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Rod Elliott on tube amp design

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18 hours ago, tube fanatic said:


 

Chokes and capacitors form a resonant, or tuned, circuit at a particular frequency (depending on value) and exhibit a -3 db point at a particular frequency (the corner frequency).  You are familiar with this from speaker crossover networks which provide a chosen corner frequency.  In an amp power supply you can inadvertently choose values which have a corner frequency which is much higher than the lowest frequency you want to reproduce.  You can demonstrate the effect with this calculator (select solving for frequency and the appropriate units):

 

http://www.1728.org/resfreq.htm

 

Try specifying an inductance of 0.3H and a capacitance of 50 uf (typical lses values as I recall) and you will see that the frequency falls in the low bass area.  Compare that with more typical values of, say, 5H and 100 uf.  
 

The above is a very diluted explanation, of course, but should help a little.  I’ll try to explain a bit about Q when time permits.

 

 

Maynard
 

 

Wow I played around with this and actually understood it.  Thank you.

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35 minutes ago, dwilawyer said:

Wow I played around with this and actually understood it.  Thank you

 

This is how early electronic organs worked. There was an LC circuit used, tuned for a specific frequency. The coil (inductor) had a screw to fine tune it and then there were dividing circuits to get all the other notes. Different oscillators were made for different tones. Early analog synths worked the same way.

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On 12/2/2020 at 8:37 AM, Marvel said:

 

This is how early electronic organs worked. There was an LC circuit used, tuned for a specific frequency. The coil (inductor) had a screw to fine tune it and then there were dividing circuits to get all the other notes. Different oscillators were made for different tones. Early analog synths worked the same way.

The liittle plastic tool we use to adjust the inductor is affectionately called a "diddle stick" Engineers do it with "slip stick" (slide rule), Technicians do it with a "diddle stick".

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My take,

 

Tektronix oscilloscopes of the mid 70s vintage were the last generation of instruments designed around discrete devices.  When you peek into a vintage Tek scope you see pretty quickly they represent an incredibly high level of design sophistication.  The engineering, the supply chain and the industry as a whole had matured to a point where they were not going to get much better without a significant engineering breakthrough.  That "step change" was leveraging integrated circuits.  The point however is that discrete device designs, given where the technology was, were very effective at solving the problems oscilloscopes were used to solve at the time.  They worked and they worked well.  When ICs were used, bandwidth went up, signal to noise went up and the improvements were obvious on the screen of the scope.  

 

Analogous to the Tek example, tube amp design, manufacturing and the tube supply chain were, by the late 50s, mature, there was no place to go.  And, they were making very good sound.  Then low cost transistors appeared.  Distortion went down, signal to noise went up and the improvements were obvious to measure on FFT and distortion analyzers.

 

What hasn't had a step change is the loudspeaker and the basic loudspeaker of 2020 isn't that much different than the ones made in the 50s.  Materials are better and magnets can have insane BL-products for a given magnet volume but they're only evolutionary changes, not technological "pivots".

 

Unlike the oscilloscope example the audio signal path "ends" using a device invented in the 1920s and refined largely to a point where it's a bit better than where it was in the late 1970s.  So yes, it's easy to measure differences between transistor amps and tube amps on distortion analyzers loading each with a resistor load.  But the end of the signal path is not a resistor, it's thing called a loudspeaker, an electromechanical device that has mass and presents a reactive load to the amplifier. And, it can take the most sophisticated, electrically engineered audio amplifier made today and send it back to 1975 or even 1955 if you're using an EV Patrician let's say. 

 

So that's why tube amps still "work".      

 

 

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Great explanation John. The average member with no or very little technical skills who own tube amplifiers knows one thing for sure about tube amplifiers. They sound so dang good with our speakers. 

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John nailed it.

 

Between cables, crossovers, and negative feedback, the laboratory-measurable differences go away and we're left with "What do YOUR ears like?"

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On 11/30/2020 at 1:16 PM, tube fanatic said:


But tubes have so much more charm😁.  Admittedly, I don’t agree with Rod on absolutely everything.  I am often asked why I bother with tubes given the performance available from SS devices.  The only answer I can give is that they attracted me from my first view of glowing filaments when the repairman came over to fix grandma’s console radio when I was 3 years old.  We all have our obsessions.....

