Re: Off topic, I will delete in a day or so.
You should not delete a message (or an entire thread) just because you say it is off-topic, while at the same time saying that it is on-topic and appropriate.? If it was really worth posting here in the first place, it should remain.
Did we not read a while back?that you would not deleting your messages?? How's that going?
Frankly, I am tired of this nonsense.
Andy
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Re: Drafted to helo a friend who designs audio amps
For those interested in the somewhat esoteric world of High End Audio....I offer some links to speaker simulators
Note: Speakers are not nice stable loads, even a single speaker rated at 8 ohms might be 8 ohms a some frequency, mount it in an enclosure and the impedance will be extremely different depending on the type enclosure.
A closed box will behave on way, a single port another, a transmision line speaker (yes they do exist) will have yet another set of impedances.
And the impedance will be a mix of inductance, coil resistance and any resonances of the cone as modified by the enclosure.
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This is one test load
https://www.stereophile.com/reference/60/index.html
Note the Zobel Netork on page 2, they can be critical in some situations.
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This site covers some of the interaction between speaker cables and real world speakers.
Loudspeaker Cable Characteristic Impedance
https://sound-au.com/cable-z.htm
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Passive crossovers
https://sound-au.com/lr-passive.htm
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Loudspeaker Enclosure Design Guidelines
https://sound-au.com/articles/enclosures.htm
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Phase Angle Vs. Transistor Dissipation
https://sound-au.com/patd.htm
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Driving a 4 or 8 ohm resistive load is easy peasy, driving any real world speaker is fraught with possibilities. Some speakers present loads that cause some very high quality amplifiers to oscillate.
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I worked part time at an electronics shop. The owner sold high end audio equipment to the demented. Great American Sound offered Son of Godzilla. And amp that would drive damn near anything, we used it to make a drill variable speed. [Hey we were bored] However when connected to a pair of KEF studio reference monitor speakers, the GAS amp went insane, destroyed the speakers in about 4 seconds. KEF withdrew that set of speakers and it isn't listed in their history. KEF claimed that speaker had constant phase correction.
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Those KEFs sounded good with my Sansui AU555A, a rather mediocre amp by any definition.
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Effects Of Source Impedance on Loudspeakers
https://sound-au.com/z-effects.htm
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At some point everything in an audio chain has an influence. And it is next to impossible to pinpoint every variable.
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Audio Wattmeter - Measures?True?Power!
https://sound-au.com/project189.htm
Shows some speaker electrical characteristics.
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DIM/TIM (Dynamic or Transient Intermodulation) Some older references call it SIM (Slew rate intermodulation)
From https://www.aes.org/par/i/#IM
"DIM/TIM (dynamic/transient intermodulation distortion)?A procedure designed to test the dynamic or transient behavior, primarily, of audio power amplifiers. The other IM tests use steady-state sine wave tones, which do not necessarily reveal problems caused by transient operation. In particular, audio power amplifiers with high amounts of negative feedback were suspect due to the inherent time delay of negative feedback loops. The speculation was that when a rapidly-changing signal was fed to such an amplifier, a finite time was required for the correction signal to travel back through the feedback loop to the input stage and that the amplifier could be distorting seriously during this time. The most popular test technique consists of a large amplitude 3 kHz square wave (band-limited to ~20 kHz). [Historical Note: This test proved that as long as the amplifier did not slew-limit for any audio signal, then the loop time delay was insignificant compared to the relatively long audio periods. Thus, properly designed negative feedback was proved not a problem. Subsequently, this test has fallen into disuse."
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Note: I can make any audio amplifier display TIM, but not with any music, even the cannon fire in the William Tell Overture has a fairly slow rise time.
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Now a 9mm pistol shot captured with a condenser microphone on a 96K digital recorder and played back into an audio amp might cause TIM. I'm not sure the microphone's rise time would capture the actual event's risetime...and the blast might destroy the microphone.
