Tube power stage vs Class-D (effective power)

[Phil Starr]

5 minutes ago, Paddy Morris said:

The trouble comes when I'm playing slap upright against a drummer who has had a bad day and is taking it out on his drums.   The transients from the slapping play absolute havoc with the amp headroom. 

 

Just a thought, with slap on an upright you are really whacking everything much harder than would be the case on electric bass a lot of the time. Electric bass doesn'tactually have much content below 80Hz but using an upright bass as a percussive instrument might be creating a lot of subsonic peaks. Ported speaker cabs will go into extremes of excursion just above and below the resonant frequency of the port. If that is the case when slapping (and this is just a theory) then an HPF on the amp might reduce the problem and less audibly than a really sharp limiter.

 

Is a castrated bass a viola?

[Paddy Morris]

1 minute ago, Phil Starr said:

 

Just a thought, with slap on an upright you are really whacking everything much harder than would be the case on electric bass a lot of the time. Electric bass doesn'tactually have much content below 80Hz but using an upright bass as a percussive instrument might be creating a lot of subsonic peaks. Ported speaker cabs will go into extremes of excursion just above and below the resonant frequency of the port. If that is the case when slapping (and this is just a theory) then an HPF on the amp might reduce the problem and less audibly than a really sharp limiter.

 

Is a castrated bass a viola?

Hiya.  Yes, I'm HPF'd to within an inch of my life.  Apart from any other reason I can't really hear my intonation on a loud gig unless I have rolled off all that LF junk.

 

I suspect I need to just take my rig (and my poor credit card) to some dealer who keeps a good stock of all-valve amp heads.

 

 

[agedhorse]

12 hours ago, Tech21NYC said:

Tube amps have more "useable" wattage when compared to most solid state designs. It's the reason a lead guitarist can gig with a 50 or 100 watt tube amp in most situations but a 50-100 watt SS bass amp is more of a practice amp. A tube amp will start clipping once it exceeds its RMS threshold but the resulting sound will not be perceived as distorted. Most SS amps become unusable once they exceed their RMS rating for any length of time. The last thing you want to do with any SS amp is run it close to it's max RMS wattage. Power is cheap. For some reason since Class D amps have become so popular many bass players seem to be going in a counterintuitive direction. Lots of power and minimal speakers. If you look at dUg Pinnick's bass rig, he's using his signature 1000 watt bass head but he's also running four 410 cabs rated at 2000 watts. That gives him a lot of headroom. 

 

 

That’s not really the reason why lower powered guitar amps sound louder. The biggest three factors are that the guitar signal resides in the most sensitive portion of our hearing, guitar speakers are very efficient in that range, and that when distortion is used (common for guitar), the THD is often 30-40% which often is part of the desired tone and this increases average power delivered to the speaker.

[Phil Starr]

16 hours ago, Tech21NYC said:

For some reason since Class D amps have become so popular many bass players seem to be going in a counterintuitive direction. Lots of power and minimal speakers. If you look at dUg Pinnick's bass rig, he's using his signature 1000 watt bass head but he's also running four 410 cabs rated at 2000 watts. That gives him a lot of headroom. 

I'm not sure this is counter intuitive.  A lot of what is happening is I think down to improvements in PA. Even fairly modest bands can carry a fairly capable PA system with no need to reach the audience with back line amps, bass goes through the PA for FOH just like the rest of the band. Increasingly people are using digital mixers with multiple aux sends and individual monitor mixes, often through in-ears. If there is back line then it only needs to reach the band on-stage so you don't need he same volume that a few years ago you used to reach the back of the venue. The other technical advance is the gradual development of long throw loudspeakers with extremely temperature resistant voice coils. They aren't efficient and need a lot more power than the 4x10's but amplifier power is so cheap nowadays that small speakers and lot's of power has become a practical option. Portability is an issue too for a lot of us. I can turn up with a SansAmp and a set of in-ears for most gigs. I have a 1x10 600W AES thermal and 800W amp for the odd occasion when I need backline.

 

[Bill Fitzmaurice]

4 hours ago, Phil Starr said:

amplifier power is so cheap nowadays that small speakers and lot's of power has become a practical option.

 

Practical but not inexpensive. Old school drivers have xmax values averaging 4mm. A driver with 8mm xmax is the equivalent of two drivers with 4mm xmax, but they can cost twice as much as well.

