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**Enzo** · 03-05-2009, 03:34 AM

In fairness to that last guys, you'd have to have the same amp available in both 2.5 and 15 watt versions. The difference between 100 and 50 watt amps is not one of loudness to any degree. it is about the performance of the power stage. He likes the way the 100 watter works better than the 50. I can drive my car down the highway at 60MPH in either 4th gear or 5th gear. I prefer 5th. You might prefer to drive down Cedar street at 30 in third gear, but that is a tough comparison to make.

I can relate. I much prefer a 500 watt bass amp over a 50 watt bass amp played at the same loudness. The 500 watt amp will have a clear effortless sound that the 50 won;t achieve.

There are so many factors to scaling down an amp as you describe. As a mechanical system, how does a speaker respond at 40 watts compared to .4 watts? Do the magnetic currents in the iron scale in any linear fashion? I sure don;t know. COnsider making a model of an army tank. You can scale down the size, but how about the mass? Or even just the weight? That 30 foot tank made into a 30" model should weight about 3/4 of a ton. I am out of my area for sure, but perhaps peripheral efects - a mechanical noise floor if you will - become a larger and larger percentage of things the smaller the iron gets.

Stuff like that enters into the discussion beyond the electronics of the circuits.

**zhyla** · 03-05-2009, 05:05 AM

I kind of doubt a "scaled down" version of any tube would sound like the original but magically break up at lower volumes. But there's probably all kinds of distinct sounds you can get from triodes that you can't magically scale up to a high wattage tube. Why replicate when you can find a sound that's both new and interesting?

I've got a firefly, they actually sound pretty good. The 75W speaker I've got it paired with probably isn't doing it any favors, but it still does fine. I kind of wish it had a cleaner sound, it's hard to get a medium-dirty sound at just the right volume (there are some modifications that make this possible, but just haven't gotten around to trying them).

**Steve Conner** · 03-05-2009, 10:09 AM

I think by far the best way out of this is just to try and forget the whole concept of a small amp emulating the tone of a large one.

It all comes down to non-linear effects. Enzo mentioned some stuff about speakers, but there is also the non-linear response of your ears themselves, as quantified by the Fletcher-Munson curves. They predict, for instance, that an amp played at conversation volume would need about 20dB of bass and treble boost to sound the "same" as one played at gig volume. No power scaling or master volume circuit that I know of will do that, and the guys who design these things would throw their hands up in horror if you asked them to add what is basically the "Loudness" button on an old Japanese stereo amp.

What this says to me, is that because of these non-linearities, there is literally no such thing as "same only quieter." Volume is mixed into the perception of tone in such a way that the very fact of making it quieter makes it sound different. The mini Super Reverbs and Hiwatts mentioned in the original post would sound nothing like the full-sized ones, even if they measured identical on a spectrum analyzer apart from the level difference. (And in order to measure the same, the cabinet and speaker would need to be the same physical size.)

Instead of worrying about power scaling and such, I propose just appreciating amps of all sizes and powers each in their own right. And viewed from that perspective, triode tubes have no limitations, they just sound different. (They make less power, clip softer, and have a lower plate resistance that damps the speaker more, so the vibe is more jazz than rock.)

**cbarrow7625** · 03-05-2009, 12:42 PM

They make less power, clip softer, and have a lower plate resistance that damps the speaker more, so the vibe is more jazz than rock

Steve really nailed it there. I have a 4 x 12AU7 amp that I have been playing & tweaking on for about 6 years now. The triodes just never really seem to get up and perform like a pentode type power tube. They are a step up from an emulated DSP version of your cranked amp but it will never get that Marshall power tube crunch in the same way.

I actually prefer to use mostly preamp / PI driver than power tube drive so it works for me quite well with a MV between the PI and 12AU7's. I use a standard LTP PI in my amp, which is a bit tricky because the bias voltage on 12AU7's is quite a bit lower than your typical pentode power amp (around 20 Volts in my amp with really high plate voltages - the tubes are right at their absolute limits). That means that the PI can actually provide waaaaay more driver than the power tubes can handle. The Post PI MV is a necessity to keep things "nice". It also means that I can't really put everything on "10" like a Marshall. It's my own comprimise that I like & can live with.

