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Old 24th December 2018, 05:04 AM   #621
Vunce is online now Vunce  United States
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Quote:
Originally Posted by shaan View Post
Hi Vunce.

Great news. You may also want to keep the input wires far from mains, rails and speaker wires and twist every pair of wires.
Thanks Shaan.
Now that I’m satisfied with the noise reduction, I can proceed with final wiring and tidy up the spaghetti mess of wires.
Maybe, it can get even better!
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Old 24th December 2018, 05:19 AM   #622
shaan is offline shaan  India
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Bests.
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Old 24th December 2018, 07:00 AM   #623
shaan is offline shaan  India
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Update:

We are moving towards the next group buy of PeeCeeBee V4H. Interested members please leave a post with your required number of boards.

Thanks
shaan
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Old 24th December 2018, 09:46 PM   #624
bvtrinh is offline bvtrinh  United States
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Hello, I just purchased a pair and would like to use them to replace a pair of First One 1.4M. I was wondering if anyone has heard both and can offer a subjective comparison? Thank you!
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Old 27th December 2018, 05:07 PM   #625
shaan is offline shaan  India
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Default UPDATE: Oscillation With Renesas MOSFETs - A Much Better And Easier Solution

Hello members.

While the previously posted solution here did solve the issue of parasitic oscillation with Renesas MOSFETs, during further tests with four channels of V4H I did manage to make one of the channels oscillate even with the capacitors installed. Some hair was pulled subsequently and the channel became stable with 100pF instead of the previously mentioned 270pF! Obviously no two MOSFETs are same and different ones would need different value of gate-source capacitor.

Anyway, I didn't stop but kept on trying to get to something that would stop me from dropping Renesas forever.

And I have good news.

--------------------------

The Solution:

R27,R29 and R28,R30 i.e. the gate resistors (initially 330R and 220R), all increased to 560R (and gate-source capacitors removed).

--------------------------

Now there is absolutely no parasitic oscillation in any of the channels, that tested 8 pairs of old and newly bought non-matched Renesas MOSFETs, and are perfectly stable for any signal level. Unlike the capacitor trick this solution has zero footprint, is symmetrical and works consistently. So I will update the original design with this one. If anyone is facing the same problem with 2S MOSFETs then please replace the 330R and 220R resistors with 560R. If biasing and offset trimming was done already then don't worry, DC operating conditions won't be affected after installing the four resistors.

Thanks and cheers.
shaan
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Old 27th December 2018, 09:15 PM   #626
Vunce is online now Vunce  United States
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Hi Shaan,

For the past two days Iíve been enjoying my fresh new V4H.
Today, after several hours of playing when the preamp volume was decreased to low level listening the V4H started to act strange. The left channel would drastically reduce in loudness, almost muted. When the volume was turned back up no problems at all, it has only happened when the volume gets turned down low. Then I read your last post that oscillation could still happen even with the 270pF caps I have installed. First, is this a symptom of that very problem? Should I stop using the amp until this is fixed?

Regards,
Vunce
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Old 28th December 2018, 04:28 AM   #627
shaan is offline shaan  India
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Hi Vunce.

The parasitic oscilation can produce many strange effects including lowering of volume. Please remove the capacitors and replace R27,28,29,30 with 560R.
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Old 28th December 2018, 05:55 AM   #628
bambadoo is offline bambadoo  Norway
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Quote:
Originally Posted by Vunce View Post
Hi Shaan,

For the past two days Iíve been enjoying my fresh new V4H.
Today, after several hours of playing when the preamp volume was decreased to low level listening the V4H started to act strange. The left channel would drastically reduce in loudness, almost muted. When the volume was turned back up no problems at all, it has only happened when the volume gets turned down low. Then I read your last post that oscillation could still happen even with the 270pF caps I have installed. First, is this a symptom of that very problem? Should I stop using the amp until this is fixed?

Regards,
Vunce
What kind of mosfets do you use?
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Old 28th December 2018, 08:48 AM   #629
prasi is offline prasi  India
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Hello Vunce,
could it be due to the pot not being able to track properly on both the gangs? (applicable more for a dual gang log carbon pot)

regards
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Old 28th December 2018, 11:28 AM   #630
Vunce is online now Vunce  United States
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Hi Bambadoo,
Iím using the Mosfets Shaan supplied.

Hi Prasi,
Iím using my AKSA Lender preamp which has a stepped attenuator, no carbon wiper here. This has not happened with the other amps I use. I will dig in again today to swap resistors as per Shaanís suggestion.
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