In bridged/balanced mode the two output stages are effectively in series.
If one passes 2.5A of ClassA current then then load and the other half of the balanced pair must also pass 2.5A of ClassA current.
Equally if the load current increases to 3A then the balanced pair will now be operating in ClassAB mode.
If one passes 2.5A of ClassA current then then load and the other half of the balanced pair must also pass 2.5A of ClassA current.
Equally if the load current increases to 3A then the balanced pair will now be operating in ClassAB mode.
Hi fellas, clueless DIY guy needs help again.
The F5 clone I've got (not made by me, must repeat I have no electronic know how) is running a bit hot about 60 degrees in a 20 degree room. I'm guessing maybe bias needs to be turned down a bit?
Is anyone willing to give some easy to follow instructions for me to check/change bias? (assuming it is relatively easy. I do have a multimeter.)
Cheers
B
The F5 clone I've got (not made by me, must repeat I have no electronic know how) is running a bit hot about 60 degrees in a 20 degree room. I'm guessing maybe bias needs to be turned down a bit?
Is anyone willing to give some easy to follow instructions for me to check/change bias? (assuming it is relatively easy. I do have a multimeter.)
Cheers
B
AndrewT said:
Hi Andrew. Here's the insides, hope the resolution is ok. Wish I knew how to overlay a grid so you could easily refer to the bit I need to tweak to adjust the bias. Cheers
B.
http://s701.photobucket.com/albums/ww17/14149324/
here's a closeup.
[Borrowed a friends Bottlehead Foreplay today and am preferring it to the passive Prometheus TVC with the F5 I think. Sounds actually too transparent and detailed with the TVC - would be great with vinyl or high rez audiophile stuff I reckon, but the tube pre is a bit more forging of most of of my cd collection. Thinking of a Peachtree Nova as dac/pre perhaps...]
[Borrowed a friends Bottlehead Foreplay today and am preferring it to the passive Prometheus TVC with the F5 I think. Sounds actually too transparent and detailed with the TVC - would be great with vinyl or high rez audiophile stuff I reckon, but the tube pre is a bit more forging of most of of my cd collection. Thinking of a Peachtree Nova as dac/pre perhaps...]
Hi Bvan,
compare your F5 PCB and components to Fig6 in the F5 manual.
The four big resistors in the middle are the 100r in the feedback loop (R5 to R8). They are coded Brn Blk Brn Gld = 1 0 1 5% = 100r 5%
The two big resistors at the outside are the source resistors attached to the FETs. They are coded Yel Vio Sil Gld = 4 7 /100 5% = 0r47 5%.
The source connection is labeled E on the PCB.
Check continuity with your multimeter from E to resistor on each side. It should read the same as the test leads shorted together.
Now read from E to the other end of the resistor. It should read test short+half an ohm (0r5).
Power up the amplifier.
Measure the voltage across each source resistor. It should be the same as quoted on Fig6 (600mVdc).
The two blue squares with the grey star adjuster are the pots P1 & P2.
Read the manual carefully and when you are clear on what to do make the adjustment to lower your FET current from Vrs=600mVdc to Vrs=550mVdc. Allow to stabilise and recheck sink temperature.
I can't see your sinks, but I wonder if they are big enough??
compare your F5 PCB and components to Fig6 in the F5 manual.
The four big resistors in the middle are the 100r in the feedback loop (R5 to R8). They are coded Brn Blk Brn Gld = 1 0 1 5% = 100r 5%
The two big resistors at the outside are the source resistors attached to the FETs. They are coded Yel Vio Sil Gld = 4 7 /100 5% = 0r47 5%.
The source connection is labeled E on the PCB.
Check continuity with your multimeter from E to resistor on each side. It should read the same as the test leads shorted together.
Now read from E to the other end of the resistor. It should read test short+half an ohm (0r5).
Power up the amplifier.
Measure the voltage across each source resistor. It should be the same as quoted on Fig6 (600mVdc).
The two blue squares with the grey star adjuster are the pots P1 & P2.
