We are thinking of transferring the content here to other places. Please feel free to comment....
We have a web site (needs work as of today):
http://www.digitalamp.com/
We have a facebook page:
http://www.facebook.com/DigitalAmpCo
We have a circle on Audio Circle:
http://www.audiocircle.com/index.php?board=174.0
It's a daunting task to manage all these things, so we're thinking of consolidating.
-Tommy O
Saturday, February 4, 2012
Friday, July 23, 2010
A word about load dependence...
There is no such thing as "completely load insensitive"...
Also, it takes wrapping feedback around the output filter to REDUCE load dependence, and in our experience, this affects the sonic quality of the amp in a negative way --- no pun intended. In fact that "too much negative feedback" sound (sometimes associated with Class-AB amps) is just what you get with all the phase margin compensation that's required to do so. As long as you're not driving a ridiculously low impedance, a low feedback design sounds so much cleaner than one designed to do better on the bench than into your ears. We can all agree that bench measurements don't tell the whole story. Without writing a book on this topic here, lets just say that we started with a design that was excellent on the bench, then tweaked it over several YEARS to get it to sound the way it does.
I have been designing Class-D amps (and listening to them) for more than 20 years, and these opinions are not based on some fly-by-night theories. There are many misconceptions regarding Class-D technology, and companies that take the risk of designing their own Class-D amps from scratch can easily fall short from inexperience. Same goes for pre-fab module makers. I have seen audio companies employ switching power supply designers that have never designed an amplifier in their life to build their "proprietary amp technology". It is also important to know analog amplifier design in order to make a good "digital" amp. Yes, I know there will be somebody out there to once again point out that Class-D doesn't mean the same thing as digital, blah, blah, blah. I designed my first analog audio amp when I was in grade school, by the way... Designing analog amps is a good way to learn what results in good sonic performance versus good bench measurements. It can be considered a good lead up to digital amp design --- a prerequisite.
-Tommy
Also, it takes wrapping feedback around the output filter to REDUCE load dependence, and in our experience, this affects the sonic quality of the amp in a negative way --- no pun intended. In fact that "too much negative feedback" sound (sometimes associated with Class-AB amps) is just what you get with all the phase margin compensation that's required to do so. As long as you're not driving a ridiculously low impedance, a low feedback design sounds so much cleaner than one designed to do better on the bench than into your ears. We can all agree that bench measurements don't tell the whole story. Without writing a book on this topic here, lets just say that we started with a design that was excellent on the bench, then tweaked it over several YEARS to get it to sound the way it does.
I have been designing Class-D amps (and listening to them) for more than 20 years, and these opinions are not based on some fly-by-night theories. There are many misconceptions regarding Class-D technology, and companies that take the risk of designing their own Class-D amps from scratch can easily fall short from inexperience. Same goes for pre-fab module makers. I have seen audio companies employ switching power supply designers that have never designed an amplifier in their life to build their "proprietary amp technology". It is also important to know analog amplifier design in order to make a good "digital" amp. Yes, I know there will be somebody out there to once again point out that Class-D doesn't mean the same thing as digital, blah, blah, blah. I designed my first analog audio amp when I was in grade school, by the way... Designing analog amps is a good way to learn what results in good sonic performance versus good bench measurements. It can be considered a good lead up to digital amp design --- a prerequisite.
-Tommy
Wednesday, July 7, 2010
2.5mm plug for remote power control
If you'd like to connect external power control and make your own connection at the amp side, try the CP3-1001-ND solder type plug from Digi-Key.
Here's a link:
http://search.digikey.com/scripts/DkSearch/dksus.dll?lang=en&site=US&WT.z_homepage_link=hp_go_button&KeyWords=CP3-1001-ND
How to use external power control is explained earlier in this blog. Thanks.
Here's a link:
http://search.digikey.com/scripts/DkSearch/dksus.dll?lang=en&site=US&WT.z_homepage_link=hp_go_button&KeyWords=CP3-1001-ND
How to use external power control is explained earlier in this blog. Thanks.