I played the amp for about 5 years with 12AU7's set up as a typical 2-per-side push-pull but always thought it lacked something vs. a pentode so I kept searching for something that would work better. What I finally tried (and like 1000 times better) is using the 2 x 12AU7's on each side in cascode driving a power transformer with the CT grounded. This arrangement sounds much more like a Pentode than just the 12AU7's by themselves. It is a 5 channel amp (including a Fender Twin-type preamp) and every single channel (especially the Fender-esque one) sound much more like the real thing. If you want to try it just be careful because you need to put a capacitor on the output of at least one half of the Push-Pull power section to avoid DC offset through the transformer (about 20uF is perfect for mine; less is thin, more is too mushy).

Anyway, just anoe man's tale of tying to take the small triode power tube thing to the next level. It can be quite good depending on how you want to use it and your expectations of what it will do. But, as Steve said, it is never going to be as authentic as the real thing, speakers & Fletcher-Munson not withstanding. (By the way, I use 25-30 Wat speakers with extended respnse to 5kHz only with this thing - much more lively and you need the extra top end to make up for some treble roll-off with the triodes).

**rozrosner** · 03-07-2009, 03:06 PM

Thank you all for your excellent responses.

Unfortunately, this is not what I wanted to hear, but, based on previous conversations with Enzo, I pretty much knew there is no easy way around this dilemma.

But you guys provided me with some very helpful information. I don't have the technical background to understand most of what you are saying (and probably should not even be on this forum) but now I what to read about this "cascode" configuration that cbarrow mentioned and maybe try to build an amp like the one he built.

My question was not really about recreating the sounds of larger amps at lower volume as much as it was about trying to build little amps that really rock. Not just clip and buzz and scream and all that but to sound like rock and roll even without being fully cranked.

The heart of this issue seems to be that, as Steve said, triode power sections "clip softer, and have a lower plate resistance that damps the speaker more, so the vibe is more jazz than rock." Enzo once put a pentode/triode switch in one of my amps, and I didn't care for triode operation. It was you, wasn't it Enzo?

However, I recently played an amp made by a guy named Quidley (in North Carolina) that sounded very rock and roll in triode operation (8 watts, I think, down from 22), at very low volume. I don't know how he did it, and the sound was not exactly my cup of tea, but it was pretty amazing how that amp rocked out at very low volume. It's a sound that would definitely appeal to many rock guitarists in a studio environment or on stage if the amp could be miked (the amp was much louder in the 22 watt mode). I think it was a master volume amp, and I don't usually care for master volumes, but this one worked really well.

I think the amp retailed at well over $2,000, maybe over $2,500, for a small combo, so I didn't even consider buying it, but it proves that triode amps can really rock without sounding buzzy or even slightly jazzy. That does not negate what Steve is saying, but this guy somehow found a way to mitigate or get around those inherent triode qualities (I believe I learned on his website that the low powered mode was triode operation). I wonder if he used the cascode configuration?? I would be very impressed if "power scaling" could sound that good in a cranked Marshally way at that volume. Based on what you guys are saying, Mr. Quidley may have figured out how to defy the laws of physics.

Another way to approach this problem is to think about various oddball vintage amps that sound great but have WAY less output than one would expect given their circuits and tube setup. Enzo is probably sick of hearing me talk about the "Dallas 30" amp I played several years ago. This goofy looking, circa 1960 British amp had two EL-34 output tubes in push-pull, sounded really great, in a gritty but not a high gain sort of way, and did not even have the output of my 2.5 watt amp (through a very efficient cab)! I could have purchased this very cool amp but passed because it just didn't have enough output and volume for me!!!

I recently got in touch with the owner of this amp and he told me that the speakers were wired out of phase when I played the amp and that he has since blown both of the speakers. The amp sounds very different and distinctive, but I think most guitarists would like this amp a lot. There is a thread about one of these in this forum or one of the other forums here, but the amp was also sold under the Shaftsbury name, and I think that's the way it is referred to in that thread.

