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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Wed 28, 2018 6:29 am 
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Pbpix wrote:
BTW John:
For your edification, here's another easy to use calculator site.
This one is for calculating DROPPER circuit component values ... so very easy.

http://www.nomad.ee/micros/transformerless/index.shtml

Try entering the values you are using on the 13v supply and for the 20v supply to see what it shows as the min/max current available to the load.

Nice.. easy too.





Neat.
That is very easy.
Although, the circuit I have for the 13v supply has a full wave rectifier.
Peter, what is an X2 type capacitor?

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Wed 28, 2018 6:43 am 
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john8750 wrote:
Neat.
That is very easy.
Although, the circuit I have for the 13v supply has a full wave rectifier.
Peter, what is an X2 type capacitor?




Basically (confusing various types) but the safe one are made so if the fail they do not short but "open".
"Class X capacitors are used in “across-the-line” applications where their failure would not lead to electric shock. Class X safety caps are used between the “live” wires carrying the incoming AC current. In this position, a capacitor failure should not cause any electrical shock hazards, rather, a capacitor failure “between-the-lines” would usually cause a fuse or circuit breaker to open.

Class Y capacitors are used in “line-to-ground” (line bypass) applications where their failure could lead to electric shock if a proper ground connection were lost. The failure of a “line-to-ground” capacitor would not open any safety fuse. In other words, the failure of a line bypass capacitor could create a 120 volt “hot” chassis that could give you a potentially fatal shock."



Read more:
http://www.justradios.com/safetytips.html

Dave sells them at Justradios in Canada.
he has a section here explaining X2, X1 Y2,Y1 caps:

http://www.justradios.com/capacitors.html

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Wed 28, 2018 7:26 pm 
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Pbpix wrote:
john8750 wrote:
Neat.
That is very easy.
Although, the circuit I have for the 13v supply has a full wave rectifier.
Peter, what is an X2 type capacitor?




Basically (confusing various types) but the safe one are made so if the fail they do not short but "open".
"Class X capacitors are used in “across-the-line” applications where their failure would not lead to electric shock. Class X safety caps are used between the “live” wires carrying the incoming AC current. In this position, a capacitor failure should not cause any electrical shock hazards, rather, a capacitor failure “between-the-lines” would usually cause a fuse or circuit breaker to open.

Class Y capacitors are used in “line-to-ground” (line bypass) applications where their failure could lead to electric shock if a proper ground connection were lost. The failure of a “line-to-ground” capacitor would not open any safety fuse. In other words, the failure of a line bypass capacitor could create a 120 volt “hot” chassis that could give you a potentially fatal shock."



Read more:
http://www.justradios.com/safetytips.html

Dave sells them at Justradios in Canada.
he has a section here explaining X2, X1 Y2,Y1 caps:

http://www.justradios.com/capacitors.html



AH-HA. Always wondered why those were different. I buy most capacitors from Dave. I should have researched. Just thought they were for audio-fools, who like to pay more. Got to admit, I bought the more expensive ones, not knowing the difference.

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Sat 03, 2018 2:37 am 
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I did some scope work and here are the results. I tested several frequencies. This is at 1020hz.
Input is at the RCA jack
Attachment:
in.jpg
in.jpg [ 108.26 KiB | Viewed 483 times ]

Here is the output from the tone section into the opamps
Attachment:
prein.jpg
prein.jpg [ 113.6 KiB | Viewed 483 times ]

And here it is into the grid
Attachment:
grid.jpg
grid.jpg [ 98.67 KiB | Viewed 483 times ]


Is that fuzz normal? Amp is sounding pretty good.
I don't remember it when I tested the Prince John.
Tomorrow I will do the same test on the 6V6 to compare.

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Sat 03, 2018 3:18 am 
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That fuzz is noise.

Isolate Isolate isolate.
First test by skiping the tone ckt. completely

Just first feed the op-275 opamp directly.
... then scope that direct input to opamp ...should be clean sharp.
Then look right at the opamp output (aka grid input)... should still be clean but larger. No noise.

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Sat 03, 2018 3:40 am 
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Pbpix wrote:
That fuzz is noise.

Isolate Isolate isolate.
First test by skiping the tone ckt. completely

Just first feed the op-275 opamp directly.
... then scope that direct input to opamp ...should be clean sharp.
Then look right at the opamp output (aka grid input)... should still be clean but larger. No noise.




I didn't think about that Peter. Man, I will do that in the morning. But it looks pretty good from the tone section into the opamp. I will also check output to speakers.
I wonder where the noise is from. Another ground problem?

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Sat 03, 2018 4:43 am 
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Even a tiny bit of noise from the tone ckt will be amplified 100 times by the op275. So you must have total clean going in opamp.
Op275 is set for gain of 100.

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Sat 03, 2018 5:03 am 
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Pbpix wrote:
Even a tiny bit of noise from the tone ckt will be amplified 100 times by the op275. So you must have total clean going in opamp.
Op275 is set for gain of 100.