Thursday, April 15, 2010
When it comes to preamps, I prefer balanced to unbalanced. My reference tube preamp is an AR SP9, and that's single ended (unbalanced). It sounds very nice with the adapters, but it's a little noisy for my tastes. Balanced preamps are typically quieter end-to-end. A black background is an important advantage to our amps.
Some people define "true balanced" differently than others. To me, it means that all signals are handled differentially throughout. That means double the contacts on selector switches, double the number of pots on volume controls, and double the number of gain stages. Some think that the disadvantage of double the gain stages, even though they work in parallel, is not worth the trouble, so they convert the inputs to single ended. The signals are then processed one per channel until it is converted back to differential (balanced) in the end. Tube units typically do this with a transformer.
You can think of it this way... Every stage of the preamp adds some noise and distortion (even if it's near zero). If you add the exact same noise and distortion on the positive version of the signal as on the negative side, they cancel out. This assumes that the error signal is exactly the same on both polarities, and that's pretty unlikely. Due to that issue, it is twice as important to have low noise and distortion in all gain stages of a truly balanced design, making it twice as difficult to achieve the same result.
In an "internally single ended" design, the signals are converted to single ended before processing. Special handling is necessary for low noise and distortion since you can't cancel out common mode "errors". One unit that converts to balanced at the end of the chain is the Purity One from Bella Extreme with the balanced output option. I'm trying to get one of those to try out.
Some people define "true balanced" differently than others. To me, it means that all signals are handled differentially throughout. That means double the contacts on selector switches, double the number of pots on volume controls, and double the number of gain stages. Some think that the disadvantage of double the gain stages, even though they work in parallel, is not worth the trouble, so they convert the inputs to single ended. The signals are then processed one per channel until it is converted back to differential (balanced) in the end. Tube units typically do this with a transformer.
You can think of it this way... Every stage of the preamp adds some noise and distortion (even if it's near zero). If you add the exact same noise and distortion on the positive version of the signal as on the negative side, they cancel out. This assumes that the error signal is exactly the same on both polarities, and that's pretty unlikely. Due to that issue, it is twice as important to have low noise and distortion in all gain stages of a truly balanced design, making it twice as difficult to achieve the same result.
In an "internally single ended" design, the signals are converted to single ended before processing. Special handling is necessary for low noise and distortion since you can't cancel out common mode "errors". One unit that converts to balanced at the end of the chain is the Purity One from Bella Extreme with the balanced output option. I'm trying to get one of those to try out.
Thursday, April 8, 2010
Remote Standby Operation
The remote jack on the back of DAC4800A and Cherry amplifiers allows you to force the unit into standby from an external source to save power. Some home theater systems have a control signal output that can be used to control the amp's standby operation.
The input takes less than a milliamp to drive. When the input is below 2V, the amp is placed in shutdown. When it is above 3V, the amp is active. When the input is not connected, the amp is active in the case of the Cherry, or controlled by the user in the case of the DAC4800A. The DAC4800A has a pushbutton standby control, and external control overrides the user setting. The Cherry series of amps does not have a pushbutton standby control.
The plug is a stabndard 2.5mm size barrel type, typically used by "wall warts".
The input takes less than a milliamp to drive. When the input is below 2V, the amp is placed in shutdown. When it is above 3V, the amp is active. When the input is not connected, the amp is active in the case of the Cherry, or controlled by the user in the case of the DAC4800A. The DAC4800A has a pushbutton standby control, and external control overrides the user setting. The Cherry series of amps does not have a pushbutton standby control.
The plug is a stabndard 2.5mm size barrel type, typically used by "wall warts".
Tuesday, November 24, 2009
A word about High Power Amps
Is more power better? We believe it is, within reason!