So I wonder if some elements of poor design or inefficient design in some of the cheaper vintage amps "helped" those amps mitigate volume in ways that didn't compromise the tone. I think Enzo told me that this amp is ultralinear and cathode biased and that it had some "bad" design elements that would have caused alot of heat buildup in a few massive resistors, etc. The amp also had eliptical speakers. Maybe it was horribly inefficient in its use of power, but to me that is a good thing!

I also played a little Lafayette amp (Univox?) at the Detroit guitar show one year that was very low powered but actually crunched and did not sound like any single-ended amp I've ever heard. I think it was push-pull and used uncommon output tubes like 6BM8 or 6AQ5 or something like that. I really wanted to buy it but, again, it was too impractical. Not nearly as loud as my 2 watter. Unfortunately, I never learned the name and model number of that Lafayette amp, and I cannot find a complete schematic of the Dallas 30. The guy who owns the one I played lives in LA, and I might pay him to have a complete schematic drawn.

So why can't one use some of these ideas (inefficient design) to design a great sounding 3-watt, push pull amp or a great sounding 30 watt push-pull amp that is about as loud as one would expect a three watt amp to be? It has been done before.

**zhyla** · 03-07-2009, 06:52 PM

So why not build a Firefly and use that as a basis to improve on? It's a reasonably simple push-pull triode design and won't really cost you much to throw together. You'll get better answers from doing a build and tweaking it (try different transformers, different tubes, etc) than from hypothetical discussions. It seems like you're really interested in this kind of thing so it will be time well spent to get something on the bench to play with.

**rozrosner** · 03-07-2009, 10:02 PM

I just might do that, Zhyla, but I am trying to squeeze out as much free expert information from you guys as I can before I get started!! I did build a single ended amp from a kit a few years ago, and it does sound quite good actually, if you don't count the intermittent interruptions in sound that are most likely due to a bad solder joint or some other wiring mistake that I made. But nothing that a good, swift kick does not remedy for about thirty seconds until the sound cuts out again.

**Steve Conner** · 03-08-2009, 07:37 PM

Sure I could design a great sounding 3 watt amp for you. But it would cost you $2500.

If you're looking for free advice, well, remember that engineers need to eat too.

Out of interest, do you like the sound of a cranked Fender Champ? If not, do you like it better with a treble booster pedal? The Champ is pretty much the reference point for the 3 watt class. The Epiphone Valve Jr. is a cheap Champ-like amp and there are lots of published mods for it that claim to give "Marshall", "Fender" etc. tones.

Any 2xEL34 amp that was quieter than a Champ would have been broken, so that says to me your idea of tonal heaven is a broken amp. Not sure if that is a good starting point for a design. Nor do I think it's valid to second-guess all the way to a decision that you need a mini triode push-pull amp, on the basis that you once played some broken amp and it sounded great.

Is this the Dallas 30 amp you liked: http://www.vintagehofner.co.uk/brita...of/shaft1.html

**rozrosner** · 03-08-2009, 09:25 PM

Steve, that is indeed the amp or its identical twin. It was not broken in any obvious way. The speakers were wired out of phase when I used it, I found out later, but the amp did not sound broken at all. It sounded very British, if that makes any sense, and it sounded great. The owner is a very good blues and soul type guitarist who owned a vintage guitar shop for years and he thought it sounded great too. The tone had a bit of grit in it, but it was not ugly sounding at all.

I've played tons of amps, old and new. I've owned many amps, vintage and non-vintage. I do have some perspective on how non-broken amps typically sound. If this amp indeed was broken and could do its thing for years without catching on fire, is there not something important to be learned from this goofy old amp for those interested in this volume/tone problem?

This would not be the first time that something really cool happened almost serendipitously or from bad design or product misuse in the world of guitar amps. Consider that distortion was considered a bad thing back in 1957!! One of the coolest things about the tweed Fender amps from our perspective today results from what Leo Fender would have considered a misuse or abuse of his product!!!!!!!!!

