drlowmu's (Jeff's) Amp Discussion

[drlowmu]

I fully concur with you on this.
And your reasoning - out of time, out of coherence.
I have seen people using subs with high end speakers such as PMC which ruins the superb qualities of such a speaker design just for the sake of getting lower and more bass.
So to each his own and back to the topic of a good amplifier.

RRR : Another thought to mention : ............LOL,

.......... most sub-added bass systems we get to hear play bass " all the time " and not " only when it is on the recording ".

- - - - - - - - - - - - - - - - - - - - - - - -

There may be some good amplifiers, commercial, out there. Very few I am afraid !!

Most I hear, and see schematically, have not a chance - to cut it. ( People dislike me when I say this, and get offended at this honest personal opinion .) There is only one commercial audio Manufacturer I would totally trust to get an amplifier from, and he is my DIY mentor for three decades now. He builds lovely SE DC 2A3 and KT150 special monoblock amplifiers. In particular, I would trust his 2021 versions, his latest, as having the highest possible audio performance.

Although we two have both built tube amps for decades, he and I have made break-through amplifier performance strides, IMHO, since about mid-2019, usually under his general guidance..

Regarding a good amplifier, to be perfectly honest with you, I believe my upcoming build, using the 6005 tube, may possibly become a ( not just good but ) a world-class amplifier. There are many very logical reasons for this - see the 16 point " laundry-list ", referred to earlier in this thread.

I will not know until I put it all together, and allow it to break in some. Likely by year-end in my case. It's lately - finally - making some decent progress. It has been hard work and frustrating at times, assembling the desired parts .

Jeff

 

[tnvijay]

Dear Mr Jeff,

It seems your series shunt is suitable for any single ended amplifier B+ . As a diyer with very short learning experience, may I ask how to arrive at those values? Series resistor i understand,and I usually bypass after that with a capacitor to ground. ( Usual RC filter). But in your thematic schema, i notice a RC parallel filter incorporated. How do we choose these values? I am eager to see what it does to my e180f + pl504 SE tube amp

 

[ktks1]

.......... most sub-added bass systems we get to hear play bass " all the time " and not " only when it is on the recording ".

Does that mean setting the sub crossover to have the least overlap with the speaker's low range extension?

And to get the best of time and phase alignment, full range drivers are the only option then? Something like the Lii Audio Silver 10

 

[drlowmu]

Some maths and facts.
The first watt is the most important watt. Majority of the musical listening happens less than one watt.A headroom of 2 more watts is safe to accommodate those Crescendos.
2. Class A amplifiers by design gives distortion free music even at sub watt levels.
3. An amplifier which is rated for 100 watts, will sound double loud as that of a 10 watt amplifier ( not 10 times!)
4. Using the same amplifier at same volume setting,a speaker of 95dB sensitivity will sound twice loud than when using a 85dB speaker.
5. To summarise, A 2watt amplifier powering a 105dB speaker will sound as loud as a 200watt amplifier powering up a 85dB speaker.

Hope this helps.

As far as dynamics, SE amplifier have a special sound signature,They have restriction in producing low frequency notes with a punch, because of core saturation happening in SE output transformers. PP design does not have that , so can give more punchy bass and may be more subjective dynamics. SE amplifier have a property to reproduce human voices and instrumental timbre with almost life like presentation. It's not that it's weak in dynamics or bass,the truth is our ears have been tuned more to a bloated bass than what actually it is.Hear a SE amplifier and then your perception of bass will change. It's not about punching , it's about just enough bass at just the right time., One can say more natural bass or bass as it is intended to be.

Dynamics :
In almost every post I read up here, by seasoned F.M.s, we get the idea that SE amps lack dynamics. Recall how I essentially inferred and said that "99.99% of the amps were not cutting the mustard?? Well, a lack of dynamic contrasting IS how most SE amps play back, and they flunk out !!