More power usually comes with a few compromises, such as zero-crossing distortion, transient distortion, and noise. We worked for decades to find a solution to these issues and think we've found it. Doing so is not cheap, but it doesn't need to be outrageously expensive either.
A quick word about zero crossing distortion... At low levels, high power Class-AB amps have real issues controlling a reactive load. Imagine driving a car where the middle 10 degrees or so of steering wheel rotation has no effect on the direction of the car.
Regarding noise, the more power output, the louder the same noise figure (dB) with respect to maximum power sounds. There's no magic, so you need really good SNR to sound good at low levels with high max power.
Another concern is peak output delivery. If you can put out 100A into 4 ohms momentarily (micro- or milli-seconds), this is equivalent to 40,000W! The path from the power supply to the speaker needs to be as direct as possible to provide clean peaks.
This is just touching on the subject, but hope it clears up a few issues that are commonly misunderstood.
Our DAC4800A and Cherry amps address zero crossing distortion. Our design inherently has 0% zero crossing distortion.
Our DAC4800A and Cherry amps address transient distortion. Our design uses output devices capable of more than 100A output.
Our DAC4800A and Cherry amps address noise. Our design achieves more than 110dB SNR. Just try the "ear to the speaker" test...
And... We can also deliver more than 1,200 total watts continuous power.
So, next time you find yourself discussing high power amps, remember that it can be DONE RIGHT!
More power usually comes with a few compromises, such as zero-crossing distortion, transient distortion, and noise. We worked for decades to find a solution to these issues and think we've found it. Doing so is not cheap, but it doesn't need to be outrageously expensive either.
A quick word about zero crossing distortion... At low levels, high power Class-AB amps have real issues controlling a reactive load. Imagine driving a car where the middle 10 degrees or so of steering wheel rotation has no effect on the direction of the car.
Regarding noise, the more power output, the louder the same noise figure (dB) with respect to maximum power sounds. There's no magic, so you need really good SNR to sound good at low levels with high max power.
Another concern is peak output delivery. If you can put out 100A into 4 ohms momentarily (micro- or milli-seconds), this is equivalent to 40,000W! The path from the power supply to the speaker needs to be as direct as possible to provide clean peaks.
This is just touching on the subject, but hope it clears up a few issues that are commonly misunderstood.
Our DAC4800A and Cherry amps address zero crossing distortion. Our design inherently has 0% zero crossing distortion.
Our DAC4800A and Cherry amps address transient distortion. Our design uses output devices capable of more than 100A output.
Our DAC4800A and Cherry amps address noise. Our design achieves more than 110dB SNR. Just try the "ear to the speaker" test...
And... We can also deliver more than 1,200 total watts continuous power.
So, next time you find yourself discussing high power amps, remember that it can be DONE RIGHT!
Sunday, January 4, 2009
Equipment and Music mentioned on our review page
Here is the link to our review page:
http://www.digitalamp.com/DAC_REVIEWS.htm
Here are a few lists of mentioned items in categories...
