I have a late model Phase Linear design, DRS900, designed by Carver. By their description it sounds like it would be a class H; 6 supplies (3 per channel) with separate plus high and minus high supplies, rated 150W RMS and 900W peak. I never knew of the class G & H designations though. Bought it at a nice discount when Jensen bought and discontinued the line. A very nice amp for the early 1980's.
In the later 1970's Hitachi pioneered the class G amps and Soundcraftsmen used class H. I purchased a Hitachi SR-804 class G receiver in 1979 and still use it as my main amp. It's weight (for a 50wpc receiver) is under twenty four pounds. Most similar units from that time were well over thirty pounds and didn't have 3dB's of headroom. The Hitachi SR-804 runs cool. Even after several hours pushing my Ohm L's (4 ohms) to loud levels in my 1,700+ cu/ft living room, the receiver top is barely warm. I did use a Marantz 2252B for a few months during 2015 but like the seemingly effortless power of the Hitachi. Great video, a lucid explanation of amp classes.
I took the chance and purchased a Hitachi SR-903 last year (~US$138, physically mint condition) via a local online listing. After cleaning (Doxit treament), basic checks (DC offsets) and careful running in (dim bulb), I found the sound exceptionally clear, full...very nice bass...beautiful. With 75W at 8 ohms RMS...up to 160W for peak transients, the Class G amp runs cool. I liked this receiver so much, I bought a second (6 mo. later) that showed up on the same site (different seller, $120)...not as clean as the minty first receiver but in EXC physical condition. Same routine...checked out sat. I did modify both with a nice glossy vinyl wrap (burled walnut; $20) that turned the factory black wooden boxes into lookers. Also changed out the hard rubber feet for machined ALU feet (58mm) with rubber base-rings ($20 on Aliexpress). The first unit sits in the family room, fed by FiiO BTA30Pro (in RX mode) paired to Dali Spektors. The later unit sits on my desk along with a Marantz EQ20, fed by PC/FiiO BTA30 Pro(DAC mode) and paired to a)Mordaunt Short 20i speakers and/or b)Sony SS-CSD1's. More than enough power, for my needs. Way more. IMHO, these are absolutely wonderful units...so glad that they are relatively unknown and do not carry the Marantz-Pioneer-Sansui "tax". I did buy all of the electrolytic caps (incl filters...I did up the voltage from 6800uF/80V to 6800mF/100V(105C) on the main filter caps) and known "issue" transistors (e.g. SC1344/1345 to be replaced by KSA992/KSC1845/2N3711); enough for a planned project revision on both receivers. The service manual is excellent and the PCB's are well-marked within each unit. I figure it will be easier to master the specs and do this for two of the same model.
@@jb678901- yeah, under the radar for sure. And thankfully, not as desirable as the big four (Marantz, Kenwood, Pioneer or Sansui) but much better IMHO. In those days (later 1970's) Hitachi components were in house built. Everything in that SR-903 was manufactured by Hitachi, even the screws holding it together. A great High Fidelity magazine review summed it up. " If discs (records) are your bag and you like concert hall volumes, this receiver (SR-903) will really show you something". A last thought, the volume control on my SR-804 goes well past the twelve o'clock setting to past two and doesn't distort. It just gets louder. Most receivers start distorting well before that. There really is something to that class G, 3dB headroom claim. Swell score on two SR-903's. Yep, clean, clear, crisp sound. I would say "clinical" and will show off or show up your connected speakers.
I have 4 RPA-16 amps. from Rockville and they are class H amp.s love them.. they weight 47 lbs. each and each for right around $400. I can get with a 4-ohm. load 1.7K. watts per side..at max output.. Great value for the money!
Thanks for another interesting video, John! I had to fix one of the power amps for the subwoofers in my home stereo. Class H - low, mid and high rail and to top it off, the 12 output transistors is configurated as sziklai pairs. Took some re-engineering before I could start the troubleshooting and repair.
I owned a couple Carver amps. The first was a receiver, I forget the model. After a week or two I sent it back because I was sensitive to a very high frequency it seemed to be emmitting. They did tests and said they found no such signal in the output. I traded it in for a 400t, no such problems. I think in hindsight it was a spurious reverse microphonics issue in the power supply, only audible outside the output signal. Being a newer product the 400t probably had these issues designed out.
Very interesting. So the distinction between G and H is that (using your letters), H just turns the Hi supplies on and off, whereas G uses the top and bottom transistors to provide pseudo Hi+/- supplies at voltage slightly beyond what the middle transistors need to avoid clipping. Essentially G provides to the middle transistors a supply voltage that tracks their needs.
