DIY Class A/B Amp The "Wolverine" build thread

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#4,621
mainframe99 said:
1. No, you do not need to turn down R11 after completing initial testing (step 17) without output transistors. This will remain at or around 5V (it will drift a little as temperatures change) so its fine to leave it and tweak it later. (It would have been put in the build guide if this was a requirement.)

2. No, you should not use a Variac on the Cobra, it will cause undesirable behavior and may blow its internal fuse or output protections.

If it is your first time, step 20 must be performed with the same "TESTING" power supply you used for step 17, ideally 30V. If you have performed step 17 with full rail voltages, I hope you first removed the temporary resistor placed across R17 (or never had installed). You may be okay to go full rail voltage at step 20 if step 17 passed full rail voltage, just be sure to have the correct fuses installed as step 20 A, and you absolutely must have passed step 19, and also checked all transistor legs for no shorts to PCB ground or the heatsink.

(The cobras output SC protection is faster than the 2A fuses if there is a rail-ground or rail-rail short anyway, I've ahem tested this)

Remember, at step 20, you are measuring bias voltage at TP's 101 and 102, NOT R111A and R111B. The build guide unintentionally confuses the reader here by saying "as done in the initial test procedure", potentially leading the builder to put the probes BACK at R111A and R111B, which is incorrect.



P.S> how did you do this? these values aren't adjustable, but they do vary slightly with rail voltage, which leads me to believe you did manage to complete step 17 with full rail voltage?
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Ok. Thanks for the clarification of measuring R101 and R102, not R111A and R111B. I was just about to pose that as a question.

I used 30DCV from my Rigol for 17 and 17.1. I have not power up since I installed the output transistors.

As I prepare for step 20, I'm more than happy to use the Rigol settings again.

I have completed step 19.

Using the Rigol at 30DCV do I retain the 0.3A limit? I understood that was necessary for Step 17 & 17.1.

If I've got it all right, I will proceed to complete step 20 using the Rigol set at 30DCV and 0.3A or advise.

Again, thanks for the guidance.
 
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#4,622
mainframe99 said:
This fuse is only protecting the internal AC line cable from shorts to the chassis running from the IEC socket to the cobras AC input. Your IEC socket should be a 3 pin, with the earth connected directly to the chassis.

The cobra is capable of pulling 1900W peaks (1200W sustained), and your American sockets are capable of ~1800W sustained, so this fuse should be 10-12A (15A at the absolute maximum) - provided the cable gauge you used from IEC to cobra can sustain this also. Otherwise the fuse must be sized to protect the maximum the cable gauge can handle. The cobra has a fuse protecting anything beyond its AC inputs from shorting on its PCB, and also has protections built in for its output rails.

If, for some reason, you used skinny * cable from the IEC socket to the cobra than can only handle 5A, you really should have this fuse at 5A. (yes i know the short distance means the skinny * cable can probably handle more but let's keep it simple and safe)
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+Cobra directed me to use a 12A fuse at the IEC. My wiring IEC to Cobra to amp boards is 14AWG.
 
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#4,623
Chiptech said:
Ok. Thanks for the clarification of measuring R101 and R102, not R111A and R111B. I was just about to pose that as a question.

Using the Rigol at 30DCV do I retain the 0.3A limit? I understood that was necessary for Step 17 & 17.1.

If I've got it all right, I will proceed to complete step 20 using the Rigol set at 30DCV and 0.3A or advise.
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0.3A should be okay when the bias is (at test points 101 and 102, you wrote resistors btw) down at 0mV at initial power on but as you bring that bias up to the target 40-44mV each rail can draw around 500mA from memory, so you are better to change that lab supply current limit from 0.3A to 1.0A for step 20.

The reason for this is when you were testing at section 17 the only “load” the amp had was the bias current through the drivers Q105/106, thanks to J103. Now you have J103 removed and the “Load” is now all of the bias current through all of the output transistors.
 
#4,625
Reconfirming at this point I have removed J-103 prior to step 20.

I have set the Rigol at 30DCV and 1A and amperage limit at 1A.

Regarding step 20, it is complete when I have biased R109 to ~40mV. I leave it at that bias point to proceed to the final bias under full power.

The next step is to install fuses per sheet 2 and power on via the Cobra and make final bias at 44mV.
 
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#4,629
Good progress this weekend, input boards done, next up the output boards.
IMG_4807.jpeg
 
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#4,636
Ideally. You can use larger power supplies with same voltages but you must use stronger parts as a consequence. The BOM has a column showing what parts to use with SMPS or way oversized power supplies

And to your original question, you can get the full 240W into 8 ohm with a 3 pair if you use a 50VAC power supply and the strongest drivers and outputs in the BOM
 
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#4,637
Step 20.k says to refer to sheet 2 of the BOM to determine correct fuses to be used with full power.
My Cobra SMPS is 64DCV out.
On sheet 2, I don't see anything that provides guidance for correct fuse amperage.

Can someone clarify what I'm missing.

Thanks
 
#4,638
mainframe99 said:
Ideally. You can use larger power supplies with same voltages but you must use stronger parts as a consequence. The BOM has a column showing what parts to use with SMPS or way oversized power supplies

And to your original question, you can get the full 240W into 8 ohm with a 3 pair if you use a 50VAC power supply and the strongest drivers and outputs in the BOM
Click to expand...
Thats what I meant,I havent yet gotten my pcbs so I dont have access to the build guide..
 
#4,639
Hi Guys,

I am just completing the build of the first power board, EF3-4 V 4.0. I am mounting drivers Q107 and Q108 under the board so that they lie on the heatsink. I noticed that my MJE15032G and MJE15033G drivers have full metal backs. This means I need to source shoulder washers front and back and use thermal pads to isolate them. Those drivers are in a TO-220-3 package. Looking on Mouser it looks like you have to measure the hole in the transistor in order to source the right one, correct? Do you use two identical washers for the front and back of each transistor?

Many thanks,

John
 
#4,640
First attempt at Step 20.
Rigol DC power supply set at 30DCV and 1A with a ceiling of 1A
All lights come on.
R109 at 0 bias - resistance is maxed
But I can only dial R11 up to 2.956 DCV. R11 is turned all the way up.
R25 is 0.

When I did step 18 I had no problem getting to 5V on R11.

I thought I'd stop here and ask if something is amiss before I started biasing R109.

Am I limited at 2.9DCV because of my 30DCV / 1A limits?
 
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