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This might be worth reading
https://sound-au.com/articles/distortion+fb.htm
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On balance, just buy a decent audio amp and speakers and use your time for more productive projects. Unless of course understanding the subtleties of high performance audio amps is your thing.
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And just when you think you've seen every crazy idea on earth....
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My friend's dummy load has inductors and capacitors with large wattage resistors to simulate a 'regular' spkeaker.
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BTW, the problem is in the driver stage of the AF power amp.
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Re: Drafted to helo a friend who designs audio amps
One comment about the Hafler test; I would load the amplifier with a reactive load, not just a resistive one. A resistive load is too easy for any amp. Hang some capacitance directly on the amp’s output to simulate a long speaker wire, and some inductance in series with the main load resistor. This is a more realistic setup. Of course, the input drive should not be large enough to get the amp into clipping, that would be unfair… -Doug R. ?
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From: [email protected] [mailto:[email protected]] On Behalf Of Bertho
Sent: Sunday, December 8, 2024 08:14
To: [email protected]
Subject: Re: [electronics101] Drafted to help a friend who designs audio amps? A couple of comments: Do the amps compare OK on static measurements? If OK presumably he is fighting a transient problem. How do they compare with narrow transients? Do the catch-all Hafler test that I mentioned. It is one thing for parts to meet specifications, but the parts might exceed the specs and cause problems. Bertho ? ? ? He came up with the preamp, tone, volume, balance, power amp designs 35 years ago. He's been forced to make minor component value changes as semiconductors came and went. The design is somewhat minimalist, the most innovative is his active bias scheme. I've never seen anything like it anywhere and trust me, while I am not an audiophile I do keep up with "State of the Art" designs as a hobby. I'm at a loss to understand how using one batch of transistors produces great sound, and yet another batch of the same transistors produces "muddy" sound. I have some nice audio programs, including some FFT with different display modes. Tomorrow we hit the amps, a good one and 'bad' one, with every trick in my inventory. I've borrowed a high end analog to digital converter that is flat +/- 2dB from DC to 1MHz. I'm hoping pink noise bursts show something. Jimmy started out as an architect but started his audio business because 'modern designs make me want to barf.' He hates parking lots that are laid out decoratively with all curves, tall bushes etc. He moved to England, was licensed and was increasingly depressed over the new buildings in London.? "Nuke the city and start over." As children we'd play and combine our Lincoln Log sets (my father marked all of mine with a T his with a J_ and Jimmy build amazing tunnels for my Lionel electric trains. He built a model of Windsor Castle from sugar cubes in the 9th grade, won a design award. He is self taught but knows his semiconductor design tech better then any real engineer I know. He is the only person I know who will tackle an failed switchmode power supply and has an almost 100% success rate for reliable repair. The few he gave up on he pointed out design flaws.
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Re: Drafted to helo a friend who designs audio amps
One steady state and slow swept tones they check out identically (well within expected variance, one amp might have 0.001%THD/IMD and the other 0.099%.
He lacks the ability to do really short, 1ms, white noise pulses.
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I'm wondering about TIM, something I've tended to dismiss (with the exception of Crown DC-300).
TIM (transient IM) would can happen if your negative feedback loop was so slow some signal made it through before the negative feedback arrived at the front end to apply correction. Given the speed with which signals flow, outgoing and return feedback, that shouldn't be an issue with any decent design (which clearly excludes Crown DC-300.)
We'll do the Hafler test, found a very detailed "how to" and the Baxandall (spelling?) compare the output with the input. The two tests should produce similar results.
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This is way out of my comfort zone, feels nice to stretch the brain a bit.
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Somehow I suspect the manufacturer changed the manufacturing process and something very subtle is different.
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As might be suspected, I absolutely hate the DC-300. It sounded gritty with muddy midrange.
We installed 20 in a sports complex. For a PA system, they were adequate, with proper LF input rejection and output DC offset protection.?