Very nice and clear presentation. Another outcome I experience with these designs, specifically with the Carver M1.5t, is a large amount of digital/switching noise from the thyristor switches. This noise made the amp impossible to use with early digital sampler keyboards like the Ensoniq.
Good series, John. I’ve seen you work on those Carvers, now I understand how they work. I believe they used thyristors for switching to the higher rails. I suppose they would use mosfets or igbt’s today, if class d had not taken over..
Your among the few channels that keep me using TH-cam. Thanks! This series has helped me clerify a lot. That being said. Efficiency is over rated in my opinion. In the real world, for me anyways, my audio battery use is my phone. Aside from that I've swapped enough light bulbs out for led to more then compensate for the very limited use of all my amplifiers combined plugged in. So for me efficiency isn't a factor in most cases. It does play a factor in size and cost though at high watt output but at some point cost goes out the window too for the right project.
Efficiency is not only about your savings, but also about the amount of engineering required to dissipate all the losses. Higher efficiency will absolutely reduce your amplifier's cooling need
A number of manufacturers these days are saying something like "our amp produces 75 Watts in Class-AB, of which the first 10 Watts are in Class-A". Would you consider doing a video to explain what that means exactly? With one of these beautifully simple schematics?
I suppose this could be said of any AB2 amp when the output current is small compared to idle current, and a few AB2s push idle current far beyond the typical 50mA up to a few amps. Requires a lot of heatsink capacity.
@@HillsWorkbench Oh, okay. My understanding of class AB2 isn't great - I thought it was something you'd basically only find in tube amps. So do you think that's what Pass Labs is doing for their integrated amplifiers? On their website they say: "the INT-60 presents 60 glorious watts per channel into 8 ohms, and doesn't leave class A until 30 watts thanks to its high-bias operation."
This concept reminds me of a feature of certain Cadillac internal combustion engines, which would operate on 4, 6, or 8 cylinders as power and speed requirements changed. As I recall, the technology never really caught on due to the added complexity. I wonder if class G & H amplifiers are less common for this same reason.
I see, so the Yamaha AST-A10 vintage amplifier is a Class H amplifier. It's a very odd design. Thank you for explaining it as clearly as water coming out from a mountain.
We're looking for gifts to get people over the holidays this year. Is there a stereo kit you'd recommend for someone semi-familiar with stereos and sound?
I think the TDA7293 has dual rail options according to the spec sheet, they call it BCD. Any ideas what BCD stands for? Its described as follows: The device described has therefore been developed in a mixed bipolar-MOS high voltage technology called BCDII 100/120. For the operation it is described as: . T1 and T2 are two power transistors that only operate when the output power reaches a certain threshold (for example, 20 W). If the output power increases, these transistors are switched on during the portion of the signal where more output voltage swing is needed, thus "bootstrapping" the power supply pins Does this mean that the TDA7293 could be considered class g or h?
@James W - I looked at the spec sheet. It's a very interesting device with optional external circuit configurations: Bridge Mode, Buffer Driver and Modular. SO THEN, BCD MUST NOT MEAN BINARY CODED (count) DECIMAL. lol What does that "C" stand for? Pin 11 is called Buffer Driver to allow additional TDA7293's to be strapped together in parallel to drive lower impedance loads. (Pins 6 and 12 are for a Boucherot HF Damper R/C Circuit.) Pin Pairs 7 & 8 and 13 & 15 allow external transistors and two diodes to accomodate the two different +/- rail voltages shown on the spec sheet figure 8 example for high effeciency. This video first shows the four external transistors for *G* first, then the second diagram shows only two _external_ transistors are required for *H.* Because the four transistors are wired as Darlington Pairs in the application notes on the spec sheet, I think they'll only count as two external transistors and that would make it, *H Class* as shown in this excellent video.
I wonder what can be done with this in regard to a guitar amplifier. In hifi distortion is a no no. In guitar amps that's fully acceptable and designed around.
There's no real reason why you couldn't aside from the fact the power levels are often a lot lower. The distortion of class G/H is not like overdrive, though.
I even didn't heard about G and H classes. Thx for the information. Interesting video as always.
Enjoyed the series, John. Thanks and happy holidays!
I was vaguely aware of these topologies but certainly had never heard of them being called class G & H, thank you for sharing !!
I just went to see about getting Bob Cordell's book. I'm in Canada, $115CAD+.. wow. Great video series btw.
I have a late model Phase Linear design, DRS900, designed by Carver. By their description it sounds like it would be a class H; 6 supplies (3 per channel) with separate plus high and minus high supplies, rated 150W RMS and 900W peak. I never knew of the class G & H designations though. Bought it at a nice discount when Jensen bought and discontinued the line. A very nice amp for the early 1980's.