But I want to tell you all that it does not have to be this way ( poor dynamic contrasting ) at all, in SE design. Of course, the amplifier designers all copy from each other, and rely on 100 year old text book theory, and apply no new thought, so we get world-wide mediocre performance. That is precisely what we have today in SE designed amplifiers.

Guess what ladies and gentlemen, some of us in audio know how to build beautiful, highly-dynamically-contrasting Single Ended amplifiers . I certainly do. I build all of mine that way, starting with my very first from-scratch-designed DHT mono amps in 1982..

It takes a whole combination of design implementations, to preserve dynamic contrasting. This virtually never gets done. Something is overlooked. So the public is largely unaware !! And when I tell them it can be done, I've done it myself, they think of me as either a liar or a nut case , and next, they often get offended ( at, with, and by ) me.

How do we get music's dynamic s and dynamic contrasting in a SE amp, you may ask? The answer is " not one or two things one does will attain that ". Everything about the amp, has to be thoughtfully considered, and designed, to achieve said goal !! In tube amp designs I see, almost every time, " something is ( unconsciously ) overlooked ", and the amplifier's performance suffers.

I would generally suggest that 90% of the dynamic contrasting challenge, has answers found in the amplifier's power supply design, and how energy is supplied to the circuit.

I have written this here before, and it is so supremely true :........ " In the end, we all listen to a music-modulated power supply. How good is it ? ".

I was lucky to have my first audio mentor, Mr. Robert W. Fulton, teach we well in 1982, about how to design my first amp. Two rules he gave me.

1) Hopefully.... zero negative feedback and
2) all the chokes in the power supply have to be 20 Ohms in Direct Current Resistance, or less, if I can find them " ( DCR ).

DCR is a huge factor in maintaining dynamics. A typical tube amp you see and use in 2021 will be well over the 20 Ohms - the 1982 goal !!

Typically, " 10 Henry at 100 Ohms " is a commonly used choke or tube amp's inductor. Five times too high.

What if I told you that a tube amplifier, and the music dies, when the choke is even 10 Ohms in DCR ????? That is precisely how I hear it, in my amplifiers. Ten Ohms DCR won't cut the mustard. Go measure your choke right now - with an Ohm meter, amplifier drained, not activated !! See Post # 6' - 6005 Thread - the L1 and L2 photos ( 6.01 Ohms ). I wrote and reported this :

" I have made several important changes, since the original post, in a way, " designing by ear ".

First, I have changed the L1 and L2 power supply chokes, so as to go lower in DCR ( D.C. Resistances ). Originally I used Stancor C-2708s, which were 10 Ohms DCR each. I did not like the music's presentation with the pair. It was slow and boring. Now, you can view Hammond 159ZAs, as L1 and L2. They are only 6 ohms DCR each, or a total of 12 Ohms DCR between the dual rectifier tubes and the output transformers' primary windings. Now, the presentation is more lively, on time, and I have lost the sense of an amplifier in the system. I have found that chokes need to be as low in DCR as feasible, to get a great sounding, dynamic music presentation, from a tube amplifier.

How much do I believe in low DCR in a tube amplifier? Well take a look at my personalized State of Missouri ( USA ) car driver's license plates : "

Of course, DCR is of extreme importance, but there are many many other things ( almost all power supply design related ) that also needs to be comprehensively addressed, to build, own and enjoy a world class amplifier !! Everything works in conjunction with all else !! The 2021 6005 amp will "have it all" in it's design - and my execution. In that thread ( on HFV's DIY Forum ) is the previously referenced 16 item list, which covers a lot. ( Post #75 ) Every single aspect listed.... is of importance. Short-change or leave one thing out, and the amp's performance suffers. Its no longer my design.

By the end of this year, perhaps six of these 6005 amps will be in the public's hands. I am ( re ) building a new one for me, and two amps unsolicited / by request / for new clients. The three remaining chassis - are for my close DIY audio friends.

It will be of interest to me, to get everyone's listening reactions !! I pretty much know what it is going to do, from my prototype's build in the ongoing 6005 article. This is exciting - for all six of us.

