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Problem with Dynalo

post #1 of 35
11/18/05 at 10:14am
Thread Starter 
Hey guys,

Just got my Dynalo up and running with two TREADs, but there is a problem. PSU power is +-16v.

The current draw on the positive rail is ~440ma, which is (from memory) way too much.

The Construction Guide i have here says that the voltage accross R11, R15, R41 and R45 should read about 1v, and if its above 1.15 then something is wrong. I am reading 1.2v. (These apparently control the current sources, u1 u2 u3 and u4, are running at 2ma).

The Construction Guide also says that voltage accross R19 and R49 should read about 0.8v. "This confirms that voltage amplifier stage is idling at about 4ma". I am reading 3.7v on one channel, and 2.4v on the other.

[edit]: Another abservation. When i measure the resistance accross R16 and R46 (both of which are 10k feedback resistors) i get a reading of 10k for R46, but 1k for R16. I have double checked each resistor - and they are both 10k when measured outside the circuit.

Any idea what may be up? All help appreciated.

Rob.

(By the way, to do these tests im shorting the imputs with a 1k resistor - is that the correct thing to do?)
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post #2 of 35
11/18/05 at 10:31am
No that's fine, but I'd put a 300ohm load on the output too just to load both sides of the amp.

Have you actually tried getting sound through it? Measure DC offset and plug in the cheapest headphoens you have and try and get sound out of it and see what happens.

You may find that the measurements are simple paranoia and it may just work. The biasing doesn't need to be perfect at every stage on this amp.
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post #3 of 35
11/18/05 at 10:34am
Thread Starter 
Quote:
Originally Posted by Garbz
You may find that the measurements are simple paranoia and it may just work. The biasing doesn't need to be perfect at every stage on this amp.
Maybe, but getting 2v-3v where i should be getting 0.8v is somewhat worrying. And the voltage regulators on the TREADs get rather hot due to the current draw. (440ma is quite a bit for a dynalo)

[edit]: And the R19/R49 would be having 17ma running accross it instead of 4ma - 4 times as much current can not be good :P

Rob.
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post #4 of 35
11/18/05 at 10:47am
Which pots do you have installed ? With the amp powered OFF, what resistances do you measure across R11, R15, R41 and R45 ? Did you measure the forward voltage drop of your LEDs ?
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post #5 of 35
11/18/05 at 10:59am
Thread Starter 
Quote:
Originally Posted by steinchen
Which pots do you have installed ? With the amp powered OFF, what resistances do you measure across R11, R15, R41 and R45 ? Did you measure the forward voltage drop of your LEDs ?
I have R14, R10, R44 and R40 pots installed.

R11 ~ 550ohm
R15 ~ 490ohm
R41 ~ 480ohm
R45 ~ 480ohm

All are labeled "4990F" (Vishay Dale), but R11's results looks a bit suss.

Forward voltage drop of LEDs according to the diode function of my multimeter is 1780-1790mv. (This was done when they were not installed in the amp).

So, i have some wierd readings, but im having trouble placing together whats actually up - what does it all mean? :S

Rob.
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post #6 of 35
11/18/05 at 11:12am
are the LEDs on one side consistently brighter then the other?
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post #7 of 35
11/18/05 at 11:30am
sounds to me like the current source is wonky. Maybe check the LEDs and the BJTs?
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post #8 of 35
11/18/05 at 12:06pm
seems like the amp is simply over-biased, with the 10K pots in parallel and 1.8V LEDs you'd better install 650R resistors for R11, R15, R41 and R45
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post #9 of 35
11/18/05 at 8:52pm
Thread Starter 
I just moved all the trimpots over to the extreme right (i thought they were already there) and now the R11, R15, R41 and R45 measure around 480/490 ohm.

Quote:
Originally Posted by Garbz
are the LEDs on one side consistently brighter then the other?
Nope, both the same.