 

 

Maynard

Amen and amen. I recently listened to a Mcintosh MC2505, a world class SS amp. It sounded fine, flat, neutral and great loud. But it didn't have the width and depth of soundstage of even my modest ST-70 Series II. It lacks that midrange emphasis and the ringing harmonics of tube amplification. If pressed, I might admit to a bit more definition, but that could have also been the difference between my highly modified but still humble Klipsch KLF-10 two-ways, and a several thousand $ pair of B&W speakers. 

 

I think the linearity of tubes becomes less of an issue with a thoughtfully designed circuit, a well-put together system, and the simple desire to listen with your ears instead of with your scope. I will never give up that gorgeous amber glow. Consider me like-mindedly obsessed. 

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On 11/30/2020 at 1:45 PM, MicroMara said:

 

What is the situation with hybrid solutions? With my Marantz PM11-S3 I only use the transistor preamplifier, I have decoupled the transistor power stage and connected 2 tube mono blocks as power amplifiers.  

 

I wonder how those monster RF-7II's would sound with a tube preamp...

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On 11/30/2020 at 8:59 PM, seti said:

I can listen to SS but just short term. I've never been able to live with a SS amp for long. Granted valve amplifiers are fraught with issues but why do they sound so f'ing good. The specs and numbers suck by comparison but they sound awesome..... PP or SET.

 

 

"I have to tell you man. In listening to sound, I guess what I'm after is the closest thing that I can get to reality. Now, I know it's not going to be reality, cause the thing gotta go through wires and gotta go through filters and this and that. I understand all that. But what I really like is to get as close to the natural sound of the instruments as possible. That's why I like analog as opposed to digital. Because I don't give a shit what anybody tells you man, I know what you guys are going to tell me...'Oh yeah, but it's clean Ray!' Well it's clean but it don't got no balls!!!" - 1999 interview with Ray Charles

EGG-ZAT-LEE!!!

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On 12/2/2020 at 7:20 AM, seti said:

 

I'm sure but at what price? My favorite is when I someone talks of a SS as being tubelike as a compoliment... Save your money just use tubes..

 

 

 

Even worse: When they say a tube amp sounds just like an SS amp. Yuk!!!

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On 12/26/2020 at 3:43 AM, John Warren said:

My take,

 

Tektronix oscilloscopes of the mid 70s vintage were the last generation of instruments designed around discrete devices.  When you peek into a vintage Tek scope you see pretty quickly they represent an incredibly high level of design sophistication.  The engineering, the supply chain and the industry as a whole had matured to a point where they were not going to get much better without a significant engineering breakthrough.  That "step change" was leveraging integrated circuits.  The point however is that discrete device designs, given where the technology was, were very effective at solving the problems oscilloscopes were used to solve at the time.  They worked and they worked well.  When ICs were used, bandwidth went up, signal to noise went up and the improvements were obvious on the screen of the scope.  

 

Analogous to the Tek example, tube amp design, manufacturing and the tube supply chain were, by the late 50s, mature, there was no place to go.  And, they were making very good sound.  Then low cost transistors appeared.  Distortion went down, signal to noise went up and the improvements were obvious to measure on FFT and distortion analyzers.

 

What hasn't had a step change is the loudspeaker and the basic loudspeaker of 2020 isn't that much different than the ones made in the 50s.  Materials are better and magnets can have insane BL-products for a given magnet volume but they're only evolutionary changes, not technological "pivots".

 

Unlike the oscilloscope example the audio signal path "ends" using a device invented in the 1920s and refined largely to a point where it's a bit better than where it was in the late 1970s.  So yes, it's easy to measure differences between transistor amps and tube amps on distortion analyzers loading each with a resistor load.  But the end of the signal path is not a resistor, it's thing called a loudspeaker, an electromechanical device that has mass and presents a reactive load to the amplifier. And, it can take the most sophisticated, electrically engineered audio amplifier made today and send it back to 1975 or even 1955 if you're using an EV Patrician let's say. 

 

So that's why tube amps still "work".      

 

 

Interesting. So, any advances in speaker tech that will render tubes obsolete and SS king of the hill?

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15 hours ago, MechEngVic said:

 

I wonder how those monster RF-7II's would sound with a tube preamp...