Dear Mr Jeff,

It seems your series shunt is suitable for any single ended amplifier B+ . As a diyer with very short learning experience, may I ask how to arrive at those values? Series resistor i understand,and I usually bypass after that with a capacitor to ground. ( Usual RC filter). But in your thematic schema, i notice a RC parallel filter incorporated. How do we choose these values? I am eager to see what it does to my e180f + pl504 SE tube amp

Some of this I am hesitant to put in the public domain. If you PM me, send me your usual email address, and a good scheamtic, and I will be happy to try to help you.

Reach me by P.M., and send me a decent schematic, and build photos. Some of this I can only share one-on-one privately, as it is not all my original work, and it is unpublished. Glad to try to assist.

I helped Hari Iyer in 2020. Ask him how that went.

Jeff

 

[tnvijay]

Dear Mr Jeff,
PM sent

 

[Kannan]

There are some never ending debates in audio from an audiophile point of view. This is one of them.
There is a constant to reference audio, but that constant can come in different ratios of speaker sensitivity, power handing, amplifier design etc.
Every design has its limitation, be it full range, 2 way, 3 way or multiway.
As long as you can reach the constant, they will all perform with aplomb.

It will be foolhardy to restrict oneself, though many folks have dabbled for decades and ended up liking one type of speaker/amplifier design, but that does not mean that it is the end game.

 

[IndianEars]

There are some never ending debates in audio from an audiophile point of view. This is one of them.
There is a constant to reference audio, but that constant can come in different ratios of speaker sensitivity, power handing, amplifier design etc.
Every design has its limitation, be it full range, 2 way, 3 way or multiway.
As long as you can reach the constant, they will all perform with aplomb.

It will be foolhardy to restrict oneself, though many folks have dabbled for decades and ended up liking one type of speaker/amplifier design, but that does not mean that it is the end game.

I totally agree.

On the other hand, this is a hobby (not a scientific study with a single conclusion) and so each person will have their take...... Often some feel very passionately about a particular approach or aspect. I think that is Superb, as it provides a channel / direction to pursue the hobby in that direction.

I respect Passion of pursuit in a hobby, even though I may not share that hobby or passion.

As with men & women, there is no Single Pretty woman. Most have something Very attractive about them

 

[Kannan]

As with men & women, there is no Single Pretty woman. Most have something Very attractive about them

And a man's heart can beat at multiple wavelengths at the same time

 

[drlowmu]

Dear Mr Jeff,

It seems your series shunt is suitable for any single ended amplifier B+ . As a diyer with very short learning experience, may I ask how to arrive at those values? Series resistor i understand,and I usually bypass after that with a capacitor to ground. ( Usual RC filter). But in your thematic schema, i notice a RC parallel filter incorporated. How do we choose these values? I am eager to see what it does to my e180f + pl504 SE tube amp

Hello Vijay,

Yes, series shunting the B+ to a sensitive stage can be applied to any sensitive stage. I usually apply it to the audio amplifier's input tube, because this is where most of the amp's gain is obtained. Any inprecision there, at the input stage, gets passed on to later stages, and it is never self-corrected by the remainder of the circuit.

Another place that is super sensitive and requires B+ precision , is the G2 node of any tetrode or pentode. ( Vijay, I usually use a tetrode, one less element to get in the way, VS any pentode ). G2's use-point should perhaps have the cleanest B+ in the entire amplifier.

What about a phono RIAA stage? That deals with small signal levels.

Surely, B+ precision must be ultra critical there. Of course it is !!!

But Vijay, no one I know has ever double series shunted B+ nodes in a tube phono stage. Some have single, maybe even double actively regulated the B+, but no one has brute-force passively double shunted a phono stage's B+, that I am aware of. Phono preamps , like amps, are usually designed with the same old almost "thoughtless" R/C filter, to feed a B+ node.