In the later 1970's Hitachi pioneered the class G amps and Soundcraftsmen used class H. I purchased a Hitachi SR-804 class G receiver in 1979 and still use it as my main amp. It's weight (for a 50wpc receiver) is under twenty four pounds. Most similar units from that time were well over thirty pounds and didn't have 3dB's of headroom. The Hitachi SR-804 runs cool. Even after several hours pushing my Ohm L's (4 ohms) to loud levels in my 1,700+ cu/ft living room, the receiver top is barely warm. I did use a Marantz 2252B for a few months during 2015 but like the seemingly effortless power of the Hitachi. Great video, a lucid explanation of amp classes.
I took the chance and purchased a Hitachi SR-903 last year (~US$138, physically mint condition) via a local online listing. After cleaning (Doxit treament), basic checks (DC offsets) and careful running in (dim bulb), I found the sound exceptionally clear, full...very nice bass...beautiful. With 75W at 8 ohms RMS...up to 160W for peak transients, the Class G amp runs cool.
I liked this receiver so much, I bought a second (6 mo. later) that showed up on the same site (different seller, $120)...not as clean as the minty first receiver but in EXC physical condition. Same routine...checked out sat.
I did modify both with a nice glossy vinyl wrap (burled walnut; $20) that turned the factory black wooden boxes into lookers. Also changed out the hard rubber feet for machined ALU feet (58mm) with rubber base-rings ($20 on Aliexpress).
The first unit sits in the family room, fed by FiiO BTA30Pro (in RX mode) paired to Dali Spektors.
The later unit sits on my desk along with a Marantz EQ20, fed by PC/FiiO BTA30 Pro(DAC mode) and paired to a)Mordaunt Short 20i speakers and/or b)Sony SS-CSD1's.
More than enough power, for my needs. Way more.
IMHO, these are absolutely wonderful units...so glad that they are relatively unknown and do not carry the Marantz-Pioneer-Sansui "tax".
I did buy all of the electrolytic caps (incl filters...I did up the voltage from 6800uF/80V to 6800mF/100V(105C) on the main filter caps) and known "issue" transistors (e.g. SC1344/1345 to be replaced by KSA992/KSC1845/2N3711); enough for a planned project revision on both receivers. The service manual is excellent and the PCB's are well-marked within each unit. I figure it will be easier to master the specs and do this for two of the same model.
@@jb678901- yeah, under the radar for sure. And thankfully, not as desirable as the big four (Marantz, Kenwood, Pioneer or Sansui) but much better IMHO. In those days (later 1970's) Hitachi components were in house built. Everything in that SR-903 was manufactured by Hitachi, even the screws holding it together. A great High Fidelity magazine review summed it up. " If discs (records) are your bag and you like concert hall volumes, this receiver (SR-903) will really show you something". A last thought, the volume control on my SR-804 goes well past the twelve o'clock setting to past two and doesn't distort. It just gets louder. Most receivers start distorting well before that. There really is something to that class G, 3dB headroom claim. Swell score on two SR-903's. Yep, clean, clear, crisp sound. I would say "clinical" and will show off or show up your connected speakers.
I have 4 RPA-16 amps. from Rockville and they are class H amp.s love them.. they weight 47 lbs. each and each for right around $400. I can get with a 4-ohm. load 1.7K. watts per side..at max output.. Great value for the money!
Thanks for another interesting video, John! I had to fix one of the power amps for the subwoofers in my home stereo. Class H - low, mid and high rail and to top it off, the 12 output transistors is configurated as sziklai pairs. Took some re-engineering before I could start the troubleshooting and repair.
I owned a couple Carver amps. The first was a receiver, I forget the model. After a week or two I sent it back because I was sensitive to a very high frequency it seemed to be emmitting. They did tests and said they found no such signal in the output. I traded it in for a 400t, no such problems. I think in hindsight it was a spurious reverse microphonics issue in the power supply, only audible outside the output signal. Being a newer product the 400t probably had these issues designed out.
Awesome series.
Thank you for putting this series together, really enjoyed every minute and learned so much.
I aspire to following your footsteps.
Thanks John keep uploading more videos, you and your fellow electronic techs keep TH-cam alive at least for us IMHO.
Very interesting. So the distinction between G and H is that (using your letters), H just turns the Hi supplies on and off, whereas G uses the top and bottom transistors to provide pseudo Hi+/- supplies at voltage slightly beyond what the middle transistors need to avoid clipping. Essentially G provides to the middle transistors a supply voltage that tracks their needs.
I really enjoyed these explanations and now I know the difference.
Very nice and clear presentation. Another outcome I experience with these designs, specifically with the Carver M1.5t, is a large amount of digital/switching noise from the thyristor switches. This noise made the amp impossible to use with early digital sampler keyboards like the Ensoniq.
