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 Post subject: Re: 807 Williamson amp
PostPosted: Sep Fri 14, 2018 3:08 am 
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john8750 wrote:
I will give that diode a try Flip. Should a 100uf for C1 help drop hum? Should R3 remain 1K?
Possibly. It's the 6SN7 filter cap and while that's a "PP" circuit too it's before the gain of the 807s.

Try it with R3 as is to begin with (saves effort and time). Then if it works we can think about changing it.


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 Post subject: Re: 807 Williamson amp
PostPosted: Sep Fri 14, 2018 3:26 am 
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Flipperhome wrote:
john8750 wrote:
B+ 486
B++ 480
60v 65.7
Remember only the right channel is connected.
Still hear some hum.
Connected FB and hum disappeared. Except at turn-on, brief hum then gets quiet.
Seems like mosfet is happy with the modified circuit.
How to lower B+, and how to rearrange wiring to eliminate more hum?

Where do you have the R18/C7 ground connected to?

I wouldn't worry too much about hum at turn on. Nothing is balanced and operating properly at turn on.

What's your AC line volts? (Btw, B+ is only 8% high).




AC line 118.8
R18/C7 has a dedicated connection to the star at C3.

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 Post subject: Re: 807 Williamson amp
PostPosted: Sep Fri 14, 2018 3:40 am 
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john8750 wrote:
Flipperhome wrote:
Where do you have the R18/C7 ground connected to?

I wouldn't worry too much about hum at turn on. Nothing is balanced and operating properly at turn on.

What's your AC line volts? (Btw, B+ is only 8% high).
AC line 118.8
R18/C7 has a dedicated connection to the star at C3.
Okay, that's good AC. And that's where they should be grounded. Where is the chassis grounded?

Measure the drop across the MOSFET (and don't pop it this time :wink: ) Like I said, it should be around 17-20 V. We may need to adjust R1/R2 to get the desired drop across the MOSFET, which will somewhat lower B+ in the process.


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 Post subject: Re: 807 Williamson amp
PostPosted: Sep Fri 14, 2018 4:04 am 
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Flipperhome wrote:
john8750 wrote:
Flipperhome wrote:
Where do you have the R18/C7 ground connected to?

I wouldn't worry too much about hum at turn on. Nothing is balanced and operating properly at turn on.

What's your AC line volts? (Btw, B+ is only 8% high).
AC line 118.8
R18/C7 has a dedicated connection to the star at C3.
Okay, that's good AC. And that's where they should be grounded. Where is the chassis grounded?

Measure the drop across the MOSFET (and don't pop it this time :wink: ) Like I said, it should be around 17-20 V. We may need to adjust R1/R2 to get the desired drop across the MOSFET, which will somewhat lower B+ in the process.




Great news.
Installed diode 3 and changed C3 to 75uf, the close's I had. I will order 100uf if that will be better. Hum level very low. Reconnected FB and now totally acceptable, no hum whatsoever. B+ still a little high. We could adjust that after connecting left bank.
The only chassis ground is at the RCA inputs.
Note--I also have the house system grounded to chassis.

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 Post subject: Re: 807 Williamson amp
PostPosted: Sep Fri 14, 2018 4:16 am 
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john8750 wrote:
Flipperhome wrote:
Okay, that's good AC. And that's where they should be grounded. Where is the chassis grounded?

Measure the drop across the MOSFET (and don't pop it this time :wink: ) Like I said, it should be around 17-20 V. We may need to adjust R1/R2 to get the desired drop across the MOSFET, which will somewhat lower B+ in the process.
Great news.
Installed diode 3 and changed C3 to 75uf, the close's I had. I will order 100uf if that will be better. Hum level very low. Reconnected FB and now totally acceptable, no hum whatsoever. B+ still a little high. We could adjust that after connecting left bank.
The only chassis ground is at the RCA inputs.
Note--I also have the house system grounded to chassis.
I thought you had a 100uF there before. What happened to it?

Did the hum go DOWN with C3 changed to 75uF?

Those grounds sound right.

I agree on B+. Let's get the whole thing connected up and see where it comes out before we try adjusting it. Like I said, it's only 8% high as it is and that's sure to come down some with both channels active.


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 Post subject: Re: 807 Williamson amp
PostPosted: Sep Fri 14, 2018 4:29 am 
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john8750 wrote:
Note--I also have the house system grounded to chassis.

What does that mean John?

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 Post subject: Re: 807 Williamson amp
PostPosted: Sep Fri 14, 2018 4:48 am 
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Pbpix wrote:
john8750 wrote:
Note--I also have the house system grounded to chassis.

What does that mean John?



The green ground wire in the AC plug is connected directly to the chassis. I wasnt sure it should be because of a possible ground loop.

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 Post subject: Re: 807 Williamson amp
PostPosted: Sep Fri 14, 2018 4:53 am 
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I thought you had a 100uF there before. What happened to it?
I used two 470's in series to get 235, may have been a problem.

