Gray sound or Transient Intermodulation distortion
Imagine each voice or instrument sound is a different color ,passing through the amp they must get squeezed out each ef them distinguishable ,similar to the tooth past that squeezes out red and white past .If the number of colors are few such as pop music ,all passes correctly, maybe whirled ,but distinguishable.The trouble starts with big orchestraras when they express altogether ,the amp mixes all these colors to squeeze a single color ,gray sound.
Before reading the joint document ,I advise you to hear first what it is .The best exemple that nearly all feedbacked amps fail, is the piano concerto [Tchaikovsky,Rubinstein ,boston,youtube] .Just the first 12 seconds are necessary .The orchestra bursts with high notes ,over-expressed purposely by the conductor. You hear at best ,the orchestra sneezing,at worst ,the artists fall tumbling upon each other.but in all cases a dirty sound.(please, do not blame theMP3).
If such events are rare ,more usual gray sound is with multiple brass horns. Whether it is walking band or a wide jazz orchestra ,in real world you feel an overwhelming sensation by the beat and textures of brass horns.When it comes to be reproduced ,you hear sometimes a single horn blown by an angry driver.Even feedbackless amps as single ended divinities ,true,they don't generate the headache, but they don't generate the expected pleasure neither. A notorious example is Benny goodman's ,Sing Sing Sing. 28 brass horns blow the sound of elefant after a jungle drums , and this ,occurring repetitively .Lucky you must feel if your amp do not pierce you ears before the ending.
I was also convinced that only single ended tube amps are exempt from gray sound.As an AD1/NF2 old radio I had ,was blushing all other amps in shame,transistor or Dynaco .
In mid 80's,well clothed , with the Rubinstein CD in hand ,I went listening it, on most unaffordable prestigious amplifiers. All vendors advised me to get my CD exchanged. Few years later ,all by hazard ,a thrown away 1967 DUAL CV4 , presented NO ANY GRAY sound.It was as clean as the best .
I used it as school to learn how to adjust feedbacks to avoid gray sound.You find joint the schematic and family picture .
I hope This post will be helpful to those who try to design for the better sound.
KOKORIANTZ
Imagine each voice or instrument sound is a different color ,passing through the amp they must get squeezed out each ef them distinguishable ,similar to the tooth past that squeezes out red and white past .If the number of colors are few such as pop music ,all passes correctly, maybe whirled ,but distinguishable.The trouble starts with big orchestraras when they express altogether ,the amp mixes all these colors to squeeze a single color ,gray sound.
Before reading the joint document ,I advise you to hear first what it is .The best exemple that nearly all feedbacked amps fail, is the piano concerto [Tchaikovsky,Rubinstein ,boston,youtube] .Just the first 12 seconds are necessary .The orchestra bursts with high notes ,over-expressed purposely by the conductor. You hear at best ,the orchestra sneezing,at worst ,the artists fall tumbling upon each other.but in all cases a dirty sound.(please, do not blame theMP3).
If such events are rare ,more usual gray sound is with multiple brass horns. Whether it is walking band or a wide jazz orchestra ,in real world you feel an overwhelming sensation by the beat and textures of brass horns.When it comes to be reproduced ,you hear sometimes a single horn blown by an angry driver.Even feedbackless amps as single ended divinities ,true,they don't generate the headache, but they don't generate the expected pleasure neither. A notorious example is Benny goodman's ,Sing Sing Sing. 28 brass horns blow the sound of elefant after a jungle drums , and this ,occurring repetitively .Lucky you must feel if your amp do not pierce you ears before the ending.
I was also convinced that only single ended tube amps are exempt from gray sound.As an AD1/NF2 old radio I had ,was blushing all other amps in shame,transistor or Dynaco .
In mid 80's,well clothed , with the Rubinstein CD in hand ,I went listening it, on most unaffordable prestigious amplifiers. All vendors advised me to get my CD exchanged. Few years later ,all by hazard ,a thrown away 1967 DUAL CV4 , presented NO ANY GRAY sound.It was as clean as the best .
I used it as school to learn how to adjust feedbacks to avoid gray sound.You find joint the schematic and family picture .