I'd loved to have been able to do the Hafler test on the DC-300. Their smaller amp (DC-75 of DC-150) sounded great.
The DC-300 had a slew rate of 8V/uS, slow by today's standards.
I need to pull up the diagram of the DC-300 and study their feedback loop....
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Re: Drafted to helo a friend who designs audio amps
On Sunday 08 December 2024 11:13:47 am Bertho wrote: It is one thing for parts to meet specifications, but the parts might exceed the specs and cause problems. Yeah, it came as a bit of a surprise to me that having transistors that had a wider frequency range could end up oscillating way too easily... -- Member of the toughest, meanest, deadliest, most unrelenting -- and ablest -- form of life in this section of space, ?a critter that can be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters" - Information is more dangerous than cannon to a society ruled by lies. --James M Dakin
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Re: Drafted to helo a friend who designs audio amps
A couple of comments: Do the amps compare OK on static measurements? If OK presumably he is fighting a transient problem. How do they compare with narrow transients? Do the catch-all Hafler test that I mentioned. It is one thing for parts to meet specifications, but the parts might exceed the specs and cause problems. Bertho ? ?
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From: [email protected] <[email protected]> On Behalf Of wn4isx via groups.io
Sent: 8 December, 2024 10:29
To: [email protected]
Subject: Re: [electronics101] Drafted to help a friend who designs audio amps? He came up with the preamp, tone, volume, balance, power amp designs 35 years ago. He's been forced to make minor component value changes as semiconductors came and went. The design is somewhat minimalist, the most innovative is his active bias scheme. I've never seen anything like it anywhere and trust me, while I am not an audiophile I do keep up with "State of the Art" designs as a hobby. I'm at a loss to understand how using one batch of transistors produces great sound, and yet another batch of the same transistors produces "muddy" sound. I have some nice audio programs, including some FFT with different display modes. Tomorrow we hit the amps, a good one and 'bad' one, with every trick in my inventory. I've borrowed a high end analog to digital converter that is flat +/- 2dB from DC to 1MHz. I'm hoping pink noise bursts show something. Jimmy started out as an architect but started his audio business because 'modern designs make me want to barf.' He hates parking lots that are laid out decoratively with all curves, tall bushes etc. He moved to England, was licensed and was increasingly depressed over the new buildings in London.? "Nuke the city and start over." As children we'd play and combine our Lincoln Log sets (my father marked all of mine with a T his with a J_ and Jimmy build amazing tunnels for my Lionel electric trains. He built a model of Windsor Castle from sugar cubes in the 9th grade, won a design award. He is self taught but knows his semiconductor design tech better then any real engineer I know. He is the only person I know who will tackle an failed switchmode power supply and has an almost 100% success rate for reliable repair. The few he gave up on he pointed out design flaws.
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Re: Drafted to helo a friend who designs audio amps
On Saturday 07 December 2024 01:37:06 pm wn4isx via groups.io wrote: I once used a 2N???? as an electronic variable capacitor by using the collector base and reverse biasing, so I know transistor junction capacitance varies with applied voltage. I wonder if the audio can modulate the variable capactance of the junction [pretty certain it does] and "Does it have any effect?"
