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Old 12th September 2013, 04:27 PM   #3751
RonD2 is offline RonD2  United States
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As I am approaching the point of no return on my layout, I thought I'd post a picture of where I am and where I'm going with the build.

I am assembling a BA-3/crippled F4 stereo chassis. BA-3 will run off the main PS. Finding it a bit tighter than I imagined prior to receiving the DIY chassis.

Do love working with the Deluxe 4U though. It brings back fond memories of building "Erector Sets" as a kid.

If all goes well with this stereo build, my plan is to build balanced monoblocks.

Looking for constructive criticism. This is an ambitious build for me and I can use all the help I can get!
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File Type: jpg Layout 1.jpg (922.3 KB, 224 views)
File Type: jpg With BA-3.jpg (162.0 KB, 212 views)
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Old 12th September 2013, 04:47 PM   #3752
6L6 is offline 6L6  United States
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I like it.
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Old 13th September 2013, 01:10 PM   #3753
RonD2 is offline RonD2  United States
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Default "Crippled" Crippled F4

My tales of woe will keep this thread alive forever it seems.

My crippled F4 board biases fine when tested as shown in the attached picture, i.e. the heatsink is not connected/grounded to the chassis base/PS. The board itself is grounded to the chassis via the CL60.

The picture was taken on powerup and after warmup is easily adjusted to 195mV bias and <5 mV offset.

However, when I attach the heatsink to the chassis (and, therefore, ground it), I get no bias and V+/V- voltages in the 100's of mV range. Feeling like I'm dancing with the devil with this, I immediately disconnected. No blown fuses and board/PS work fine when once again separated.

I then attached the heatsink to the PS/chassis base with the power off and find that all the mosfet drains are grounded.

This leads me to believe that I have improperly "crippled" my crippled F4. I have attached a close-up of the board. The cap in C2 is 1000 mF. I have jumpered across the empty C1 and planned to connect the input here.

I eliminated Q1, Q2, D3, D4, R1, R2, R3, R4, R24, R25, C1, C3 and C4.

Wish I could figure this out on my own but really need some help. Thanks again!
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File Type: jpg Seperated Bias.jpg (332.9 KB, 185 views)
File Type: jpg Crippled F4.jpg (115.7 KB, 180 views)
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Old 13th September 2013, 02:32 PM   #3754
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Quote:
Originally Posted by RonD2 View Post
My tales of woe will keep this thread alive forever it seems.

My crippled F4 board biases fine when tested as shown in the attached picture, i.e. the heatsink is not connected/grounded to the chassis base/PS. The board itself is grounded to the chassis via the CL60.

The picture was taken on powerup and after warmup is easily adjusted to 195mV bias and <5 mV offset.

However, when I attach the heatsink to the chassis (and, therefore, ground it), I get no bias and V+/V- voltages in the 100's of mV range. Feeling like I'm dancing with the devil with this, I immediately disconnected. No blown fuses and board/PS work fine when once again separated.

I then attached the heatsink to the PS/chassis base with the power off and find that all the mosfet drains are grounded.

This leads me to believe that I have improperly "crippled" my crippled F4. I have attached a close-up of the board. The cap in C2 is 1000 mF. I have jumpered across the empty C1 and planned to connect the input here.

I eliminated Q1, Q2, D3, D4, R1, R2, R3, R4, R24, R25, C1, C3 and C4.

Wish I could figure this out on my own but really need some help. Thanks again!
With all due respect, using the same color green wire for ground, V+ and V-may not be helping you resolve the problem. It may contribute to the problem. You are also using a twisted pair of black wires for power output and ground. Can you tell which is which at the loudspeaker terminal? It is also possible the MOSFETs were damaged as their rail fuses blew. Slo or fast blow may have made a difference. Which have you used?

NB. I see you tagged the V+ green wire with a red sleeve, and the V- green wire with a black sleeve. Works.

Last edited by Antoinel; 13th September 2013 at 02:51 PM. Reason: tweak
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Old 13th September 2013, 02:51 PM   #3755
RonD2 is offline RonD2  United States
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Apologize for the all green power wires. V+/V- are/were properly connected.

The twisted black pair is signal output and ground, never connected to anything other than the dmm.

The fuses are/were 2.5A slo blow.

Would blown MOSFETS bias properly as they now do (when heatsink ungrounded)?
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Old 13th September 2013, 03:14 PM   #3756
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Quote:
Originally Posted by RonD2 View Post
Apologize for the all green power wires. V+/V- are/were properly connected.

The twisted black pair is signal output and ground, never connected to anything other than the dmm.

The fuses are/were 2.5A slo blow.

Would blown MOSFETS bias properly as they now do (when heatsink ungrounded)?
My apology RonD2. I did recognise that you properply tagged the power rail wires with red and and black and none. MOSFETs OK.
  • Disconnect V+ , V- and ground leads at the main chassis PSU.
  • Isolate electrically the heat sink assembly from the main chassis.
  • With ohmmeter; is heat sink assembly shorted to its own ground , to its V+ and to its V-pcb joints?
  • Affix the heat sink assembly on the main chassis; but keep the 3 pcb power leads disconnected. Is heat sink shorted to chassis ground.
  • Connect pcb ground wire only to power supply star ground. Shorted heat sinkto ground?
  • Connect V+ wire of pcb to power supply V+. Is heat sink shorted to ground . Ditto wiyh V-.
There is gotto be an answer with a methodical pursuit.
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Old 13th September 2013, 03:33 PM   #3757
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Well it looks like your Heatsink is connecting something to another dunnit ?
Since it looks like mosfets are all nicely isolated The problems prob not there.

Why not try removing all those screws (and mounting hardware) that are holding the pcb to the Heatsink?

Seems likely one of them is connecting the Heatsink to some trace on the pcb that doesn't appreciate being tied o ground......
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Old 13th September 2013, 04:25 PM   #3758
RonD2 is offline RonD2  United States
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Thanks all for the help!

Iíll try to make my situation clearer. I completed my second board. Never connected before. Using it I found the following:

1. F4 board mounted on heat sink. Heat sink physically and electrically isolated from chassis/PS. Mounted F4 board connected to V+/V- supply and the boards ground connected to CL60 chassis ground. Drains are not shorted.

Runs for 45 minutes with stable bias and no offset.

2. Power down and let some time pass. Keeping the above setup, I add a ground wire from the heatsink to the chassis.

Now either all 3 P or all 3 N Mosfetís drains short to ground. No power applied.

Is this normal? My naive intuition tells me it is not.

Itís what makes me suspect that there is something wrong with my crippling surgery. I am tempted to just build out the whole F4 and forget the crippling but as I am intending to use this with a BA-3 front end I would rather not.

My determination to fix this far exceeds my electrical wherewithal to get it done!
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Old 13th September 2013, 04:37 PM   #3759
lhquam is online now lhquam  United States
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How did you measure the resistance from the drains to ground? What range on the ohmmeter? Did you measure the resistance from the drains to the heatsink with the heatsink isolated from ground?
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Old 13th September 2013, 04:42 PM   #3760
flg is offline flg  United States
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Did you use a clearance drill on the MOSFET mounting hole, maybe a 6x32 size bit?
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