I hope This post will be helpful to those who try to design for the better sound.
KOKORIANTZ
Attachments
Grey sound is just noise modulation - its intermodulation distortion but not 'transient'. Calling it TIM will be a distraction from an otherwise interesting discussion about the role of noise modulation in 'dimming out' instrumental timbres.
I agree high frequency intermodulation distortion can ruin especially piano recordings, as well as bells cymbals etc. I use piano source as my sound system fidelity test.
Unfortunately these two recordings you mention are flawed from the microphone out.
Sing sing sing was recorded in 1936, when microphones were very primitive. The recording you hear was probably cut straight to 78 rpm acetate disk, then remastered various times over the decades. The medium and microphones were not hi fidelity.
I have several Rubenstein recordings , all made before RCA changed over from their "okay" sounding ribbon mikes, to condensor mikes. I suspect your recording was also made with ribbon mikes. They were good for 1950, but by 1958 they had been supplanted by condensor mikes from germany. You still hear the 1958 condensor mike origin recordings on classical radio - from Mercury, Colombia, London FFRR, NOT from RCA and their obsolete ribbon mikes. RCA changed over to consensor sometime in the sixties. I don't have a spec sheet for RCA ribbon mikes, but shure is selling what they call a good imitation. The spec sheet on those rolls off about 10 khz. If you don't have frequencies above 10 khz from your mike, you don't have high frequency intermodulation distortion in the playback.
Simpler amps like your dual CV4 are capable of sounding very good IMHO, when the operating points and centering are okay. These old single end designs have difficulty with temperature stability. I have a similar design but silicon transistor dynaco ST120 transistor amp, and after the obvious poor crossover distortion was reduced by a bias mod designed by djoffe, the sound was very good. I also changed the output transistors to NTE60, which may have also helped fidelity. The original 40636 were a bit slow. I had to keep the temperatures stable on the ST120, however, by putting fans on the heatsinks. That is driving speakers. I had trouble with the ST120 blowing the sense transistor on the djoffe circuit, however.
when I test for system fidelity, I play the top octave portion of a piano solo by Peter Nero, When I Fall in Love off the Young & Warm & Wonderful album. This is on RCA dynagroove with condensor mikes from the late seventies, and the sound can be superb. When the system is sub-normal, I get vibrato on those top octave notes. As pianos do not produce vibrato, obviously this is high frequency IM distortion. When it was not tripping the breaker, the Peavey CS800s also passed my piano source IM distortion test. It is put away awaiting new Power supply caps after I finish a ST120 driver board and a PV-1.3k protection circuit.
When I can get a high fidelity amp to work stably, I'll try the Tchaikovsky piano concerto out, but not by Rubenstein. Wonderful player, substandard recordings. I'll try to get someone on Colombia, Mercury Living Presence, London FFRR, or Telearc.
Right now I'm using a very mid-fi amp and speaker from a 1970 design Schober Recital organ amp, because they work reliably, if the sound is not all that great. The ST120 is on the bench, where the AX6 driver board is centering the output at 1/6 of the supply rail, which obviously will cause 2nd harmonic distortion if I don't correct it.
Unfortunately these two recordings you mention are flawed from the microphone out.
Sing sing sing was recorded in 1936, when microphones were very primitive. The recording you hear was probably cut straight to 78 rpm acetate disk, then remastered various times over the decades. The medium and microphones were not hi fidelity.
I have several Rubenstein recordings , all made before RCA changed over from their "okay" sounding ribbon mikes, to condensor mikes. I suspect your recording was also made with ribbon mikes. They were good for 1950, but by 1958 they had been supplanted by condensor mikes from germany. You still hear the 1958 condensor mike origin recordings on classical radio - from Mercury, Colombia, London FFRR, NOT from RCA and their obsolete ribbon mikes. RCA changed over to consensor sometime in the sixties. I don't have a spec sheet for RCA ribbon mikes, but shure is selling what they call a good imitation. The spec sheet on those rolls off about 10 khz. If you don't have frequencies above 10 khz from your mike, you don't have high frequency intermodulation distortion in the playback.