Over the next few months, I am experimentally "cloning " a Trevor Lees Cascode 12AX7 RIAA stage, and it will be double series shunted. Likely this will be the first phono stage ever done that way. But - I am going two steps further. Each stage will be additionally double series filtered with " Final Filters".

What are these series Final Filters you may ask ?

It is two L/C sections in series, right AT the point of use. The Ls are small, and ultra low in DCR ( hash chokes ) and the Cs are small-value films, of high quality. This would be EE notated as L1/C1/L2/C2. L1+L2's total DCR will be under 3 Ohms, and C1+C2's total film capacitance will be under 6 uF. But, but, but............ C2 will be only 1/8th of an inch from where the audio circuit uses it, right on the plate, or plate resistor of the triode tube !! Energy storage for the circuit .............. with almost zero lead length.

So Vijay, what is being done in 2021 is applying FOUR sections of passive filtering to sensitive B+ areas in a ( upcoming amp and preamp ) circuit, whereas the rest of the audio world typically applies one stage, a R/C.

We ( a group of five audiophile listeners ) all heard this ( three, not four passive filters ) in a high quality 2019 SE KT88 amp build of mine ( pictured below ). We all loved it. We heard my $39.00 a tube E.H KT88 amp ( triple B+ filtered ) readily outperform a VAIC 2A3 mesh plate amp ( about a $1,500 tube if NOS ), because of the power supply to the front end.

This year's 2021 6005 amp build, was the first amp ever to get FOUR filter sections to two different sensitive circuit positions. ( The Ra of the Driver / Input tube, and, to the G2 of the Tetrode Finals tube).

The reason the 2021 amp got four was because it was a stereo amp, and extreme isolation of the B+ was required in dynamic conditions, to get the overall listening resolution / and performance, I sought.

So, in that amp, to those sensitive areas, I listened to two series shunts first. Not good enough - sounded like everyone else's amplifier.

Then I added a Final Filter, just a single L/C, after the two shunts. ( Better sounding, actually..... pretty good ).

And finally, when I added a second Final Filter, both in series. I got the sound and resolution I was wanting to hear. ( Lovely ). So, to sensitive areas ( to both driver and G2 ) , the 6005 amp's B+ filtering became FOUR-FOLD :

....................... SHUNT 1 / SHUNT 2 / Final Filter 1 / Final Filter 2. .......................( versus a typical R/C .)

Frankly, I now can't wait to get the metalworking for the chassis done, and the 6005 amps built and into end-users hands. I already know, from my multi-stage filter listening experiments earlier this year, precisely what this sounds like !

I am also VERY curious, to finish the Trevor Lees Cascode phono preamp "clone", ( with four stages of passively filtered B+ ) and compare it to any one of the three stock ( ~ 1976-1978 ) Trevor Lees preamps we have on hand !!

Recall this please : " In the end, we all listen to a music-modulated power supply. How good is it ? "

GOD willing, all of these things should happen, to several amps and preamp, between now and the end of 2021.

Jeff

Disclosure : Final Filter technology are ideas that I was taught by Mr. Dennis Fraker, who runs Serious Stereo, and is my Mentor and good friend.

2019 SE Directly-Coupled ( oh boy ) KT88 amp............ with triple passive B+ filtering below the deck :

 

[Hari Iyer]

Does that mean setting the sub crossover to have the least overlap with the speaker's low range extension?

And to get the best of time and phase alignment, full range drivers are the only option then? Something like the Lii Audio Silver 10

I cut my H-frame OB sub around 40 Hz to prevent overlap with my main speakers.

Dynamics :

In almost every post I read up here, by seasoned F.M.s, we get the idea that SE amps lack dynamics. Recall how I essentially inferred and said that "99.99% of the amps were not cutting the mustard?? Well, a lack of dynamic contrasting IS how most SE amps play back, and they flunk out !!

But I want to tell you all that it does not have to be this way ( poor dynamic contrasting ) at all, in SE design. Of course, the amplifier designers all copy from each other, and rely on 100 year old text book theory, and apply no new thought, so we get world-wide mediocre performance. That is precisely what we have today in SE designed amplifiers.