Any diode will do that, and a transistor junction is basically a diode... I remember reading how rectifiers could be used as varactors to tune circuits. -- Member of the toughest, meanest, deadliest, most unrelenting -- and ablest -- form of life in this section of space, ?a critter that can be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters" - Information is more dangerous than cannon to a society ruled by lies. --James M Dakin
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Re: Drafted to helo a friend who designs audio amps
On Saturday 07 December 2024 08:08:20 am wn4isx via groups.io wrote: I've been dragooned to help a friend I've known since the second grade. Jimmy designs and builds ultra high end audio systems, he builds everything up to the speakers. How do you define high end? Recently he's ran into some odd problems where "identical" transistors behave differently in high end audio. He purchases directly from the manufacturer so the chances of counterfeits is pretty low. But "identical" parts usually aren't. The amount of variation is really somehting to see, sometimes. It's been a life time [1968~1973] since I designed any serious audio amps. I realized my talents lay elsewhere and it was a better value to > trade money for decent amps then spend nearly unlimited hours to obtain similar results. I have a stero receiver and equalizer in the other room that have been sitting there for 3-4 years and I haven't yet gotten around to hooking them up. Got a small amp based on a couple of LM386 chips and a Radio Shack "headphone amplifier'" board that I picked up at some hamfes years ago. Got some LM380 chips that pomise a bit more in the way of output power but I have yet to get around to doiing anything with them yet. That would pretty much cover the extent of my efforts in that area... Note: I do not consider myself an audiophile, I damaged my hearing riding a motorcycle for 35 years and had tinnitus as a young child. It used to be that word had some positive connotations, but lately it more often than not translates to "audiophools" with people claiming absurd things and paying ridiculous money for such things as $1000 power cords. I ain't going there. In my case it was too much sound intensity during my work with pro audio gear and doing sound ffor a number bands. At first it was one hearing aid, for the left ear which was worse than the right one. Then it was a pair of them, as insurance would cover. The latest set is even better, they're rechargable and also have bluetooth connecton to my phone, which has come in handy on a number of occasions. Sooo, I'm refamiliarizing myself with the issues of high end audio design, theory and reality.
No amplifier is perfect, they all have artifacts. One thing that is very different today from way back when is moderate priced USB audio I/O 'cards' allow meaningful FFT analysis that actually matches reality, within limits. I haven't even looked at going there yet. I downloaded this book to start with....
Bob Metzler - Audio Measurement Handbook
An interesting read, so far. I'm about 89 pages into it at the moment. I'm reminded of some of he gear I worked with at one pro sound outfit that I worked for at one point. A "White Sound Analyzer" in particular comes to mind. I'm also reminded of an HP audio osccillator that's in the other room that needs a little TLC. And for projects, I bought some modules from Banggood a while back, basically an LM3915 chip and some LEDs. It was convenient to have a pre-made board for these. Unfortunately whoever they used to supply those chps didn't bother to connect two of the pins at one end of the 18-pin package, so the first two LEDs never lit up, until I sourced some chips from another supplier. They gave me a partial refund for that, but it left a bad taste in my mouth and I'm rather reluctant to order from china at all at this point. While copyrighted it appears in quiet a few respectable locations, I'm guessing the author has waived copyright issues. Or he just wants it out there. I've found one heck of a lot of books online, and have been adding to the pile on my server at times. Rod Elliot of ESP audio has quite a few articles on design and measurement of distortion.
Uses a sound card to measure distortion
Perhaps I'll follow some of those links when I ge done with reading that book... Perhaps the single most useful trick shown by Mr. Elliot is his "distortion adder." It allows sanity checks, which, when dealing with audio distortion is necessary. It is way too easy ending up chasing your tail like a puppy or kitten. Heh. That's why I gave up on amplifier design in 1973. A quasi-comp Sansui AU-555A sounded much better then my best efforts at about 1/2
the cost in material and 1/gazillionth the wasted time. I could have collected sodapop bottle along the highway, turned them in for the
deposit and been time ahead. I'd reached a point where I'd lost confidence in my ability to measure differences in slight design variations.
One important issue, I've been playing with several USB sound cards for several years and realizee "The 5V power rail in most USB systems simply suck!" Modify your USB cable and add your own 5V power supply. I went with a LM7805 with the standard design with an added 1uF tantalum (I hate and distrust tantalums but they have the best filtering capacity for size and a 100uF and 1000uF on the 5V out. I'm not convinced the added capacitors were worthwhile but the PCB I used had the pads for them so I decided to toss them in. Those caps around those regulator chips are important. [Be certain to tie your 5V power supply V-/ground to PC USB V-/ground! I spent an hour late one night wondering "Why doesn't this damn thing work!"]