[Tech21NYC]

11 hours ago, agedhorse said:

That’s not really the reason why lower powered guitar amps sound louder. The biggest three factors are that the guitar signal resides in the most sensitive portion of our hearing, guitar speakers are very efficient in that range, and that when distortion is used (common for guitar), the THD is often 30-40% which often is part of the desired tone and this increases average power delivered to the speaker.

 

I have to disagree with you there because the same holds true when comparing a 50-100 watt SS guitar amp with their tube counterparts. I'm not talking about what most players would consider "distorted." 30-40% is quite distorted. I doubt most guitarists on these forums are playing archtops. Tube amps are usually rated "clean" at 5-15% THD. The guitar amp is 1/2 the instrument. It's musical instrument "production" vs reproduction which is what SS amps are designed for. You used to work for Mesa Boogie right? Randy said old school "engineers" thought he was nuts try to make an amp "intentionally" distort. 

 

While I will agree with you that it's way easier to listen to a loud bass amp vs guitar amp, the problem with bass (or low end in general) is that when you start getting down to 200Hz the bass frequencies become omnidirectional. On big stages the low end backwash from the PA system can make all instruments difficult to hear. That causes everyone to start turning up or playing harder. Some of the newer more sophisticated systems use cardioid arrays to address this. I'm constantly bitching at my sound tech to move the subs as far from the stage as possible. I need to hear by bass player. A loud PA makes it very difficult to distinguish the actual pitch of the bass. 

[Phil Starr]

2 hours ago, Bill Fitzmaurice said:

Practical but not inexpensive. Old school drivers have xmax values averaging 4mm. A driver with 8mm xmax is the equivalent of two drivers with 4mm xmax, but they can cost twice as much as well.

Of course you are right, I was really just thinking of amplifier prices and did not make that clear. In the UK in the early 1970's a month's average wages wouldn't pay for a 100W bass amp. Currently an average UK week's wage would buy a 500W amp and leave you some change.

[Bill Fitzmaurice]

I paid $350 for my '65 Bassman. That was the average monthly wage at that time in the US. I paid the same for my '65 Jazz Bass.

[agedhorse]

11 hours ago, Tech21NYC said:

 

I have to disagree with you there because the same holds true when comparing a 50-100 watt SS guitar amp with their tube counterparts. I'm not talking about what most players would consider "distorted." 30-40% is quite distorted. I doubt most guitarists on these forums are playing archtops. Tube amps are usually rated "clean" at 5-15% THD. The guitar amp is 1/2 the instrument. It's musical instrument "production" vs reproduction which is what SS amps are designed for. You used to work for Mesa Boogie right? Randy said old school "engineers" thought he was nuts try to make an amp "intentionally" distort. 

 

While I will agree with you that it's way easier to listen to a loud bass amp vs guitar amp, the problem with bass (or low end in general) is that when you start getting down to 200Hz the bass frequencies become omnidirectional. On big stages the low end backwash from the PA system can make all instruments difficult to hear. That causes everyone to start turning up or playing harder. Some of the newer more sophisticated systems use cardioid arrays to address this. I'm constantly bitching at my sound tech to move the subs as far from the stage as possible. I need to hear by bass player. A loud PA makes it very difficult to distinguish the actual pitch of the bass. 

 

Yes, I currently work for Mesa Boogie, I'm the principle engineer behind all of the Subway bass products but also handle various aspects of the guitar amp world as well. I work(ed) hand in hand with Randy, John, Jim and Doug, spent a lot of time with them, in addition to all the other folks. While I'm the "new guy", I've been designing Mesa for about 12 years, and prior to that I designed for Genz Benz/Fender for about 30 years, plus all my pro audio designs, so I've been around the block more than a few times.

 

I've spent quite a bit of time quantifying guitar amp distortion characteristics (not surprising given our experience in the hard rock and metal world) and in general the desired distortion tones (especially lead) run between say 25% and 40%, but there are a whole family of tones that go beyond this too. Of course the amp is ~1/2 the instrument, the texture and tone of overdrive and distortion are a big part of the creative elements of "guitar tone", specifically how it sits in a mix.