Guess what ladies and gentlemen, some of us in audio know how to build beautiful, highly-dynamically-contrasting Single Ended amplifiers . I certainly do. I build all of mine that way, starting with my very first from-scratch-designed DHT mono amps in 1982..

It takes a whole combination of design implementations, to preserve dynamic contrasting. This virtually never gets done. Something is overlooked. So the public is largely unaware !! And when I tell them it can be done, I've done it myself, they think of me as either a liar or a nut case , and next, they often get offended ( at, with, and by ) me.

How do we get music's dynamic s and dynamic contrasting in a SE amp, you may ask? The answer is " not one or two things one does will attain that ". Everything about the amp, has to be thoughtfully considered, and designed, to achieve said goal !! In tube amp designs I see, almost every time, " something is ( unconsciously ) overlooked ", and the amplifier's performance suffers.

I would generally suggest that 90% of the dynamic contrasting challenge, has answers found in the amplifier's power supply design, and how energy is supplied to the circuit.

I have written this here before, and it is so supremely true :........ " In the end, we all listen to a music-modulated power supply. How good is it ? ".

I was lucky to have my first audio mentor, Mr. Robert W. Fulton, teach we well in 1982, about how to design my first amp. Two rules he gave me.

1) Hopefully.... zero negative feedback and

2) all the chokes in the power supply have to be 20 Ohms in Direct Current Resistance, or less, if I can find them " ( DCR ).

DCR is a huge factor in maintaining dynamics. A typical tube amp you see and use in 2021 will be well over the 20 Ohms - the 1982 goal !!

Typically, " 10 Henry at 100 Ohms " is a commonly used choke or tube amp's inductor. Five times too high.

What if I told you that a tube amplifier, and the music dies, when the choke is even 10 Ohms in DCR ????? That is precisely how I hear it, in my amplifiers. Ten Ohms DCR won't cut the mustard. Go measure your choke right now - with an Ohm meter, amplifier drained, not activated !! See Post # 6' - 6005 Thread - the L1 and L2 photos ( 6.01 Ohms ). I wrote and reported this :



" I have made several important changes, since the original post, in a way, " designing by ear ".

First, I have changed the L1 and L2 power supply chokes, so as to go lower in DCR ( D.C. Resistances ). Originally I used Stancor C-2708s, which were 10 Ohms DCR each. I did not like the music's presentation with the pair. It was slow and boring. Now, you can view Hammond 159ZAs, as L1 and L2. They are only 6 ohms DCR each, or a total of 12 Ohms DCR between the dual rectifier tubes and the output transformers' primary windings. Now, the presentation is more lively, on time, and I have lost the sense of an amplifier in the system. I have found that chokes need to be as low in DCR as feasible, to get a great sounding, dynamic music presentation, from a tube amplifier.

How much do I believe in low DCR in a tube amplifier? Well take a look at my personalized State of Missouri ( USA ) car driver's license plates : "

View attachment 58236


Of course, DCR is of extreme importance, but there are many many other things ( almost all power supply design related ) that also needs to be comprehensively addressed, to build, own and enjoy a world class amplifier !! Everything works in conjunction with all else !! The 2021 6005 amp will "have it all" in it's design - and my execution. In that thread ( on HFV's DIY Forum ) is the previously referenced 16 item list, which covers a lot. ( Post #75 ) Every single aspect listed.... is of importance. Short-change or leave one thing out, and the amp's performance suffers. Its no longer my design.

By the end of this year, perhaps six of these 6005 amps will be in the public's hands. I am ( re ) building a new one for me, and two amps unsolicited / by request / for new clients. The three remaining chassis - are for my close DIY audio friends.

It will be of interest to me, to get everyone's listening reactions !! I pretty much know what it is going to do, from my prototype's build in the ongoing 6005 article. This is exciting - for all six of us.