Simpler amps like your dual CV4 are capable of sounding very good IMHO, when the operating points and centering are okay. These old single end designs have difficulty with temperature stability. I have a similar design but silicon transistor dynaco ST120 transistor amp, and after the obvious poor crossover distortion was reduced by a bias mod designed by djoffe, the sound was very good. I also changed the output transistors to NTE60, which may have also helped fidelity. The original 40636 were a bit slow. I had to keep the temperatures stable on the ST120, however, by putting fans on the heatsinks. That is driving speakers. I had trouble with the ST120 blowing the sense transistor on the djoffe circuit, however.
when I test for system fidelity, I play the top octave portion of a piano solo by Peter Nero, When I Fall in Love off the Young & Warm & Wonderful album. This is on RCA dynagroove with condensor mikes from the late seventies, and the sound can be superb. When the system is sub-normal, I get vibrato on those top octave notes. As pianos do not produce vibrato, obviously this is high frequency IM distortion. When it was not tripping the breaker, the Peavey CS800s also passed my piano source IM distortion test. It is put away awaiting new Power supply caps after I finish a ST120 driver board and a PV-1.3k protection circuit.
When I can get a high fidelity amp to work stably, I'll try the Tchaikovsky piano concerto out, but not by Rubenstein. Wonderful player, substandard recordings. I'll try to get someone on Colombia, Mercury Living Presence, London FFRR, or Telearc.
Right now I'm using a very mid-fi amp and speaker from a 1970 design Schober Recital organ amp, because they work reliably, if the sound is not all that great. The ST120 is on the bench, where the AX6 driver board is centering the output at 1/6 of the supply rail, which obviously will cause 2nd harmonic distortion if I don't correct it.
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😀Weird and wierder.
IF one actually owns one of the "better" design Amps. There is NO problem whatsoever with the lack of Resolution.
PS: I've owned one of those Duals.. Decades ago.. Mehh! was/is the most charitable descriptor.
Same goes for the Dynas : budget amps using a budget determined circuit. period
Lm3886 chips are surprisingly good.. for a Amp contained in a 10$ Chip.
Hardly 'high end' by Any stretch though.
Tough to soar like an Eagle when one is actually a Turkey 🙂
Actually Try something better?
IF one actually owns one of the "better" design Amps. There is NO problem whatsoever with the lack of Resolution.
PS: I've owned one of those Duals.. Decades ago.. Mehh! was/is the most charitable descriptor.
Same goes for the Dynas : budget amps using a budget determined circuit. period
Lm3886 chips are surprisingly good.. for a Amp contained in a 10$ Chip.
Hardly 'high end' by Any stretch though.
Tough to soar like an Eagle when one is actually a Turkey 🙂
Actually Try something better?
I think, with those 1960's germanium output transistors and the singleton input stage in those early Dual models , that you are really just tweaking good old, straightforward harmonic distortion components - to get enhanced, musically pleasing sound effects. There's nothing transient about their distortion, it's simply in large quantities and low order (particularly 2nd and 3rd harmonic)
There's nothing wrong with pursuing that type of sound quality for its pleasing audiophile qualities. Also, for those like me who's hearing is slowly losing the definition once provided by higher frequencies. However, let's not give this mysterious titles that don't apply. There are many folk here and some who are very clever and successful at tinkering with amplifier distortion effects to enhance their "musicality". Perhaps by reading some of the current threads about experiments with various other quasi-complementary output stages, you will find something even more interesting and pleasing to listen to.
With more power, modern components and definitely less noise than those old Dual models, you'll soon see the greater benefits of DIY designs, should you take up the activity 😉
There's nothing wrong with pursuing that type of sound quality for its pleasing audiophile qualities. Also, for those like me who's hearing is slowly losing the definition once provided by higher frequencies. However, let's not give this mysterious titles that don't apply. There are many folk here and some who are very clever and successful at tinkering with amplifier distortion effects to enhance their "musicality". Perhaps by reading some of the current threads about experiments with various other quasi-complementary output stages, you will find something even more interesting and pleasing to listen to.
With more power, modern components and definitely less noise than those old Dual models, you'll soon see the greater benefits of DIY designs, should you take up the activity 😉
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