Theory, Practice and Sexlife of the "Reflected Plate Amplifier" Hybrid, low Voltage Tube circuit

[thor.zmt]

Class A triode is as basic as it gets.

Yup.

My early Moscodes did exactly that - NFB to the K of the input stage w/20db NFB. I decided to go NFB to the 2nd stage on out with only 10 db.

Your call. Depends on context. In my circuit 20dB (wideband, into MHz) is the least feedback level around the class AB output stage that is needed to improve things across the board, instead of making actually things worse.

Of course that leaves overall gain up to the 1st stage, but no one complained.

Works okay because it's a virtual cascode, especially if the input tube is degenerated.

The amp has a 6/12 fil auto select for tube rolling. I.e. 6DJ8 or 12AU7 works.

Nice feature. I like tube tasting in low/no feedback amps.

Did you ever look at Modjer Modjeski's Counterpoint SA4 OTL? 1 servo from back to front using zener level shifters run at very low current bypassed with coupling caps.

Yes, many ways to skin the pussy after it got fried by 5kV with 500mA current.

As Harvey would say, "The Search for Musical Ecstasy".

Yes, I'm more like "commercially viable solutions for the most musical extacy for the least possible money".

Or perhaps the most happiness for the mostest people for the leastest money.

More democratic, less elitist. Harvey might actually approve. I guess I'm still a commie at heart, or a Christian.

I get more kicks out of making a Stereophile Class D something for < 200 Bux than Stereophile Class A for > 10,000 Bux. It's much harder, more satisfying and better karma for the first...

Thor

 

[Mr. Moscode]

Funny decades as sound engineer and drummers always bitch on a recording their expensive Zildjan/Paiste/et al Cymbals sound like cheap sh!t. Thy rarely b!tch with me, even live with an all digital system and Class D amps, shows it is not what you do, but how.

Thor

Well live, they're on stage not in the audience. Live concert mixing depends on the music. I've had to deal with rock guys who like subsonic bass and bass drums in a jazz trio setting. They don't understand the structure of the music.

Jimmy Cobbs cymbals still sound amazing on Kind of Blue - 1959. Ampex 350s, Neumans, passive mixing consoles, musicians as engineers, Columbia 30th St Studios, an old Armenian church converted to a studio.

 

[thor.zmt]

My last phono preamp design used an input JFET gain stage running open loop.

For fun, what is essentially my recommend "supa cheap" phono.

Preserving the "El-Cheapo" DIY Phono Preamp Documentation

Something based on this, fully electronically controlled (and originally designed with automatic impedance based cartridge detection and resulting configuration which got deleted by marketing as "too advanced for cheap") manages to sell for 150 Bux in an extrided "mid century modern" metal case and make a good profit...

iFi's "Cost Is An Object" Zen Phono MM/MC Phono Preamplifier

Thor

 

[Tubetec]

Hopefully that joke doesnt bring a ton of complaints crashing down on Johns desk ,

I had been thinking of repurposing an older Mac Pro enclosure to make a big tube hifi amp ,
I have the remains of a 1940's mil grade Williamson amp including a huge output transformer that needs resurection .

 

[JohnRoberts]

For fun, what is essentially my recommend "supa cheap" phono.

Preserving the "El-Cheapo" DIY Phono Preamp Documentation

Something based on this, fully electronically controlled (and originally designed with automatic impedance based cartridge detection and resulting configuration which got deleted by marketing as "too advanced for cheap") manages to sell for 150 Bux in an extrided "mid century modern" metal case and make a good profit...

iFi's "Cost Is An Object" Zen Phono MM/MC Phono Preamplifier

Thor

I tapped out after designing my preamp to end all preamps... I received night and day bad/good magazine reviews from different reviewers for the exact same preamp (likely the reviewers were accurately hearing flaws or performance of their personal home playback systems). This convinced me that just building a better mousetrap was not an effective way to sell into the hifi market. I prefer the professional (and semi-professional) live sound market because it is harder to hypnotize an auditorium full of listeners at the same time.

JR

 

[JohnRoberts]

They do great with rock and metal too, an example of "right".

