That's the type I use. I wonder when Thomas is here I can put him to the task of lubing these up!!!
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Amp Dummy Load
- Thread starter Sal1950
- Start date
Holy Cow!
Why didn't he build an industrial power plant while he was at it????
Call Homeland Security.
As a horse I get rather nervous when I see lube..That's the type I use. I wonder when Thomas is here I can put him to the task of lubing these up!!!
OP
- Thread Starter
- #24
1khz tone for warmup as good as anything? Dummy load should be here soon.
Sure. It shouldn't matter what the frequency is.
You'll burn a 1kHz hole in your power capacitors and output transistors, not to mention the dummy load itself!
Yeh, it is like burn in with CRT displays. The amp forever will be scarred and won't be able to reproduce 1 kHz correctly!!!
No, burn-in is to fix the problems due to fresh, unburned components, so with a 1 kHz tone used for burn-in then only 1 kHz will sound good. You still need to burn in all the other frequencies. Pink noise should work, but maybe white would be better since no tweeters in a dummy load and you don't want to burn in the pink noise curve.
OP
- Thread Starter
- #30
Wouldn't blue noise sound a little cooler.No, burn-in is to fix the problems due to fresh, unburned components, so with a 1 kHz tone used for burn-in then only 1 kHz will sound good. You still need to burn in all the other frequencies. Pink noise should work, but maybe white would be better since no tweeters in a dummy load and you don't want to burn in the pink noise curve.
It's so good to have friends.
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Yeh, it is like burn in with CRT displays. The amp forever will be skerred and won't be able to reproduce 1 kHz correctly!!!
I fixed it for you Amir.
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Blue noise, the opposite of pink noise, rises 3 db per octave as frequency rises, is always cool.Wouldn't blue noise sound a little cooler.
It's so good to have friends.
Here a couple youtube links for hours of blue noise.
OP
- Thread Starter
- #33
Thanks D, I've seen these before along with others for all types of noise and test signals, handy.
But sometimes I just wonder "who uploads this stuff"? LOL
Wouldn't blue noise sound a little cooler.
It's so good to have friends.
What, no red noise(Brownian)?
https://en.wikipedia.org/wiki/Colors_of_noise
OP
- Thread Starter
- #35
Let us know. And of course take some pictures if you blow it up!!!
Here's a recap of my first foray into the bias adjustments on my stack of Adcom amps. Today I just started on the pair of small GFA 535 II amps I use to power the 4 Klipsch overhead ATMOS speakers. The main thing that suprised me a bit was the one amp measured about 5 uV bias in both channels with the other amp measured 10+ uV in both channels? That doesnt look to have been a result of age drifting, more likely the tech's were aiming for a different target at the factory for some reason? The factory spec on the 535 II bias is 7 uV and the DC offset is self adjusting. Does so very well BTW, I couldn't measure "zero" offset at all 4 of the channels speaker terminals. Also since both amps had identical readings in the L & R channels it doesn't look as if any drift at all was a play in either amp after 25 some years of use.
Adcom 535 II #AP15041-142 Japan
Cold 10 mV both channels.
Hot dropped to around 8mV both channels
Adcom 535 II #AP25331-342 Taiwan
Cold 5 mV both channels
Hot dropped to around 3 mV in both channels
Factory recommended bias is 7 mV for the GFA-535 II.
My adjustment procedure was to first measure the bias with the amp cold (after 5-10 minutes idling). Then drive the amp with a 1khz signal to roughly 5 watts (6V) across the dummy load for about 10 minutes which made the heat sinks quite hot. Bias would drop about 1.5 uV from idle to very hot so I set the bias to about 8.2uV at cool idle which should give a nominal 7uV at a normal running temperatures?
So far so good guys, I didn't blow up the first two amps.
Two down a three to go.
