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Old 6th February 2012, 08:17 AM   #11
dazed is offline dazed  Norway
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Quote:
Originally Posted by artosalo View Post
How about a simple differential amplifier without any transformers like this.


Click the image to open in full size.

You can connect this as a SE or balanced input and output as you wish.
The low frequency response can be lowered to 20 Hz by replacing C2 and C3 with 220 nF if necessary.
Interesting. I must admit I'm not that familiar with these circuits and schematics, so: Do you have an URL or something to where I can read up a bit?

Thanks.
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Old 6th February 2012, 08:28 AM   #12
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Quote:
Do you have an URL or something to where I can read up a bit?
About the above schematic ?
Sorry, I do not have any link to this because I just designed and simulated this after reading your thread.

But, please feel free to ask anything. I try my best to answer.
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Old 6th February 2012, 08:49 AM   #13
dazed is offline dazed  Norway
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Wow. Thanks! I'll take a closer look at it later today, an get my head around how it works. (I told you I'm a newbie.)
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Old 6th February 2012, 09:06 AM   #14
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What is the output impedance of the differential gain stage? Gain?

dazed, FYI, the topology here is what BAThttp://balanced.com use in all their preamps. If you parallel more tubes you'll get lower output impedance. Don't worry about the coupling capacitors they don't hurt as much as some people want us to believe. Use e.g. Mundorf Zn capacitors.
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Old 6th February 2012, 09:12 AM   #15
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Quote:
I'll take a closer look at it later today, an get my head around how it works.
There is no big magic in this circuit. These tubes are connected as a differential amplifier ( try to Google "differential amplifier" to get more info).

There are two inputs available to feed the balanced signal in.
If you feed non balanced, then just connect one input to ground.
Volume control can be arranged with dual 100 k pot at the inputs.
You can also add such input and output selectors as you prefer.

There are also two outputs and between them there is balanced signal output.
If you want to output only non balanced signal, you can choose one output only, inverted or non inverted.

This 6N6P tube has suitably low gain, good linearity (low THD) and low output impedance to feed 50 kohms load.

But do you need to see a simple power supply circuit for this or do you buy one from China ?

Last edited by artosalo; 6th February 2012 at 09:14 AM.
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Old 6th February 2012, 09:23 AM   #16
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Quote:
What is the output impedance of the differential gain stage? Gain?
Output impedance is 2.1 kohms. Gain is 10 dB.
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Old 6th February 2012, 10:16 AM   #17
dazed is offline dazed  Norway
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Quote:
Originally Posted by Nelson Bass View Post
What is the output impedance of the differential gain stage? Gain?

dazed, FYI, the topology here is what BATBalanced Audio Technology use in all their preamps. If you parallel more tubes you'll get lower output impedance. Don't worry about the coupling capacitors they don't hurt as much as some people want us to believe. Use e.g. Mundorf Zn capacitors.
Thanks. I'll read up on the topology.
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Old 6th February 2012, 10:37 AM   #18
dazed is offline dazed  Norway
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Quote:
Originally Posted by artosalo View Post
There is no big magic in this circuit. These tubes are connected as a differential amplifier ( try to Google "differential amplifier" to get more info).
I'll certainly do that.

Quote:
There are two inputs available to feed the balanced signal in.
If you feed non balanced, then just connect one input to ground.
Volume control can be arranged with dual 100 k pot at the inputs.
You can also add such input and output selectors as you prefer.

There are also two outputs and between them there is balanced signal output.
If you want to output only non balanced signal, you can choose one output only, inverted or non inverted.
I understand. (I think)

Quote:
This 6N6P tube has suitably low gain, good linearity (low THD) and low output impedance to feed 50 kohms load.
Great. It's also readily available "everywhere", I assume.

Quote:
But do you need to see a simple power supply circuit for this or do you buy one from China ?
Well.... I guess if I were to build an amp from scratch with p2p wiring, I'd try to do the same with the psu parts, but realistically; the easiest way for me to accomplish this project probably is buying PCBs (populated or not) and wiring them together with pots, switches and a power transformer and putting it all in a nice enclosure.

I've only ever built one small guitar tube amp p2p, which I have yet to dare plugging in to see if it works, and that wiring looks like an awful worm's nest.

Getting populated PCBs for the amp and psu from China and then getting the transformer, switches and terminals locally sounds doable and is tempting, if it's likely that this method will yield good results.

...Or I could get just PCBs from China and get all the parts locally (or from mouser etc.) if there's reason to doubt the quality of the Chinese components. (?) Of course: There's always the option of upgrading the through hole components at a later time-

What do you guys think?

Last edited by dazed; 6th February 2012 at 10:40 AM.
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Old 6th February 2012, 11:14 AM   #19
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6N6P is available from Ebay. Try to search.
Similar tube would be ECC99 by JJ.

You can find power supply PCB from China, but not a PCB for this circuit (6N6P dif.amp.).

This kind of power supply is all you need.

Click the image to open in full size.
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Old 6th February 2012, 11:16 AM   #20
dazed is offline dazed  Norway
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...Or maybe even something like this?

Complete Balanced Tube Preamplifier kit, 6DJ8x4 /ls-69

Complete Bal Tube Preamplifier, ref A Research /ls60
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