Jeff

One more Mr Fultons statement - " An inch of bad wire will ruin your entire music listening experience". How true.

@tnvijay - I have built @drlowmu SE Directly coupled double shunt filtered with LSES power supply last year. If you happen to be in Mumbai, you can drop in for a listen if you wish. Will be happy to host you.

 

[drlowmu]

I cut my H-frame OB sub around 40 Hz to prevent overlap with my main speakers.

At what slope ??

 

[Hari Iyer]

At what slope ??

-12dB/octave - manual pot - so some tolerance can be expected. I usually set by ear.

 

[tnvijay]

@tnvijay - I have built @drlowmu SE Directly coupled double shunt filtered with LSES power supply last year. If you happen to be in Mumbai, you can drop in for a listen if you wish. Will be happy to host you.

Sir,
Thankyou very much for the invite. If I happen to be in Mumbai anytime, will be eager to visit your place for a listen. I am sure you have the best of the two stage direct coupled amplifier, based on Jeff's Optimization techniques.

 

[Hari Iyer]

Sir,
Thankyou very much for the invite. If I happen to be in Mumbai anytime, will be eager to visit your place for a listen. I am sure you have the best of the two stage direct coupled amplifier, based on Jeff's Optimization techniques.

Yes Vijay, they sound great to my ears. But unfortunately I could not retain all the details of Jeff's design especially on the chassis making and layouts which I think you learn only with experience of building many tube amps over the years. But they do sound great with no hum whatso ever, very dynamic, accurate and live.

 

[deafbykhorns]

Come listen to my 3watt system with a pair of highly modified Khorns if you don't believe what Jeff is saying. A couple guys from an audio club in Orlando heard my system a few months back and said it blew away every system in their club, some of them spending 100k or more....
The amps on the floor are for my office system and not permanent, it was temporary for a short time to hear live performance db's.
I built the 2A3 mono blocks using 5k OPTs from Dave Slagle, preamp is passive except for the phone preamp, no tone controls.

I have extensive repair experience and may be an asset to someone on the forum, I repaired (pro bono) a Mastersound 845 amp for one of the guys from Orlando. Hadn't worked in a year and couldn't afford or trust a local repairman.

 

[IndianEars]

WELCOME to this Forum, deafbykhorns.

Super to have someone with extensive repair experience!

Yes, the 2A3 can create magic with suitably efficient speakers.

While it may distract a bit from the thread, can you please share some info or link on your speakers, preferably with a pic or two ?

 

[z@m]

Hello Dr. Low μ,

I just discovered this very interesting thread!

I'm trying to make my way onto the path that you tread - large, sensitive speakers and flea-watt tube amps with no negative feedback.

To that end, I've been reading John Broskie's articles at tubecad.com trying to grasp whatever I can - as much as any beginner can.

It would be interesting to know your thoughts on his numerous line stage amps and tube buffers available at his glassware store and how a beginner might go about selecting one.

Any pointers would be most helpful.

Cheers!

 

[IndianEars]

Interesting site, z@m. Thanks for the pointer.

However I don't see any Power / integrated Amps on the site. Am I missing something ?

Can you please share links of your short listed products ?

 

[z@m]

Hello Dr. Low μ,

I just discovered this very interesting thread!

I'm trying to make my way onto the path that you tread - large, sensitive speakers and flea-watt tube amps with no negative feedback.

To that end, I've been reading John Broskie's articles at tubecad.com trying to grasp whatever I can - as much as any beginner can.

It would be interesting to know your thoughts on his numerous line stage amps and tube buffers available at his glassware store and how a beginner might go about selecting one.

Any pointers would be most helpful.

Cheers!

@drlowmu / others any thoughts?

 

[z@m]

Interesting site, z@m. Thanks for the pointer.

However I don't see any Power / integrated Amps on the site. Am I missing something ?

Can you please share links of your short listed products ?

Some discussion and designs but no PCBs.

Haven't short-listed anything so far.