The residual noise floor was just under 10dB lower with the external supply versus the laptop USB 5V power.
You mileage will vary because every maker of USB almost certainly has different noise issues.. I bought a powered hub some time back, but now it has some issues and needs to be replaced. I suspect Jimmy is running into the hard wall of physics, where each device is inherently different even if made at the same time. This is something I have no idea how to verify.
They don't call it the bleeding edge of technology for nothing.
Oh, and don't bother trying to test the modulator in your SSB/AM/FM ham rig, they all suck. I'm not even gonna go there... -- Member of the toughest, meanest, deadliest, most unrelenting -- and ablest -- form of life in this section of space, ?a critter that can be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters" - Information is more dangerous than cannon to a society ruled by lies. --James M Dakin
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Re: Drafted to helo a friend who designs audio amps
He came up with the preamp, tone, volume, balance, power amp designs 35 years ago. He's been forced to make minor component value changes as semiconductors came and went.
?
The design is somewhat minimalist, the most innovative is his active bias scheme. I've never seen anything like it anywhere and trust me, while I am not an audiophile I do keep up with "State of the Art" designs as a hobby.
?
I'm at a loss to understand how using one batch of transistors produces great sound, and yet another batch of the same transistors produces "muddy" sound.
?
I have some nice audio programs, including some FFT with different display modes. Tomorrow we hit the amps, a good one and 'bad' one, with every trick in my inventory. I've borrowed a high end analog to digital converter that is flat +/- 2dB from DC to 1MHz. I'm hoping pink noise bursts show something.
?
Jimmy started out as an architect but started his audio business because 'modern designs make me want to barf.' He hates parking lots that are laid out decoratively with all curves, tall bushes etc. He moved to England, was licensed and was increasingly depressed over the new buildings in London.?
"Nuke the city and start over."
?
As children we'd play and combine our Lincoln Log sets (my father marked all of mine with a T his with a J_ and Jimmy build amazing tunnels for my Lionel electric trains. He built a model of Windsor Castle from sugar cubes in the 9th grade, won a design award.
?
He is self taught but knows his semiconductor design tech better then any real engineer I know.
He is the only person I know who will tackle an failed switchmode power supply and has an almost 100% success rate for reliable repair. The few he gave up on he pointed out design flaws.
?
?
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Re: Drafted to helo a friend who designs audio amps
Think harmonic distortion. With an FFT analyser you might see it (or not??? I think I got a glimpse of it…) It might happen at 250kHz, but will extend far into the MHz, and AUDIO spectrum! Those with the ears to detect it, WILL HEAR IT! From my very limited experience with these high end audio equipment, you should look at the circuitry from a radio perspective. Harmonic distortion spreading far… (It’s my best guess, anyway) ? Nuno T. ?
