Hi ctong,
Well, that is one reason I think you should be constructing circuits to experiment with, then put what you have found out into practice.
The people who are really involved with the "design by ear" method are those who use the popular parts at the time they "voice" their creation. They will become involved in endless upgrades and improvements that often do nothing more than lighten your wallet, and change the sound of the product. One shinning example of this would be the Counterpoint product line, and Elliot's continuing modifications to those products.
-Chris
Well, that is one reason I think you should be constructing circuits to experiment with, then put what you have found out into practice.
Actually, that isn't really true at all. How the amplifier sounds must be considered along with how it measures. Amplifiers designed while the measurements are ignored can always be improved. I can't think of any successful designer that doesn't do both. The same can be said if someone attempts to design an amplifier by using a THD meter alone. Again, that amplifier can be improved.
The people who are really involved with the "design by ear" method are those who use the popular parts at the time they "voice" their creation. They will become involved in endless upgrades and improvements that often do nothing more than lighten your wallet, and change the sound of the product. One shinning example of this would be the Counterpoint product line, and Elliot's continuing modifications to those products.
-Chris
A few days ago I reduced the current through the 2nd voltage gain stage, which resulted in a higher Vds (by 0.9V) for the gain mosfet (IRFD9210) as I am using a 52ohm source resistor. The were noticeable improvements in the sound. This leads me to wonder whether further increasing the Vds (currently 3.5V) will improve the performance even more. I am thinking of replacing the zener diode connected to the cascoding mosfet (IRF610) from 9.1V to a higher voltage (10V?).
Is there any downside to increasing this voltage? Thanks very much.
Is there any downside to increasing this voltage? Thanks very much.
Nelson Pass said:Give it a try and see.
Thanks. I will go ahead and try it.
Also, I found that a gain of 32 db sounds best for the current circuit setup. Thus there is less NFB than the Aleph 0, which has a 26 db gain (both have similar open loop gain, as far as I can tell). I wonder whether this difference is because the Aleph 0 has a single-ended output stage.
Hi ctong,
For longer term listening, this isn't as critical as you would naturally put the overall gain to approximately the same level.
Another cause for this is that your preamp, or signal source, does not put out the same level now with a higher gain amp (before clipping that is). The output of your preamp is actually 6 dB less than it was with the stock gain. What I am saying is that some reduction in distortion may be due to the preamp (or output signal source) lowered by the 6 dB difference. It would be nice to know where your gains in sound quality truly are being made. Once you know that, you can make some valid conclusions.
The fact that you are testing on your own is great! Now you're learning things first hand.
-Chris
It's critical to keep the actual output level the same when making comparisons for short term observations. It's well known that the louder amp will sound better as long as you are not into clipping or compression.
For longer term listening, this isn't as critical as you would naturally put the overall gain to approximately the same level.
Another cause for this is that your preamp, or signal source, does not put out the same level now with a higher gain amp (before clipping that is). The output of your preamp is actually 6 dB less than it was with the stock gain. What I am saying is that some reduction in distortion may be due to the preamp (or output signal source) lowered by the 6 dB difference. It would be nice to know where your gains in sound quality truly are being made. Once you know that, you can make some valid conclusions.
The fact that you are testing on your own is great! Now you're learning things first hand.
-Chris
anatech said:
Hi Chris,
The comparisons are made with the levels matched to within 0.5db. My preamp is a DIY Aleph P. So the output level should not affect its distortion characteristics. The improvements going from the stock 29db to 32db are unmistakable. BTW, I am using a pair of Sennheiser HD600 headphones driven by the preamp as reference.
You have made changes, and you can hear them.
Unfortunately, the resistor and transistor you call out is not the
same as on my schematic, however I speculate that you have
increased the voltage across the cascoded gain transistor, which
alters its gain and its load line. Also you have increased the open
loop gain by reducing the degeneration resistor value.
Unfortunately, the resistor and transistor you call out is not the
same as on my schematic, however I speculate that you have
increased the voltage across the cascoded gain transistor, which
alters its gain and its load line. Also you have increased the open
loop gain by reducing the degeneration resistor value.
Nelson Pass said:You have made changes, and you can hear them.
Unfortunately, the resistor and transistor you call out is not the
same as on my schematic, however I speculate that you have
increased the voltage across the cascoded gain transistor, which
alters its gain and its load line. Also you have increased the open
loop gain by reducing the degeneration resistor value.
Nelson,
Thank you for the explanation. There was a typo in my post above. The cascoding transistor is IRF9610, the same as in Aleph 0, not IRF610.
