Solid state/class d vs tube amps

[Passinwind]

the grid stoppers are typically found on the g of a triode, its confusing when the nomuclare (bad spelling) we use has multiple names for the parts on the tubes. The grid and the screen, I believe is same component on a triode, and on some pentodes, you have three grids, others a beam deflector, and two grids. And you can have a grid stopper and a grid resistor on the same tube, but not the same grid.
Now that I have been very verbose, the 470 ohm resistor I replaced was a grid resistor, and not a grid stopper.

Roger that, but "screen resistor" is the common layman's term, and using that term makes it a lot easier to differentiate what we're talking about, IMHO.

 

[Drgonzonm]

To get back to topic, I believe an amp that is a class d tube amp, will not have grid stoppers on the tubes in the class D power section.

 

[agedhorse]

In common usage, the grid is taken to be the control grid and the screen is taken to be the screen grid. This goes back as far as I am aware of.

Grid stoppers are used on both triodes and pentodes. The most common reason is (in combination with the grid capacitance) to form a low pass into the grid to minimize instability.

 

[dlb1001]

Op: if fender bassman is your sound, frenzel makes a 100 watt bassman that's 25 lbs. Haven't tried it but it's worth a look in addition to the ampegs on your list, newer bassmans (300 and 100 versions) plus vintage bassman like the Silverface 100/135.

Just checked it out...only $995!

 

[Rodslinger]

ok guys. As generic of a topic as this is I have a big dilemma.

If you check my sig, you will see that I am a (proud) owner of Aguilar amps.

They sound great and all but yesterday I tried to hook up a fender bassman tube clone.

Wow! I couldn't believe the sound I was getting. Barefaced big twin 2 has a renown of being a cab that is able to pump monstrous lows, that are sometimes even hard to control. But with the clone, every low note has a clear and round, veery warm low end that doesn't extend over the limits. What surprised me even more is that every note I played, even on higher registers is still meaty and has a great low mid presence and just keeps on going and seamlessly blends with the low notes with zero volume difference.

My aguilar amps work great as well but there was an obvious and immediate difference in the sound the moment I plugged in.

I immediately felt groovier and a better bass player.

Should I go after an all tube amp? I never played a solidstate with a similar warmth and meat to the sound and I am starting to think I never will.

The bassman clone was 40w and I couldn't believe how loud it actually was.

The size of these amps is bugging me though.

I have owned many tube amps back in the day. I've been running an Ampeg PF800, SVT 7 Pro, SVT 4 Pro, SVT 3 Pro & Fender Rumble 500 V3 head & various cabs for the past 10 years. I just picked up an Ampeg SVT 2 Pro 300 Watts all tube head (to go with my two Ampeg SVT-212AV cabs) which is basically an all tube SVT 4 Pro. All I can say is the sheer power, presence, note depth, bloom, definition, growl & 3D punch was all it took to set my 4 pro off to the side and contemplate selling it. Everything I remember loving about my old tube heads was there and then some. Yeah it weighs a ton but so does the sound! In the end my sound & my tone is my essence. I spent years trying to lighten up my rig to the point it all became anemic. The Fender Rumble 500 & Ampeg PF800 can't even ride the same wave as the SVT 2 Pro. The SVT 4 Pro has a tube preamp but still hasn't got the 3D body of sound the 2 Pro has. As far as maintenance goes. Both SVT 7 Pro's died on me as well as the PF800 which died at a show. Both of those were digital. Never had an issue with any of my tube heads or my class A/B heads except the bias going out on my SVT 3 pro which was an easy fix for my tech. I was actually about to buy the Mesa Subway D800+ but I saw the SVT 2 Pro used and remembered how amazing my SVT II Non Pro was. I made the right decision.

 

[DavesnothereCA]

....Taking into account the "duty cycle", which thanks to various contributors we now know is about 12.5 % for a bass amp....

~
Respectfully, I do not believe that we KNOW this.

In my 'elephant' thread, I directly queried Agedhorse about what purpose of power amps have (or NEED to have) how large of a duty cycle, and he stated (among figures for other functions) that for a bass guitar (and for a bass bin of a P.A. system), that the number was (or ought to be) between 25% and 40% for decent quality recent models of amps.