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From: [email protected] [mailto:[email protected]] On Behalf Of Epignathus
Sent: 07 December 2024 21:00
To: [email protected]
Subject: Re: [electronics101] Drafted to help a friend who designs audio amps
Importance: Low? Years ago, I purchased new an Adcom GFA-545 which also sounded terrible. One channel was oscillating at around a megahertz, which bleed into the other channel too. The manufacturer “stopped at nothing” to fix it, so I added a zero to counter the pole in the right-half-plane after the input differential pair in both the left and right channels, which reduced the high end bandwidth to about 100 kHz, and stopped the instability. There is no logical reason to have the -3 dB response extend to 250 kHz, especially when it leads to an unstable amplifier. -Doug, W6DSR ? From: [email protected] [mailto:[email protected]] On Behalf Of wn4isx via groups.io
Sent: Saturday, December 7, 2024 11:49
To: [email protected]
Subject: Re: [electronics101] Drafted to helo a friend who designs audio amps ? Jimmy designs complete home theater systems, video switching, audio switching, audio tone/volume/balance, he provides a loop for special effects like 3D decoders, and power amplifiers, "regular" stereo and subwoofer. The last two orders of Freescale (Motorola) act funny. He orders premium units, each one comes with it's own spec sheet. The specs are within norms for his previous but the power amps sound odd, hollow, sort of like left/right mixing giving sort of L-R. Even when he only drives one channel, or both channels in mono. The mid range, ~1kHz to ~4kHz is "wonky." He's my age and has been considering retiring, this might decide for him. ? But he enjoys his work. He is one of the few people I'd even consider going to this level of trouble. ? I warned him we are up against physics that neither of us understand nor have the training to understand. ? He has enough older stock to complete his current orders and isn't taking additional orders until/unless we can solve the problem. ? Oddly they work fine for sub-woofer amps and low level preamps. ? Somewhere I have a file devoted to snake oil smoke and mirrors. My favorite is a set of adaptors that allow the output of a AF power amp to a NEMA 15-R with matching NEMA 15-P to wires for the speaker so you can use a standard AC extension cord. ? The insanity was so intense I didn't believe it was real, so I ordered a set. They occupy a place of shame on my radio room wall. ? I love the "hand made porcelain speaker cable lifters." They hold the speaker cables off the floor, God knows dust mites might cause distortion. ? Although I think RCA connectors and 3.5mm connectors are both abominations and crimes against nature and man. -- Nuno T.
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Re: Drafted to helo a friend who designs audio amps
There is a never ending, intense, perhaps psychotic, argument over "Can humans detect phase differences [or phase distortion.] and it shows up in the amplifier wars...
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This paper takes hard core look at the question...
https://www.researchgate.net/publication/286939870_Sensitivity_of_Human_Hearing_to_Changes_in_Phase_Spectrum
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The paper presents data showing "Yes human can detect phase difference" but the data appears to suggest "Not in the real world."
Very few of us ever experience an anechoic chamber. I suspect multiple reflections in most real world scenarios swamp phase issues.
Earphones are clearly different. But the recording and mixing probably destroy any phase relationship to the original.
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Consider how many albums are created as a series of over dubs, sometimes over a period of months.
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Good Vibrations might win the most complicated production and mix down process.
https://en.wikipedia.org/wiki/Good_Vibrations
You might be interested by the production details...and ask yourself "What was the original phase relationship between the various instruments."
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My HP laptop has two microphones and it's interesting to launch an audio vectorscope program. Slight movement of either the laptop or a person speaking totally change the display in unexpected ways.
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I've played with ultrasonic emitters and receivers since I was 14 and built my first oscilloscope. I'd built an ultrasonic down converter from an article in Popular Electronics and used the same type transducer as a emitter in a 'beacon.'
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When I built the scope I bought another ultrasonic receiver, scrapped the down converter and built two pre amps, fed one to the vertical the other to the horizontal for an XY display. It was interesting to see how little movement was required to produce wildly rotating XY displays.
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Re: Drafted to helo a friend who designs audio amps
My plan is to compare old good devices with new wonky devices and see if there are any determinable differences.
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Re: Drafted to helo a friend who designs audio amps
The matching (testing) amp needn't be perfect - just good enough
to compare devices. That's the point.
Donald.
On 12/7/24 16:20, wn4isx via groups.io
wrote:
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On Sat, Dec 7, 2024 at 04:04 PM, Donald H Locker wrote:
sockets
Sockets tend to be a bad idea for transistors in high
performance audio systems. Even with gold plated transistor
leads and sockets, they are a severe failure point.
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If we can figure out what parameters are effecting the amps,
we can probably match pairs.
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Frankly if anyone but Jimmy called me with this problem, I'd
say they were crazy,
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Re: Drafted to helo a friend who designs audio amps
On Sat, Dec 7, 2024 at 04:04 PM, Donald H Locker wrote:
sockets
Sockets tend to be a bad idea for transistors in high performance audio systems. Even with gold plated transistor leads and sockets, they are a severe failure point.
