-No feedback design
-Two stage design
-Capacitor coupling between stages
-No electrolytic capacitors
-Input stage with no bypass capacitor
-Choke input supply
-Two stage design
-Capacitor coupling between stages
-No electrolytic capacitors
-Input stage with no bypass capacitor
-Choke input supply
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Really like it. No need for active loads, interstages, plate chokes or SIC diodes in the cathode. Just resistor loads and all the better for that.
2 stage design, cap coupled. Good parts and there's not much better you can build.
Be nice to see some more photos.
2 stage design, cap coupled. Good parts and there's not much better you can build.
Be nice to see some more photos.
Very nich! Does it sound like a rich man’s 300B amplifier?
With all the Lundahl and other iron, Mundorf caps and EC8010 it looks more like a rich man’s GU50 than a poor mans’ 300B 🙂
With all the Lundahl and other iron, Mundorf caps and EC8010 it looks more like a rich man’s GU50 than a poor mans’ 300B 🙂
I do not have the output transformers yet, i expect them to arrive next week. I have only static parameters measured, see the schematic. You should see how nice the supply ramps from 0 to full voltage. When it is complete, in one rainy day i will measure the complete performance. I do not expect big surprises, maybe a wobbled beyond recognition square wave.
Inevitably there are more capacitors in signal path, at least are not electrolytic.
Inevitably there are more capacitors in signal path, at least are not electrolytic.
The chassis have the same footprint like my EC8010-AD1-845 monoblocs. Do you like it? In my eyes is more beautiful than most of hiend products.
That looks very nice.
4 caps in the signal path.
B+ #2
B+ #1
GU50 self bias bypass cap
plate to grid coupling cap
As you noted, good, they are not electrolytic caps
You might need a little more capacitance in the B+ filters, to reduce hum.
Watch out for those ground loops that cause hum. Keep them short, and isolated from each other (easier said than done).
Happy Listening!
4 caps in the signal path.
B+ #2
B+ #1
GU50 self bias bypass cap
plate to grid coupling cap
As you noted, good, they are not electrolytic caps
You might need a little more capacitance in the B+ filters, to reduce hum.
Watch out for those ground loops that cause hum. Keep them short, and isolated from each other (easier said than done).
Happy Listening!
The schematic has an error in the power supply grounding. Signal ground is shown shorting half on the bifilar choke.
All good fortune,
Chris
All good fortune,
Chris
Transformers arrived, see first post.
I got a pleasant surprise, my wiring technique is great, I got only 0.45mV hum, the amp is extremely quiet.
In triode mode distortion is high and output power is low. With Lundahl transformers you have 5 options: Pentode, Triode, UL25%, UL50%, UL75%; combine this with mild negative feedback, and the options are almost endless.
I got a pleasant surprise, my wiring technique is great, I got only 0.45mV hum, the amp is extremely quiet.
In triode mode distortion is high and output power is low. With Lundahl transformers you have 5 options: Pentode, Triode, UL25%, UL50%, UL75%; combine this with mild negative feedback, and the options are almost endless.
You can reduce the value of the cathode resistor of GU50 to have higher plate current and get better linearity and more power.
Now the total power dissipation of GU50 is only some 26 W while the max. is 45 W (Pa + Pg2).
You could also improve THD by biasing the EC8010 to generate more 2nd harmonic, which will cancel the 2nd harmonic generated by GU50.
I have no intention to push GU50 harder. There is enough power for me.
THD improvemet by harmonic cancelation, in theory works but in practice EC8010 and GU50 are different tubes. Have you done this in your amps? I will be glad to see some measurements.
The simplest and better way to improve THD remains ultra linear connection.
THD improvemet by harmonic cancelation, in theory works but in practice EC8010 and GU50 are different tubes. Have you done this in your amps? I will be glad to see some measurements.
The simplest and better way to improve THD remains ultra linear connection.
Yes, I have done. It also works in practice. Any triode as a 1st stage of SE amplifier can be biased (from optimum) to generate more 2nd harmonic distortion. All this will cancel the 2nd harmonic distortion of the output tube. The result is reduced overall THD.
This can be quickly demonstrated with LT Spice. You can also replace the cathode resistor of EC8010 with an adjustable resistor and see how this affects to total THD.
It will be a very bad thing to reduce only 2nd harmonic.
Still believe that UL is the way to go, practically not LTspice.
Still believe that UL is the way to go, practically not LTspice.
Now, take a challenge, and use that LT Spice program to do some real research about input stage 2nd H. distortion canceling with output stage 2nd H. distortion.
Triode Wire the output tube.
Remove any global negative feedback, local output tube cathode negative feedback, any Schade negative feedback, and any UL negative feedback.
That way, the real nature of the input stage and output stage 'cancellation' shows up.
Negative feedback can be applied later, after the study is done.
Set your amplifier software model for 1 Watt output, 8 Ohm secondary loaded with 8 Ohms.
Use an easy test frequency, 1 kHz.
Write down the input signal voltage that is necessary to get 1 Watt output 8 Ohm tap and 8 Ohm load.
Always apply that same input voltage, for tests 1, 2, and 3 below.
1. Load the amplifier output transformer 8 Ohm secondary with 4 Ohms. Check the 2nd H. distortion.
2. Load the amplifier output transformer 8 Ohm secondary with 8 Ohms. Check the 2nd H. distortion.
3. Load the amplifier output transformer 8 Ohm secondary with 20 Ohms. Check the 2nd H. distortion.
What did you just test? You simulated a real world loudspeaker.
You tested the input stage to output stage 2nd H. distortion cancellation.
But, the output stage 2nd H. distortion is not a constant when you change the load impedance (even though the signal to the output stage control grid is constant for all 3 tests above.
Have fun . . .
Prove me wrong.
Easy to do, since you do not even have to build anything, and you already have the software model for 8 Ohms on the 8 Ohm tap.
You only change one single parameter for the three runs of LT Spice: 4 Ohms, 8 Ohms, 20 Ohms.
Please report back your findings.
Thanks!
Triode Wire the output tube.
Remove any global negative feedback, local output tube cathode negative feedback, any Schade negative feedback, and any UL negative feedback.
That way, the real nature of the input stage and output stage 'cancellation' shows up.
Negative feedback can be applied later, after the study is done.
Set your amplifier software model for 1 Watt output, 8 Ohm secondary loaded with 8 Ohms.
Use an easy test frequency, 1 kHz.
Write down the input signal voltage that is necessary to get 1 Watt output 8 Ohm tap and 8 Ohm load.
Always apply that same input voltage, for tests 1, 2, and 3 below.
1. Load the amplifier output transformer 8 Ohm secondary with 4 Ohms. Check the 2nd H. distortion.
2. Load the amplifier output transformer 8 Ohm secondary with 8 Ohms. Check the 2nd H. distortion.
3. Load the amplifier output transformer 8 Ohm secondary with 20 Ohms. Check the 2nd H. distortion.
What did you just test? You simulated a real world loudspeaker.
You tested the input stage to output stage 2nd H. distortion cancellation.
But, the output stage 2nd H. distortion is not a constant when you change the load impedance (even though the signal to the output stage control grid is constant for all 3 tests above.
Have fun . . .
Prove me wrong.
Easy to do, since you do not even have to build anything, and you already have the software model for 8 Ohms on the 8 Ohm tap.
You only change one single parameter for the three runs of LT Spice: 4 Ohms, 8 Ohms, 20 Ohms.
Please report back your findings.
Thanks!