Those are numbers which I am inclined to believe, both from the credibility of the info source, and from some personal experience with older tube and s/s amps.
~

 

[AE1]

~
Respectfully, I do not believe that we KNOW this.

In my 'elephant' thread, I directly queried Agedhorse about what purpose of power amps have (or NEED to have) how large of a duty cycle, and he stated (among figures for other functions) that for a bass guitar (and for a bass bin of a P.A. system), that the number was (or ought to be) between 25% and 40% for decent quality recent models of amps.

Those are numbers which I am inclined to believe, both from the credibility of the info source, and from some personal experience with older tube and s/s amps. ~

The concept of "duty cycle" arose from a discussion regarding comparison of manufacturer power ratings for their amplifiers. Contributors explained how an implied continuous rating can be ethically attributed even though the amplifier will rarely or never be called upon to deliver that rating because of the duty cycle effect.

If there is no industry or national standard duty cycle then there is a case for manufacturers to publish the value used to support their power ratings.

IMHO the actual number of the duty cycle is not as important as the need to know it

 

[AE1]

In common usage, the grid is taken to be the control grid and the screen is taken to be the screen grid. This goes back as far as I am aware of.

Grid stoppers are used on both triodes and pentodes. The most common reason is (in combination with the grid capacitance) to form a low pass into the grid to minimize instability.

Wholly agree

It is common though for the control grid (Grid #1) to have TWO resistors - connected in series.

One (the grid stopper) connects directly to the grid and the other (grid resistor or grid leak) connects directly or indirectly to the cathode

The coupling circuit from the previous stage is connected to the junction of the two grid resistors. The grid resistor forms part of the load on the previous stage.

The system may be applied to any power or voltage amplifier tube - triode or tetrode or beam tube - but is most commonly used on power tubes

Series resistors supplying the screen grids (Grid #2) are commonly called "screen resistors"

 

[AE1]

To get back to topic, I believe an amp that is a class d tube amp, will not have grid stoppers on the tubes in the class D power section.

why not ?

 

[Drgonzonm]

why not ?

the grid stoppers are lpf and remove those all important pulses, which will be removed by the butterworth filters leaving the amplified signal in the audio range for the speakers.I guess if you remove the pulses, there will nothing to amplifly, so no grid stoppers.

 

[agedhorse]

Actually, low frequency class D amps that use a tube output stage could benefit from grid stoppers. The principal benefit would be to reduce the tendency of unwanted oscillations and ringing. Additional benefits include the control of switching times. This technique is commonly used on the gate of the class D switching FETs, which are equivalent components.

 

[DavesnothereCA]

....If there is no industry or national standard duty cycle, then there is a case for manufacturers to publish the value used to support their power ratings....

~
Yes, I'm completely with you on that, which is why I began the 'elephant' thread, as well as the 'RMS Watts' thread not long before it.
~

 

[DavesnothereCA]

Sorry DavesnothereCA, the pic was intended to show the transformer drive configuration only....

~
Yes, and it did that well.
~

....The use of a low-impedance cathode follower permits a lower ratio transformer to be used to deliver better frequency response and lower distortion, but conventional plate circuit drivers are usually used for Class AB, which is the most common mode for guitar and bass amps

Cathode-follower drivers are commonly used in hi-fi and some guitar amps but require an extra stage - which adds to cost....

~
I think I was alluding to similar observations, but using different words.

The driver stage in that 2nd schematic which you attached (of the amp with the four EL34s)
View attachment 2872003
looks a lot like how Garnet did their RC coupled driver stage, which I described a few posts ago.
~

 

[Rodslinger]

This says a lot about tube vs solid state and the sound quality involved. It’s also got so much more. 3:20 into the video says it all.

 

[agedhorse]

This says a lot about tube vs solid state and the sound quality involved. It’s also got so much more. 3:20 into the video says it all.

IME it says a lot about how gullible consumers with surplus funds are.

