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

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#2,582
mainframe99 said:
hmm, running a higher test rail voltage seems to fix almost everything, Just still have that initial low bias of 400mV and max I can wind it is 1.4V, This normal behavior? DC offset now +-0.25mV
Click to expand...
As long as you have some adjustment close to the range mentioned in the build guide, then the bias circuitry is working
 
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#2,583
mainframe99 said:
No blown fuses or smoke 😀 however Im testing without output transistors in, and I'm getting the following issues, identical on both channels - testing with a Variac and a small 30VA 0.63A 15-0-15VAC tx / 20VDC power supply.

A. TP107 and TP108 I get only ~400mV initially, guide states this should be 750-800
G. Im using TTC/TTA for Q101 and only getting 1.2V for both of these measurements, guide states 1.5V
H. My DC offset is 255mV both channels. R25 cannot get this down enough.
I. bias circuit does still function with R109, but due to being so low initially (point A) the highest I can get it to is 1.39V.

Is this all due to a low voltage/bad power supply for testing perhaps? I have a larger transformer here I can try..
Click to expand...
I'm using a +-24dc 2amp power supply, Fluke digital dual trace O-Scope and a Fluke 87 multimeter. I'm also using the TTC/TTA semi's.
My measurements;
A. TP107 and TP108: Board one,(B1) 493mv and Board two,(B2) 458mv.

E. R11 adjusts for 5.008 vdc on both boards

F. TP-3 and TP-4: 0.594 vdc on both boards

G. TP-105: (B1)1.29 and (B2) 1.27 vdc
TP-106: (B1)1.28 and (B2) 1.26 vdc

H. DC offset is (B1) 29mv and (B2) 22.5mv and that's all the adjustment I can get.
Switch to measure AC (B1) 1.3mv and (B2) 0.2mv. Are you guys sure these can get down to less than 0.080mv? That's less than 0.00008 volts ac! Is this a typo.. Should it say less than 80mv or 0.080 vac?

I. Bias adjusts to 1.42vdc on both boards.

One other thing I saw... Step E. TP-1 (DMM +) and TP-2 (DMM +) Should one of these be a negative.

If you all say it's all good, I'll press on to the next stage of testing.
Scott
 
#2,585
I'm thinking about building a second Wolverine.....the EF3-4...not sure yet. I've got these old EI Transformers from a Harman Kardon 665VXi. They both work...that I know but I don't know the VA rating. The service manual says this but the question is...is that for both or just one of them. I tend to think both so 175 VA per transformer which might be a little bit lowish....
Does anyone know these?

thx in advance

w.
WhatsApp Image 2023-08-20 at 15.56.09.jpeg

Screenshot 2023-08-20 180849.png
 
#2,589
@90scaraudio
I think you are on the correct road......I never use low psu for the first setup....hahaha.... i use direct +/-71Voltages .

G. TP-105: (B1)1.29 and (B2) 1.27 vdc
TP-106: (B1)1.28 and (B2) 1.26 vdc
A bit low measurements but you use and low voltage psu.
And your offset too high for this amp ....i get 0.150mv
Did you match the Q.123456 etc....
 
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#2,591
Yes it's close... 40vac x 1.414 = 56.56. It's usually close to that.
So, Nikos, you think once I get the Output semis installed and 57ish rails, the test numbers will be more normal? Or should put +-57v ish and do the first test again without the finals installed?
 
#2,592
First of all put the correct resistors on your IPS for the right working voltage.... let's say 57vdc.
Triple eye check your IPS
Put the trimmers at correct value Ω according to build manual.
Put all the necessary jumpers according to build manual.And put also jumper to Input. Fire it up check the voltages.....
 
#2,594
Before testing I’d since made adjustments for 71V rails (from 63)

My DC offset when testing with a 20VDC power supply (so I’d assume similar may be happening to you) was way off , like 250mV both channels with the DC offset pot set to halfway as per the earlier guide instruction. Maxing the dc offset pot with this test voltage still wouldn’t get it to 0. I returned it back to where it was, and started testing sequence again this time with a higher voltage 45VDC then all the way up to 63VDC (using a variac to slowly bring it up) and when I checked the offset again at 45VDC one channel was bang on 0.2mV and the other channel was about 4mV and I was able to just adjust using a couple turns on the pot.

Also D10 and 11 only just lit up at 45V I think fully lit at 50V. Seems like testing with too low a voltage means some of the components aren’t doing what they need to.

Maybe worth some adjustments to this section to help future noobs? I feel bad making any criticisms on such an amazing project though, and I did manage to figure it out in the end.
 
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#2,597
Yeah also my voltages to confirm the regulating on q101 and q102 (to 105 and tp106 to rails) were not the 1.5V as they should be until I got the rail voltage up to near the design rail voltage. They were just 1.2V with 20VDC test supply. So your good there too.
 
#2,599
600VA 50-0-50VAC per channel if you are doing a dual mono transformer LPS with 71VDC rails. 71VAC transformers would make 100VDC rails, far too high.

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:cop: Mod edit: Please note the 50-0-50VAC is erroneous. Post a new question in the thread if you want correct information, or look at #3108 or #3113. :cop:
 
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