[was ist los?]

Ok, so i've built aa Gilmore Dynamic on a Subsonic board, but have massive amounts of DC. There is around 2.4v on the left channel and around 7.2 on the right side. The right side has an irregular brighter led and the 389's and 109's heat up way fast. I have a matched set of transistors complements of Arzela. They are "Y" grades. What is my problem?
I am using a Welborne PS-1 at 16.4v per rail.
*Edit* a picture of the led: http://f1.pg.photos.yahoo.com/ph/cha...em.jpg&.view=t

 

[BoyElroy]

Hey Was Ist Los--

What are you getting as your +/- vdc from your power supply?

7vdc is just a massive number. Check and see that all your transistors are oriented properly, esp. your 1015's and 1815's.

 

[was ist los?]

OMG, the right side did turn out that i put a 1815 instead of a 1015. Those 8s and 0s look so similar. Damn!
Anyway, i've got the right side at around a managable amount of dc. It's around 72mV at start up and lowers to around 30 IIRC. The left side is still at around 2.4V so i'll have to look and check all the trannies.
*EDIT* just checked the trannies on the left side and none of them are off. Any other suggestions?

 

[was ist los?]

Anyone?

 

[BoyElroy]

From what I know about the Gilmore, one of the few ways you could get such a high DC offset number would be if you've turned around one of the transistors back-to-front.

I know that you've checked already, but are you absolutely certain that all the 1015/1815 trannies are facing the correct way?


Also, have you checked to see if the 2sj109/2sk389 trannies are placed correctly?

If you're still drawing a blank, I know that Arzela put in servo wiring options for both balanced and unbalanced modes. You would get a large DC offset (>2 vdc) if you use an unbalanced servo circuit in a balanced amp and vice versa. You may want to contact Arzela re: this issue.

 

[Ben_Tech]

I lowered my DC from 50-90mv to >5mv by matching the LED's better and then replacing the servo opamps with brand new ones.

 

[was ist los?]

Heres an update. I found the source of the 2.4v dc. It was a stupid solder bridge!! Now the left side has start up of 35mV and an average of under 10mV. The right side; however, still has slight problems. It starts out at around 75mV and lowers to 37mV. I've switched my OPA627s to AD8610s, but that made things worse, so i switched back. I can try the AD797s and the OP27.
*EDIT* I've determined the AD797 and AD8610 react the same in the amp and both give higher dc. The OPA627 and OP27 give near exact numbers of dc. Any more tips anyone?

 

[tangent]

Does the OPA627 make sense at all in the Gilmore? It's just a DC servo. The default OPA227 should be just fine.

 

[aos]

tangent is right, people, don't change things if you don't understand what they're for. A servo is usually a filter with a VERY low cutoff, like a few Hz or even less than that, therefore you want an opamp with superb DC like OPA227, but anything with low offset and low thermal drift - and low cost - will do. You'll be wasting money or even compromising performance if you use an expensive chip that has inferior DC offset.

 

[Nisbeth]

Quote:

Originally posted by aos tangent is right, people, don't change things if you don't understand what they're for. A servo is usually a filter with a VERY low cutoff, like a few Hz or even less than that, therefore you want an opamp with superb DC like OPA227, but anything with low offset and low thermal drift - and low cost - will do. You'll be wasting money or even compromising performance if you use an expensive chip that has inferior DC offset.

Obviously, yes. But which op-amps are then suited for the job (Other than the 227 of course)? And what is considered to be "low DC-offset"?

/U.

 

[aerius]

The OP27 works fine for me and I've been getting about 1mV of DC using a craptacular surplus +/-15V power supply. Maybe it's just luck, I picked parts at random from my local electronics supply store and built it up without matching or testing.

 

[was ist los?]

I now have OP27s in the circuit, like in the original schematic; however, there is still 35mV in the right channel.

 

[Arzela]

Perhaps that bright LED became compromised. Did you try replacing it?
I think I sent you an extra one.

 

[was ist los?]

That LED is no longer bright. It was because i put a 1815 in a 1015's place. I swapped the extra led in and no difference methinks.

 

[was ist los?]

Here's an update. The left channel has a start up of 34mV and an average .5mV after warm up. The right side; however, has a start up of 64mV and an average of 41-46mV. Anyone have solutions on the right channel? Keep in mind that my LEDs, trannies, and resistors were matched. I'm also using brand new OP27s.