in the 1970's -I thought a couple bands of parametric EQ were interesting & really useful for bass "tone"
Back in late September of 2017 TI decided to sell the EVB's for several of their high powered class D chip amps for half price. This fact was picked up here on this forum creating a feeding frenzy for their EVB's. OK, a 600 watt amp board built and tested was under $100, so I got in the middle of the frenzy. Unfortunately, this overwhelmed TI and their offshore builder of the EVB's. I placed my order in early October and did not get my EVB until December. During that time, I got a couple emails explaining the delay and one that offered me the Side Gig for a similar discount. I was more interested in the nice looking knobs on the unit in the picture than the guitar preamp itself, so I ordered it. I was not amused when it arrived with no knobs at all.
It arrived long before the 600 watt amp EVB that it plugs into did, so I emailed the creator to get enough info to hook it up to a tube amp. He explained that there were a few other "Side Gig" projects created by TI engineers to use with the class D amp EVB's. None of them were officially endorsed or supported by TI and neither was the guitar preamp. My guess is that it was a cut and paste design with the "best of" from several of the creators favorite solid state amps. I did tube amp "designs" that way when I was a kid. A Fender preamp section feeding the vertical output stage from a TV set was a popular "design" for me as a kid and all the parts were free at the local trash dump.
The guitar Side Gig did let me know that I could drive the two channels of a Tubelab SSE board out of phase with a push pull OPT wired across the two plate connections to create a screaming guitar amp capable of squeezing over 50 watts from a pair of Chinese 6L6GC's. It didn't sound too bad either as long as you kept the Side Gig far from the distortion zone and drove the SSE hard enough to get the distortion.
When the big class D EVB showed up I played with it for a while and played it loud enough to make me think that I had blown my "blow proof" speakers. Then I hooked up the Side Gig and fried a couple of cheap speakers to death. The "blow proof" speakers turned out to be OK, I had just rattled all the mounting nuts loose. There are now two nuts on each bolt. Neither the Side Gig or the monster EVB have seen power since, but the EVB will wind up in a powered subwoofer if I ever get to building it.
I've never had that luxury. It sounds nice, though!
I'm not really a bass player, though I know enough to work out and lay down bass parts on my own original songs. The only bass guitar amplifier I own is a little Acoustic B20 bass practice amplifier ( https://reverb.com/item/37011568-acoustic-b20-1x12-bass-combo-amplifier ) bought a decade or so ago.
For a budget 20-watt amp, the B20 has surprisingly good tone - and four-band EQ (bass, low-mid, high-mid, treble). Not parametric, but there's still lots of tone-shaping ability.
I'm not very fussy about my bass tone. My main concern is to make it audible in the mix, without having to
Acoustic (a brand name that died decades earlier) were trying to come back from the grave at that point, and I think their first few products (including the B20) punched well above their weight category.
-Gnobuddy
I'm not really a bass player, though I know enough to work out and lay down bass parts on my own original songs. The only bass guitar amplifier I own is a little Acoustic B20 bass practice amplifier ( https://reverb.com/item/37011568-acoustic-b20-1x12-bass-combo-amplifier ) bought a decade or so ago.
For a budget 20-watt amp, the B20 has surprisingly good tone - and four-band EQ (bass, low-mid, high-mid, treble). Not parametric, but there's still lots of tone-shaping ability.
I'm not very fussy about my bass tone. My main concern is to make it audible in the mix, without having to
Acoustic (a brand name that died decades earlier) were trying to come back from the grave at that point, and I think their first few products (including the B20) punched well above their weight category.
-Gnobuddy
I've been using a little Flamma FS06 Preamp for some months, running it straight into a few different flat-response powered speakers. I've been very impressed by the sound quality from some of the amp models in this little box. My favourite one is a model of a Two Rock Coral.
I have never seen a real Coral, so I don't know how realistic the Flamma model is. But what matters to me is that the simulated Coral is beautifully touch-sensitive over a wide range of picking dynamics, and its clean channel is delightfully "tubey" too. I really like that particular model!
There is also the inevitable Fender model (Blues Deluxe, I think). On the clean channel, it produces lovely "tubey" cleans, sounding very much like my real (tube) Fender Princeton Reverb.
Most recently, I've been running the Flamma into the input of my Boss Katana, set to its "Acoustic" amp model. I stuffed a log pot and a couple of resistors into a die-cast box and built a variable attenuator to bring the output of the Flamma down to the mic-level signal the Katana expects.