OK- I will isolate the tone amp. Where could that noise come from?

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Sat 03, 2018 5:30 am 
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john8750 wrote:
I did some scope work and here are the results. I tested several frequencies. This is at 1020hz.
Input is at the RCA jack
Attachment:
in.jpg

Here is the output from the tone section into the opamps
Attachment:
prein.jpg

And here it is into the grid
Attachment:
grid.jpg


Is that fuzz normal? Amp is sounding pretty good.
I don't remember it when I tested the Prince John.
Tomorrow I will do the same test on the 6V6 to compare.
Unless my eyes are playing tricks on me it looks like that scope trace from the output of the tone amp has 'notches' about half way up on each half of the waveform. They shouldn't be there and look like crossover notch distortion.

As for the noise/fuzz on the 6V6 grid, it's true that the opamps are multiplying the input by 100 (less with negative feedback) but your scope trace is knocking it back down. There shouldn't be any more noise/fuzz there (after scaling) than on the input to the opamps.

My gut feel is you have some grounding issues. Just doing a 'star' ground isn't sufficient. Remember, follow the CURRENT paths and return them to the filter from whence they came but you don't want a 'high current path', like the tube CCS, taking the same ground return as, for example, the preamp (opamps). Each section should have it's own local ground and take THAT to the 'star' (or more than one if appropriate).


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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Sat 03, 2018 6:21 am 
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I can isolate the CCS and opamp grounds Flip. Also thinking about the whole star ground system. I located it right on the secondary of the PT. Might be better to follow the power supply schematic, C1/C2/ star. The star point on the Prince John is right on the last filter cap.
Peter located his CCS, built right on the 1000uf cap, right at the cathode pin on the tube socket.

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Sat 03, 2018 8:57 am 
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john8750 wrote:
I can isolate the CCS and opamp grounds Flip. Also thinking about the whole star ground system. I located it right on the secondary of the PT. Might be better to follow the power supply schematic, C1/C2/ star. The star point on the Prince John is right on the last filter cap.
Peter located his CCS, built right on the 1000uf cap, right at the cathode pin on the tube socket.
The CCS and opamp ground should be separate and have separate paths to the filter cap ground.

You're right that star grounding at the CT is a bad idea. The heavy cap charge currents (what's worse, for everything powered) go though there and that's bad (for noise). Ground at the filter cap negative avoids those charging currents and is where the (main) star should be. Again, think of the circulating current paths.

Wire has resistance, no matter how short, and the preamp is looking at miniscule input signals that are affected by everything, no matter how small, including a ground jumping around. The filter cap is a reservoir of electrons. It's charged by the transformer and supplies current to the rest of the circuit. The current path BACK to the transformer will be bumping with the heavy charge currents into the cap. If you place ground AT the cap it won't be bumping because that, by definition (since you placed it there), is the ground. Then the 'star' should be separate to the circuit for high power and low power sections for the same reason. You can't avoid ground 'bumping' on the remote end of the high power section but it's not sensitive to ground noise (and only occurs during the 'B' portion of the output tube's operation). The preamp section is VERY sensitive so you want a separate path to your ground at the filter.

Did you follow that?


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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Sat 03, 2018 9:10 am 
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Flipperhome wrote:
john8750 wrote:
I can isolate the CCS and opamp grounds Flip. Also thinking about the whole star ground system. I located it right on the secondary of the PT. Might be better to follow the power supply schematic, C1/C2/ star. The star point on the Prince John is right on the last filter cap.
Peter located his CCS, built right on the 1000uf cap, right at the cathode pin on the tube socket.
The CCS and opamp ground should be separate and have separate paths to the filter cap ground.

You're right that star grounding at the CT is a bad idea. The heavy cap charge currents (what's worse, for everything powered) go though there and that's bad (for noise). Ground at the filter cap negative avoids those charging currents and is where the (main) star should be. Again, think of the circulating current paths.

Wire has resistance, no matter how short, and the preamp is looking at miniscule input signals that are affected by everything, no matter how small, including a ground jumping around. The filter cap is a reservoir of electrons. It's charged by the transformer and supplies current to the rest of the circuit. The current path BACK to the transformer will be bumping with the heavy charge currents into the cap. If you place ground AT the cap it won't be bumping because that, by definition (since you placed it there), is the ground. Then the 'star' should be separate to the circuit for high power and low power sections for the same reason. You can't avoid ground 'bumping' on the remote end of the high power section but it's not sensitive to ground noise (and only occurs during the 'B' portion of the output tube's operation). The preamp section is VERY sensitive so you want a separate path to your ground at the filter.

Did you follow that?




I sure did follow that. The way I wired it, shares a conductor for the filters and signal ground. I can fix it. This amp sure has been a learning experience.