 

Randy's a very cleaver, creative guy, he quickly recognized what players were desiring and through a lot of work (including trial and error since there weren't many if any to copy from) developed the driven tones through cascading gain stages, then voicing these gain stages to be more and more useful for particular genres. If you were to study his products and their progression, you would see that he was constantly learning and evolving his designs as the music styles and player demand evolved. John has taken over the guitar amp design work now that Randy retired. At 80 years old, he had earned the opportunity for some new adventures that didn't involve day to day obligations.

 

I have designed several solid state guitar amps as well, mostly with tube preamps, and I haven't run into any limitations of solid state power amps, especially when they were designed with guitar amplification in mind. Some of these turned into commercial products, some are just stepping stones to other implementations of technology. 

 

Hope this helps explain my perspective.

Edited Thursday at 02:20 by agedhorse

[Tech21NYC]

14 hours ago, agedhorse said:

Yes, I currently work for Mesa Boogie, I'm the principle engineer behind all of the Subway bass products but also handle various aspects of the guitar amp world as well. I work(ed) hand in hand with Randy, John, Jim and Doug, spent a lot of time with them, in addition to all the other folks. While I'm the "new guy", I've been designing Mesa for about 12 years, and prior to that I designed for Genz Benz/Fender for about 30 years, plus all my pro audio designs, so I've been around the block more than a few times.

 

Does Mike Bendinelli still work there or is he long gone? He used to be one of the guys I would talk to there. I had one of the first Mesa MKII's (1978?) back when you would deal directly with Randy and his first wife Raven. My favorite amp was the MKIII Simulclass for lead guitar. I had a Studio Preamp and their old 50/50. The only thing I have left is their 112 Thiele which is not a good guitar cab but works for bass. 

 

I don't have problem with SS. When paired through a good SS or tube power amp our stuff can get very close to a tube amp sound. Recorded, you would be hard pressed to tell the difference. When push comes to shove I have not found any SS tech that can compete with what a good tube amp can do in terms of "feel" and tonal complexity. If you take something like my old BF Deluxe RVB amp. Our engineer replaced the output transformer with a Bandmaster transformer which makes it "sound" like a bigger amp but the wattage is technically the same. It also was modded with a cathode bias switch that removes the negative feedback. Substitute a 12AY7 in the first preamp stage and use a 12at7 in the PI slot and the sound and "feel" drastically changes and that's running the amp clean. You would be hard pressed to do that in a SS design. The Mosvalve was my favorite SS power amp for guitar and Quilter is doing some interesting things but it never gets quite there. Of course for some sounds and designs SS can be superior. 

 

Bass is a bit different. For the maximum amount of headroom in a tube bass amp, the weight and cost can be deal breakers for most. 

[agedhorse]

Mike’s still here, doing mostly legacy repairs and touring support of legacy products. 
 

There are lots of things being done with solid state that can address most of the feel issues, your example of the MOSValve amps is one approach that was originally designed by BK Butler, we acquired the brand after it fell on very hard times (we built cabinets for TubeWorks for a while, before they shut down) and developed some new products, but the brand reputation was just too damaged to overcome the legacy issues. 
 

The work on solid state power amps for guitar continues on under the radar, Pat Quilter’s efforts are probably some of the most successful but then there’s also the Tonemaster series that’s gaining ground and popularity.

 

It’s a very complicated balancing exercise to develop new technology that convincingly emulates both the tone/voicing and the feel of the older technology. Of course you already know this with your products, specially the SansAmp. 

[jrixn1]

On 15/04/2025 at 18:26, Paddy Morris said:

The trouble comes when I'm playing slap upright against a drummer who has had a bad day and is taking it out on his drums.   The transients from the slapping play absolute havoc with the amp headroom.  With smaller powered amps the Class D module goes into protection mode for 2 seconds at a time, and the 800w ones just break up.

 

So something's clipping, but is it possible the problem originates upstream of the amp?  What's your entire signal chain?

[pete.young]

@agedhorse @Tech21NYC this is absolutely fascinating stuff. Thank you for sharing your memories and experiences. I wonder whether either of you came across Greg Burman?

[Bill Fitzmaurice]

On 15/04/2025 at 13:26, Paddy Morris said:

The trouble comes when I'm playing slap upright against a drummer who has had a bad day and is taking it out on his drums.   The transients from the slapping play absolute havoc with the amp headroom.  I have to put a fast attack limiter across the input to stop the amps cracking on the transients in the most horribly digital way you could imagine.

