Fungi Posted December 5, 2008 Report Posted December 5, 2008 Standard build with AD8620 for LR and 8610 for G, class A bias with JFETs, LMH6321 buffers, unity gain, 24V AC adapter. The AD8610 in the ground channel gets burning hot, and I was measuring something... DC? from power to V- or V+ of one of the leads of the 8610 and it was going back and forth. Also, the LED (this) doesn't even light up. RLED is 7.68k. I'm new to this whole thing so I'm not sure what I should be measuring and what they mean... if anyone can help I'd be forever grateful.
Pars Posted December 6, 2008 Report Posted December 6, 2008 Well, you can start with the Test the amp section of Step-by-Step Assembly Guide. Also, I hope you did the Test the power supply portion of this as well. Given the state of the ground opamp, did you use C6? Also, measure the DC offset between IG and OG... should be 0mV or very close. If so, then check the L and R DC offset (L -> OG and R -> OG). Also sounds like you may have the LED In backwards as well. And I didn't quite get what you meant by this: V- or V+ of one of the leads of the 8610 and it was going back and forth.
The Monkey Posted December 7, 2008 Report Posted December 7, 2008 Funny to stumble on this thread. My Pimeta used to be haunted. But I'm listening to it now with the Proto DAC only Pico. And all's well. Post pics. Nate will be able to help. I'll add more useless posts. Also, if you have a scanner, using that for the image will be even better.
Fungi Posted December 8, 2008 Author Report Posted December 8, 2008 AC adapter measures 24V properly Power GND to OG: 0.2mV V+ to V- on each chip: about 1.3mV IG to V+/V- on each chip: 0mV OG to OR/OL: about 0mV I was mistaken in the first post, it was the AD8620 LR chip getting hot, not the AD8610, and the going back and forth was probably me not having my leads pressed up against something correctly. And I just realized I need to use the IR/IL/IG 2 for the pot I'm using, but that still doesn't solve the mystery of the non-lighting LED but the datasheet says the longer leg is the anode and that's what I have hooked up.
n_maher Posted December 8, 2008 Report Posted December 8, 2008 Please tell me the wallwart is putting out DC and not AC.
n_maher Posted December 8, 2008 Report Posted December 8, 2008 And you're sure you have the PS wired correctly? Before you do anything else take the opamps out too.
Fungi Posted December 8, 2008 Author Report Posted December 8, 2008 Yeah, datasheet says pin is + and that's how I have it hooked up. Opamps removed. I did the measurements on Tangen'ts basic amp testing except for current draw testing, anything else I could try?
ieatteflon Posted December 9, 2008 Report Posted December 9, 2008 http://tangentsoft.net/audio/pimeta/bitmaps/pimeta-1.1a-hires.png Why do you have your inputs wired like that? I only see 2 wires for the input pads next to the Alps pot connected to what looks like some pads in the power section. The original input pads [which you have wired] is pointless if you're using the alps pot.
n_maher Posted December 9, 2008 Report Posted December 9, 2008 Yeah, datasheet says pin is + and that's how I have it hooked up. Opamps removed. I did the measurements on Tangen'ts basic amp testing except for current draw testing, anything else I could try? Don't trust the data sheet, check it with your meter. Measure the pads at the PCB and see what you're getting there. Also, measuring current with the opamps isn't going to yield anything meaningful. What are you using for buffers? Are they soldered on the bottom side? Pic?
Fungi Posted December 9, 2008 Author Report Posted December 9, 2008 http://tangentsoft.net/audio/pimeta/bitmaps/pimeta-1.1a-hires.png Why do you have your inputs wired like that? I only see 2 wires for the input pads next to the Alps pot connected to what looks like some pads in the power section. The original input pads [which you have wired] is pointless if you're using the alps pot. I covered that in an earlier post. Don't trust the data sheet, check it with your meter. Measure the pads at the PCB and see what you're getting there. Also, measuring current with the opamps isn't going to yield anything meaningful. What are you using for buffers? Are they soldered on the bottom side? Pic? Buffers are LMH6321s soldered on the bottom in accordance to Tangent's "leave pin 5 lifted, don't use R11", pic attached. How would I test the power supply?
n_maher Posted December 9, 2008 Report Posted December 9, 2008 I assume that the power supply is plugged into a jack right? If so, take the PS out of the jack, and given that your data sheet says pin positive you should shove the red meter probe inside the barrel connector and you can hold the black (negative) probe on the outside of the barrel. Unloaded you'll probably read a little higher than 24V, but that's not really a concern. Alternatively you could just measure across any of the power supply caps, I think that should yield half the power supply voltage since those caps are after the TLE splits the voltage. That might be a good check anyway to see if the TLE is doing its job correctly.
Fungi Posted December 9, 2008 Author Report Posted December 9, 2008 Datasheet is right, and TLE does split the voltage properly. With the LED, should I test the spare I have? Based on the schematic if 24V is going through properly (which I assume it is based on the 12V after TLE) it should light up.
luvdunhill Posted December 9, 2008 Report Posted December 9, 2008 Datasheet is right, and TLE does split the voltage properly. With the LED, should I test the spare I have? Based on the schematic if 24V is going through properly (which I assume it is based on the 12V after TLE) it should light up. is the LED in backwards? and where is the LEDs current source / current limiter whatever-the-term-is?
Fungi Posted December 9, 2008 Author Report Posted December 9, 2008 I'm pretty sure the LED is in correctly: LED - long leg (anode on the datasheet as well) - blue wire - square pad - RLED - V+
luvdunhill Posted December 9, 2008 Report Posted December 9, 2008 hm, you should have included D1, yes optional, but still a good idea. Also, LED should go to V-
n_maher Posted December 9, 2008 Report Posted December 9, 2008 No, the anode is the positive leg (long leg) and should be wired to LED +.
The Monkey Posted December 9, 2008 Report Posted December 9, 2008 hm, you should have included D1, yes optional, but still a good idea. Also, LED should go to V- D1 is the crowbar, correct?
Fungi Posted December 9, 2008 Author Report Posted December 9, 2008 D1 is whatever kind of diode you want, but yeah Tangent suggests a crowbar diode there. I (foolishly, in retrospect) left it out.
n_maher Posted December 9, 2008 Report Posted December 9, 2008 As long as you didn't hook up the power backwards it's irrelevant to the discussion here. Did you flip the freakin' LED yet?
Pars Posted December 9, 2008 Report Posted December 9, 2008 D1 is the crowbar, correct? Yes. A no brainer to put it in.
Fungi Posted December 9, 2008 Author Report Posted December 9, 2008 As long as you didn't hook up the power backwards it's irrelevant to the discussion here. Did you flip the freakin' LED yet? Yeah, I just did and it didn't light up. Looking for the other LED now.
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