I worked in the audiophile industry as an engineer for a few months out of college. I left after witnessing a wholesale industry wide misrepresentation of products and performance, for the sole purpose of separating customers from their money. Falsified listening tests, faked or paid for reviews were the norm, and many of the designers and company owners believed their own drivel because of this blind faith in something that simply was not there.

I left after faking a double-blind listening test where I substituted two very average amp circuits inside very expensive amp chassis. The tests went as expected, one amp was clearly superior to the other, all the discussion about sound stages, harmonic sensitivity, chocolate notes, woody finish, lush blueberry aroma, etc. and the air of exclusivity that comes with appreciating things that average mere mortals could not.

When I pulled the covers on the amps any the participants were debating the superior merits of $200 amps are they were $20k amps, the crap hit the fan and I (of course) found myself no longer employable in that industry. The emperor really had no clothes.

 

[seamonkey]

This says a lot about tube vs solid state and the sound quality involved. It’s also got so much more. 3:20 into the video says it all.

Ironic that Youtube - a digital streaming service, is always used as a reference point.
I can wait for a peer reviewed paper published in a real journal.

 

[Drgonzonm]

~
Yes, and it did that well.
~

~
I think I was alluding to those observations, but using different words.
~
~
The driver stage in that 2nd schematic (of the amp with the four EL34s)
View attachment 2872003
looks a lot like how Garnet did their RC coupled driver stage, which I described a few posts ago.
~

I believe the amp you referenced, is a class AB. I found a Garnet, that possibly could be a class B, the BTO PA260, The last preamp tube is a 6sn7, with both triodes wired in parallel, and the combined plates are feeding what looks like a center tap choke. If you give us a model, it will help.

 

[DavesnothereCA]

I believe the amp you referenced, is a class AB. I found a Garnet, that possibly could be a class B, the BTO PA260, The last preamp tube is a 6sn7, with both triodes wired in parallel, and the combined plates are feeding what looks like a center tap choke. If you give us a model, it will help.

~
Yes, I have also noticed the schematic of the power amp which you just mentioned (BTO 260 series), and I agree/suggest that the choke with the CT seems to be behaving as an autotransformer in order to create the phase inversion needed in half of the power stage (and I may have misjudged it as a full isolation transformer in my earlier posts about Garnet, though still yielding the same functionality).

But the other driver stage design which I mentioned again later on is completely RC coupled, from a single triode to the power stage, and not in the Marshall way.

This driver stage method is used in quite a lot of Garnet amps, all the way from smaller push-pull with 6V6 outputs thru to some with 6L6GC or EL34.

Note the 100K resistors in the plate AND cathode circuits of the driver stage, which cause the stage itself to have no gain, but do let it split the phase of its input signal, and in other examples, those resistors were sometimes 47K each.

Also note the use of control grid 'stopper' resistors (and capacitors) in the power stage, as well as screen grid resistors.

The screenshot which I chose to post was the most clear and easy to read of all of the related examples which were in the huge compilation PDF which I found online somewhere, back last November.

And BTW, Garnet did use the Fender/Marshall/Traynor/etc driver circuit in some of their models, but the dates (or lack thereof) on the various schematics do not make it clear whether they used it in earlier or later production.

~

 

[agedhorse]

There are 2 nested feedback loops plus a global feedback loop in that amp, with high impedance phase splitter combined with grid stoppers and hefty grid to cathode capacitance, my guess is that they had some real stability problems under higher gain conditions. 220pF is about 100x the typical grid capacitance to the cathode, and the high drive impedance is going to cause some significant HF rolloff. Maybe the feedback will improve this a bit, like stealing from Peter to pay Paul.

 

[somebrains]

Except that on a properly designed amp, load boxes, power soaks, and such devices are used all the time without any of the issues that you are postulation.

You are trying WAY too hard.

Here's my solution to how I used to choke down SVTs and Bass 400's with big cabs at home.

Fits, BARELY, in the passenger seat of a BMW Z3.

I really like it with singlecoil basses.

I got a pile of other stuff too, I like it all with specific basses.
Sometimes I get all bored and spin basses amps, cabs, whatever in diff combos from all 4 corners of my home office.

Stuff is cool.
There is no best.
At least music gear doesn't become essentially useless like a Playstation 1.