From Lorne Hammond Sent Fri, May 3rd 2019, 14:06
From Lorne Hammond Sent Fri, May 3rd 2019, 14:06
I have two polymoogs. One original and one someone rebuilt before I got = it. The rebuild had a lot of work done (i was there to buy the road = cases and it was awesome so...) including all new LEDS but each had a resistor added to drop the = current as early leds were not as efficient with power. The pedalboard = uses two huge old leds.=20 Given the number of power inefficient LEDS and the fact the polymoog = power supply design gets darn close to the draw of all those circuits = and LEDS, the LED upgrade=20 adds a significant stabilizing safety zone for the workload on the power = supply. And that means the power supply parts last longer.=20 I would also follow that age old advice I have heard from techs over and = over again: Start with the power supply and replace parts that are likely to = eventually fail there and make sure that is on spec first before all = else.=20 Then go to mechanical connectors. In any problematic polymoog simply = gently pulled the connectors off and push back on to break any=20 micro corrosion causing odd behaviour. It was the key to bad presets on = one of my polymoogs, not soldering. A good electronic set of the factory service manuals (huge) runs 200+ = megs. This is the best polymoog resource hub I found years ago:=20 http://www.dubsounds.com/polymoog.htm You may find the manuals there. = Its for owners. Fairly sure you will find the led issue covered at that site. I think I = got a set of manuals there years ago but for ease of use I now have a = factory paper set=20 and a photocopy set. But there are lots of restoration individual = thread out there. =20 Lorne -----Original Message----- From: chris <xxxxx@xxxxxxxxxx.xx>=20 Sent: May-03-19 3:28 AM To: xxxxxxxx@xxxxxxxxx.xxx Subject: Re: [AH] Replacing LEDs in a Polymoog I wouldn't expect much in terms of an original data sheet, at least not = online - that was 20 years before the internet took off.=20 And - LED usage wasn't as sophisticated as it is now. Gee, even other = colors than red weren't that common.=20 Rule of thumb for red was 1.2V, 20mA, which meant 180R for 5V TTL = operation. That was the same I did back then without thinking.=20 Oh, and flat side is negative, but that was about all you needed to know = abut LEDs. BTW, I think forward voltage mainly is determined by physical properties = of LED color and hasn't changed since then. Current is a different = thing, 20mA would be considered much by now for indicating purposes (in = contrast to illumination). Chris On Thu, 2 May 2019 20:11:18 -0700 Brian Willoughby = <xxxxxx@xxxxxxxxxxxx.xxx> wrote: > If this were my Polymoog ( ;-) ), I would try to find the model number = of the original manufacturer=C3=A2=E2=82=AC=E2=84=A2s LED and look for a = data sheet. Hopefully, that data sheet would list the exact color = wavelength of those LEDs in nanometers. I would personally want the = =C3=A2=E2=82=AC=C5=93same=C3=A2=E2=82=AC=C2=9D color of red, not just = any old red. >=20 > Modern LEDs are available in various shades, usually with good = documentation on the exact color wavelength. Of course, the really cheap = LEDs just say =C3=A2=E2=82=AC=C5=93red=C3=A2=E2=82=AC=C2=9D but you can = still afford LEDs with better quality control. Some have just a single = wavelength, while others have a wide range, but can still be = =C3=A2=E2=82=AC=C5=93binned=C3=A2=E2=82=AC=C2=9D by measured wavelength = in much narrower ranges. You could save a little money by buying the = unmeasured LEDs, but the savings isn=C3=A2=E2=82=AC=E2=84=A2t worth the = tradeoff at your quantity. Instead, I think it=C3=A2=E2=82=AC=E2=84=A2s = worth paying a little more to control the color. >=20 > Assuming you can find the original specifications (or perhaps measure = them), then finding a modern match should be easy. Most modern data = sheets have graphs showing brightness versus color, and you can match = the brightness as well. >=20 > As Murray pointed out, you=C3=A2=E2=82=AC=E2=84=A2ll have to change = the resistors, too. The 180 ohm resistor sets the current, based on the = LED supply voltage and the LED forward voltage drop. If the modern LED = has the same voltage drop, then you=C3=A2=E2=82=AC=E2=84=A2ll surely = have to change the resistor to get lower current. = There=C3=A2=E2=82=AC=E2=84=A2s a random chance that you could find a = modern LED with a higher forward voltage (that = isn=C3=A2=E2=82=AC=E2=84=A2t too high for the existing LED voltage) and = this would lower the current without changing the resistor, but it seems = unlikely that it would work out precisely. >=20 > One option that you should consider is buying modern LEDs with the = same current rather than lower current. The reason for doing this is = that you wouldn=C3=A2=E2=82=AC=E2=84=A2t need to change the resistors. = Of course, forward voltage and efficiency are factors. >=20 > One thing to note is that LED brightness can be measured in lumens or = candles, so you might have to convert between the standards if you want = to dial in the same brightness. Also look out for the dispersion pattern = - a directional LED will only be bright directly in front, while a = non-directional LED will spread out the brightness across a wider angle. = The difference between lumens and candles is related to dispersion in = different ways. >=20 > I suppose that I=C3=A2=E2=82=AC=E2=84=A2ve made this sound like an = incredibly difficult task, but it=C3=A2=E2=82=AC=E2=84=A2s actually = quite simple if you do the math. A good LED data sheet will give all the = information you need to calculate a match to the Moog original and = perhaps even save you from changing the resistors. >=20 > Good luck! >=20 > Brian >=20 >=20 > On May 2, 2019, at 1:51 PM, Dan Goldstein <xxxxxxxx@xxx.xxx> wrote: > > I=C3=A2=E2=82=AC=E2=84=A2ve got a Polymoog = I=C3=A2=E2=82=AC=E2=84=A2m restoring, and I=C3=A2=E2=82=AC=E2=84=A2d = like to replace the old, original LEDs with new, modern ones. The = originals were 5mm bulbs, = =C3=A2=E2=82=AC=C5=93SSL-22=C3=A2=E2=82=AC=C2=9D, each with a 180 ohm = resistor hooked up to it. > > =20 > > I=C3=A2=E2=82=AC=E2=84=A2d like to replace them with new, modern = red LEDs of equivalent brightness and lower current use. There are so = many different LED values these days, and I=C3=A2=E2=82=AC=E2=84=A2m not = sure how to know what would be the ideal replacement LED. Can anyone = offer any advice on specs for replacement LEDs for a Polymoog? > > =20 > > Thanks! > > Dan > >=20