SonicTrance
Member of the Trade: Custom Amp Builder
Baron is referring to top of anode resistor, so B+.
No, because the cathodes are not grounded. Cathode node will be at about 1V.
You can connect the decoupling cap lead in the same ground hole as the cathode resistor was, if it fits?
I just looked at your connections in the picture.
There is no anode connection, only B+.
B- and filter are the same thing, B- for the CCS is the filter output (I realise you plan to try the CCS before adding the filter). Just making sure you understand to not connect unfiltered B- after you have the filter.
Not to be annoying, but precision is very important.
Yes, ground connection for driver stage B+ decoupling.so we are just providing the ground connection to the anode decoupling circuit, but wouldn't that circuit be broken without the cathode resistor in situ?
Looks pretty good to me, I don't know about the connections to the board though, not my expertise.
So how's it sound?
I predict the extra B- filter has no effect on sound quality. The improved balance should take care of all common mode noise, as per explained earlier in great detail. I originally added it to the schematic as a "final blow" to the doubts about the efficacy of the balanced common mode noise rejection. (Common mode noise rejection has been known for over a 100 years so shouldn't be too controversial.)
It's possible though it might, taking the circuit as a whole. Unknown interactions in a (semi)complex circuit are always a possibility. Interesting to hear results!
Switch it on!see what Sonic thinks.
Measure bias voltage at cathode node. Should read slightly higher at boot before the B- supply starts, then go to normal.
Wheres your B- connection btw? Cant see it?
Ok, all good then!It's here:
5K1 resistor.... to …… opposite end of 470R from FET.
Switch it on!
I can't see if all connection are correct though as I'm on thr phone. But I'm sure you're fine if you double and triple check!
I too want to hear your impressions!
The initial and main impression is one of total clarity, I may be imagining this but I felt that some harmonic distortion had disappeared.
Overall the sound was of the same order as the best anode/cathode setting but totally free of distortion
So those are my intial impressions, I'm going to have to live with this for a while before I decide on what to do next, so the filter can wait until then.
One thing is for sure, the level we are at now it's not going to be easy looking for yet more improvements..... or maybe.... !
baronbeehive, good work!
You are not imagining it, assuming you built the thing correctly it has lower distortion. To understand why I recommend you reread the big topology theory / experiment post from this thread. I tried my best to make it understandable but it takes some time and revisiting.
When you take out distortion, there is EXTRA stuff underneath, music signal details. Add distortion and you mask stuff in the signal.
Much more efficient to make the circuit do the balance, not to try and find a tube that is decently balanced. Have you tried different tubes with the CCS? Do they sound significantly different?
Not totally free of distortion, there's a long way to go still. You'd be surprised.
So I'm guessing no harsh IMD from B- ripple then? No 7H and up tearing your sweet music signal to shreds?
Understand theory and topology. Makes this hobby less poking around in the dark and more fun.
In the LD the limiting factor is physical space. Also the direct drive topology is problematic to improve.
Since the output follower has such a high output impedance and no way to force fully balanced operation (you cannot use a CCS there since it's a pair of followers), PSU improvements would be the way to go.
I'd go for actual (even very simple) regulation, not crazy C. Now there is just a voltage setter there. It sets the voltage and not much more. If the decoupling cap (right at the B+/- nodes) has a noticeable effect on sound quality, you are not dealing with any degree of PSU regulation.
Good work baron!
I don't think there's anything you can do to the ps(s) without extending the chassis or have a external chassis for the ps(s), unfortunately.