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Sun 04, 2018 1:23 am 
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OK
I installed a separate ground conductor for the CCS section. Cut the trace between the two sections, CCS and opamps. Then lifted the ground star point from the PT. Connected a wire from the first filter, C1, to the negative terminal on the power transformer. Then the circuit goes to the second filter, and back to the star ground.
I am amazed at the difference that makes. Now the amp sounds just about perfect.
Thanks to you guys for the suggestions.
Here is the scope now.
Signal, 1khz input at the RCA jack- right channel.
First is the point between the tone board and opamp input.
Attachment:
prein.jpg
prein.jpg [ 94.85 KiB | Viewed 456 times ]

Here it is at the output to the speaker. Actually, it is a dummy 10ohm resistor.
Attachment:
out,resistor.jpg
out,resistor.jpg [ 101.47 KiB | Viewed 456 times ]

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Sun 04, 2018 1:30 am 
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I do notice just a little fuzz on the output. Don't know what else to re-arrange though. And the amp sounds sharp and clean now.
I nudged my scope over to see it better, and now I don't have the dual trace. I can see them one at a time, but not together. Maybe if I nudge it the other way.....

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Sun 04, 2018 1:30 am 
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john8750 wrote:
OK
I installed a separate ground conductor for the CCS section. Cut the trace between the two sections, CCS and opamps. Then lifted the ground star point from the PT. Connected a wire from the first filter, C1, to the negative terminal on the power transformer. Then the circuit goes to the second filter, and back to the star ground.
I am amazed at the difference that makes. Now the amp sounds just about perfect.
Thanks to you guys for the suggestions.
Here is the scope now.
Signal, 1khz input at the RCA jack- right channel.
First is the point between the tone board and opamp input.
Attachment:
prein.jpg

Here it is at the output to the speaker. Actually, it is a dummy 10ohm resistor.
Attachment:
out,resistor.jpg
Looking pretty good but I don't know about 'the second filter'. It that the one supplying power to the amp? If so, THAT is where the star ground should be.


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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Sun 04, 2018 4:36 am 
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I don't know why the output still looks fuzzy... Almost looks like the scope trace is not focused.
What does the grid look like?
Each trace should be sharp no fuzz at all.

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Sun 04, 2018 4:45 am 
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john8750 wrote:
I nudged my scope over to see it better, and now I don't have the dual trace. I can see them one at a time, but not together. Maybe if I nudge it the other way.....

Huh?
What do you mean?

What do you mean "nudged" it over?
Do you mean you physically moved the whole scope a little bit?
How would that change the dual trace signal or not?
I'm not understanding you.

With 2 probes you should be able to have two traces on the screen at once... say: input#1 and output#2

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Sun 04, 2018 6:47 pm 
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Flipperhome wrote:
john8750 wrote:
OK
I installed a separate ground conductor for the CCS section. Cut the trace between the two sections, CCS and opamps. Then lifted the ground star point from the PT. Connected a wire from the first filter, C1, to the negative terminal on the power transformer. Then the circuit goes to the second filter, and back to the star ground.
I am amazed at the difference that makes. Now the amp sounds just about perfect.
Thanks to you guys for the suggestions.
Here is the scope now.
Signal, 1khz input at the RCA jack- right channel.
First is the point between the tone board and opamp input.
Attachment:
prein.jpg

Here it is at the output to the speaker. Actually, it is a dummy 10ohm resistor.
Attachment:
out,resistor.jpg
Looking pretty good but I don't know about 'the second filter'. It that the one supplying power to the amp? If so, THAT is where the star ground should be.




I could re-route all commons over to the second filter. Will need to lengthen some wires. But the amp sounds really good now. Compared to the other amps I built, this is the only one that the star wasn't located right on the last cap. And it makes a difference.

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Sun 04, 2018 6:53 pm 
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Pbpix wrote:
I don't know why the output still looks fuzzy... Almost looks like the scope trace is not focused.
What does the grid look like?
Each trace should be sharp no fuzz at all.



Looking at the output trace, don't know about it. Could still have some noise. But the sound is very nice.
I did not look at the grid.

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Sun 04, 2018 7:02 pm 
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Pbpix wrote:
john8750 wrote:
I nudged my scope over to see it better, and now I don't have the dual trace. I can see them one at a time, but not together. Maybe if I nudge it the other way.....

Huh?
What do you mean?

What do you mean "nudged" it over?
Do you mean you physically moved the whole scope a little bit?
How would that change the dual trace signal or not?
I'm not understanding you.

With 2 probes you should be able to have two traces on the screen at once... say: input#1 and output#2




That's correct. When I moved the scope so I could see it better, input #1 stopped working. Only #2 stayed on the screen.
Now, I can still see both but only one at a time. Any ideas about what could have happened?
The scope is old and probably out of date by todays standards. I will do some checking.
I got a new turn table, just for backup. It has a built in, switchable preamp. Gonna try to get my RIAA amp working.
Or it will have to be external.

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