Did the hum go DOWN with C3 changed to 75uF?
Yes, but think 100 will be even better, as you designed

Those grounds sound right.

I agree on B+. Let's get the whole thing connected up and see where it comes out before we try adjusting it. Like I said, it's only 8% high as it is and that's sure to come down some with both channels active.
Good deal

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 Post subject: Re: 807 Williamson amp
PostPosted: Sep Fri 14, 2018 5:43 am 
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john8750 wrote:
I thought you had a 100uF there before. What happened to it?
I used two 470's in series to get 235, may have been a problem.

Did the hum go DOWN with C3 changed to 75uF?
Yes, but think 100 will be even better, as you designed
Ah, of course. I had forgotten you used two 470s.

Hum should go down more (say 3 dB or so) with the 100 uF (and with the 1k as well).

The reason I asked was to see where the residual hum was coming from, ground or the amp (via B+). While in theory PP 'cancels' hum in reality it's never 100% in balance. There's tolerances on everything, including mismatch between the two halves of the 6SN7 and well as the 807s. Even if bias is 'exactly' the same on the two 807s their mu won't be the same. It might be an interesting experiment to see if the hum can be nulled further with the bias balance pot, i.e. seeking a mu match rather than bias, per see. Not a drastic balance offset, say no more than 10% either way from the 'exact' bias balance point. I'm really not sure if it'll have much of an effect but why not give it a shot?

The original Williamson design also included an "AC Balance" pot on the 6SN7 plates to null it out (to the extent it could be). The later revised design eliminated that as they said it wasn't necessary because it isn't that much to begin with and NFB reduces overall hum so much. I took the 'revised' design as the starting basis for mine.


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 Post subject: Re: 807 Williamson amp
PostPosted: Sep Fri 14, 2018 6:01 am 
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Flipperhome wrote:
john8750 wrote:
I thought you had a 100uF there before. What happened to it?
I used two 470's in series to get 235, may have been a problem.

Did the hum go DOWN with C3 changed to 75uF?
Yes, but think 100 will be even better, as you designed
Ah, of course. I had forgotten you used two 470s.

Hum should go down more (say 3 dB or so) with the 100 uF (and with the 1k as well).

The reason I asked was to see where the residual hum was coming from, ground or the amp (via B+). While in theory PP 'cancels' hum in reality it's never 100% in balance. There's tolerances on everything, including mismatch between the two halves of the 6SN7 and well as the 807s. Even if bias is 'exactly' the same on the two 807s their mu won't be the same. It might be an interesting experiment to see if the hum can be nulled further with the bias balance pot, i.e. seeking a mu match rather than bias, per see. Not a drastic balance offset, say no more than 10% either way from the 'exact' bias balance point. I'm really not sure if it'll have much of an effect but why not give it a shot?

The original Williamson design also included an "AC Balance" pot on the 6SN7 plates to null it out (to the extent it could be). The later revised design eliminated that as they said it wasn't necessary because it isn't that much to begin with and NFB reduces overall hum so much. I took the 'revised' design as the starting basis for mine.




Very pleased so far. I will try the 'dead reckoning' of the 807 balance and let you know. They are set very close to middle right now.
I'm agonna order some 100uf 600 volt axials and rebuild the power supply. I believe your original component values were correct. But will change R3 to 1K. and add D3.
As I increase the gain, with the input grounded at the RCA, I can hear a slight 'open input' sound, but no hum.

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 Post subject: Re: 807 Williamson amp
PostPosted: Sep Fri 14, 2018 6:09 am 
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john8750 wrote:
Very pleased so far. I will try the 'dead reckoning' of the 807 balance and let you know. They are set very close to middle right now.
I'm agonna order some 100uf 600 volt axials and rebuild the power supply. I believe your original component values were correct. But will change R3 to 1K. and add D3.
As I increase the gain, with the input grounded at the RCA, I can hear a slight 'open input' sound, but no hum.
You mean 'hiss' or what? With or without NFB applied?

Btw, you do have the inputs shielded, right?


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 Post subject: Re: 807 Williamson amp
PostPosted: Sep Fri 14, 2018 6:26 am 
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Flipperhome wrote:
john8750 wrote:
Very pleased so far. I will try the 'dead reckoning' of the 807 balance and let you know. They are set very close to middle right now.
I'm agonna order some 100uf 600 volt axials and rebuild the power supply. I believe your original component values were correct. But will change R3 to 1K. and add D3.
As I increase the gain, with the input grounded at the RCA, I can hear a slight 'open input' sound, but no hum.
You mean 'hiss' or what? With or without NFB applied?

Btw, you do have the inputs shielded, right?



Hiss, maybe, but not a bad sound.
Not shielded. In fact, right now I got wires everywhere. Looks like a map of the Los Angeles freeway system.
That's why I'm not so worried about it right now.
Tomorrow I'm gonna put some music in and see how she reacts.
Thanks Flip.