Through experimentation I have learned a great deal about the effects of the different aspects of the amp on the sound. Nonetheless, without a distortion meter my best shot in optimizing the amp may be to change all the resister values to those in Aleph 0 (v1.4-1.6).
I also have another question. Is there some sort of synergy going on between the input stage and the cascoded stage? For example, by intelligently choosing the load lines, the two stage combined might be more linear than the individual stages, thereby canceling some distortion. Thanks.
Variac or Soft-Start/Stop Circuit?
I haven’t yet used my J2 and F4 amps, as Jim Salk and Soundlab’s Roger West are building my bi-amped speakers and subs that I’ve co-designed with them-along with fellow diyaudio.com member Gary Dahl, who I am especially indebted to for his superb GPA Altec 416-8B sealed midwoofer concept. Next up for purchase from Reno Hi-Fi will be the B4 crossover.
Far be it from me to ever question anything about Nelson Pass’s designs, much less his power supplies. But from what little I know about amplifier design, I do wonder why no active soft-start/stop circuitry appears (?) to be included in the J2 and F4. I say this only because what I found absent in their manuals and what Scott Hull said in his review of the J2 Mini Review: First Watt J2 Amplifier | Confessions of a Part-Time Audiophile : “There’s no standby and no soft-start, either. You hit the switch on the J2 and the amp goes on, the blue LEDs light up, and sound comes out full voice about 3 seconds from power up. By contrast, my Plinius has a delayed-start — hit the switch, the LED blinks for 30 seconds and that then clicks over into Standby Mode. Output requires manual intervention before the signal begins flowing.”
However, the Plinius’s power turn ON/OFF feature may not necessarily be a true “soft-start” power ON/OFF circuit-one that would ideally reduce the rate of inrush current-at least from what I gathered from Scott’s description. More on this later.
Another big issue for me are audible turn ON/OFF transients. Nelson states in both J2 and F4 manuals “that turn-on and turn-off thumps and noise are small in this amplifier, and should not present any hazard to delicate drivers.” This is very welcome assurance, as my hearing is quite sensitive and, needless to say, priceless. I would never deliberately subject my ears to average midband SPLs much above 78db-if that much-at 11 feet away in my listening room.
Of course J2 and F4 owners here know from experience, but I’ll have to wait for my speakers to arrive and with my amps then powered ON/OFF to know for myself.
Regarding brownout or blackout-induced power line transients, I would think that standalone surge suppression like this http://www.surgex.com/pdf/cutsheetSA20.pdf would instantly and sharply attenuate them sufficiently before they impact systems-thereby protecting my ears from even moderately loud transients.
But to recap, what I’d like for my J2 and F4 is to have soft-start power ON/OFF power management:
1.) To protect my hearing from even moderately loud speaker thumps. This would be especially important with my second F4 amp, which will drive the small system in my 12 ft x 13 ft bedroom, where the speakers will be closer to my ears.
2.) So that my amps won’t be subject to inrush current high enough during power up and power down to otherwise reduce the life of their filter caps and other power supply components.
Indeed, all of these concerns are why I thought to soft-power ON/OFF my amps with a Variac. Parts Express 3A Variac Variable AC Power Transformer 0-130 VAC
However, are brand new, well-built single-phase Variacs too noisy, or have other issues that would make them unwise to use for this purpose?
If so, can anyone recommend an add-on device that offers reliable, automatic
soft-power ON/OFF management with no sonic consequences? The only ones
that I know of that may fill the bill are PS Audio’s P10 and P5 Power Plants-but way, way more than I want to spend Power | Product Categories | PS Audio
And the entry level P3 doesn’t include this feature.
So is there a diy alternative? I’d prefer an add-on device if it was certain not to make operation unsafe or unstable due to overly long circuit paths from control/power cables. That is, would the soft-power ON/OFF circuitry need to be installed inside of the J2 and F4?
But how about this idea: Unless the consensus here would condone use of a specific make/model Variac, if someone can suggest a specific soft-power ON/OFF circuit, maybe it could be added internal to the Surgex SA-20 conditioner? Of course, I’d bear the risk of thus invalidating the Surgex warrantee.
I know someone locally who might build this mod for me if I could provide him that circuit. If not, would anyone here care to build it? And no expense to be spared on any appropriate use of polypropylene film caps for bypassing, decoupling, etc. Post or pm me as you please.
I haven’t yet used my J2 and F4 amps, as Jim Salk and Soundlab’s Roger West are building my bi-amped speakers and subs that I’ve co-designed with them-along with fellow diyaudio.com member Gary Dahl, who I am especially indebted to for his superb GPA Altec 416-8B sealed midwoofer concept. Next up for purchase from Reno Hi-Fi will be the B4 crossover.
