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Sony Vfet Illustrated build guide
Sony Vfet Illustrated build guide
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Old 14th February 2018, 08:20 PM   #491
Eric is offline Eric  United States
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Sony Vfet Illustrated build guide
Ha- that's too funny, Brandan! A few years ago, I was describing my system to a co-worker only to learn that her father had been using my IB sub web page as a guide to what he was building. We were in a van on the way to the airport when she started texting her father: "You'll never believe who I am sitting next to..." What fun! I hear from people all around the world each week because of my web pages.
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Old 28th February 2018, 01:00 PM   #492
vintagejapan is offline vintagejapan  Australia
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Quote:
Originally Posted by 2 picoDumbs View Post
This is a very good amp don't give up on it just yet.
If you have 32V rails then increase R15 and R16 to 47.5k or 48.7k, this will give you more voltage swing before clipping.
Essentially it will convert it to around a 25W amp.

If you have 31.5V rails use 47.5k
If you have 32.5V rails use 48.7k

We can also increase the gain a little bit but I don't think we need to go there just yet.
Finally managed to change the resistors 15 and 16. After a more accurate reading the rail voltages were just above 32 so I used 48.7k resistors. there is audible improvement. I am beginning to think the amp needs a preamp with lot of gain. The volume on my pre is at about 1'oclock, with other sources never go past 11. I can live with that though. The initial burn in has been completed and everything is very stable now. Was able to get less than 10mV on DC balance. I been comparing the amp with few other vintage Vfets I have and is a worthy contender. Thank you Mr Pass! And thank you to all offering help to complete the project.
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Old 28th February 2018, 01:31 PM   #493
Rodeodave is offline Rodeodave  Austria
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Sony Vfet Illustrated build guide
The stock DIY Sony VFET amp does 15W rms into 8R and has a closed loop gain of 16dB. The input sensitivity is thus about 1.7V rms, which is well within line level, um, levels.

Are you sure your R1 at the input is 2.2k? Maybe you have unintentionally formed a potential divider by using a higher resistance.

Also, a logarithmic pot at 12 o'clock (50% rotation angle) will only pass around 10% of the signal, so you'd just be wasting even more signal and passing more noise with a higher gain preamp.
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Old 16th March 2018, 05:14 AM   #494
soundslave is offline soundslave  United States
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Got my boards stuffed and they have passed the resistance test. Applied voltage as required for part 2 and I'm not sure what to think of some of the readings. Everything looks good until I get to t-6 to t-11 where I have +16.15 volts. At t-8 to t-13 I have -16.15 volts and at G to t-18 I get -16.69 volts. Should I be concerned or is this normal before the pots have been adjusted?
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Old 19th March 2018, 06:17 PM   #495
soundslave is offline soundslave  United States
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No reply in several days have I stumped the experts? Posted in wrong thread?
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Old 19th March 2018, 06:57 PM   #496
Rodeodave is offline Rodeodave  Austria
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Sony Vfet Illustrated build guide
Are T14 and T15 to G close to zero? Sounds like Q3 and Q4 are not turned on properly. Check that Q3 and Q4 are the correct part and are correctly orientated in regard to their respective pinout. Also, check R7 to R10, they're supposed to be 2.21k each. That's where I'd start at least...

Also, pics, plz. Why doesn't anyone post pics, it makes troubleshooting so much easier.
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Last edited by Rodeodave; 19th March 2018 at 07:00 PM. Reason: R7-R10
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Old 20th March 2018, 03:48 AM   #497
soundslave is offline soundslave  United States
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G-T6=30.6v. G-T8= -30.6v
G-T4=-24.1v G-T2= 24v
T6-T7= 0.714v T8-T9=0.822v
T6-T11=16.15v T8-T13=-16.15v
G-T18=-16.69v
G-T14=14.36v G-T15=-14.34v
G-T19=12.43v G-T20=-12.68v
G-T17=-13.36v G-T16=7.38v

All of the resistors are in the correct position. The semiconductors seem to be installed correctly as well. Q3-Q4 seem good also. I have inspected the solder side and found nothing. I will post photos later when I have a chance
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Old 20th March 2018, 01:54 PM   #498
Dennis Hui is online now Dennis Hui  Canada
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Sony Vfet Illustrated build guide
Can you please verify that you correct values for R35, R34 (221 ohm) and P3, P4 (500 ohm)?

The T6-T11, T8-T13 voltages seem very high, assuming reasonable Idss values.
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Old 20th March 2018, 02:30 PM   #499
soundslave is offline soundslave  United States
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R34,R35 are 500 ohm and P3,P4 are 1k ohm.
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Old 20th March 2018, 08:25 PM   #500
soundslave is offline soundslave  United States
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Here are the photos, hope someone can see something I would really like to hear this baby sing
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