PeeCeeBee V4H GB

[mj777]

Hi Shaan, is it ok to use 0R22 instead of 0R1 for the output resistors?
Regards,
Marjohn

 

[shaan]

Hi Marjohn.

Yes 0.22R is fine.

 

[mj777]

Thanks a lot Shaan, one additional question I would like to ask is, can I use the complimentary C3503 and A1381 instead of mje340/350 without affecting stability of the amplifier? Attached is the picture of the transistors and my build in progress.

Regards,
Marjohn

 

[shaan]

I haven't used them in this circuit (can't get this pair here), but I think they will work without problem as the VAS stage is well-tamed now.

 

[Harry3]

Hi mj777,
I'll be interested in your results using the C3503 and A1381. Keep us posted.

Regards
Harry

 

[Torvbakkane]

Hi mj777,
Have used alternative transistors for MJE340 / MJE350 with the transistors KSA1220A / KSC2690A with good results. The V4H amplifier with version rev.1 and performed all upgrades that a rev.2 version requires. Adjustment and testplay went straight ahead.
Is very satisfied with the finished product of V4H. I chose to use SMPS at 800Watt (it continuously delivers 500W at 25 ° C), and the amplifier is set up as Dual Mono.
Regards
Helge
(PS! Adding photos as attachments to this post was not performed due to the fact that all photos are only stored locally)

 

[mj777]

Thank you guys for your comments and suggestions, i will try and let you know the outcome, right now just waiting for other parts I ordered to complete it.

Regards,
Marjohn

 

[giaspyr]

Hi Giaspyr.

Does the offset change when turning the VR1 and VR2 trimmers?

HI Shaan, with trimmers removed it does change.

 

[giaspyr]

I did try to set up the amp from the start and I noticed that with probes of the MM connected to either R25 or R26 when powering it up I get a reading of 0.0 mV even when turning it off but with power on after turning the trimmers a couple of turns I start to get a reading of mV.

 

[giaspyr]

After setting up the amp from the start DC offset starts from +12.0mV climbs to +300mV when warm and after that suddenly drops back to +29.0mV and there it is stabilized.

The other channel has a DC offset of -5.0mV when warm.
That is a strange behavior.

 

[shaan]

I did try to set up the amp from the start and I noticed that with probes of the MM connected to either R25 or R26 when powering it up I get a reading of 0.0 mV even when turning it off but with power on after turning the trimmers a couple of turns I start to get a reading of mV.

After setting up the amp from the start DC offset starts from +12.0mV climbs to +300mV when warm and after that suddenly drops back to +29.0mV and there it is stabilized.

The other channel has a DC offset of -5.0mV when warm.
That is a strange behavior.

Hi giaspyr.

I just checked the pictures again in here Post 1364 and both rev 1 and rev 2 mod are there, so the channels should be stable. If the offset is behaving strangely then I suspect it is due to a faulty component. Did you replace all the trimmers in the problematic channel?

 

[giaspyr]

Thank you Shaan, for start I'll replace all trimmers and report back, if after replacing trimmers DC offset problem still exists should I replace any of the small transistors?

 

[shaan]

If the problem still persists, then remove power and check all BJTs for base-emitter and base-collector voltage with the multimeter's diode test mode. Small ones should read between 700 and 800mV, Q9/10 should read between 550 and 650mV.

 

[J.M.K]

V4H Rev2 boards in transit somewhere ?

Hi

Did anybody already receive the new set of boards?
According to 17Track, mine went to Kolkotta, then to Mumbai foreign post office
and still there ..........
Any info ? Covid lockdown ?

JM

 

[shaan]

Hi JM.

According to what the tracking results it's already off the shores. Expect news from your domestic shipper soon.

 

[giaspyr]

Hi Shaan, I did replace the trimmers but unstable offset still there, if it helps I noticed that tapping the D5 led with a screwdriver or my fingernail makes offset DC jump up and down.

 

[shaan]

Ahh... Looks like you already found the culprit here. Replace it with a good LED and check.

 

[giaspyr]

After replacing the led to set up the offset again do I need to put the 1.0 Ohm resistors in series to the power lines again?

 

[shaan]

As offset is supposed to be set before mosfet bias, you need to first turn VR3 to lowest resistance. Then install the 1ohm rail resistors and set the vas bias again, then the offset and finally the mosfet bias.

 

[giaspyr]

Is it OK to leave the 1.0 Ohm resistors in place after set up till I take offset measurements and make sure that the problem is resolved?