Far be it from me to ever question anything about Nelson Pass’s designs, much less his power supplies. But from what little I know about amplifier design, I do wonder why no active soft-start/stop circuitry appears (?) to be included in the J2 and F4. I say this only because what I found absent in their manuals and what Scott Hull said in his review of the J2 Mini Review: First Watt J2 Amplifier | Confessions of a Part-Time Audiophile : “There’s no standby and no soft-start, either. You hit the switch on the J2 and the amp goes on, the blue LEDs light up, and sound comes out full voice about 3 seconds from power up. By contrast, my Plinius has a delayed-start — hit the switch, the LED blinks for 30 seconds and that then clicks over into Standby Mode. Output requires manual intervention before the signal begins flowing.”
However, the Plinius’s power turn ON/OFF feature may not necessarily be a true “soft-start” power ON/OFF circuit-one that would ideally reduce the rate of inrush current-at least from what I gathered from Scott’s description. More on this later.
Another big issue for me are audible turn ON/OFF transients. Nelson states in both J2 and F4 manuals “that turn-on and turn-off thumps and noise are small in this amplifier, and should not present any hazard to delicate drivers.” This is very welcome assurance, as my hearing is quite sensitive and, needless to say, priceless. I would never deliberately subject my ears to average midband SPLs much above 78db-if that much-at 11 feet away in my listening room.
Of course J2 and F4 owners here know from experience, but I’ll have to wait for my speakers to arrive and with my amps then powered ON/OFF to know for myself.
Regarding brownout or blackout-induced power line transients, I would think that standalone surge suppression like this http://www.surgex.com/pdf/cutsheetSA20.pdf would instantly and sharply attenuate them sufficiently before they impact systems-thereby protecting my ears from even moderately loud transients.
But to recap, what I’d like for my J2 and F4 is to have soft-start power ON/OFF power management:
1.) To protect my hearing from even moderately loud speaker thumps. This would be especially important with my second F4 amp, which will drive the small system in my 12 ft x 13 ft bedroom, where the speakers will be closer to my ears.
2.) So that my amps won’t be subject to inrush current high enough during power up and power down to otherwise reduce the life of their filter caps and other power supply components.
Indeed, all of these concerns are why I thought to soft-power ON/OFF my amps with a Variac. Parts Express 3A Variac Variable AC Power Transformer 0-130 VAC
However, are brand new, well-built single-phase Variacs too noisy, or have other issues that would make them unwise to use for this purpose?
If so, can anyone recommend an add-on device that offers reliable, automatic
soft-power ON/OFF management with no sonic consequences? The only ones
that I know of that may fill the bill are PS Audio’s P10 and P5 Power Plants-but way, way more than I want to spend Power | Product Categories | PS Audio
And the entry level P3 doesn’t include this feature.
So is there a diy alternative? I’d prefer an add-on device if it was certain not to make operation unsafe or unstable due to overly long circuit paths from control/power cables. That is, would the soft-power ON/OFF circuitry need to be installed inside of the J2 and F4?
But how about this idea: Unless the consensus here would condone use of a specific make/model Variac, if someone can suggest a specific soft-power ON/OFF circuit, maybe it could be added internal to the Surgex SA-20 conditioner? Of course, I’d bear the risk of thus invalidating the Surgex warrantee.
I know someone locally who might build this mod for me if I could provide him that circuit. If not, would anyone here care to build it? And no expense to be spared on any appropriate use of polypropylene film caps for bypassing, decoupling, etc. Post or pm me as you please.
Last but not least: If I build these full range ESL kits Acorn Electrostatic Loudspeaker Kit , I would want the XA30.5 to drive them. Though the XA30.5 has a standby switch, there are times that I’d want to fully power down that amp. Accordingly, I’d need for this variac or soft-power ON/OFF Surgex modded device to be capable of managing this with ease and no sonic compromises. Please advise on this too.
Fine, thanks for that tip against using a variac.
But what about a soft-start circuit, as GRollins seems to suggest the advantages of here
http://www.diyaudio.com/forums/pass-labs/109601-a75-adcom-gfa-5400-a.html
And/or those like the one Walt Jung posted in the August 1980 issue of AUDIO
http://www.diyaudio.com/forums/powe...3-3kva-1-000-000uf-per-rail-capacitors-7.html
Might Walt's soft power ON/OFF circuit be an added plus for use with the XA30.5 (higher inrush current draw than the First Watt amps), when not powering it OFF/ON (i.e. not using standby mode)?
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