• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required. There are many reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

Amp Dummy Load

Sal1950

Grand Contributor
The Chicago Crusher
Forum Donor
Joined
Mar 1, 2016
Messages
14,068
Likes
16,598
Location
Central Fl

Attachments

  • GFA-545-II Service Manual.pdf
    1.5 MB · Views: 875
OP
Sal1950

Sal1950

Grand Contributor
The Chicago Crusher
Forum Donor
Joined
Mar 1, 2016
Messages
14,068
Likes
16,598
Location
Central Fl
Should work. Just don't touch it during use as it may get quite hot depending on how much power you pump into it.
Well the 545 talks of 10 minute pre-conditioning at 1/3 power/ 33watts, and the 5400 at full power 120watts for 5 minutes. In any case I thought the 300 watt spec of the 8 ohm resistor to be sufficient but yea probably not a good idea to touch it in any case. LOL
Thanks
 

RayDunzl

Grand Contributor
Central Scrutinizer
Joined
Mar 9, 2016
Messages
13,198
Likes
16,981
Location
Riverview FL
Do your amps have a problem, or are you just trying to create one?
 

tomelex

Addicted to Fun and Learning
Forum Donor
Joined
Feb 29, 2016
Messages
990
Likes
572
Location
So called Midwest, USA
Scrutinizer you are funny! But true though, setting amp bias needs to be down slowly and over time/temperature, and if its fairly close, I would not touch it given the age of the pots etc. I did try a long time ago to bias my old hafler amp closer to class a but all it did was make the darn thing get too hot and no change to the sound.
 
OP
Sal1950

Sal1950

Grand Contributor
The Chicago Crusher
Forum Donor
Joined
Mar 1, 2016
Messages
14,068
Likes
16,598
Location
Central Fl
Do your amps have a problem, or are you just trying to create one?
LOL, Neither, just that seeing as all 5 are at a minimun of 20 years old I thought it might be interesting to see what there is to see after all that time, how much drift there's been, etc.

I don't feel good at all cooking the thing at full power for 5 minutes. Recipe for potential damage. Just run a bit till it is warm and good and then set it.
setting amp bias needs to be down slowly and over time/temperature, and if its fairly close, I would not touch it given the age of the pots etc

Yes I agree, thanks. I wonder how far off from the spec'd 7mv you'd live with before an attempt to adjust was made? I'm thinking +or- 1/2mv would be called good enough but......... Never tweaked SS amp bias before. I did my VTL tube amps a couple times a year and they could be held to a fairly stable 300-325 of the 300mv spec?

You wimp!
You just want to see the smoke come out. :eek:
 

tomelex

Addicted to Fun and Learning
Forum Donor
Joined
Feb 29, 2016
Messages
990
Likes
572
Location
So called Midwest, USA
Theres bias and offset, offset at the output of the amp, I would say if it is within plus or minus 10mv its fine, up to +/- 20mv as well would not touch. Bias is setting the idling current in the output transistors, consult your service manual for both adjustments. Solid state should hold its settings for decades and be within spec. Millivolts of offset will not even get passed your crossover components in your speakers, its not that important until you deal with headphones.
 
Last edited:
OP
Sal1950

Sal1950

Grand Contributor
The Chicago Crusher
Forum Donor
Joined
Mar 1, 2016
Messages
14,068
Likes
16,598
Location
Central Fl
Theres bias and offset, offset at the output of the amp, I would say if it is within plus or minus 10mv its fine, up to +/- 20mv as well would not touch. Bias is setting the idling current in the output transistors, consult your service manual for both adjustments. Solid state should hold its settings for decades and be within spec. Millivolts of offset will not even get passed your crossover components in your speakers, its not that important until you deal with headphones.
Thanks bud. Offset is self-adjusting. Bias spec for the 545 is 7mV, +/- 1mV. We'll see how they measure
 
OP
Sal1950

Sal1950

Grand Contributor
The Chicago Crusher
Forum Donor
Joined
Mar 1, 2016
Messages
14,068
Likes
16,598
Location
Central Fl
What a group of supportive friends I have here. :eek: LOL
 

RayDunzl

Grand Contributor
Central Scrutinizer
Joined
Mar 9, 2016
Messages
13,198
Likes
16,981
Location
Riverview FL
1528693896026.png
 

RayDunzl

Grand Contributor
Central Scrutinizer
Joined
Mar 9, 2016
Messages
13,198
Likes
16,981
Location
Riverview FL
The bias setting is just like setting the idle speed on a carb.

Too low, no good.
Too high, no good.
 

Wombat

Master Contributor
Joined
Nov 5, 2017
Messages
6,722
Likes
6,459
Location
Australia
Bias setting occurs in many audio forums.
 
OP
Sal1950

Sal1950

Grand Contributor
The Chicago Crusher
Forum Donor
Joined
Mar 1, 2016
Messages
14,068
Likes
16,598
Location
Central Fl

Timbo2

Senior Member
Joined
Feb 27, 2018
Messages
497
Likes
396
Location
USA

amirm

Founder/Admin
Staff Member
CFO (Chief Fun Officer)
Joined
Feb 13, 2016
Messages
44,368
Likes
234,384
Location
Seattle Area
Top Bottom