Quote:
Originally Posted by steinchen
seems like the amp is simply over-biased, with the 10K pots in parallel and 1.8V LEDs you'd better install 650R resistors for R11, R15, R41 and R45
In all honesty - i dont see how that could be the issue. The voltage over those resistors are 1.2v, a touch higher than they are meant to be - but not stupidly high.

On the flipside, the voltage over R19 and R49 is 2.4v, when it should be 0.8v. Would R11, R15, R41 and R45 cause this?

I did find out another thing - i had a 1015 where a 1815 should be for the voltage amplifier stage (grr, argh...). Swapping these around the right way caused the heat outputed by the output stage to go WAY down (the heat is what i was trying to fix) and also drag the voltage across R49 down from 4.3v to 2.4v.

[edit]: Yay, more symptoms! Voltage accross R23, R24, R53, R54 and all resistors like them (the ones tha pair up with the transistors on the output stage) all have from .5v to .6v on them. When they should have between .32v and .44v - they do get rather hot aswell.

Another odd thing - the left side apperas to have NO dc offset? What so ever..... (While the right side had 40mv of offset, which i balanced out with one of the pots)

Any more ideas? Thanks.

Rob.
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post #10 of 35
11/18/05 at 9:26pm
yeah here's a crazy idea, try the amp. It normally runs very hot anyway. You may find the bias problem isn't a problem at all. I didn't make any attempt to match transistors on any of my 4 Dynalos, the voltages on each side definitly don't match each other and often not the test voltages. All have worked flawlessly.
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post #11 of 35
11/18/05 at 9:34pm
Thread Starter 
Quote:
Originally Posted by Garbz
yeah here's a crazy idea, try the amp. It normally runs very hot anyway. You may find the bias problem isn't a problem at all. I didn't make any attempt to match transistors on any of my 4 Dynalos, the voltages on each side definitly don't match each other and often not the test voltages. All have worked flawlessly.
Yeah - now that ive sorted out on issue this really does sound like the best approach. Ive started hooking everything up now.

My guess is that the left channel wont work though, because of the 0 dc offset i keep on reading on it. But we'll see how it goes.... 1h30m to Melbourne Meet :P

Rob.
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post #12 of 35
11/18/05 at 9:49pm
just out of curiousity, is there a single pcb for the dual powersupply needed to run a dynalo, or is it required that two seperate boards be populated?
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post #13 of 35
11/18/05 at 9:53pm
Thread Starter 
Quote:
Originally Posted by euclid
just out of curiousity, is there a single pcb for the dual powersupply needed to run a dynalo, or is it required that two seperate boards be populated?
If your using TREADs - you need two.

Okay, hooked it all up -
  • Volume pot only works for first few degrees, then the volume is on the highest it can be - which is no louder than what the source is itself (And ive double checked that ive done the pot correctly)
  • Output transistors get very hot. But some more than others. One row i cant hold my finger on for more than a couple of seconds

Thanks,
Rob.
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post #14 of 35
11/18/05 at 10:03pm
Quote:
Originally Posted by euclid
just out of curiousity, is there a single pcb for the dual powersupply needed to run a dynalo, or is it required that two seperate boards be populated?
The Dynahi PSU is a single pcb and works very well. The downside is that it is sort of expensive to build and is a bit big.
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post #15 of 35
11/19/05 at 12:24am
Quote:
Originally Posted by robzy
The current draw on the positive rail is ~440ma, which is (from memory) way too much.
I don't know what technique you are using to measure this but it is too high. You can expect to see about 140mA per rail. Even with the current sources running a little too high, you should see no more than 170mA per rail.

Sounds silly, but check the board to make absolutely sure you have all the other resistor *values* correct. Look at the markings carefully. It is sometimes easy to be off by a power of 10 on something.

Report back the curent draw on the negative rail if you get a chance...

EDIT: Report back the voltage you see across any one one of the 24.9ohm resistors on the output stage. Measure one on each side of the amp.
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