I do recall one casual discussion with Rudy when I asked him why didn't he port his huge "concert Grand". On paper this would deliver extended LF response that the market would likely reward with higher sales (more is always better right?). His response was that the bass in a ported cabinet just did not sound right on classical music. I was not worthy to debate him about speaker design.

All my various phonostages that get awards left, right etc. Use open loop first stage, sometimes open loop after.

and me thinking I did something novel...

JR

Don't you know, electrons that travel in Vaccuum are faster and bigger? ; )

For the best sound, 833 Transmitter tubes in Class A1 with 5kV anode voltage on exposed anode cap's. Honestly I tried. Until it fried the office cat. We decided not to commercialise the design at that point.

Thor

 

[thor.zmt]

I do recall one casual discussion with Rudy when I asked him why didn't he port his huge "concert Grand". On paper this would deliver extended LF response that the market would likely reward with higher sales (more is always better right?). His response was that the bass in a ported cabinet just did not sound right on classical music.

Solution, adjust driver Qt and use on EBS6 tuning.

Actually, if you know to your onions, you tune size constrained systems to 42 Hz and those that are not, to 16Hz or 32Hz (the latter is better for all but extreme organ music).

and me thinking I did something novel...

Whenever I get such delusions of grandeur, I fire up google and try to find prior art. My Google Foo is excellent, so usually I do.

I don't mind playing Eratosthenes (famously called duteros because he was supposedly second best at everything whatsoever).

Thor

 

[JohnRoberts]

Solution, adjust driver Qt and use on EBS6 tuning.

Actually, if you know to your onions, you tune size constrained systems to 42 Hz and those that are not, to 16Hz or 32Hz (the latter is better for all but extreme organ music).

to repeat I am not a speaker guy, at Peavey we had a whole department for that, I do have another Peavey speaker story.

Back last century I was tasked with designing a Peavey response for Fender's cheap consumer portable sound system. Fender used a bunch of small mid range drivers in series-parallel. They spread a BS marketing story about how loud/efficient using speakers that way are. Well before Bose did it, there was a popular "sweet 16" DIY speaker project in one of the hobby magazines (I was well familiar with the pros and cons of the technology).

Since I was designing with a blank sheet of paper, and impervious to marketing BS I reviewed what value speaker systems were most popular for delivering good bang for the buck. I eventually distilled my solutions down to a single 10" driver with a piezo tweeter. Over the years I have found that the people who sling the most BS, are most likely to fall for other people's BS.

My boss was convinced that we needed to copy Fender's multi-driver approach. I got him to agree to a shoot out between my way, and his way. The day of the shootout in the transducer lab area, my box seriously spanked his, it wasn't even close. He was cursing up a storm and all the junior transducer engineers hiding in their offices were too scared to venture out. Then we went out to lunch.

We did the portable system speakers my way and we even tooled up a nice horn for the piezo tweeter into the plastic cabinet.

Whenever I get such delusions of grandeur, I fire up google and try to find prior art. My Google Foo is excellent, so usually I do.

I have 9 patents but at least one was not completely novel as I learned years later. I have even encountered sleazy patent lawyers who advised against doing a comprehensive search (they don't get paid if a search finds a conflict). By then web patent searches were fairly competent so I did my own letting my fingers do the walking. Back in the 70s I drove down to Arlington VA and actually did a physical patent search, myself.

I don't mind playing Eratosthenes (famously called duteros because he was supposedly second best at everything whatsoever).

Thor

Apple is notorious for taking other people's ideas, and just executing better.... The customers don't care who did it first, only who did it better.

JR

 

[thor.zmt]

to repeat I am not a speaker guy

I'm a "system" guy.

People who specialise in speakers or those who specialise in amplifiers have a tendency to make a combined system that combines the worst possible solutions from a system viewpoint.

Well before Bose did it, there was a popular "sweet 16" DIY speaker project in one of the hobby magazines (I was well familiar with the pros and cons of the technology).

Bose 802's have distinct advantages over, say a 15/3 type system, if high SPL and low frequency output are not needed.

My boss was convinced that we needed to copy Fender's multi-driver approach. I got him to agree to a shoot out between my way, and his way. The day of the shootout in the transducer lab area, my box seriously spanked his, it wasn't even close. He was cursing up a storm and all the junior transducer engineers hiding in their offices were too scared to venture out. Then we went out to lunch.

