babadono Posted August 23, 2012 Share Posted August 23, 2012 Coytee, Only 2 feet! Just about any wire configuration should work. It sounds like you have confirmed that you are talking about unbalanced equipment (I own a 3BX also, I know it is unbalanced). The chassis of the 2 pieces of equipment must be tied togrther some how. Otherwise there is no circuit. But at a length of 2 feet it is not going to matter if is the shield or the white conductors or both that are connecting the chassis together. BTW if your 3BX is as old as mine, which it probably is since they only made them for a few years long ago, make sure you give those RCA jacks a good cleaning.[] babadono Quote Link to comment Share on other sites More sharing options...
babadono Posted August 23, 2012 Share Posted August 23, 2012 Coytee, BTW what subs are you getting to go with those jubs? babadono Quote Link to comment Share on other sites More sharing options...
babadono Posted August 23, 2012 Share Posted August 23, 2012 Terminate the amplifier input with a low value resistor and any roll-off from capacitance will become moot. I use 2.2K, most preamps can drive that with ease. This will also reduce 1/F noise on long cable runs, as much as 10dB. djk, When you say terminate what do you mean? 2.2K right across the input signal to ground? Or in series with the signal? babadono Quote Link to comment Share on other sites More sharing options...
DrWho Posted August 23, 2012 Share Posted August 23, 2012 Some of us just design our output stages to drive the capacitive load...lowering the input impedance is just lowering the impedance seen at all frequencies in the same way that the capacitor is reducing the impedance at high frequencies - not at all an elegant solution if you ask me, and one with quickly diminishing returns. Btw, JJK - it's not uncommon for a lot of mic-preamps to have an input impedance << 5kohm. However, the reasons for it usually end up compromising other performance attributes. babadono, the resistor goes in parallel to the input on the receiving device. As far as 1/f noise - that is incredibly dependant on the specifics of the application. From what I've measured, the majority of modern equipment would be unaffected. Quote Link to comment Share on other sites More sharing options...
Coytee Posted August 23, 2012 Author Share Posted August 23, 2012 BTW what subs are you getting to go with those jubs? I've got a pair of Danley DTS-10's on the way. Never heard them. I went to their place in Georgia once specifically to hear them (went unannoucned). Turns out they did a show or something the week prior and were still putting their showroom back together. Of all things in there, these were the last and not yet hooked up so, never heard them. I went to a forum members house in Hilton Head once...he's got (I think) the Spud and some Khorns/Belle's. Ironically, his amp petered out so THOSE weren't working either. Seems the powers that be are trying to prevent me from listening to them. Seeing as I've already paid for them, I hope I like them. Quote Link to comment Share on other sites More sharing options...
Coytee Posted August 23, 2012 Author Share Posted August 23, 2012 BTW if your 3BX is as old as mine Probably as it's the original style, wooden sides. (I'm also original owner) Quote Link to comment Share on other sites More sharing options...
Panacea Engineering Posted August 23, 2012 Share Posted August 23, 2012 Richard, You will like the Danley's if you like Earth Shaking, Clean, Powerful Bass. They are the best Sub's I have heard to date, that I why I have them in my HT. Quote Link to comment Share on other sites More sharing options...
djk Posted August 23, 2012 Share Posted August 23, 2012 "As far as 1/f noise - that is incredibly dependant on the specifics of the application. From what I've measured, the majority of modern equipment would be unaffected." The RCA SSD-204 handbook (where I got the idea) says different, as does actual practice. Quote Link to comment Share on other sites More sharing options...
babadono Posted August 23, 2012 Share Posted August 23, 2012 Some of us just design our output stages to drive the capacitive load...lowering the input impedance is just lowering the impedance seen at all frequencies in the same way that the capacitor is reducing the impedance at high frequencies - not at all an elegant solution if you ask me, and one with quickly diminishing returns. Dr Who?/djk I'm getting confused. The lower input resistance is still getting even lower at higher frequencies because of the capacitve reactance (of the cable) isn't it? Maybe that is what you mean by a non elegant solution. This sounds like hocus pocus to me. What's the difference if the 2.2 k is at the output of the driving circuit or the input of the receiving circuit? It still attenuates the signal because of the non zero output impedance of the driving circuit. Quote Link to comment Share on other sites More sharing options...
djk Posted August 23, 2012 Share Posted August 23, 2012 It needs to be at the amplifier input. "Hum and Noise Below continuous power output Input shorted.................104dB Input open.......................88dB With 2kΩ resistance on 20-ft cable on input.....................104dB Input resistance................18kΩ " Page 496 RCA SSD-204C (1975) Quote Link to comment Share on other sites More sharing options...
JJkizak Posted August 24, 2012 Share Posted August 24, 2012 That's nice without the next unit/amp hooked up. What would the spec be running into the amp with the 2.2k resister in play? JJK Quote Link to comment Share on other sites More sharing options...
