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Sony Vfet Illustrated build guide
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Old 14th February 2020, 04:29 PM   #981
Dennis Hui is online now Dennis Hui  Canada
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Sony Vfet Illustrated build guide
Nice.

You might want to check the front end bias and offset and verify that the
T16 and T17 voltages are sufficiently high for your vfets. If that all
checks out then you're ready to install the vfets.

Cheers,
Dennis
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Old 14th February 2020, 04:35 PM   #982
Stanney2017 is offline Stanney2017  United Kingdom
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Will do.

Thanks Dennis.

Andrew
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Old 15th February 2020, 12:24 AM   #983
JoeyDD is online now JoeyDD  Canada
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Sony Vfet Illustrated build guide
Quote:
Originally Posted by metallicus69 View Post
I see the bridged amp very similar to a balanced amp , the difference being the way feedback is applied. In your case the resistive inputs to the common ground will create two equal but out of phase signals for the two halves without the necessity to bring pin 1 to the boards. That's asking for trouble. But I think this is easy to verify yourself if one channel is ready and working. I would just test this to eliminate all the doubts
Do you mean if I leave R4 to ground vs connecting both R4 together (like what Gyuri implemented some time ago based on ZM's suggestion)?
If I lift both R4 from ground and connect them together, at that point pin 1 should go directly to chassis?


I read other builders' experience with changing offset and voltages as the Vfet warms up. In my case, after warming up the amp for about an hour, I managed to adjust the output offset to about 40 mV, the FE offsets to <200 mV with the voltage drop across R5 and R6 at about 1.56 V.
The thing is that now, when I turn on the amp (cold), I have an initial output offset of about 20 mV which is fine, but the FE offsets are 0.6 and 1.1 V, (voltage across R5 and R6 is about 1.1 V).
Is it normal to have such high FE offsets when cold, even though they steadily drop to <200 mV as it warms up?
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Old 15th February 2020, 02:34 AM   #984
metallicus69 is offline metallicus69  Netherlands
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Quote:
Originally Posted by JoeyDD View Post
Do you mean if I leave R4 to ground vs connecting both R4 together (like what Gyuri implemented some time ago based on ZM's suggestion)?
This is the difference between bridge and balanced and this is what I would do when I will build this project (hopefully in the actual incarnation Sony Vfet Illustrated build guide

Quote:
If I lift both R4 from ground and connect them together, at that point pin 1 should go directly to chassis?
I say that I would do this irrelevant if the above modification is made or not. You donít always control what happens in the stage before the final amp and if you tie the pin 1 to the chassis you prevent hum no matter what. Especially when you have both channels in one chassis.



Quote:
I read other builders' experience with changing offset and voltages as the Vfet warms up. In my case, after warming up the amp for about an hour, I managed to adjust the output offset to about 40 mV, the FE offsets to <200 mV with the voltage drop across R5 and R6 at about 1.56 V.

The thing is that now, when I turn on the amp (cold), I have an initial output offset of about 20 mV which is fine, but the FE offsets are 0.6 and 1.1 V, (voltage across R5 and R6 is about 1.1 V).

Is it normal to have such high FE offsets when cold, even though they steadily drop to <200 mV as it warms up?

This is something that should be addressed first. I cannot advice anything here as I am still collecting the parts to build a dual balanced power stage. I think it is not normal and you should always have offsets below 50mV no matter the time since start of the amp.
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Old 15th February 2020, 04:29 AM   #985
JoeyDD is online now JoeyDD  Canada
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Sony Vfet Illustrated build guide
Thank you for the help Metallicus!
I've connected pin 1 as you suggested and the amp is completely silent when using a test speaker.
I'll try the R4 connection on the second monoblock after I adjust that one and see if I can hear a difference.

As for the high FE offset when cold, it seems Ben Mah's build had a similar behaviour (Sony Vfet Illustrated build guide). In the end, it looks like it was fine to leave it as is.

Paul
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Old 16th February 2020, 05:43 AM   #986
metallicus69 is offline metallicus69  Netherlands
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You're welcome ! Good to know what I should expect as well Sony Vfet Illustrated build guide
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Old 16th February 2020, 08:33 AM   #987
Zen Mod is offline Zen Mod  Serbia
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Default Maybe wrong thread .... Sony VFet DIY amp Feb. 2020

Pa sent me last night , to stop bugging

I couldn't resist ...... I must share with rest of Greedy Boyz

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File Type: pdf Sony DIY amp Feb. 2020.pdf (17.6 KB, 162 views)
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Old 16th February 2020, 01:59 PM   #988
Berny is offline Berny  Belgium
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Old 16th February 2020, 02:15 PM   #989
ItsAllInMyHead is offline ItsAllInMyHead  United States
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Quote:
Originally Posted by Zen Mod View Post
Pa sent me last night , to stop bugging

I couldn't resist ...... I must share with rest of Greedy Boyz

Bad, Bad, Zen Mod.

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Old 16th February 2020, 03:35 PM   #990
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nope

Pa is baaaaad!

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