Speakers:
Dennis Murphy
Canton Karrat
Apogee Caliper Signatures
ACI Sapphire
Magnepan MG1.6
Gradient Helsinki 1.5
B&W 805s
SPTech Minis
Von Schweikert VR-4SR MKii
Von Schweikert VR4JR
VAC PA100/100 amp
Joseph Audio RM7si
Quad ESL 57
Quad 22L2
Ohm5 MKii
Advent lG
Bose sub/sat (unknown model)
Hafler 300 Series
Amps:
Pioneer/Luxman Hybrid Amps
Denon
Parasound
NAD
Manley Stingray Integrated Tube Amp
Conrad Johnson CAV 50 Integrated Tube Amp
Cary Slam 100 Mono Blocks
AVA Insight 440H
ICE-based H2O Audio S250 Signature
Exodus Audio UcD400
Aberdeen Signature TacT S2150
PrimaLuna tube integrated
Channel Island D200s
Sunfire Signature 600 watt
Aragon 2004
Pass Labs
Nuforce
Nakamichi PA-7 (stasis)
DAC 4800a
DAC4800A
Cherry
DAC/Cherry
Preamps and D/A:
MacIntosh tube pre-amp
Bel Canto pre-3
NAD C160 preamp
Jeff Rowland Capri
Bel Canto PRe3
Red Wine Isabella DAC/PRE
VAC Standard MKII preamp
Promitheus TVC rev 3 passive preamp
DACT CT-1 (volume control pot)
Cables:
Theils and Silver Cabling
Balanced KCI Gold Cable
Black Sand Silver Ref V Power Cord
VandenHul carbon fiber interconnects
DIY 8’ Axon cables
Misc Equipment:
Shanling T200A SACD Player
Audio Technica AT440MLa Cartridge
Adcom GFT-555 II Tuner
Rotel 1072 CD Player
Resolution Audio CD55 Player
Misc Terms:
Pro-Ject Perspective Carbon
Tube Box SE
GIK, 8th Nerve panels
Reality ICs
Black Sand PCs
PRAT, pace rhythm and timing
CLDjam
1.5" thick, braced walls on heavy 24"steel stands
350w into 8ohms and almost 700w at 4ohms
15A breaker
XLR inputs
binding posts
removable IEC plug
750VA torroidal transformer
1500VA transformer
thermal, shorted, voltage and over current protection
standby/operate switch
Music:
Dire Straights "Love over Gold"
Cowboy Junkies "Trinity Sessions", "Mining for Gold" (Margo Timmins solo), "Misguided Angel"
Portishead "Dummy", "Mysterons"
Peter Murphy "Deep", "Marlene Dietrich's Favorite Poem"
Yello
Everything but the Girl
Peter Gabiel "Shaking the Tree"
Monster Magnet "God Says No"
Radiohead "Kid A"
Delerium "Poem", "Aria"
Paganini Caprices
Bach's great organ works
Rob Wasserman’s Duets "Angel Eyes"
Ani Difranco’s "Garden of Simple" and "So What"
Ben Harpers "Fight for your mind" title song, as well as "Burn one down" portrays the drums with excellent speed and timbre. Impressive!
The Trinity Session by Cowboy Junkies
Patricia Barbers Modern Cool, "Company"
Red Rose Music vol 1 track 6 (twenty-third psalm, Shane Cattrall)
The Belfast Harp Orchestra, Earth Water Wind and Fire
McIntosh Test Disc "Voices of Angels" (Track 5)
David Manley recordings #8 Cantos de los Gitanos
Diana Krall
Tsuyoshi Yamamoto (piano)
Boston Pops
Cincinnati Orchestra
Pink Floyd
Eva Cassidy "You take my breath away"
Rebecca Pigeon "Spanish Harlem"
"The worlds Greatest Audiophile Vocal Recordings" produced by Chesky records
Red Rose Recordings "In a sentimental mood", "Misty"
George Winston "Autumn"
The Grande Piano Concert by Rick Wakeman
Red Rose "Recitative in Scherzo for Solo Violin" (track 4)
Ottmar Liebert + Luna Negra's "Viva", "Buddhas Flower" (track 2)Stravinsky's "Firebird Suite"
Tchaikovsky's "1812 overture", "Fanfare for the Common Man"
Dagda "Druids in the Glen"
Pink Floyd "Dark Side of the Moon"
http://www.digitalamp.com/DAC_REVIEWS.htm
Here are a few lists of mentioned items in categories...
