The AM Forum

WHAT are we doing wrong??? These people get 35 Watts out of a single ended 6BQ5 or EL84 at 0.02% harmonic distortion!!!! Absolutely MAGIC

The answer is obvious! They are using dark plate double D getter oxygen free copper anodes with applied cryogenic technology. I thought everyone knew that?  When a $3000.00 power cord is used, you can expect even better performance!

 I see several hits when searching for this amplifier. There is a video describing the unit, and one thing stands out in that they say it is a "hybrid" design.  Also the video I saw shows a closeup, and I think the tube number for the larger tubes is a 6P1.

The video is down near the bottom of this ebay auction:
https://tinyurl.com/yamdfhpr


This might be like some of the Shiit audio DAC's that have one or two tubes. The tubes run on low B+ at a low level to "colorize" the audio, and the solid state stuff does the power amplification.

Jim
Wd5JKO

I had a preamp that used a 12AX7, with a supply voltage of only 12V. It had an inherent 60hz hum. It's now part of my junk box. I still question if the 12AX7 was there for anything more than "show".

I think I had that same preamp.  A friend saw it, I warned him, he bought it anyway, and now I have a piece of crap and he has a source follower!



Anyway, Rockville.  I'm not affiliated in any way.  But, I do have one of their products......  The Rockbox.  It's a Bluetooth speaker.

It's no distortion generator, has great clarity, good volume, recharges my phone, fm tuner, etc.  Everything you want for a jobsite radio.

It advertises 100 watts out.  In no way, shape or form will it get that power out.  Maybe 10 watts, rms as the audio fools say.

Other than always seeming to forget to put the decimal point in the right place, their products seem OK.  Thus far.

--Shane
KD6VXI

Well Done!   LOL

Those are Plastic Watts or Chinese Watts.

Denon used to be top notch. Just saw one of their surround receivers. 100w /ch, @ 10% THD. Thats all those TI digital amps at work.

I purchased a Denon receiver/amp around 1993 that is 100 watts per channel (2) and it has been fantastic! According to the manual this amplifier while not having a massive heat sink is supposed to be rated at 100 watt per channel in class A. It has an opt amp circuit that keeps it in class A at all power levels? I don't pretend to know a lot about how it does this but that's what the manual says? This was my first realization that an audio amplifier could make 100 watts output at any frequency throughout the audio spectrum. Most tube amps that I had did ok in the mid rage but they were lacking power at the extreme low end as well as the high.

You will get no argument from me if you disagree with anything I have said above as I am no expert when it comes to these things, other than to say that Denon is a great product!  

Most of this new equipment is being used by the younger generation whose definition of high quality audio originates from an mp3 file. If you feed it into a decent amp, it’s still comes down to garbage in, garbage out. So I work for Panasonic. We reintroduced the Technics brand and currently offer 7 turntables, the most expensive being about $25k. BTSOM, but that same younger generation is rediscovering vinyl. What’s next, VHS?

I like your definition. Unfortunately true for a hughe percentage of audiophiles. I did read things like" Metal film resistors sound blue, carbon resistors sound pink" and that they even hear the the loudspeaker cable is uni directional. When I measure these resistors they are the same upto 1 GHz!!! These guys have very good ears. ;D
 I like an amp designed well without all that nonsense.

We of the old school call them audiophools. I've been having a running "discussion" with one who came up in the world from a room full of car radio speakers, some out of phase, with a record player buried in there somewhere, to a $10,000 vinyl based system in a huge basement that did it justice. I was expecting better when we reconnected recently. To spare tou the misery I won't bother mentioning the URL for his 196kb/s 44.1KHz Internet audio scream that gives me ear bleed. He uses Sam automation and Stereo Tool FM broadcast processor mashing the living daylights out of music that already has the life processed out of it when recorded on CD or HDD. It's so awful sounding to my old school ears most of it sounds completely different from my original vinyl and he insists hundreds of recording engineers and musicians say it sounds great. Yeah, the younger generation that doesn't know any better and half of them blew their hearing out fighting the decibel war. Basically he's a BS artist from way back, I expected an audiophile and found an audiophool. Then there's Monster Inc. making money hand over fist on audiophools but I digress.

Oh, I just remembered as you probably know vacuum tube audio is making a comeback with a passion, but it's not all triode amps costing a few kilobucks. Yesterday I got into a small discussion of the 6146 (not great for hi fi audio) vs. the 807 that shines. Back in the day I worked for Ampeg at the Linden, NJ shop and became familiar with the BB4 Baby Bass and 300W SVT amp that used 6 6146s. Never mind my opinion of that abortion. My modest 75W 807 amps (2 for stereo) were designed around a modulator in a 1957 Radio Amateur's Handbook and sounded great. I discovered they're showing up in moderately priced handmade amps, some in parallel single ended configuration. I also discovered to my surprise NOS JAN 807s are going for $12, OK until I found brand new From Russia With Love for $7. (;->) As for me, now I'll sit back and enjoy a cold 807.

I completely agree, the simple straight forward designs with 807, EL34, 6L6 and alike do a good job. I do not see much reason for single ended design that need driving the amp close to the limit to have some volume with dynamics in the music. But MP3 doesn't have dynamics, so the audiophools love single ended amps.  ;). I did design several amps this way and found that the main reason why an amp is good is the transformer (Interleaved winding, low spread inductance) and negative feedback per stage, not overall. I always use cathode resistors without decoupling, that does linearize the tube characteristics nicely without phase problems related with neg. feedback over more stages. Than, a longtail pair for phase inverter for the class AB final driven in the cathode by a good current source, often a FET. That guarantees a equal drive of the two finals. Further non decoupled cathode resistors in the finals to make them very closely matched. I like to drive the final in UL, especially the KT77 does a great job in UL, but the 807 and alikes as well. All stages have ample headroom, I never drive them more than 50% of max output.
My amps are quite straight forward. The only defect I have is adding a tone control in order to try to compensate for bass boost, treble boost price boost and all boosts used at recording to prevent some beautiful dynamics in the music..
The RIAA amps I make from J-Fet's 2SK170, often more in parallel. No tube can beat that in noise,  frequency range and microphonics.
Everybody has his philosophy designing amps, but I am happy with mine and the results but I am open for other ideas when they make sense.
I can't afford expensive vinyl players, but I have the Philips Extra Low mass system which in my opinion does a very good job.

While we are talking about audio, I have a question? I have noticed that most amplifiers (tubes) are using a voltage amplifier to drive the grids of the output tubes and it is extremely rare to see any cathode followers employed. It seems to me to balance the output tubes using a cathode follower makes this job simpler and if you needed more power, AB2 is at hand.

One of the latest things I see going on in the guitar amplifier world is people sending in their Fender amps etc to have the circuit changed to a cathode follower. Why is that? People who have had this modification done, rave on about it!