Well, to get back to the shielding stuff...
I wonder why a piece like the Blowtorch isn't making use of carbon as a shielding material? It's not that much more expensive than machining a big billet of aluminum, and it offers better shielding per thickness than aluminum...and is surely non-magnetic.
Magura 🙂
I wonder why a piece like the Blowtorch isn't making use of carbon as a shielding material? It's not that much more expensive than machining a big billet of aluminum, and it offers better shielding per thickness than aluminum...and is surely non-magnetic.
Magura 🙂
Go for it! We just did what was available to us at the time.
Thanks for the memories of Bob, JB. It's true that is what we said together. I could NOT understand how a preamp with gain could sound better than a 20 turn quality dual wirewound pot, but now the pot is in the closet with the JC-80.
Thanks for the memories of Bob, JB. It's true that is what we said together. I could NOT understand how a preamp with gain could sound better than a 20 turn quality dual wirewound pot, but now the pot is in the closet with the JC-80.
Hi John,
Did you try this with one amp or many? Were they tube, BJT or J-FET input types? I am assuming the possible inductance of that pot was negligible (have to ask 😉 ).
-Chris
I imagine there are times when BJT differential pairs must be driven with a low impedance source. That is something a control can not give you. Then it is simply the least of the less than perfect choices.
Did you try this with one amp or many? Were they tube, BJT or J-FET input types? I am assuming the possible inductance of that pot was negligible (have to ask 😉 ).
-Chris
anatech said:
Exactly!! In my experience, excellent active preamp always sounds better than any passive, just for the reason you mentioned.
Only in case the passive divider is LOW IMPEDANCE, the resulting sound is neutral. Then you need buffered output to drive it.
Unless the active preamp's output stage is fronted by BJT differential pairs? As long as a potentiometer is in the circuit at some point a 'passive' drives an active stage. To meet the criteria appears to require a low Zout input buffer > low impedance pot > output buffer.
john curl said:
Which FET's have you experienced the best results with as input buffer?
Magura 🙂
You misunderstand. The test was with the Vendetta phono stage directly driving the pot and the pot in front of the power amp with a distance of 1 foot, between the power amp and the pot. The POWER AMP has a 50K resistive input impedance and fet inputs.
Hi John,
I wonder. I don't like the sound of complimentary differential pairs. I have a Luxman C-05 that was a disappointment to me. My thoughts turn to repeating your experiment with a straight J-FET diff pair type circuit. The complimentary types seem to sound a touch harsh, but not as bad as a BJT equivalent.
Hi Pavel,
I'm glad to see I'm not the only one who has noticed this. 🙂
-Chris
Thanks, that answers that question.
I wonder. I don't like the sound of complimentary differential pairs. I have a Luxman C-05 that was a disappointment to me. My thoughts turn to repeating your experiment with a straight J-FET diff pair type circuit. The complimentary types seem to sound a touch harsh, but not as bad as a BJT equivalent.
Hi Pavel,
I'm glad to see I'm not the only one who has noticed this. 🙂
-Chris
Please good people: Those of you who do NOT like or appreciate complementary differential fet input designs should refrain from considering this thread or any effort by Charles Hansen as potentially useful to you, since that is what we make, and I have done so for more than 1/3 of a century. My experience will not be useful to you.
Hi John,
Sorry. Accept my apologies then. In no way did I intend to attack your products. I can only comment from experience (personally, over 35 years).
My own experiments lead me to believe that high impedance sources work better with tube and FET inputs and not BJT types. I'll leave it to that.
You know what John? I learned a long time ago that I should listen to people. Even those who don't know as much because there are those experiences and tidbits of information that I may not know. You have far more experience than I do, so I do listen to what you have to say. That does not mean I accept everything, it does mean I may rethink things though.
-Chris
Sorry. Accept my apologies then. In no way did I intend to attack your products. I can only comment from experience (personally, over 35 years).
My own experiments lead me to believe that high impedance sources work better with tube and FET inputs and not BJT types. I'll leave it to that.
No sweat. Since you had experimented I thought you might have been interested in this possible variable. A simple "no thank you" would have sufficed.
Actually, it is. Even if I don't agree with you all the time.
You know what John? I learned a long time ago that I should listen to people. Even those who don't know as much because there are those experiences and tidbits of information that I may not know. You have far more experience than I do, so I do listen to what you have to say. That does not mean I accept everything, it does mean I may rethink things though.
-Chris
Are you still confused? I am. I haven't use a complementary differential BIPOLAR TRANSISTOR input since 1972. I USED the complementary differential bipolar input for 4 years, from 1968 to 1972. In 1972, I SWITCHED over to complementary differential JFET inputs, except when it is better just to use a simple differential JFET input. Sometimes it is slightly better, but not usually. Charles does the same. Is this really a problem?
Now the question is: What is the characteristic difference between a complementary differential JFET input and a simple diff JFET input?
Now the question is: What is the characteristic difference between a complementary differential JFET input and a simple diff JFET input?
john curl said:
Hi John,
"Sealed, thick walled aluminum enclosure". Is the sealed part very important here ... thick walled i understand, and of cause the walls should be well connected - but sealed!.
Is this why you use teflon for the RCA Jack panel in the beck (at least it looks like teflon).
Vogue
Hi John,
Exactly. I hear a difference. Whether the reason for the difference is known or not is another question. You may not hear the difference either. This may depend a great deal on the equipment you use in your systems.
Basically, the question popped into my head once you mentioned the bit about the control alone being inferior to an active stage. I agree with you on that and am simply looking for an answer. I have noticed this often. Most members here know I am not a fan of "passive preamps". I even strongly dislike the term.
-Chris
Nope. I answered and commented in a general sense. Nothing was actually directed at you or your design choices.
Sorry, do my comments above help clarify?
No. Those are your design choices and are completely valid. I am simply curious about your findings and how they may have differed when the input stage was a single J-FET differential type.
Yes!
Exactly. I hear a difference. Whether the reason for the difference is known or not is another question. You may not hear the difference either. This may depend a great deal on the equipment you use in your systems.
Basically, the question popped into my head once you mentioned the bit about the control alone being inferior to an active stage. I agree with you on that and am simply looking for an answer. I have noticed this often. Most members here know I am not a fan of "passive preamps". I even strongly dislike the term.
-Chris
I can't tell YOU why you hear a difference. I designed BOTH topologies in the original Levinson JC-2 pre amp in 1973. Just LOOK at the schematic.
Usually, a single differential input can be slightly quieter for a given open loop capacitance, BUT the overall distortion is about twice as much and the dynamic input current available (important in power amps), is much less.
I know what I heard, your hearing may vary.
Usually, a single differential input can be slightly quieter for a given open loop capacitance, BUT the overall distortion is about twice as much and the dynamic input current available (important in power amps), is much less.
I know what I heard, your hearing may vary.
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