Speakers:
Dennis Murphy
Canton Karrat
Apogee Caliper Signatures
ACI Sapphire
Magnepan MG1.6
Gradient Helsinki 1.5
B&W 805s
SPTech Minis
Von Schweikert VR-4SR MKii
Von Schweikert VR4JR
VAC PA100/100 amp
Joseph Audio RM7si
Quad ESL 57
Quad 22L2
Ohm5 MKii
Advent lG
Bose sub/sat (unknown model)
Hafler 300 Series
Amps:
Pioneer/Luxman Hybrid Amps
Denon
Parasound
NAD
Manley Stingray Integrated Tube Amp
Conrad Johnson CAV 50 Integrated Tube Amp
Cary Slam 100 Mono Blocks
AVA Insight 440H
ICE-based H2O Audio S250 Signature
Exodus Audio UcD400
Aberdeen Signature TacT S2150
PrimaLuna tube integrated
Channel Island D200s
Sunfire Signature 600 watt
Aragon 2004
Pass Labs
Nuforce
Nakamichi PA-7 (stasis)
DAC 4800a
DAC4800A
Cherry
DAC/Cherry
Preamps and D/A:
MacIntosh tube pre-amp
Bel Canto pre-3
NAD C160 preamp
Jeff Rowland Capri
Bel Canto PRe3
Red Wine Isabella DAC/PRE
VAC Standard MKII preamp
Promitheus TVC rev 3 passive preamp
DACT CT-1 (volume control pot)
Cables:
Theils and Silver Cabling
Balanced KCI Gold Cable
Black Sand Silver Ref V Power Cord
VandenHul carbon fiber interconnects
DIY 8’ Axon cables
Misc Equipment:
Shanling T200A SACD Player
Audio Technica AT440MLa Cartridge
Adcom GFT-555 II Tuner
Rotel 1072 CD Player
Resolution Audio CD55 Player
Misc Terms:
Pro-Ject Perspective Carbon
Tube Box SE
GIK, 8th Nerve panels
Reality ICs
Black Sand PCs
PRAT, pace rhythm and timing
CLDjam
1.5" thick, braced walls on heavy 24"steel stands
350w into 8ohms and almost 700w at 4ohms
15A breaker
XLR inputs
binding posts
removable IEC plug
750VA torroidal transformer
1500VA transformer
thermal, shorted, voltage and over current protection
standby/operate switch
Music:
Dire Straights "Love over Gold"
Cowboy Junkies "Trinity Sessions", "Mining for Gold" (Margo Timmins solo), "Misguided Angel"
Portishead "Dummy", "Mysterons"
Peter Murphy "Deep", "Marlene Dietrich's Favorite Poem"
Yello
Everything but the Girl
Peter Gabiel "Shaking the Tree"
Monster Magnet "God Says No"
Radiohead "Kid A"
Delerium "Poem", "Aria"
Paganini Caprices
Bach's great organ works
Rob Wasserman’s Duets "Angel Eyes"
Ani Difranco’s "Garden of Simple" and "So What"
Ben Harpers "Fight for your mind" title song, as well as "Burn one down" portrays the drums with excellent speed and timbre. Impressive!
The Trinity Session by Cowboy Junkies
Patricia Barbers Modern Cool, "Company"
Red Rose Music vol 1 track 6 (twenty-third psalm, Shane Cattrall)
The Belfast Harp Orchestra, Earth Water Wind and Fire
McIntosh Test Disc "Voices of Angels" (Track 5)
David Manley recordings #8 Cantos de los Gitanos
Diana Krall
Tsuyoshi Yamamoto (piano)
Boston Pops
Cincinnati Orchestra
Pink Floyd
Eva Cassidy "You take my breath away"
Rebecca Pigeon "Spanish Harlem"
"The worlds Greatest Audiophile Vocal Recordings" produced by Chesky records
Red Rose Recordings "In a sentimental mood", "Misty"
George Winston "Autumn"
The Grande Piano Concert by Rick Wakeman
Red Rose "Recitative in Scherzo for Solo Violin" (track 4)
Ottmar Liebert + Luna Negra's "Viva", "Buddhas Flower" (track 2)Stravinsky's "Firebird Suite"
Tchaikovsky's "1812 overture", "Fanfare for the Common Man"
Dagda "Druids in the Glen"
Pink Floyd "Dark Side of the Moon"
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