FWIW, my current "beachbum's Beach sound" system has 40liter vented cabs (42hz Tuning) with a decent Chinese copy of a JBL K110 plus an equally decent copy of a 075 ring radiator.

Plus a pair of vented 12" subs with build in "1,000 Watt" (I estimated 400W RMS) amplifiers.

98dB/1m/2.83V

We did the portable system speakers my way and we even tooled up a nice horn for the piezo tweeter into the plastic cabinet.

I would probably used 4 x max SPL 4" midranges as Line Array, Quad piezo in a slot radiator in the center of the line and a 10" driver in a bandpass enclosure, with dynamic EQ.

Should manage 100dB/W with 200W RMS on the Midrange and treble (no dynamic processing).

Bass we can use class D @ 1kW (directly off mains too, no stepdown PSU).

Build in dynamic EQ/limiter that replaces the EQ (at low levels) with low order harmonics when the limiter is active.

Driver frames moulded into the plastic box, then drivers assembled into this in the factory in china that can use toxic cancerous glue on the voice coils.

Net cost for all drivers, "low". Injection forms, I know one of the best guys in south china for that, he's a Cristian send doesn't cheat and I can get you discount.

Electronics, also pretty low.

123dB sustained above 100Hz in a compact box with favourable dispersion characteristics.

Clean vocals even if the bass is overloaded 10dB...

Apple is notorious for taking other people's ideas, and just executing better....

Or actually marketing them better and executing them worse.

And using non-industry standard connectors for industry standard signals and charging ten times what is fair for a crappy charging cable that dies after two months, while the cheapest USB-C canble lasts 6-12 month and costs 1/10...

The customers don't care who did it first, only who did it better.

Nope, they don't care "better", unless "better advertising".

Apple and Bose are an applied lesson in "tech product" selling.

For every dollar you spend on the product, spend at least four on marketing, eight on lawyers and charge fourty Bux at the point of sale.

Thor

 

[JohnRoberts]

I'm a "system" guy.

People who specialise in speakers or those who specialise in amplifiers have a tendency to make a combined system that combines the worst possible solutions from a system viewpoint.

I found that peavey by making and selling pretty much everything in the audio chain, our stuff had to work nicely with our other stuff. I have seen some speaker guys design passive crossovers that were wishful thinking and amp killers.

Bose 802's have distinct advantages over, say a 15/3 type system, if high SPL and low frequency output are not needed.

No highs, no lows, must be Bose... Back in the 70s, I rolled my own 16 driver version of the Bose format (2 front facing, 14 rear facing), including the active EQ.... I eventually ended up adding tweeters to my boxes because the HF was still missing despite all that HF boost.

FWIW, my current "beachbum's Beach sound" system has 40liter vented cabs (42hz Tuning) with a decent Chinese copy of a JBL K110 plus an equally decent copy of a 075 ring radiator.

Plus a pair of vented 12" subs with build in "1,000 Watt" (I estimated 400W RMS) amplifiers.

98dB/1m/2.83V



I would probably used 4 x max SPL 4" midranges as Line Array, Quad piezo in a slot radiator in the center of the line and a 10" driver in a bandpass enclosure, with dynamic EQ.

good luck selling that to the entry level market for birth day parties.

Should manage 100dB/W with 200W RMS on the Midrange and treble (no dynamic processing).

Bass we can use class D @ 1kW (directly off mains too, no stepdown PSU).

Build in dynamic EQ/limiter that replaces the EQ (at low levels) with low order harmonics when the limiter is active.

Driver frames moulded into the plastic box, then drivers assembled into this in the factory in china that can use toxic cancerous glue on the voice coils.

Net cost for all drivers, "low". Injection forms, I know one of the best guys in south china for that, he's a Cristian send doesn't cheat and I can get you discount.

Electronics, also pretty low.

123dB sustained above 100Hz in a compact box with favourable dispersion characteristics.

Clean vocals even if the bass is overloaded 10dB...



Or actually marketing them better and executing them worse.

marketing is about convincing the customer he wants what you are selling

And using non-industry standard connectors for industry standard signals and charging ten times what is fair for a crappy charging cable that dies after two months, while the cheapest USB-C canble lasts 6-12 month and costs 1/10...



