If by checked you mean the right ones are where they are supposed to be then yes. The mosfets have been lovingly snugged to the heatsink and I have checked for shorts. All good.
Very nice quality build! Continue that good way!
I have build F5T - Monoblocks 2 years ago. I love them - especially driving
my electrostatic loudspeakers. Beautiful combination.
You will like your F5 - I am pretty sure!
Greets
Dirk
Thanks Dirk. I do believe the 5T is next on my bucket list and perhaps a pair of monoblocks at that. Did you do a build thread? Would love to see that.
Can't make out your attached image by the way.
it is important to know that JFets are well and alive
easiest to check with 9V battery Idss matching jig
bjts are dirt cheap, just replace them , if you already didn't
for mosfets - simple buzzer (when less than 30R) test function of your DMM is usually more than adequate to catch fried one - there can't be any buzz between mosfet legs
if in doubt , replace them too ....... they're also dirt cheap , especially when compared with value of amp you are making
then proceed with iterative setting procedure ...... input shorted, no load on output ,input drain trimpots on 0R (confirmed with ohmmeter across drain resistors), one DVM across output posts (DC offset) , second DVM across one mosfet source resistor .....
Ah yes... well you either assume I have a lot more knowledge about all this than I have explicitly pointed out that I do not, or you are just funning me. I have built three amps, including two Elekit tube kits, by following along with the instructions provided and surfing the relevent forums - but I haven't a clue what a 9V battery Idss matching jig is nor do I quite get what you mean by input drain trimpots on OR. So at the risk of hearing your eyeballs roll from northern Canada, where this morning we have been blessed with 4" of snow, I'm just going to say so.
I ordered a complete new set of parts, two new boards and a set of matching Jfets. I measured all the resistors best as I could and followed along on the build threads and the V1 of the build guide pdf as much as it made sense to (to me). Now I'm at the point where I can power up the psu and set the bias. This I do not quite know how to do regarding the use of the bulb tester as a safety measure. Perhaps this has been detailed in a post somewhere but there are literally thousands of posts and the search function is somewhat wanting.
to Trismos #105
Hello Trismos,
I did not make a build guide from my F5T - build. I read more than 450 pages
in the diyAudio - Pass Labs - forum and the article from Nelson Pass about the F5.
How I started my F5:
Step 1: I measured the Trimpots, if they are adjusted correctly -
P1 and P2 at 0 Ohm - this is very important - if set the wrong way
you will see some smoke!
P3 set to mid (you can measure this with your dmm (3 pins at the
trimpot; mid pin is wiper; you measure from mid to right
outer pin and then to left outer pin (DMM set to Ohm) turn
adjustmentscrew till resistance from mid to left or right pin
is the same.
Or if you used a 25 turn Trimpot: turn the adjustscrew to one
side till you feel resistance at the adjustmentscrew or you hear a
'click'. Then you turn back 12,5 turns - not super exact, but
works)
TH1 and TH2 (4.7Kohm) should have good contact to the
MosFets!
Step 2: with the amp pcbs NOT connected to the PSU I measured the
voltages at PSU. + voltage and - voltage should be symmetrical
(referenced to ground)
Step 3: I connected one side (left or right channel) amp pcb to the PSU
Step 4: USE YOUR BULB TESTER NOW! Amp is switched off!
Put your bulb tester between wallsocket and powercable of your
amp.
Step 5: Switch the amp on. The bulb of your lightbulbtester will shine
and then should dim down till bulb is off (in the first 2 to 3
seconds)
If the bulb doesn't turn off /stays bright- something is wrong.
SWITCH OFF THE AMP IMMEDIATELY. Be prepared!
There will be a short or any other fault.
If bulb is off - continue with step six
Step 6: Disconnect your amp pcb from PSU
Step 7: Do exactly the same with the other channel from Step 3 to
Step 5
If your lightbulbtester turned off you know that everything
should be o.K. with your other channel.
Step 8: Now you can connect left channel pcb and right channel pcb
with your PSU again. You are prepared for switching your F5 on
without the lightbulbtester. Nothing should happen -
No smoke in the amp!
In the next post I will describe the adjustment of P1 and P2. I hope I didn't
forget anything! I am not perfect - definitively not.
Perhaps other diyAudio - members can chime in with tips.
Greets
Dirk
Hello Trismos,
I did not make a build guide from my F5T - build. I read more than 450 pages
in the diyAudio - Pass Labs - forum and the article from Nelson Pass about the F5.
How I started my F5:
Step 1: I measured the Trimpots, if they are adjusted correctly -
P1 and P2 at 0 Ohm - this is very important - if set the wrong way
you will see some smoke!
P3 set to mid (you can measure this with your dmm (3 pins at the
trimpot; mid pin is wiper; you measure from mid to right
outer pin and then to left outer pin (DMM set to Ohm) turn
adjustmentscrew till resistance from mid to left or right pin
is the same.
Or if you used a 25 turn Trimpot: turn the adjustscrew to one
side till you feel resistance at the adjustmentscrew or you hear a
'click'. Then you turn back 12,5 turns - not super exact, but
works)
TH1 and TH2 (4.7Kohm) should have good contact to the
MosFets!
