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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Aug Wed 24, 2016 5:24 am 
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Here's another on Ebay, all built also only $15 with shipping. Has on board power splitter.... just feed it 18 to 24v DC :
... even shows the whole schematic
it uses the njm4556A chip
You couldn't even buy those pats for $15... look at those big fat audiophile 4.7uf input caps :

http://www.ebay.com/itm/HV-10-RA1-Avail ... SwtJZXURvh

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Aug Wed 24, 2016 5:57 am 
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john8750 wrote:
Pbpix wrote:
Here's a headphone amp on Ebay using op275 that's all built for $15
http://www.ebay.com/itm/Dual-AC12V-16V- ... 1939769491



Another good idea Peter, thanks. Would it work on 2 9 volts?

I don't know.

But if you want low power, Here's one on Ebay runs on only 1.8 to 6 v fully assembled I think.
http://www.ebay.com/itm/DC-1-8V-6V-MAX4 ... SwHQ9WUSOT

http://www.ebay.es/itm/ws/eBayISAPI.dll ... 1986500323

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Aug Wed 24, 2016 6:49 am 
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Pbpix wrote:
Here's a headphone amp on Ebay using op275 that's all built for $15
http://www.ebay.com/itm/Dual-AC12V-16V- ... 1939769491
I can't make heads or tails of that no spec sino-babble.


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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Aug Thu 25, 2016 4:44 am 
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weird PS I think. But I like the circuit. Is there something missing across c7-c8?

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Aug Thu 25, 2016 4:53 am 
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john8750 wrote:
weird PS I think. But I like the circuit. Is there something missing across c7-c8?

I don't have any idea what that drawing convention means.

But another interesting thing there is the strange opamp feedback ratio values of 464 ohms to 121,000 ohms.

Maybe flip can shed light on that?
Image

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Aug Thu 25, 2016 6:39 am 
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That is strange. Maybe that those values are what he had on hand?

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Aug Thu 25, 2016 6:44 am 
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Could that PS be for something else? I cant understand needing it for the amp circuit. I really like it.

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Aug Thu 25, 2016 7:19 am 
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Pbpix wrote:
john8750 wrote:
weird PS I think. But I like the circuit. Is there something missing across c7-c8?

I don't have any idea what that drawing convention means.

But another interesting thing there is the strange opamp feedback ratio values of 464 ohms to 121,000 ohms.

Maybe flip can shed light on that?
Image
The 'weird' power supply creates a virtual ground because the opamps need a ground. Seems kind of a waste for a good 20 Watt audio amp... but whatever.

The 'strange' value 464 Ohm and 121K are standard 1% (or 2%) resistor values.

The flying leads on C7 and C8 look like something was originally intended to go there but was erased. Maybe a jumper.


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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Aug Thu 25, 2016 7:32 am 
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Is the PS drawn backwards?

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Aug Thu 25, 2016 7:37 am 
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john8750 wrote:
Is the PS drawn backwards?
Depends on how you define 'backwards'. Power enters on the right and connects to the opamps on the left.


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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Aug Thu 25, 2016 8:09 pm 
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Flipperhome wrote:
john8750 wrote:
Is the PS drawn backwards?
Depends on how you define 'backwards'. Power enters on the right and connects to the opamps on the left.




.dnatsredun I won KO

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Aug Thu 25, 2016 10:36 pm 
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john8750 wrote:
Flipperhome wrote:
john8750 wrote:
Is the PS drawn backwards?
Depends on how you define 'backwards'. Power enters on the right and connects to the opamps on the left.




.dnatsredun I won KO

nuderstand?

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Aug Thu 25, 2016 11:32 pm 
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Now your catching on Peter.

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Aug Fri 26, 2016 1:35 am 
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Hello john
Anyway that design looks like it will fit the bill
By the way john I got the package today :-)


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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Aug Fri 26, 2016 3:39 am 
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Flipperhome wrote:
Pbpix wrote:
john8750 wrote:
weird PS I think. But I like the circuit. Is there something missing across c7-c8?

I don't have any idea what that drawing convention means.

But another interesting thing there is the strange opamp feedback ratio values of 464 ohms to 121,000 ohms.

Maybe flip can shed light on that?
Image
The 'weird' power supply creates a virtual ground because the opamps need a ground. Seems kind of a waste for a good 20 Watt audio amp... but whatever.

The 'strange' value 464 Ohm and 121K are standard 1% (or 2%) resistor values.

The flying leads on C7 and C8 look like something was originally intended to go there but was erased. Maybe a jumper.

Flip:
Why do you suppose they did that for virtual ground?
Couldn't they simply divide the supply voltage in half with the two 10k resistors and use that?
After all.... that is how we are creating the virtual ground on the 6v6 & 5902 amp... right?
We divide +40v in half and feed it to the non-inverting input..

So why is this so elborate?
Also.. if they need to, ... why not use a rail-splitter chip?

I guess to make a buffered virtual ground.
"These techniques make the voltage divider appear to have a very low impedance while still drawing little current. This keeps the virtual ground point nicely centered between the rails under load."

REF:
Virtual ground ideas:
https://tangentsoft.net/elec/vgrounds.html

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Aug Fri 26, 2016 4:26 am 
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Pbpix wrote:
Flipperhome wrote:
The 'weird' power supply creates a virtual ground because the opamps need a ground. Seems kind of a waste for a good 20 Watt audio amp... but whatever.

The 'strange' value 464 Ohm and 121K are standard 1% (or 2%) resistor values.

The flying leads on C7 and C8 look like something was originally intended to go there but was erased. Maybe a jumper.

Flip:
Why do you suppose they did that for virtual ground?
Couldn't they simply divide the supply voltage in half with the two 10k resistors and use that?
After all.... that is how we are creating the virtual ground on the 6v6 & 5902 amp... right?
We divide +40v in half and feed it to the non-inverting input..

So why is this so elborate?
Also.. if they need to, ... why not use a rail-splitter chip?

I guess to make a buffered virtual ground.
"These techniques make the voltage divider appear to have a very low impedance while still drawing little current. This keeps the virtual ground point nicely centered between the rails under load."

REF:
Virtual ground ideas:
https://tangentsoft.net/elec/vgrounds.html
Convenient and sloppy, maybe using parts on hand. As hinted, I wouldn't waste a 20 Watt audio amp on a simple rail splitter, not to mention placing caps on the output (the wrong place) and then keeping loop gain of 10 to make it stable.

The simple resistor divider on the 5902 amp isn't ideal but you get away with it because there's very little loading on the virtual ground. It just feeds a high impedance opamp input and a 470k feedback resistor. A rail splitter (conveniently) eliminates any concerns over current draw and balance.


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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Aug Fri 26, 2016 5:00 am 
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radiorich wrote:
Hello john
Anyway that design looks like it will fit the bill
By the way john I got the package today :-)



Good deal Rich. Enjoy..

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Aug Fri 26, 2016 7:13 am 
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Hello Peter
That link you posted is got lot of good info
Thanks
john I will start a post when ready to build the amp

Rich


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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Aug Sat 27, 2016 1:55 am 
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radiorich wrote:
Hello Peter
That link you posted is got lot of good info
Thanks
john I will start a post when ready to build the amp

Rich

Yes, I agree. it's a good read.

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Aug Wed 31, 2016 6:08 am 
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radiorich wrote:
Hello Peter
That link you posted is got lot of good info
Thanks
john I will start a post when ready to build the amp

Rich



Let us know Rich. I will follow it.

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