Some amps that are horrible from an engineer's perspective may be incredible from a guitarist's perspective. I'm just wondering if it was indeed broken, if there is not something to be learned about why and how a broken amp could sound great and operate for a long time without catching on fire or damaging itself.

If an amp has speakers wired out of phase, is that almost analogous to being broken? What about the big resistors that Enzo pointed out that could get really hot? What if lots of those sort of bad design elements added up, none of them individually being a serious defect but all of them individually being something that would make an engineer cringe. Just wondering.

Isn't it possible that the eliptical speakers were horribly inefficient and that being wired out of phase also affected the volume? Is the fact that the speakers blew of importance here? Does that not tell us that there was something inherently unstable about the amp? Like a doomed long-distance love affair?

The amp's owner used it for years until the speakers blew. If it was broken, then I want my next amp to be broken in the same way!

I have a 1.7 watt (2.5 watt in boost mode) single ended amp that sounds far better than any single-ended amp I've ever had, and that amp and my single-ended kit amp (that one is based on the Cornell Romany) are, in my opinion, better than any single-ended amp I've played in any guitar store (the Victoria tweed Champ is right up there, it sounded great to me), so I want something different. I already have two excellent single-ended amps. I want a low watt, push-pull amp.

Also, since I like my crazy efficient detuned 112 cab, I need an amp that can get a driven tone at a very low power level. When I practice with the band, I can't crank up my 2.5 watter, so I need the Rat pedal.

My 2.5 watter uses a 5687 (or 7044) triode and does have a certain roundness to the tone. It does rock but does not really crunch and the treble response is limited, so I often use a Rat pedal with the amp for both the drive sound and the added treble, and to get a rock sound at reasonable volume because I use a very efficient detuned cab and the amp is unbelievably loud for 2.5 watts. I want my next amp to be a push-pull amp that allows me to ditch the Rat pedal.

Thanks for your help. I realize that some of my comments reflect my lack of knowledge on these subjects, and that I'm probably trying to have my cake and eat it too. I should have bought that Dallas amp so I could have hauled it into Enzo and said "what the heck is going on here?"

**Steve Conner** · 03-08-2009, 10:23 PM

Originally posted by rozrosner View Post

If an amp has speakers wired out of phase, is that almost analogous to being broken?

Yes, that counts as a fault. And if the amp blew its speakers, it didn't "operate for a long time without damaging itself."

Isn't it possible that the eliptical speakers were horribly inefficient and that being wired out of phase also affected the volume? Is the fact that the speakers blew of importance here? Does that not tell us that there was something inherently unstable about the amp? Like a doomed long-distance love affair?

Yes, being wired out of phase would affect the volume negatively, make the tone sound weird with very little bass and lower mids, and it would probably make the speakers blow, too. Not directly, but the lack of volume and body caused by phase cancellation would probably motivate the player to crank the volume and bass controls right up.

I think it's likely that you have an irrational fondness for the tone of elliptical speakers wired out of phase and driven to the point of cone shredding. Good luck replicating that one!

**BackwardsBoB** · 03-09-2009, 12:40 AM

Rozrosner -

You seem to be talking about two different things.

1. A low-power amp that emulates the power-stage overdrive of a high-powered amp well, whatever "well" means.

2. A low-power amp that rocks.

For (1.), I think your best bet is to start with a high-powered amp, and power-scale the output stage by dropping the supply voltage to the output stage and adjusting the bias and PI output level to compensate. No way some little triodes are going to break up and color tone like EL34s or 6L6s in agony. For reasons previously mentioned, the resulting amp won't get your blood pumping in the same way that risking ear damage will.

For (2.), you site several successful examples. Once we say that the amp only has to "rock", everything becomes subjective, and you embark on your personal tone quest. We can share no solution, since we can't share the goal. I'm pretty sure I'd find your midget amps repulsive.

You're already on your tone quest, listening, and aquiring a few tasty bits.