Step 2: with the amp pcbs NOT connected to the PSU I measured the
voltages at PSU. + voltage and - voltage should be symmetrical
(referenced to ground)
Step 3: I connected one side (left or right channel) amp pcb to the PSU
Step 4: USE YOUR BULB TESTER NOW! Amp is switched off!
Put your bulb tester between wallsocket and powercable of your
amp.
Step 5: Switch the amp on. The bulb of your lightbulbtester will shine
and then should dim down till bulb is off (in the first 2 to 3
seconds)
If the bulb doesn't turn off /stays bright- something is wrong.
SWITCH OFF THE AMP IMMEDIATELY. Be prepared!
There will be a short or any other fault.
If bulb is off - continue with step six
Step 6: Disconnect your amp pcb from PSU
Step 7: Do exactly the same with the other channel from Step 3 to
Step 5
If your lightbulbtester turned off you know that everything
should be o.K. with your other channel.
Step 8: Now you can connect left channel pcb and right channel pcb
with your PSU again. You are prepared for switching your F5 on
without the lightbulbtester. Nothing should happen -
No smoke in the amp!
In the next post I will describe the adjustment of P1 and P2. I hope I didn't
forget anything! I am not perfect - definitively not.
Perhaps other diyAudio - members can chime in with tips.
Greets
Dirk
Awesome post Dirk. I'm heading out of town for a week so won't be able to give it a go until I get back but will let you know. Excited to give it a go now - I've had this project on the go for quite a while now.
Jims tutorials have been very helpful but this particular issue is missing from the build tutorial linked to on the store site, and his other build uses a different board (Peter Daniels).
Jims tutorials have been very helpful but this particular issue is missing from the build tutorial linked to on the store site, and his other build uses a different board (Peter Daniels).
F5 - adjustment of P1 and P2 - biasing the amp up
Do this first for the right channel (not both channels together!)
you will need 3 DMMs:
Step 1: connect the first DMM to the loudspeaker - output
red probe to + output
black probe to - output
set DMM to mV (milliVolts)
Step 2: connect second DMM over bias resistor R8. Easiest way is to use
crocodile clips. Red probe to one side of the resistor wire/ black probe
to the other side of resistor (you measure voltage over the resistor)
Take care that crococlips have only contact with the resistor
set DMM to mV (milliVolts)
Step 3: connect third DMM over bias resistor R7 (same procedure as Step 2)
set DMM to mV (milliVolts)
Now you are prepared to measure one channel.
Switch the amp on. Be prepared to switch it off in a case of emergency.
All 3 DMMs should show 0.0 mV - if not - something is wrong.
Now you start to adjust P1 and P2:
Turn P1 a half turn
Check if something happens on any of the 2 DMMs over the bias resistors ( it will take some turns of the P1 till a very low voltage will show up (anywhere in the 0.1mVto 1mV region - turn slowly - always a half turn - wait - watch all 3 DMMs if anything happens - if you see a voltage).
Now you turn P2 till the corresponding DMM also shows 0.1 to 1mV.
Your 3rd DMM at the loudspeaker output should not show a higher offset
voltage of more than 50mV ( but I also had 100mV offset without any damage).
Adjust P2 till offset at loudspeakeroutput is close to 0 milliVolts.
Wait a short while if offset stabilizes (It will drift a little bit - that is normal)
Now the adjustment continues the same way:
Turn P1 a little bit higher (till offset at loudspeaker output is at 50mV)
Turn P2 a little bit higher (till offset at loudspeaker is close to 0 mV again)
Your readings on the 2 DMMs over the bias resistors should be similar
(not exactly the same value in mV - depends on how good your MosFets are matched)
Do this till the 2 DMMs over the bias resistors will be at around 250mV.
Keep always an eye on the loudspeakeroffset.
Let the amp 'cook' (for 30 minutes to 1 hour). This means your heatsinks will get warm. Should never become hotter than 50 C (temperature). Measure with an infrared thermometer
or use Nelson - Pass- 10 second rule. You should be able to touch the heat sink with your hands for 10 seconds.
This procedure takes time. I needed often more than one hour to adjust one
channel. Patience is necessary. Never turn the P1 and P2 too fast.
Always keep an eye on all 3 DMMs!
Same will have to be done with the other channel. Same procedure.
I wish you success!
And happy listening!
After a few days you should be able to bias the amp higher. Values of
300mV to 400mV over the bias resistors should be possible. If your heatsinks
can handle the heat (never over 50 C).
I hope I could help you.
Any other hints of forum members are welcome!
Greets
Dirk
Do this first for the right channel (not both channels together!)
you will need 3 DMMs:
Step 1: connect the first DMM to the loudspeaker - output
red probe to + output
black probe to - output
set DMM to mV (milliVolts)
Step 2: connect second DMM over bias resistor R8. Easiest way is to use
crocodile clips. Red probe to one side of the resistor wire/ black probe
to the other side of resistor (you measure voltage over the resistor)
Take care that crococlips have only contact with the resistor
set DMM to mV (milliVolts)
Step 3: connect third DMM over bias resistor R7 (same procedure as Step 2)
set DMM to mV (milliVolts)
Now you are prepared to measure one channel.