Read the manual carefully and when you are clear on what to do make the adjustment to lower your FET current from Vrs=600mVdc to Vrs=550mVdc. Allow to stabilise and recheck sink temperature.
I can't see your sinks, but I wonder if they are big enough??
I'm not sure you have stated this unambiguously.alazira said:
I'll re-phrase to hopefully make it clear.
Connect the third wire (the earth wire or equi-potential wire) of the mains input cable directly and permanently to the chassis.
Connect a CL60, or similar Disconnecting Network, to chassis and take the other lead to the main Audio Ground or to the Main PSU Zero Volts connection.
I have experience similar with different amp
It was missing connection to a driver
The reason was fragile traces cracked on a 4layer board
Some of the soldering on your amp board looks a little suspect, but its hard to see exactly, without looking at actual amp board
Not kind of me to say, but the issue with fakes popped up in my mind
But you need to make some specific measurements to reveal whether theres an issue with a driver
I dont have skills to tell you how, sorry
It was missing connection to a driver
The reason was fragile traces cracked on a 4layer board
Some of the soldering on your amp board looks a little suspect, but its hard to see exactly, without looking at actual amp board
Not kind of me to say, but the issue with fakes popped up in my mind
But you need to make some specific measurements to reveal whether theres an issue with a driver
I dont have skills to tell you how, sorry
Thanks for your last reply Andrew.
Seems to be running a bit cooler now that I've lowered to ±550mVdc.
Was told by someone else to measure DC offset at binding posts and try get it to zero by balancing between both pots. Seems not to have changed after lowering bias. Dont know if I'm measuring it right with my digital multimeter, seems to fluctuate by the second between 10 and 40 mVdc and between +ve and -ve, not what I was expecting to see, but is the first time I've even used a multimeter. Many thanks.
Seems to be running a bit cooler now that I've lowered to ±550mVdc.
Was told by someone else to measure DC offset at binding posts and try get it to zero by balancing between both pots. Seems not to have changed after lowering bias. Dont know if I'm measuring it right with my digital multimeter, seems to fluctuate by the second between 10 and 40 mVdc and between +ve and -ve, not what I was expecting to see, but is the first time I've even used a multimeter. Many thanks.
Debugging help
This is my first discrete transistor amp and I'm having a couple of issues getting it working.
I let it warm up for a few hours and tried to set the bias. On some of the bias adjustments, the bias was jumping around as I tweaked the resistor. It changed so much that I couldn't tell if I was turning the pot in the right direction, but by letting it settle after each tweak I was able to get the correct setting. On some adjustments the voltage changed very smoothly as I tweaked the pot. I'm not sure if this is normal or not.
I finally got all 4 transistors biased at around .6V and went to check the output offset.
One channel was around 7V. I tweaked the bias settings until it was close to 0, but bouncing around by a couple hundred millivolts. After about 10 minutes it had drifted back up to around 1.1 volt.
The offset on the other channel was -22V.
Any hints on how to proceed?
This is my first discrete transistor amp and I'm having a couple of issues getting it working.
I let it warm up for a few hours and tried to set the bias. On some of the bias adjustments, the bias was jumping around as I tweaked the resistor. It changed so much that I couldn't tell if I was turning the pot in the right direction, but by letting it settle after each tweak I was able to get the correct setting. On some adjustments the voltage changed very smoothly as I tweaked the pot. I'm not sure if this is normal or not.
I finally got all 4 transistors biased at around .6V and went to check the output offset.
One channel was around 7V. I tweaked the bias settings until it was close to 0, but bouncing around by a couple hundred millivolts. After about 10 minutes it had drifted back up to around 1.1 volt.
The offset on the other channel was -22V.
Any hints on how to proceed?
What set of PCBs are you using?
If you are using the Peter Daniels ones - are you sure you have the output resistors in the right holes?
Its possible you have totally or partially cooked your source resistors. Pull one end from the PCB and measure their resistance.
Let us know how you get on.
Fran
If you are using the Peter Daniels ones - are you sure you have the output resistors in the right holes?
Its possible you have totally or partially cooked your source resistors. Pull one end from the PCB and measure their resistance.
Let us know how you get on.
Fran
