I noticed today in my amp that I had forgotten a bypass capacitor....I won't fit one because it sounds so good at the moment. My Bastanis open baffles use a subwoofer for bass anyway.
Will update with voltages etc.
Will update with voltages etc.
So, it could have been done with a DC bleed from B+. Or just live with the degeneration. Yours is probably (no, certainly) a better choice.
All good fortune,
Chris
HI Bas,
without GNFB and especially without decoupling of the EL509 cathode resistor you will have an extremely high output impedance, i. e. low damping factor. Is this your intention? I wouldn't do that.
Best regards!
Hi Kay,
I understand your concern. It's just I haven't had a better sounding amp. I might add a switch for decoupling of the cathode resistor. But with GNFB back in I might as well throw it in a dumpster. It's an absolute lemon with the GNFB....
I understand your concern. It's just I haven't had a better sounding amp. I might add a switch for decoupling of the cathode resistor. But with GNFB back in I might as well throw it in a dumpster. It's an absolute lemon with the GNFB....
Old experiment, i have no values but it is easy to change G2 voltage by adjusting EL84 resistors, and easy adjustinc current by changing RK. Somwhere I read that Rp should be lowish to avoid that Va drops too much below Vg2.
And if I look again
Connecting a resistor between the cathodes would give current stabilisation.
Connecting a resistor between the cathodes would give current stabilisation.
I've got the feeling that driving the screen from a cathode follower is superior than this idea. But I can't tell you exctly why ... 🤔
Best regards!
Best regards!
One final question - what is the cathode current of the EL509 (for future builders to check)?
Added polyprop 70uF cap as cathode bypass. Can't say I was happy...might add a switch to better compare. But at least Kay is a little happier now.
70uF might be a bit low for decoupling a 330R resistor all the way down to 20Hz?
I was qoing to suggest CFB (cathode feedback) by inserting the OPT secondaries in the cathode circuits but the schematic in post 167 should to the same thing and could also be made adjustable with a pot.
I was qoing to suggest CFB (cathode feedback) by inserting the OPT secondaries in the cathode circuits but the schematic in post 167 should to the same thing and could also be made adjustable with a pot.
I'm going to put up another thread on that bypass capacitor in this amp. It really changes it from something is irritating me....To: WOW! I LOVE this amp. So my version does NOT have that bypass cap. It's day and night. That and the global negative feedback have been the 2 biggest improvements by a change in an amp ever by a country mile.
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Bas,
I think you have created a schematic that will have a long life. May I suggest that you add (in the schematic) a note that you are using this amp with a separately driven sub-woofer and note the cross-over frequency. I expect some of the “beauty” of this amp is in the fact that damping factor is not an issue in the frequency range you are using it. Possible?
I think you have created a schematic that will have a long life. May I suggest that you add (in the schematic) a note that you are using this amp with a separately driven sub-woofer and note the cross-over frequency. I expect some of the “beauty” of this amp is in the fact that damping factor is not an issue in the frequency range you are using it. Possible?
Hi Francois, not sure what the issue is. I was looking at Tim de Paravicini's EAR 859 schematic and it has a 2200uF cap and he knew what he was doing so its not just something that was lying around in his parts bin.... Perhaps the 470uF I used was too small still...not going low enough and only going down to say 500Hz...making the sound strident (unfortunately I don't know how to calculate the value). I could try a bigger cap still. If only I could find the caps I had in my hand just last week 🙂. To be continued.
Also there was this story about Bob Carver saying he could make a solid state amp sound like a tube amp by lowering damping factor or output impedance. Maybe I'm just crazy. But without the cap everything becomes fluid and is just a pleasure to listen to.
Personally I think it also has to do with the efficiënt quasi single driver ( I call it that because it is supposed to go up to 8k and slowly a compression driver takes over.) Whereas if you have say 86dB efficiënt speakers you need the lower impedance and better damping factor....all just speculation ofcourse.
I have no problems with the RH-84's I've built and used in the past few years. They all have a bypass cap...also sound great.
Also there was this story about Bob Carver saying he could make a solid state amp sound like a tube amp by lowering damping factor or output impedance. Maybe I'm just crazy. But without the cap everything becomes fluid and is just a pleasure to listen to.
Personally I think it also has to do with the efficiënt quasi single driver ( I call it that because it is supposed to go up to 8k and slowly a compression driver takes over.) Whereas if you have say 86dB efficiënt speakers you need the lower impedance and better damping factor....all just speculation ofcourse.
I have no problems with the RH-84's I've built and used in the past few years. They all have a bypass cap...also sound great.
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