 

The limiter fixes the problem but completely castrates the sound of the instrument.

 

A compressor that tames the initial transient peaks but doesn't have any other effect should fix the problem. I'd say whatever limiter you're using either can't do that or it's not set up correctly to do that. I used to be able to get my Hartke 3500 to go into protect mode. It certainly wasn't caused by a lack of power or headroom. But I didn't have a compressor, and it only happened when I slammed a chord at the end of a song. It didn't bother things all that much, as my feed to the PA was unaffected. 

[Dood]

4 hours ago, pete.young said:

@agedhorse @Tech21NYC this is absolutely fascinating stuff. Thank you for sharing your memories and experiences. I wonder whether either of you came across Greg Burman?

 

Absolutely agree, all of these names that I used to read about all the time in guitar magazines when I was a teen (and onwards). I'd pour over those pages pre-internet learning about amplifier design. Really fascinating to hear these memories and experiences! 

I feel sure it fuelled my interests (not to mention hassling a certain british valve amplifer manufacturer for schematic diagrams to study! - We used to receve them by letter or, if I was very lucky, fax!!!!)

[agedhorse]

6 hours ago, pete.young said:

@agedhorse @Tech21NYC this is absolutely fascinating stuff. Thank you for sharing your memories and experiences. I wonder whether either of you came across Greg Burman?

I've heard the name but never run into him, or any of his amps.

 

I was indeed fortunate to have grown up in the right era, learned from the right folks and took every opportunity that I possibly could. For example, my supervising engineer while I was working for one of Fender's companies was Bill Hughes (lead engineer behind the SVT and some of Fender's big bass amps like the Fender/Sunn 1200S, Bassman 300 Pro, along with the PassPort PA series). He was pretty old school, talking with him was always a learning experience. In the pro audio side of things it was even more interesting because many of the concepts that we take for granted today were just being discovered and I got to experience it first hand. It was smaller companies and more personal interactions, much more enjoyable (IMO) than with today's very large business entities.

[Paddy Morris]

7 hours ago, jrixn1 said:

 

So something's clipping, but is it possible the problem originates upstream of the amp?  What's your entire signal chain?

Thanks.  In fact I have had issues with clipping and overloading further upstream in the past, but I've managed to iron them all out.  This is definitely a problem in the final power stage.  If I take a feed of the DI output from the amps then the problem isn't present.  Also if I put a fast attack limiter across the amp input the problem goes away, but then also so does all the attack on my transients.   And I miss them.

[Paddy Morris]

6 hours ago, Bill Fitzmaurice said:

A compressor that tames the initial transient peaks but doesn't have any other effect should fix the problem. I'd say whatever limiter you're using either can't do that or it's not set up correctly to do that. I used to be able to get my Hartke 3500 to go into protect mode. It certainly wasn't caused by a lack of power or headroom. But I didn't have a compressor, and it only happened when I slammed a chord at the end of a song. It didn't bother things all that much, as my feed to the PA was unaffected. 

Thanks Bill.  I think I said somewhere earlier, a fast attack peak limiter does fix the problem.  But it does also really hobble the sound I get.  I've been through a fair few dynamics control devices and the soft knee / fast attack setting on a Keeley compressor pro is the best compromise I have found so far.  But I still prefer the sound with it switched out entirely.

 

So I was wondering if a valve output stage would handle those transients more gracefully.  I guess the best way is to try it and see.  I'm sure I know someone who will lend me an Ampeg or HiWatt head for a few hours. 

[Downunderwonder]

On 16/04/2025 at 05:26, Paddy Morris said:

limiter fixes the problem but completely castrates the sound of the instrument.  At lower volume, without the limiter, the sound is pretty much what I want (when I'm playing the right notes!)

 

I don't want a valve crunch sound or even any more warmth, as I already spend a lot of time dialing out the excessive warmth of the intrument.  All I need is something that will deal with those transients at a reasonable volume without making a horrific noise.

You want compression that sounds like you want it to sound. You can either disappear down the compression rabbit hole or learn to do it with your fingers.

 

At low volume your slap sounds are less bassy to the ear (Fletcher Munson). The extra HF in the slap is welcomed. Everything is coming out uncompressed. Life is good.

 

The slapped bass overdriving the preamp is your problem? You turn down the input gain and turn up the loud knob. What happens then? Turn down some of the bass EQ!