DrWho Posted August 24, 2012 Share Posted August 24, 2012 Some of us just design our output stages to drive the capacitive load...lowering the input impedance is just lowering the impedance seen at all frequencies in the same way that the capacitor is reducing the impedance at high frequencies - not at all an elegant solution if you ask me, and one with quickly diminishing returns. Dr Who?/djk I'm getting confused. The lower input resistance is still getting even lower at higher frequencies because of the capacitve reactance (of the cable) isn't it? Maybe that is what you mean by a non elegant solution. This sounds like hocus pocus to me. What's the difference if the 2.2 k is at the output of the driving circuit or the input of the receiving circuit? It still attenuates the signal because of the non zero output impedance of the driving circuit. Ya, but the rate of the high frequency roll-off is ever so slightly slower due to how parallel impedances sum. The capacitance reacts against the effective output impedance of the amplifier and the parallel resistor serves to lower the effective output impedance of the amp, but at the cost of signal attenuation. You're not increasing the output at the higher frequencies - you're just attenuating the lower frequencies. I went ahead and did a quick simulation to see how much of a difference it'd make. With 100 ohm output impedance, you're talking 0.1dB at 1MHz with 1nF of cable capacitance. With 600 ohm output impedance, you're talking 2dB at 1Mhz with the same cable. Notice that I divided the V(out2k2) signal by the attenuation difference of the resistive pads. Quote Link to comment Share on other sites More sharing options...
DrWho Posted August 24, 2012 Share Posted August 24, 2012 With 600 ohm output impedance: Quote Link to comment Share on other sites More sharing options...
DrWho Posted August 24, 2012 Share Posted August 24, 2012 It needs to be at the amplifier input. "Hum and Noise Below continuous power output Input shorted.................104dB Input open.......................88dB With 2kΩ resistance on 20-ft cable on input.....................104dB Input resistance................18kΩ " Page 496 RCA SSD-204C (1975) Thermal noise of 18k resistor is -112dBV, so let's say 24dB of gain gives -88dBV noise floor. Thermal noise of 2k resistor is -122dBV, so right there we should see a 10dB improvement for a -98dBV noise floor. The other 6dB is probably a change to the 60Hz hum being picked up on the unterminated cable. A 100ohm output impedance would have far more attenuation than 2.2k on the amplifier input. Or you could just go to an inverting stage on the amplifier input so that the unterminated input has -infinity gain... Quote Link to comment Share on other sites More sharing options...
DrWho Posted August 24, 2012 Share Posted August 24, 2012 "As far as 1/f noise - that is incredibly dependant on the specifics of the application. From what I've measured, the majority of modern equipment would be unaffected." The RCA SSD-204 handbook (where I got the idea) says different, as does actual practice. Haha, gear from the 1970's doesn't exactly constitue as modern... And the reasons for the 1/f noise actually have very little to do with the input impedance of the amplifier... in other words, you're talking about a band-air rather than a direct reason for physical behavior we see in nature. Quote Link to comment Share on other sites More sharing options...
djk Posted August 24, 2012 Share Posted August 24, 2012 Tube guys do something similar as well. Instead of using a grid leak resistor, they use a grid choke. I'm sorry you don't understand how the source impedance affects noise, it's also why MC cartridges sound better than MM types. Tom Holman wrote some good articles about phono circuits and SN ration that were quite good, how to design a circuit that would be quieter driven by an actual cartridge rather than designing for the best SN with a shorted input. "Haha, gear from the 1970's doesn't exactly constitue as modern..." Just shows that you education needs a little rounding out................. Quote Link to comment Share on other sites More sharing options...
DrWho Posted August 24, 2012 Share Posted August 24, 2012 Just shows that you education needs a little rounding out................. Ya know, maybe 4 years ago I would have believed that, but at work I've already designed preamps that outperform the old stuff in every measurable metric - and they also happen to be less expensive. I'm pretty sure that doesn't happen without understanding the effects of source impedance on noise. [] The stuff you're alluding to in this thread is easy sauce basics - don't be giving me the crotchety old man lecture. [] Quote Link to comment Share on other sites More sharing options...
djk Posted August 24, 2012 Share Posted August 24, 2012 Sorry, but at times you sound like the still-wet-behind-the-ears EEs I run into at work all the time. I used to discuss this from time to time with my father (an EE Prof, now retired). The guys at work that had him seldom say good things about him, they just complain how hard he was (they don't even make the connection that he is my father). Quote Link to comment Share on other sites More sharing options...
babadono Posted August 27, 2012 Share Posted August 27, 2012 DrWho, In both graphs there are two sets of curves, excuse my ignorance but one is amplitude and one is phase? Ok that's cool. But 1 Mhz, even the dogs in my neighborhood can't hear up there and I'll be lucky if I can hear 15 kilohertz. But thanks very much for anaysis. I still don't understand the original claim by djk that loading down the input of an amplifier magically cancels the effect of cable capacitance. I do understand of course that measuring or listening to an amp that has its input unterminated is noisier than an amp whose input is shorted to ground through 2.2k. babadono Quote Link to comment Share on other sites More sharing options...
DrWho Posted August 27, 2012 Share Posted August 27, 2012 Well if you're getting roll off in the audio band, the same concept applies. Although I'm still of the opinion that it's not a good solution. Btw, I still very much consider myself a green engineer, but the old guys that get my respect are those that demonstrate greater insight in their designs. Not the close-minded curmudgeon old farts that gotta complain to feel smart. Engineers should be judged by their solutions, not what they claim to know. Anyone suggesting that lowering input impedance to reduce 1/f noise and extend high frequency response is the highest fidelity solution, has no business trying to play the experience card. Quote Link to comment Share on other sites More sharing options...
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