?
If we can figure out what parameters are effecting the amps, we can probably match pairs.
?
Frankly if anyone but Jimmy called me with this problem, I'd say they were crazy,
?
?
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Re: Drafted to helo a friend who designs audio amps
I think as I remember at the time, all the rage was about phase. An amplifier could brag about having little to no phase shift over the passband of 20 to 20,000 Hz. That higher bandwidth helped keep the phase constant over the bandwidth – just a guess… ?
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From: [email protected] [mailto:[email protected]] On Behalf Of wn4isx via groups.io
Sent: Saturday, December 7, 2024 13:07
To: [email protected]
Subject: Re: [electronics101] Drafted to help a friend who designs audio amps ? On Sat, Dec 7, 2024 at 03:59 PM, Epignathus wrote: -3 dB response extend to 250 kHz
What moron decided an AF amp needed that frequency response!? That's not asking for trouble, that's begging for it.
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Re: Drafted to helo a friend who designs audio amps
On Sat, Dec 7, 2024 at 03:59 PM, Epignathus wrote:
-3 dB response extend to 250 kHz
What moron decided an AF amp needed that frequency response!?
That's not asking for trouble, that's begging for it.
?
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Re: Drafted to helo a friend who designs audio amps
No idea if this is practical. How many devices in the
amplification chain need to be matched or are critical spec-wise?
If there are a small number, he could build a "matching amp" with
sockets specifically for devices to be matched. Swapping
individual devices and tagging matched pairs/groups as they are
identified would build a stock of usable devices. It might also
allow him to better identify the characteristics important to
achieve matching.
Donald.
On 12/7/24 14:49, wn4isx via groups.io
wrote:
Jimmy
designs complete home theater systems, video switching,
audio switching, audio tone/volume/balance, he provides a
loop for special effects like 3D decoders, and power
amplifiers, "regular" stereo and subwoofer.
The
last two orders of Freescale (Motorola) act funny. He orders
premium units, each one comes with it's own spec sheet. The
specs are within norms for his previous but the power amps
sound odd, hollow, sort of like left/right mixing giving
sort of L-R. Even when he only drives one channel, or both
channels in mono.
The
mid range, ~1kHz to ~4kHz is "wonky."
He's
my age and has been considering retiring, this might decide
for him.
[snip]
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Re: Drafted to helo a friend who designs audio amps
Years ago, I purchased new an Adcom GFA-545 which also sounded terrible. One channel was oscillating at around a megahertz, which bleed into the other channel too. The manufacturer “stopped at nothing” to fix it, so I added a zero to counter the pole in the right-half-plane after the input differential pair in both the left and right channels, which reduced the high end bandwidth to about 100 kHz, and stopped the instability. There is no logical reason to have the -3 dB response extend to 250 kHz, especially when it leads to an unstable amplifier. -Doug, W6DSR ?
toggle quoted message
Show quoted text
From: [email protected] [mailto:[email protected]] On Behalf Of wn4isx via groups.io
Sent: Saturday, December 7, 2024 11:49
To: [email protected]
Subject: Re: [electronics101] Drafted to helo a friend who designs audio amps ? Jimmy designs complete home theater systems, video switching, audio switching, audio tone/volume/balance, he provides a loop for special effects like 3D decoders, and power amplifiers, "regular" stereo and subwoofer. The last two orders of Freescale (Motorola) act funny. He orders premium units, each one comes with it's own spec sheet. The specs are within norms for his previous but the power amps sound odd, hollow, sort of like left/right mixing giving sort of L-R. Even when he only drives one channel, or both channels in mono. The mid range, ~1kHz to ~4kHz is "wonky." He's my age and has been considering retiring, this might decide for him. ? But he enjoys his work. He is one of the few people I'd even consider going to this level of trouble. ? I warned him we are up against physics that neither of us understand nor have the training to understand. ? He has enough older stock to complete his current orders and isn't taking additional orders until/unless we can solve the problem. ? Oddly they work fine for sub-woofer amps and low level preamps. ? Somewhere I have a file devoted to snake oil smoke and mirrors. My favorite is a set of adaptors that allow the output of a AF power amp to a NEMA 15-R with matching NEMA 15-P to wires for the speaker so you can use a standard AC extension cord. ? The insanity was so intense I didn't believe it was real, so I ordered a set. They occupy a place of shame on my radio room wall. ? I love the "hand made porcelain speaker cable lifters." They hold the speaker cables off the floor, God knows dust mites might cause distortion. ? Although I think RCA connectors and 3.5mm connectors are both abominations and crimes against nature and man.