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Well at least your recap, didn't involve any actual re-capping of the amps.Here's a recap of my first foray into the bias adjustments on my stack of Adcom amps. Today I just started on the pair of small GFA 535 II amps I use to power the 4 Klipsch overhead ATMOS speakers. The main thing that suprised me a bit was the one amp measured about 5 uV bias in both channels with the other amp measured 10+ uV in both channels? That doesnt look to have been a result of age drifting, more likely the tech's were aiming for a different target at the factory for some reason? The factory spec on the 535 II bias is 7 uV and the DC offset is self adjusting. Does so very well BTW, I couldn't measure "zero" offset at all 4 of the channels speaker terminals. Also since both amps had identical readings in the L & R channels it doesn't look as if any drift at all was a play in either amp after 25 some years of use.
Adcom 535 II #AP15041-142 Japan
Cold 10 mV both channels.
Hot dropped to around 8mV both channels
Adcom 535 II #AP25331-342 Taiwan
Cold 5 mV both channels
Hot dropped to around 3 mV in both channels
Factory recommended bias is 7 mV for the GFA-535 II.
My adjustment procedure was to first measure the bias with the amp cold (after 5-10 minutes idling). Then drive the amp with a 1khz signal to roughly 5 watts (6V) across the dummy load for about 10 minutes which made the heat sinks quite hot. Bias would drop about 1.5 uV from idle to very hot so I set the bias to about 8.2uV at cool idle which should give a nominal 7uV at a normal running temperatures?
So far so good guys, I didn't blow up the first two amps.
Two down a three to go.
Looks like a product that maintains its operating conditions pretty darn well after so many years.
At least now you can audition them for a month at 7 mV, reset them to 10 mV and see if one condition sounds better, smoother, more nuanced, more emotionally evocative or like veils have lifted.
OP
- Thread Starter
- #37
Wait another day or two till I report on the other amps that handle the most influential channels of L, C, R and Surrounds. Then I'll really be able to wax lyrically on the massive improvements I've made in sound, my prose might have Atkinson call me for to offer a job. Hell Mr Pass might want to come by and hear them for himself.
All kidding aside, I was a bit worried the pots might give me some issue with being dirty, wiper issues, etc. So far no such problem has raised it's head. Adjustments were able to be performed cleanly.
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OP
- Thread Starter
- #38
I'll finish posting the results of the minor tune-up of my system amps.
Adcom GFA-545 II's # 0019041 & 0008602 CA 1990-1995 Japan
Both of these had held there bias settings amazingly well!
With a factory spec of 7uV one amp was reading in the high 6's and the to other in the mid-upper 7's.
A very slight tweak brought of them both home.
As in the earlier GFA-535's measured, these also have a auto-DC offset circuit and measured at zero in all channels.
Adcom GFA-5400 #A541FB-02252 CA 1995-2000 Taiwan
Nelson Pass second amp series for Adcom, this time switching from bipolars to mosfets on the outputs.
They spec a higher bias of 35uV, run considerably hotter, and use a higher quiescent current of 150, vs 50 VA of the GFA 545 series.
Bias was running a bit high in the 50uV range on both channels which I brought to spec.
These amps do have a DC offset adjustment that required minor tweaking in both channels to get offset right.
So was all this work worth the time invested? Ya, if for no other reason than the piece of mind that all 5 look to running in good order.
OH did I mention the thousands of blankets lifted?
Adcom GFA-545 II's # 0019041 & 0008602 CA 1990-1995 Japan
Both of these had held there bias settings amazingly well!
With a factory spec of 7uV one amp was reading in the high 6's and the to other in the mid-upper 7's.
A very slight tweak brought of them both home.
As in the earlier GFA-535's measured, these also have a auto-DC offset circuit and measured at zero in all channels.
Adcom GFA-5400 #A541FB-02252 CA 1995-2000 Taiwan
Nelson Pass second amp series for Adcom, this time switching from bipolars to mosfets on the outputs.
They spec a higher bias of 35uV, run considerably hotter, and use a higher quiescent current of 150, vs 50 VA of the GFA 545 series.
Bias was running a bit high in the 50uV range on both channels which I brought to spec.
These amps do have a DC offset adjustment that required minor tweaking in both channels to get offset right.
So was all this work worth the time invested? Ya, if for no other reason than the piece of mind that all 5 look to running in good order.
OH did I mention the thousands of blankets lifted?
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Good for you, boring for us since nothing blew up!!!
Yah, good job, but what's a train wreck without the wreck?