I don't know how close to flat the Katana's frequency response actually is when set to its Acoustic channel. I'm sure Boss put some corrective EQ into it, but they're still dealing with a guitar speaker in an open-back cab.
Still, flat response or not, I was able to dial up what I think are some really good guitar sounds from the Flamma running into the Katana. (Better than the Katana by itself, IMO.)
I bet this magic little Flamma pedal would sound good running into your monster class D power amp eval board and a FRFR speaker!
-Gnobuddy
What the rest of the picture hows, at least personal analysis is that TI wants to sell their power modules (duh!), they also wanted to cover the Guitar Amp market (so far so good) ,so they commissioned some young or inexperienced Engineer to design "something"
Bet he read some Guitar Amp pages and copypasted "something" to fill the job.
Again: a Tube Screamer (or 90% of it) into a very basic guitar preamp, to which he later copypasted an inverting stage to meet TI chipamp needs (balanced input):
As gnobuddy and others noticed, such kludges are messy at best.
To which I add: Tone Control values are WRONG, yet nobody at TI noticed.
Maybe they didn´t even test it with an actual guitar 😱 , just fed some tone and turned knobs to check they "did something". 🙄
As a general rule EVBs get designed by “Junior Level Circuit Designers”. At least that’s what we used to call them - someone with just a CAD background. The chip designers didn’t usually have the time, and didn't have their work flows set up for board-level design. Apps folks who usually did know what’s going on were flooded with customer questions and stuck routing useless paperwork (spec changes, updating all forms to a latest version) and doing EVB level testing so they didn’t have time to really sit down and design anything (they wished they could, because it would solve a lot of problems customers were having). EVBs became the step child that no one wanted to mess with because it interfered with everything else. Youre just not going to get a world-class reference design.
Well, that's a very interesting (and rather depressing) bit of information. Thanks for your insight!
-Gnobuddy
IMO your hypothesis fits the facts very well. It explains bizarre things like the useless BJT input buffer, and the useless third op-amp.
I think you nailed it! 🙂
-Gnobuddy
I think these TPA-Eva-boards are mostly intended to verify the technical data given in the data sheet by real world measurements. Which is what they obviously achieve. Thus they are not "reference" design claiming the ultimate physical incarnation. They are the reference for the starting point of any serious design. And this guitar pre-amp is just a bye-product to give it some additional support, there is nothing to call home about it.
I agree, there isn't much, if any, redeeming value to it. I revisited the schematic of an amp I really like and own since the 80`s. It's seen more than a fair share of gigging and still my practice and backup amp. The Traynor Bloc 100G has no integrated op amps in it. There are a series of Bi-Fet (directly coupled) stages, and the distortion channel has a pair of clipping diodes feeding back from it`s Bi-Fet output to the JFET source. Although the distortion stage isn't too convincing to me , it`s still pretty good, but the clean channel has a great quality sound to it, responsive, alive and shimmery..pretty close to a blackface era Fender Twin. There is some complex switching and filter networks around the stages, but the core circuit is pretty straightforward..interesting if you have time to go over it.
I recently watched a NetFlix wildlife documentary about "Sea Wolves" (they live on Vancouver Island, swim in the ocean, and hunt on the shore).
A dead whale washed up on one of the island's many beaches, and it made a lot of animals (bears, wolves, eagles, etc) very happy for quite a while. Free food, and in large quantities - what a wonderful thing!
And here, in this thread, you see a dead horse making a bunch of middle-aged men very happy for quite a while. 🙂
More seriously, I think dissecting the failures of this particular EVM guitar preamp is a good learning exercise for many people who might want to build a solid-state guitar amp or preamp. Part of learning analogue electronics is developing the ability to tell a good circuit from a bad one.
(Everybody's favourite electronics textbook - The Art of Electronics by Horowitz and Hill - includes exercises where you have to identify the bad circuits from the good ones. An excellent idea!)
-Gnobuddy
That Traynor sounds very interesting. Do you, by any chance, have a link to a readable schematic?
I found a 'Web page with quite a few Traynor schematics, but the model you described isn't listed there: https://www.thetubestore.com/traynor-schematics
Traynor's are Canadian made, are well loved here, and have a good reputation. But I'm a relative newcomer to Canada, and have never owned any of their products, and am not familiar with them. If you know of any other Traynor amps on the list above that are similar to the Bloc 100G, could you point it out?