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Re: Drafted to helo a friend who designs audio amps
Jimmy designs complete home theater systems, video switching, audio switching, audio tone/volume/balance, he provides a loop for special effects like 3D decoders, and power amplifiers, "regular" stereo and subwoofer.
The last two orders of Freescale (Motorola) act funny. He orders premium units, each one comes with it's own spec sheet. The specs are within norms for his previous but the power amps sound odd, hollow, sort of like left/right mixing giving sort of L-R. Even when he only drives one channel, or both channels in mono.
The mid range, ~1kHz to ~4kHz is "wonky."
He's my age and has been considering retiring, this might decide for him.
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But he enjoys his work. He is one of the few people I'd even consider going to this level of trouble.
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I warned him we are up against physics that neither of us understand nor have the training to understand.
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He has enough older stock to complete his current orders and isn't taking additional orders until/unless we can solve the problem.
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Oddly they work fine for sub-woofer amps and low level preamps.
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Somewhere I have a file devoted to snake oil smoke and mirrors. My favorite is a set of adaptors that allow the output of a AF power amp to a NEMA 15-R with matching NEMA 15-P to wires for the speaker so you can use a standard AC extension cord.
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The insanity was so intense I didn't believe it was real, so I ordered a set. They occupy a place of shame on my radio room wall.
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I love the "hand made porcelain speaker cable lifters." They hold the speaker cables off the floor, God knows dust mites might cause distortion.
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Although I think RCA connectors and 3.5mm connectors are both abominations and crimes against nature and man.
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Re: Drafted to helo a friend who designs audio amps
I second your view! ? Lots of snake oil and smoke around. Those who do know, keep their mouths shut, and their bank accounts are getting bigger ? Nuno t. ?
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From: [email protected] [mailto:[email protected]] On Behalf Of wn4isx via groups.io
Sent: 07 December 2024 18:37
To: [email protected]
Subject: Re: [electronics101] Drafted to helo a friend who designs audio amps ? The problem my friend is almost certainly facing is the parameter(s) that are driving him nuts aren't standard and aren't specified. I'm sure a process engineer could provide us with a wealth of information but just try and talk to one. They are guarded closer then Roman Vestal Virgins. Hfe at different collector currents, well away from the standard tests levels Ft at different current collector currents Actual switching speed at different collector currents I'm trying to figure a practical way of measuring the collector base, base emitter, and collector emitter junction capacitance under different voltages. I once used a 2N???? as an electronic variable capacitor by using the collector base and reverse biasing, so I know transistor junction capacitance varies with applied voltage. I wonder if the audio can modulate the variable capactance of the junction [pretty certain it does] and "Does it have any effect?" I'm so far over my head I might drown. And a lot of audiophile "Standard of belief" is snake oil and smoke. The idea a special power cable can improve an AC mains powered amp is silly, consider how many feet of house wiring is between the amp and breaker box, how long the cables from the home to the step down transformer, how many miles of wire between "your' transformer and the substation and how many miles of wire between substation and power plant, add to that the interconnectivity of the various national sub-grids.... ? Double blind tests are the only subjective tests I accept. Others are entitled to their own beliefs. -- Nuno T.
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Epignathus
Bertho