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valves to replace opamps in cd player

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I am trying to replace the opamps with valves.
I have a tda1541 based cd.
I have one of those china based 6n3 buffer kits .
it runs at 70dc.

It is unity gain .I want to change it so it amplifies instead.

does anyone know how to change cicuit design for this,
 

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I am trying to replace the opamps with valves.
I have a tda1541 based cd.
I have one of those china based 6n3 buffer kits .
it runs at 70dc.

It is unity gain .I want to change it so it amplifies instead.

does anyone know how to change cicuit design for this,

You must have figured out that a unity gain tube "amp" has about as much "tube sound" as a length of wire. They need to amplify. So you are on the right track but you are missing a critical piec of information...

How much gain is required?

Your best bet would be to leave the op amp in place but reduce the gain in the op amp circuit to unity.

Then you would need a tube circuit with the same gain the op amp used to have. But what is that?

The next question is what will this new tube circuit be driving?
 
The current board is a cathode follower so slightly less than unity gain. You'll need to quite a lot of etch cutting to reconfigure as a common cathode gain stage - probably would be worthwhile to just build from scratch possibly on a piece of vector board.

You are correct about that. PCBs are not good if you want to modify the circuit. Also 70V is not much and there are better tubes available for only a few bucks.

I built a basic line level booster with gain from scratch and put it inside a box that once held a CDROM drive. It uses a 12V AC plug-in power supply (AKA "wall wort") and inside the box is 12.6 volt transformer running "backwards" that steps the 12VAC up to 120VAC which gives about 145 volts DC which is enough to make the 12AX7 tube happy. The heater runs off the 12VAC. Cost is "not much". The little pre-amp tubes make so little heat that they can live inside the box, out of sight and protected from damage. The trick is finding an AC wall wort, most are DC and don't work for this. It is a very easy first tube project.

For this case I'd use two tubes 12AX7 for the common cathode gain stage. Use local feedback to control the gain to the required amount. This drives a 12AU7 cathode follower that in turn drives the output jack. Each tube has two triodes,use one for left and one for right.

Sell the Chinese buffer on eBay. Use the cash to build the above
 
One thing to remember if you remove the op-amp is that it normally is a low pass filter to help remove sampling artifacts.

If you remove/bypass the op-amp and replace it with a tube amp, you need to add LPF to achieve a clean design.

Otherwise you will be amplifying a bunch of hash as well as the desired signals.
 
One thing to remember if you remove the op-amp is that it normally is a low pass filter to help remove sampling artifacts.

If you remove/bypass the op-amp and replace it with a tube amp, you need to add LPF to achieve a clean design.

Otherwise you will be amplifying a bunch of hash as well as the desired signals.

The simplest way, maybe is to reduce the gain in the CD player by (say) a factor or 20 with a 20:1 resistive voltage diver. (a.k.a. "volume control") and then set your tube amp for a gain of 20. This way you leave the guts of the CD player alone.

There is a long tradition of this in guitar amps. They have multiple gain stages and each is cut down with a resister divider before going to the next stage. You can build up all kinds of distortion in this way. I'm a little serious - that "tube sound" you are looking for adds a percent or so of distortion, mostly second harmonic. You need gain to get that.
 
Hi intensate, I've been in your shoes before. If you want no op-amp all together
I highly recommends you to have ECDesign's common gate Jfet I/V and your current tube buffer. Very transparent sounding but some works on the PCB needed.

check here for my work on tubing out Sony CDP950 with TDA1541
 
6N3P with 12K anode resistor, 2K cathode resistor bypassed with 22uF, 150V supply:

Direct Newton iteration for .op point succeeded.
Fourier components of V(out)
DC component:-0.00162395

Harmonic Frequency Fourier Normalized Phase Normalized
Number [Hz] Component Component [degree] Phase [deg]
1 1.000e+03 6.654e+00 1.000e+00 -179.00° 0.00°
2 2.000e+03 3.767e-01 5.662e-02 91.29° 270.29°
3 3.000e+03 9.815e-03 1.475e-03 -179.08° -0.08°
4 4.000e+03 1.824e-04 2.742e-05 93.33° 272.33°
5 5.000e+03 7.049e-05 1.059e-05 -177.93° 1.07°
6 6.000e+03 5.919e-06 8.895e-07 -89.71° 89.29°
7 7.000e+03 8.660e-08 1.301e-08 169.23° 348.23°
8 8.000e+03 4.890e-07 7.348e-08 -105.87° 73.13°
9 9.000e+03 2.011e-07 3.022e-08 -179.59° -0.59°

Total Harmonic Distortion: 5.663559%
 
Hi intensate, I've been in your shoes before. If you want no op-amp all together
I highly recommends you to have ECDesign's common gate Jfet I/V and your current tube buffer. Very transparent sounding but some works on the PCB needed.

check here for my work on tubing out Sony CDP950 with TDA1541

What we don't know is the OP's goal. If he is trying to get a "transparent" sound out of the CD player or if he wants a "tube sound" out of the CD player.

As spice sim of the tube sows, the "tube sound" is simple some added 2nd harmonics, hardly "transparent" but very listenable and many people like it.

Hopefully the OP has not gone AWOL and ail come back and tell us if his gola is to remove the op-amp or add the tube. From a purely HiFi perspective his best option is to upgrade the opamp but I doubt he's hear much difference , like buying that buffer, if well engineered it sounds like a length of wire. Same with opamps. When you get it right they sound like "nothing is there".

I guess you can all figure that I think the best use of tubes is in musical instruments where their added sound is a Good Thing.
 
6N3P with 18K anode resistor, 470R cathode resistor no bypassed, 70V supply 4.7K load and 1uF coupling cap:

Direct Newton iteration for .op point succeeded.
Fourier components of V(out)
DC component:-1.02151e-005

Harmonic Frequency Fourier Normalized Phase Normalized
Number [Hz] Component Component [degree] Phase [deg]
1 1.000e+03 4.045e+00 1.000e+00 -179.46° 0.00°
2 2.000e+03 2.530e-01 6.254e-02 90.28° 269.74°
3 3.000e+03 4.663e-02 1.153e-02 -179.38° 0.07°
4 4.000e+03 1.030e-02 2.546e-03 -89.26° 90.19°
5 5.000e+03 1.887e-03 4.664e-04 1.15° 180.60°
6 6.000e+03 2.455e-04 6.069e-05 91.89° 271.35°
7 7.000e+03 9.632e-06 2.381e-06 -4.84° 174.62°
8 8.000e+03 2.200e-05 5.439e-06 90.98° 270.44°
9 9.000e+03 1.058e-05 2.616e-06 -179.08° 0.38°
Total Harmonic Distortion: 6.365029%

If the OP wants transparent, use a current source in the anode, LED in the cathode and keep the next stage impedance high.
 
...
I want to add a passive lpf ,any idea's on cicuits.
Thanks all....

At audio frequency a passive LPF is going to be an RC circuit. There are not a lot of options. Likely you'd use a "CRC", pi type filter. That is, the signal passes through a resistor and at each end of the resister there is a cap connected with the other end of each cap tried to ground.

For passive filter designs this is the best web site, I've found
RC Low-pass Filter Design Tool
 
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