Nope, they don't care "better", unless "better advertising".

Apple and Bose are an applied lesson in "tech product" selling.

For every dollar you spend on the product, spend at least four on marketing, eight on lawyers and charge fourty Bux at the point of sale.

Thor

I have already told my horror stories about working for a house that didn't believe in advertising. For many years Peavey flourished on the strength of a strong dealer network. That went the way of the dodo bird after consumer level advertising and now web sales made old school dealers moot.

JR

 

[Tubetec]

Were down to a single music store in my city now , the one that survived always catered to the music student population , supplied tabs and music books more so than gear ,
I was friends with the local Peavey dealership , they folded around 2014 , it was our main music shop , the one that sold Rory Gallagher his strat , Mick the owner passed away suddenly despite being a clean living guy ,sadly internet sales had undercut them to the point they ended up sinking into loss , a lot of my musician friends spent time behind the counter there to keep themselves from self destruction , I miss strolling up the road from my workshop which was on the far end of the street for a chat .

 

[Mr. Moscode]

I found that peavey by making and selling pretty much everything in the audio chain, our stuff had to work nicely with our other stuff. I have seen some speaker guys design passive crossovers that were wishful thinking and amp killers.

No highs, no lows, must be Bose... Back in the 70s, I rolled my own 16 driver version of the Bose format (2 front facing, 14 rear facing), including the active EQ.... I eventually ended up adding tweeters to my boxes because the HF was still missing despite all that HF boost.

good luck selling that to the entry level market for birth day parties.

marketing is about convincing the customer he wants what you are selling

I have already told my horror stories about working for a house that didn't believe in advertising. For many years Peavey flourished on the strength of a strong dealer network. That went the way of the dodo bird after consumer level advertising and now web sales made old school dealers moot.

JR

It's a bitch getting old. The replacements are here. . .

 

[Yash]

Some cool circuits and info here. I was bitten by the Thermionic bug after building my SET Tube amp based on a George Anderson design (Tubelab). This SET accompanied all USB isolation and clean power experiments for my small but mighty iFi iDSD Nano, and acted like the final Revelator.

It was great getting a free firmware update from iFi to support DSD256.

My little tube experiments started with 12AX7s salvaged from a Behringer Tube Compressor. The original plan was to design and build a normal higher-voltage implementation of a preamp so that I could use it in the Behringer again or with other devices like my mixer, microphones, vinyl turntable (an old Direct-Drive Technics), my synths (analogue, Hybrid, V.A./DSP).

But tubes were scarce in my lab, so I told myself I'd investigate low-voltage implementations. I took the sockets from the Behringer and then soldered leads to one, enabling the use of the tube with a breadboard circuit.

Most of the testing was done with cheap headphones, so I also have a MOSFET for current at the output.

Low-voltage is fun. The biggest scare I had was thinking the MOSFET had blown after there was no sound. Turns out everything still worked and probably a wire had moved or something like that.

Found an unconventional way to hook up the tube and got quite a good sound this way - specifically for attack transients.

Experiments are in storage, but the storage is right in front of my main Lab desk, so can be taken up anytime. I can experiment with Thor's circuit too rather easily, so thanks for sharing.

Some of the next projects were going to be a better Tube compressor and other studio gear.

BTW, I read all I could from Dr. Gizmo before settling on a S.E.T. Tube amp as my first Tube Amp build (or the first one I heard in real life).

 

[Yash]

BTW #2, I really like reading about these industry anecdotes from great insiders. They are to be treasured - insiders and anecdotes alike.

 

[Mr. Moscode]

What of Gizmo's did you read?

 

[Yash]

What of Gizmo's did you read?

Approximately everything on the website.

 

[Mr. Moscode]

Hopefully that joke doesnt bring a ton of complaints crashing down on Johns desk ,

I had been thinking of repurposing an older Mac Pro enclosure to make a big tube hifi amp ,
I have the remains of a 1940's mil grade Williamson amp including a huge output transformer that needs resurection .

ME, too. Except a Futterman OTL.

 

[Mr. Moscode]

Approximately everything on the website.

Did you read "In Search Of Musical Ecstasy" or "Understanding Tube Electronics"?

 

[Yash]

No.