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 Post subject: Re: 807 Williamson amp
PostPosted: Sep Fri 14, 2018 6:27 am 
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NFB is connected.

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 Post subject: Re: 807 Williamson amp
PostPosted: Sep Fri 14, 2018 6:40 am 
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john8750 wrote:
Flipperhome wrote:
john8750 wrote:
Very pleased so far. I will try the 'dead reckoning' of the 807 balance and let you know. They are set very close to middle right now.
I'm agonna order some 100uf 600 volt axials and rebuild the power supply. I believe your original component values were correct. But will change R3 to 1K. and add D3.
As I increase the gain, with the input grounded at the RCA, I can hear a slight 'open input' sound, but no hum.
You mean 'hiss' or what? With or without NFB applied?

Btw, you do have the inputs shielded, right?
Hiss, maybe, but not a bad sound.
Not shielded. In fact, right now I got wires everywhere. Looks like a map of the Los Angeles freeway system.
That's why I'm not so worried about it right now.
Tomorrow I'm gonna put some music in and see how she reacts.
Thanks Flip.
Not shielded is probably why there's 'something' there as you increase volume. Unshielded wires on the input are an antenna for any and all EMI and it's going into a pretty high gain amp.

Yeah, I'm not worried either. Things will get even better once you clean up the wiring.

I'm surprised you've resisted putting audio on it for this long. I wouldn't have been able to wait. :wink:


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 Post subject: Re: 807 Williamson amp
PostPosted: Sep Fri 14, 2018 7:56 am 
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Flip. I have been interrupted to help the wife almost all day. From re potting plants, to rearranging the bedroom furniture.
But not getting in a hurry keeps the fun in it.
I agree, shield the input leads and clean up the wiring.
Here is a plan for the new power supply. Should build in a breeze.
Attachment:
PS new.png
PS new.png [ 22.18 KiB | Viewed 26 times ]

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 Post subject: Re: 807 Williamson amp
PostPosted: Sep Fri 14, 2018 8:24 pm 
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Plays very good music. Plenty of bass. :D Still has a slight static behind the music, very slight. 'Hint' I forgot to switch the inverter power at first. Then switched to house circuit. With the inverter power, the static was louder than with the house power. Would a .01 or so at the AC input help? I realize that a shielded input will help that also.
Didnt fiddle with the bias balance because the hum is totally gone.
MOSFET pin2/pin3 difference is 5.8v.

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 Post subject: Re: 807 Williamson amp
PostPosted: Sep Sat 15, 2018 5:16 am 
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Do we need to change anything in the power supply? I am gettin ready to order C1-C2- and a 1K 2watt for R3. Let me know about any other changes.
Plenty of gain with this amp, and just feels strong. Wait for the left channel 8)

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 Post subject: Re: 807 Williamson amp
PostPosted: Sep Sat 15, 2018 5:43 am 
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john8750 wrote:
Plays very good music. Plenty of bass. :D Still has a slight static behind the music, very slight. 'Hint' I forgot to switch the inverter power at first. Then switched to house circuit. With the inverter power, the static was louder than with the house power. Would a .01 or so at the AC input help? I realize that a shielded input will help that also.
Didnt fiddle with the bias balance because the hum is totally gone.
MOSFET pin2/pin3 difference is 5.8v.
I don't know if a .01 uF would help. Maybe, but it really depends on how the noise of getting in and I think it much more likely to be the unshielded inputs.

Hard to reduce hum when it isn't there anymore. :wink:

We'll just have to see what the differential across the MOSFET is when both channels are active. Btw, that voltage matters (although I don't know how much). It's supposed to be around 17-20 volts to prevent voltage droop on C3 from causing the MOSFET filter to drop out, allowing ripple (hum) to pass through.


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 Post subject: Re: 807 Williamson amp
PostPosted: Sep Sat 15, 2018 5:46 am 
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john8750 wrote:
Do we need to change anything in the power supply? I am gettin ready to order C1-C2- and a 1K 2watt for R3. Let me know about any other changes.
Plenty of gain with this amp, and just feels strong. Wait for the left channel 8)
Seems it's working just fine now so no more changes, unless we run into another problem.

Glad to hear the amp is performing well. With both channels it should be twice as good. :wink:


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 Post subject: Re: 807 Williamson amp
PostPosted: Sep Sat 15, 2018 6:10 am 
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Flipperhome wrote:
john8750 wrote:
Do we need to change anything in the power supply? I am gettin ready to order C1-C2- and a 1K 2watt for R3. Let me know about any other changes.
Plenty of gain with this amp, and just feels strong. Wait for the left channel 8)
Seems it's working just fine now so no more changes, unless we run into another problem.

Glad to hear the amp is performing well. With both channels it should be twice as good. :wink:



Great then, for now. I will go on with the other side. Then we will re-examine the power supply.

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