is needed to a) not damage anything and b) get linear noise-free sound transmission?Or does anyone know a good source for a 1:1 power transformer that is cheap and small? The ones I´ve found are at least 10x10x10 cms and would be massively oversized for the max. 3 W I´d need...SeppomanBTW: d2k - I think the problem is that the 7809 needs more than 9V AC to produce 9V DC from it. That´s the reason why you need to build the PSU-optimized cirquit anyway. Perhaps you could put anoter 7809 on the PSU board and distribute the resulting 9 V to the SIDs, but the normal way you at least stay flexible in case you should decide to use a 6581 someday and it costs max. 20 minutes and 5 euros more... Quote
seppoman Posted January 28, 2004 Author Report Posted January 28, 2004 Hi again,today I found a 1:1 transformer at Conrad:This one is 30 W, prim. 230V sec. 2x115 V, about 5x5x5 cm, 15 EUR.I just connected it with the two 115v s in series. so far everything´s fine, I get perfect 9V AC on the secondary side without load. But when I connect the Nanoverb, the voltage drops down to about 4,5 V, which of cause is too few to drive the Nanoverb. No measurable current on either side.Am I doing anything wrong or is a normal 230V 1:1 transformator not usable for low voltages?Seppoman Quote
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.