Most amps have a bunch of knobs on them, which dramatically affect the sound. Finding your perfect amp without turning the knobs would be tough. You'd have to find an amp that was set just right. Well, inside the amp, there are "fixed knobs", that, with expertise, you can change. It's possible to identify and understand the circuits and successfully modify them, but hands-on experience is required to predict the resulting sound and drive the amp tone in the direction you want to go.

This is the trap. One dives into the amp, diddling with this and that, looking for "tone", when one should really be practicing. The activity is very satisfying, but "tone" is a beast that morphs frequently, so the quest becomes endless pursuit.

Is "tone" as subjective as I make it out to be? The whole concept of good and evil sounds is a bit ridiculous, giving weight to my argument, but music is a language full of idioms. Scales, tone, volume, etc. all carry emotion in a way that is both shared and arbitrary. Major chords sound "happy" and minor chords sound "sad". Hard to argue that that isn't an idiom. Especially on this forum, you can see attempts to speak in the voice of another whose voice is admired. There's a great deal of attention paid to the overdriven voicing of early Fender amps, though, as you pointed out, the tone was pretty much randomly generated initially, from the collective mis-behavior of clouds of electrons, crummy power supplies and carboard speaker cones, and the frequency response of several configurations of lots of wire wrapped around a magnet, influenced by the personal taste of designers who were trying to make a different noise. That voice has picked up "rock" connotations, and become an idiom. Some idioms are sonically unpleasant, but still have their ideals. Saxophone, violin, banjo and ukelele come to mind. It's possible that "great overdrive amp tone" is another example in this class, and that the sweet/sour balance is a matter of taste. So it's possible that the tone quest is a search for remembered idioms one likes, but that's subjective too.

I grew up in Chicago, where they make great deep-dish pizza that is sorely lacking in other parts of the universe. I've learned that the wood-fired ovens of Northern Italy produce a lovely thin-crust pizza, I like a calzone with no pepperoni, and I'll even enjoy a pineapple/canadian bacon monstrosity. If there were only one good tone, we would have found the formula, and there would be no need for discussion or the quest.

Once you recognize that there is more than one good tone, the quest can take a scary turn. GAS sets in, and you spend your time acquiring the different tones, once again, in lieu of practice.

You can sell everything but your Martin, go acoustic, and avoid all this. Get a D-28. It's got that tone. And a 12-string. Either a tempermental old Guild or maybe a shiny Takamine. And square-neck and round-neck dobros. And a Guild jumbo for fingerstyle. And a classical guitar, and a flemenco version. And an archtop. And a gypsy jazz guitar. Then you'll be happy. We all can't wait to be happy.

**rozrosner** · 03-09-2009, 02:35 AM

Guys, check out this blog blurb about a 2-watt, push-pull, Fender deluxe inspired 6G6 amp (ZABS blues PP 6G6). I have not listened to the sound clip. It's a bit down the page.

http://tubeknoppert.blogspot.com/

Without getting into the whole subjectivity-of-tone debate, can you think of reasons not to believe that this guy built a "good" sounding 2-watt, push-pull amp using 6G6 pentodes as power tubes? Do 6G6 tubes have some inherent disadvantages as power tubes that more commonly used pentodes don't (other than power issues)? Thanks.

**Steve Conner** · 03-09-2009, 11:06 AM

Sorry, but it's impossible to answer your question without getting into the subjectivity-of-tone debate, because you said "good-sounding".

Ultimately, probably any combination of tubes will make some kind of noise that some blogger somewhere will be inspired to wax lyrical about. Heck, someone probably even bought a Metasonix F**ing F**er:

http://www.metasonix.com/index.php?o...ask=view&id=36

I'll pass on the challenge to make a sweet-sounding amp entirely out of 2D21 thyratrons, though

**Enzo** · 03-09-2009, 10:52 PM

2D21s suck, for the real vintage tone, we prefer the 2050.

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"Mini" Push-Pull Amps - Limitations of Triodes as Power Tubes

"Mini" Push-Pull Amps - Limitations of Triodes as Power Tubes

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