Well I don´t know  LOL ....The Problem is that there isnt´t a tube pre in the market that has 7 Line Inputs which I need for my gear ..1 x Balanced for SACD/ DAC , 1 x CD Line for Networkplayer with a external sec. DAC, 1 x Phono MM & MC as Transisitor Solution, 1 x Line for external Phono Tube Stage, 1 x Line for BlueRay , 1 x Tape for the TEAC ,1 x Tape for the Tandberg R2R and got connected my TV via Toslink as well . Sure someday I got one , but I´m so happy with this both Cayin Monos , there is nothing that I miss and I can play by changing the amp power section as transistor or tube controlled like I want. And those Monster RF7 MK IISE  will blow your brain out of your skull, believe me , they´re real high end killers .

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16 hours ago, MechEngVic said:

Even worse: When they say a tube amp sounds just like an SS amp. Yuk!!!

 

True...

 

I might do a SS DIY some day but tubes are just more fun and the asthetic is cool as hell. Terrible reasons but gotta be honest I love the glow of tubes.

 

 

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12 hours ago, seti said:

 

True...

 

I might do a SS DIY some day but tubes are just more fun and the asthetic is cool as hell. Terrible reasons but gotta be honest I love the glow of tubes.

 

 


If you try the SS build, talk to Henry (henry4841) as he has lots of experience with Nelson Pass’ tube mimicking designs.

 

Maynard

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Have many tube amps along with SS, mostly class A. A SE First Watt class A amplifier sounds much like a tube. And why not, he uses mosfets which have curves like a pentode tube other then one amplifier. The ones with SIT transistors that have curves like a triode tube. The SIT transistor curves do resemble a triode tube but no where as linear as say the 300B. Most of Nelson's designs are simple circuits, like tube circuits, using mosfets that resemble pentodes. 

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1 hour ago, tube fanatic said:


If you try the SS build, talk to Henry (henry4841) as he has lots of experience with Nelson Pass’ tube mimicking designs.

 

Maynard

 

Fortunately I have a retired tech friend who is a design genius.. Next on the list is a phono pre and a pre amp. In SS world I'm more interested in the 47 Labs SS amp that looks like a joke but sounds amazing.

 

 

 

 

 

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On 12/17/2020 at 11:52 PM, babadono said:

Engineers do it with "slip stick" (slide rule), Technicians do it with a "diddle stick".

 

This needs to be on a tee-shirt.....

 

 

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29 minutes ago, seti said:

 

Fortunately I have a retired tech friend who is a design genius.. Next on the list is a phono pre and a pre amp. In SS world I'm more interested in the 47 Labs SS amp that looks like a joke but sounds amazing.

 

 

 

 

 


Similar to 47 Labs are amps from Peter Daniels out of Canada, both “gain card” designs or chip amps. I have a Daniels Specilaiized chip amp which incorporates at volume pot. I believe a 3875 chip.Daniels puts his spin on the 47 design but in amplifier version are near identical. High quality innards, extremely short wire paths, copper ground/heat sinks and exemplary construction. They use virtually no power and should be left on 24/7. Matter of fact I haven’t listened to mine in a while, she may be running this weekend. 

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8 minutes ago, richieb said:


Similar to 47 Labs are amps from Peter Daniels out of Canada, both “gain card” designs or chip amps. I have a Daniels Specilaiized chip amp which incorporates at volume pot. I believe a 3875 chip.Daniels puts his spin on the 47 design but in amplifier version are near identical. High quality innards, extremely short wire paths, copper ground/heat sinks and exemplary construction. They use virtually no power and should be left on 24/7. Matter of fact I haven’t listened to mine in a while, she may be running this weekend. 

 

Not sure if I'll ever get to it but it is in the back of my mind. I have so many tubes and so many parts for building tube amps not sure it makes sense to do SS yet.

 

 

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7 hours ago, henry4841 said:

Have many tube amps along with SS, mostly class A. A SE First Watt class A amplifier sounds much like a tube. And why not, he uses mosfets which have curves like a pentode tube other then one amplifier. The ones with SIT transistors that have curves like a triode tube. The SIT transistor curves do resemble a triode tube but no where as linear as say the 300B. Most of Nelson's designs are simple circuits, like tube circuits, using mosfets that resemble pentodes. 

This was a valuable information...Thanx for that ...

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