Good series, John. I’ve seen you work on those Carvers, now I understand how they work. I believe they used thyristors for switching to the higher rails. I suppose they would use mosfets or igbt’s today, if class d had not taken over..
Your among the few channels that keep me using TH-cam. Thanks! This series has helped me clerify a lot. That being said. Efficiency is over rated in my opinion. In the real world, for me anyways, my audio battery use is my phone. Aside from that I've swapped enough light bulbs out for led to more then compensate for the very limited use of all my amplifiers combined plugged in. So for me efficiency isn't a factor in most cases. It does play a factor in size and cost though at high watt output but at some point cost goes out the window too for the right project.
Efficiency is not only about your savings, but also about the amount of engineering required to dissipate all the losses. Higher efficiency will absolutely reduce your amplifier's cooling need
A number of manufacturers these days are saying something like "our amp produces 75 Watts in Class-AB, of which the first 10 Watts are in Class-A". Would you consider doing a video to explain what that means exactly? With one of these beautifully simple schematics?
I suppose this could be said of any AB2 amp when the output current is small compared to idle current, and a few AB2s push idle current far beyond the typical 50mA up to a few amps. Requires a lot of heatsink capacity.
@@HillsWorkbench Oh, okay. My understanding of class AB2 isn't great - I thought it was something you'd basically only find in tube amps. So do you think that's what Pass Labs is doing for their integrated amplifiers? On their website they say: "the INT-60 presents 60 glorious watts per channel into 8 ohms, and doesn't leave class A until 30 watts thanks to its high-bias operation."
@@jonathanvanier Yup, Up to half power is taking it a bit far though...
*EXCELLENT*
Thanks John!! Great series!
Hi JohnAudioTech
Are you going to do a video on the amplifier circuit configuration for Bridge tied Load.
But why there is two inputs in H ?
sweet stuff thanks
This concept reminds me of a feature of certain Cadillac internal combustion engines, which would operate on 4, 6, or 8 cylinders as power and speed requirements changed. As I recall, the technology never really caught on due to the added complexity. I wonder if class G & H amplifiers are less common for this same reason.
In the RF world, Class G amps are called Doherty amps
I see, so the Yamaha AST-A10 vintage amplifier is a Class H amplifier. It's a very odd design.
Thank you for explaining it as clearly as water coming out from a mountain.
What Thomas Yeats said. I can’t help but wonder what class K amplifiers will come up with.
I think NAD uses class G in their Power Envelope feature found in their amps?
nice
We're looking for gifts to get people over the holidays this year. Is there a stereo kit you'd recommend for someone semi-familiar with stereos and sound?
I think the TDA7293 has dual rail options according to the spec sheet, they call it BCD. Any ideas what BCD stands for? Its described as follows: The device described has therefore been developed in a mixed bipolar-MOS high voltage technology called BCDII 100/120.
For the operation it is described as: . T1 and T2 are two power transistors that only operate when the output power reaches a certain
threshold (for example, 20 W).
If the output power increases, these transistors are switched on during the portion of the signal where more output voltage swing is needed, thus "bootstrapping" the power supply pins
Does this mean that the TDA7293 could be considered class g or h?
@James W - I looked at the spec sheet. It's a very interesting device with optional external circuit configurations: Bridge Mode, Buffer Driver and Modular. SO THEN, BCD MUST NOT MEAN BINARY CODED (count) DECIMAL. lol What does that "C" stand for? Pin 11 is called Buffer Driver to allow additional TDA7293's to be strapped together in parallel to drive lower impedance loads. (Pins 6 and 12 are for a Boucherot HF Damper R/C Circuit.) Pin Pairs 7 & 8 and 13 & 15 allow external transistors and two diodes to accomodate the two different +/- rail voltages shown on the spec sheet figure 8 example for high effeciency. This video first shows the four external transistors for *G* first, then the second diagram shows only two _external_ transistors are required for *H.* Because the four transistors are wired as Darlington Pairs in the application notes on the spec sheet, I think they'll only count as two external transistors and that would make it, *H Class* as shown in this excellent video.
Any book for class h design
I want to know about class T,,perspective of an audio engineer,,pliz make a small video or put it in some video.....🙏
👌
I believe my Arc Audio car amps are class g/h
I wonder what can be done with this in regard to a guitar amplifier. In hifi distortion is a no no. In guitar amps that's fully acceptable and designed around.
There's no real reason why you couldn't aside from the fact the power levels are often a lot lower. The distortion of class G/H is not like overdrive, though.
Looks like NPC converter
I've think in germany most of the techs call it class h :D
I love your videos, but I have to be honest... an ad every 90 seconds really makes me want to just leave this channel.