Switch the amp on. Be prepared to switch it off in a case of emergency.
All 3 DMMs should show 0.0 mV - if not - something is wrong.
Now you start to adjust P1 and P2:
Turn P1 a half turn
Check if something happens on any of the 2 DMMs over the bias resistors ( it will take some turns of the P1 till a very low voltage will show up (anywhere in the 0.1mVto 1mV region - turn slowly - always a half turn - wait - watch all 3 DMMs if anything happens - if you see a voltage).
Now you turn P2 till the corresponding DMM also shows 0.1 to 1mV.
Your 3rd DMM at the loudspeaker output should not show a higher offset
voltage of more than 50mV ( but I also had 100mV offset without any damage).
Adjust P2 till offset at loudspeakeroutput is close to 0 milliVolts.
Wait a short while if offset stabilizes (It will drift a little bit - that is normal)
Now the adjustment continues the same way:
Turn P1 a little bit higher (till offset at loudspeaker output is at 50mV)
Turn P2 a little bit higher (till offset at loudspeaker is close to 0 mV again)
Your readings on the 2 DMMs over the bias resistors should be similar
(not exactly the same value in mV - depends on how good your MosFets are matched)
Do this till the 2 DMMs over the bias resistors will be at around 250mV.
Keep always an eye on the loudspeakeroffset.
Let the amp 'cook' (for 30 minutes to 1 hour). This means your heatsinks will get warm. Should never become hotter than 50 C (temperature). Measure with an infrared thermometer
or use Nelson - Pass- 10 second rule. You should be able to touch the heat sink with your hands for 10 seconds.
This procedure takes time. I needed often more than one hour to adjust one
channel. Patience is necessary. Never turn the P1 and P2 too fast.
Always keep an eye on all 3 DMMs!
Same will have to be done with the other channel. Same procedure.
I wish you success!
And happy listening!
After a few days you should be able to bias the amp higher. Values of
300mV to 400mV over the bias resistors should be possible. If your heatsinks
can handle the heat (never over 50 C).
I hope I could help you.
Any other hints of forum members are welcome!
Greets
Dirk
I'll just add a minor point to Step 1 on the initial setting of P1 and P2. You can verify
this by checking the resistance across R5 and R6; they should be close to zero
if you have P1 and P2 turned all the way in the desired direction.
(Referring to schematics on page 2 here:
http://www.firstwatt.com/pdf/art_f5_turbo.pdf )
this by checking the resistance across R5 and R6; they should be close to zero
if you have P1 and P2 turned all the way in the desired direction.
(Referring to schematics on page 2 here:
http://www.firstwatt.com/pdf/art_f5_turbo.pdf )
And attention that you don't touch anything inside the amp!
You know there is lethal voltage inside!
And be careful with your screwdriver during adjustments - don't touch anything - only the tiny screw of the trimpot.
I use special isolated screwdrivers for that.
Greets
Dirk
And now - a beer
You know there is lethal voltage inside!
And be careful with your screwdriver during adjustments - don't touch anything - only the tiny screw of the trimpot.
I use special isolated screwdrivers for that.
Greets
Dirk
And now - a beer
F5 - adjustment of P1 and P2 - biasing the amp up
After a few days you should be able to bias the amp higher. Values of
300mV to 400mV over the bias resistors should be possible. If your heatsinks
can handle the heat (never over 50 C).
I hope I could help you.
Any other hints of forum members are welcome!
Greets
Dirk
Shouldn't the bias voltage be 600mV to start? I run mine at 700mV and could go higher without overheating.
copied from Nelson Pass article: 'It's the F5 Turbo amp'
As a rule of thumb, the output devices should not be operated at more thanabout half their maximum rating, and generally the case temperature needs tobe under 100 deg C. For most amplifiers this means a heat sink temperatureof about 50 to 55 deg C., which is the temperature that you can put your handon for about 10 seconds.The devices are biased at about 1.3 amps in the original circuit for adissipation of about 30 watts per device. We are not in a good position to askthe original heat sinks to dissipate more, so if you increase the supply to 32volts, you may need to operate at a lower bias point – I used about 1 amp(0.47 volts across R7 and R8). This will still get you a decent distortion specto 50 watts. If you have difficulty keeping the bias stable, you can increasethe values of R7 and R8 to 0.68 ohms without significant penalty.
Greets
Dirk
As a rule of thumb, the output devices should not be operated at more thanabout half their maximum rating, and generally the case temperature needs tobe under 100 deg C. For most amplifiers this means a heat sink temperatureof about 50 to 55 deg C., which is the temperature that you can put your handon for about 10 seconds.The devices are biased at about 1.3 amps in the original circuit for adissipation of about 30 watts per device. We are not in a good position to askthe original heat sinks to dissipate more, so if you increase the supply to 32volts, you may need to operate at a lower bias point – I used about 1 amp(0.47 volts across R7 and R8). This will still get you a decent distortion specto 50 watts. If you have difficulty keeping the bias stable, you can increasethe values of R7 and R8 to 0.68 ohms without significant penalty.
Greets
Dirk
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