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Single 6N6P stereo pre-amp

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Hi guys,

I'm going to have a shot at a very simple cathode follower pre-amp but using both sides of double triode like the 6N6P for the left and right channels.

I have attached a photo (don't have any software to design these yet; if anyone knows of a good freeware please advise).

How does this look?
 

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It looks nothing like a cathode follower

Just a rather minor embarrassing mistake!!:clown:

Quickly brushing my error aside what I was trying to achieve was using a single double triode for a stereo pre-amp. I've read that there shouldn't be any crosstalk between the channels.

This was basically a design taken from a DecaWare driver stage.
 
The circuit has other problems besides C1. The output caps are too small if you ever want to drive a power amp with 100K or lower input impedance for example. I think you should either look for a published preamp project or work through a book like Morgan Jones on learning to design one.
 
I think you should either look for a published preamp project or work through a book like Morgan Jones on learning to design one.

Looks like I need to go back to the books.:xeye:

I've got my Aikido up and running on the breadboard right now. Very nice:) .




What is the purpose of C1? If it's meant to be a cathode bypass, that's not the way to do it.

I guess I should have drawn 2 caps there. One bypassing each Cathode resistor.
 
thks guys.

In the meantime JB's journals are great. Got some other pdf files from some other members.

What I was trying to achieve was using both sides of the triode, for both channels.

This is one channel of a very simple design that I'd like to modify using the same triode for both channels.

How would I apply this concept to this design?
 

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A typical pre-amp will drive 2V into 1Megohm, so the best possible preamp for a CD player is just to connect it to the power amplifier.

Your stage has far too much current. You need to spend some time looking at datasheets and calculating the operating point and quiescent current of a few different stages.

Read a book on amplifier design.

w
 
I'm learning along the way. I have just built a very nice Aikido 5687 realizing after it has just a little bit too much gain when connected to my SS power amp!:xeye:

I believe that if I want to use a valve pre-amp then I need to build a buffer with no gain. That's on my list of things to do, maybe with the 6N6P's.

Now I have my Aikido I need to decide what I'm going to do with it.

Maybe a SE KT88 amp? Nice and simple with few parts.
 
Brit01 said:
I'm learning along the way.

I have just built a very nice Aikido 5687 realizing after it has just a little bit too much gain when connected to my SS power amp!

I believe that if I want to use a valve pre-amp then I need to build a buffer with no gain.

Power amp, preamp, integrated amp, linestage, these are all terms that lead to confusion.

Right now you are learning by stabbing in the dark.

It's better to learn in a more organised manner, although that may not be consistent with a hobby.

You have to look at and understand the paper I/O specifications of any 2 pieces of equipment you intend to connect together.

'I believe' is OK for church, all others pay cash.

w
 
Right now you are learning by stabbing in the dark. It's better to learn in a more organised manner, although that may not be consistent with a hobby.

Linestage and pre-amp were the confusing terms when I first entered this hobby. I was given a lot of advice and tutorials.
I'm reading a lot but it's not easy when you are just starting.

I am totally hooked on these beautiful glowing valves and the smoke of the solder:D
I'm currently tweaking my Aikido, I think it's a great kit to start with. Also I've had a lot of contact with Bas due to his psu and first valves he sent to me

:D :D


Now I'm reading and learning about the output stages and transformers. Very interesting.
 
hey-Hey!!!,
You'll have a gain of about 15 with that circuit. That will take your 2V source to 30V at full throttle. I suspect your amp is not going to need that level of signal, but that is a very uninformed opinion. I've built several with that gain structure along the way...:)

Just a suggestion, use a much larger coupling cap. 2-3 uF would be my starting point. It is a lot larger than the usual calculation would suggest is needed, but I found larger than that to be *MY* sweet spot...:)
cheers,
Douglas
 
You'll have a gain of about 15 with that circuit. That will take your 2V source to 30V at full throttle. I suspect your amp is not going to need that level of signal, but that is a very uninformed opinion. I've built several with that gain structure along the way... Just a suggestion, use a much larger coupling cap. 2-3 uF would be my starting point. It is a lot larger than the usual calculation would suggest is needed, but I found larger than that to be *MY* sweet spot...

Thanks Douglas. Luckily my power amp has a line level control so I can turn that way down to control the Aikido.
I'll give the coupling caps a shot. I have the 2 positions so I can parallel 2. Got some 1uF RTI and Auricaps, also a PIO 0,47uF.


I will probably end up building a unity buffer amp for the SS.

Now I've got to decide what I want to do with the Aikido.

Maybe JB suggestion: (But I'd like to use KT88)

He uses massive Cathode resistors here for the 12AX7'a. I've got 6N1P/5687. Some 6N6P's arriving soon. Also safety R5/R6 he changed to 10m to increase the gain I read.
 

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Hi Brit

I will present here a very simplified discussing of the last schematic you posted, so you can judge what you need in terms of gain. It is just an illustration, the amplifier with a KT88 would already be a different case!

Starting at the extreme right we obseve that the 300B has 70VDC on the cathode. This is the cathode to grid voltage! At this point it conducts a steady current. To make it conduce more or less we want to change the voltage between cathode and grid. We do this by applying an AC signal to the grid. With this AC signal we can decrease the voltage to about 10V, which will yield an enormous increase in current (check the datasheet!). Decreasing the 70V to 10V requires a negative swing of 60V, that is half the sine. On the other half of the sine these 60V will be added to the 70V at the cathode, leading to a cathode-grid voltage of 130V! At this point the valve will barely conduce current. So we need a signal of 120V peak to peak to take the 300B from maximum conduction to minimum conduction. This signal should come from the driver stage, in this case the Aikido. The second stage from the Aikido has a voltage gain of ~1, so it will not contribute to the required voltage gain: that is the responsibility of the first stage of the aikido. This stage is built around the 12AX7, which has a mu of 100. In the aikido stage the gain is mu/2, so the gain of that stage is 50x. We do divide the 120V by these gain, which results in the value 2,4. That is, if one presents a voltage of 2,4V peak to peak to the grid of the 12AX7, the first stage will increase this 2,4V P2P with a factor 50, resulting in 120V needed at the grid of the 300B. 2,4V PtoP is about 1V RMS. This is called the sensitivity for maximum power output. You can follow the same reasoning to determine what the input sensitivity will result when using the KT88, given you know how you will bias the tube. Then you can also play with the first valve of the Aikido, choosing a mu that yealds a reasonable input sensitivity (1V RMS is good, I think).

Sorry if this is not new for you, I just was in the mood of writing :)

BTW, I second the opinion of buying a book. Learning is always very rewarding!
 
What a question! Lol

With 99% of foreigners here there is always a partner involved. Mine was an Uruguayan girl I met in Cancun while teaching Scuba!!!

Now I've been here 4 years and probably the best place to be while Europe is in recession. The GBp has dropped significantly. Good for me here as I earn USD.

Love to see Brazil one day. We have a lot of Brazilians coming to Punta Del Este here. Scenery is very nice;)

Now back to valves. I'm understanding that if I want a valve stage (+volume control between my CDP) with my SS amp it's probably best to build a Cathode follower acting as a 'buffer'. Vin=Vout almost.
 
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