Now I'm really intrigued. I've only heard "BiFET" used to describe a semiconductor manufacturing process used to create both FETs and BJTs on the same substrate. I think the only context in which I've seen that term used was to describe op-amps that have FET inputs and BJTs elsewhere.
Were there discrete devices called Bi-FETs? Maybe like a Darlington pair, but with one of the two devices being an FET?
Can you point me at any information about the BiFETs used in the Bloc 100G?
Wow. That's practically the holy grail of "clean" tube amplifier tone. If that Traynor gets anywhere in that vicinity, that's pretty impressive!
A few years ago, in another diyAudio thread about solid-state guitar amplifiers, diyAudio member mjd_tech said he uses the made-up word "gling" to describe the sound of clean tones from a Fender Twin or similar amplifier.
I like mjd_tech's made-up word a lot. It's onomatopoeic (a word that sounds like the thing it describes, like "meow" or "purr" or "tinkle".) To me, the sound of the word "gling" does somehow capture a little bit of the sound of those amplifiers.
Anyhow, I've never heard "gling" from any analogue solid-state amplifier. If the Traynor Bloc 100G has "gling", that is a pretty amazing achievement on the part of the designer(s).
I do hear "gling" from my Boss Katana 50 set to the Fenderish channel, and also from the little Flamma Preamp on both the Fender Deluxe and Two Rock Coral amp models. Those are the first two solid-state products from which I've heard anything like this.
Intriguingly, some of the newer reverb pedals (which include "shimmer mode", "modulated reverb", and other DSP trickery that has nothing to do with actual acoustic reverb) seem to be able to warm up the thin, cold, steely sound of a too-clean solid-state guitar amplifier a bit, adding something that sounds a wee bit like a tube amp.
I suspect the sprinkling of additional frequencies created by these pedals pleases the ear in a way similar to all the additional frequencies generated by slightly nonlinear tube amps. And there's no additional harshness at all, unlike the result of any kind of actual clipping or waveform distortion.
I've been surprised and pleased at how good my Flamma Preamp sounds, run through a Flamma Ekoverb (set quite subtly), and then run into a Katana 50 set to its Acoustic channel.
The Katana has its own reverb and delay, and those sound very good, in an entirely conventional way. The Ekoverb, with toggle switch set to the middle position, brings something else to the party, something that somehow adds a little more tubey "grain" to ever-so-slightly overdriven clean tones from the Preamp.
The manual for the Ekoverb says that this setting (toggle switch in the middle) provides "Analog real echo delay combined with modulated reverb effect".
I think it's the "modulated reverb effect" that's producing the benefits I hear.
-Gnobuddy
Yes the basic circuit can be individual components and is sometimes described as a Bi-Fet amplifier, but they are also available as integrated pairs. The Bloc 100G uses individual FET and PNP BJT connected as directly coupled. I linked above the Bloc 100G circuit diagram. It`s not a great scan but readable for the most part. I like the idea of this type of ''gain block'' as an alternate to op-amps. Not to say that op amps aren`t useful, but as with the EVM board, there`s a ton of generic circuitry based on op-amps used in solid state guitar amplifiers..which sound pretty much the same.
Thanks a lot!
Now I need to find a little time to study that schematic a little more closely.
I think op-amps were an incredible invention, and they work wonderfully well in a lot of applications. An almost-perfect linear amplifier in a tiny package for a buck or two - what a gift!
Unfortunately, IMO, there is one place where they do not perform well. Op-amps, in standard textbook configurations, are just not well suited to guitar amplifiers.
A discrete design is much more complicated that dropping an off-the-shelf op-amp into a schematic. Parts count will be much higher, and you actually have to know about things like biasing and operating points, and how to calculate them.
Looking at the crudely slapped-together Sidegig schematic, with its plethora of blunders, I wonder what percentage of EEs today have any idea how to design an audio gain stage without using an op-amp. Many of them will never have seen any semiconductor device other than a microcontroller or microprocessor. Never mind an entire discrete analogue audio amplifier.
The good news is that DSP simulations (tube amp models) are getting really good, and starting to become really affordable. Microprocessor simplicity with discrete-device sound quality is a winning combination for manufacturers, and for musicians too.
The little Flamma preamp has opened up a whole world of new guitar playing techniques for me to study and work on. Now I can finally dial up Gary Moore guitar sounds at apartment-friendly volume levels, which I've never been able to do with actual tube amps.
-Gnobuddy
Now I need to find a little time to study that schematic a little more closely.
I think op-amps were an incredible invention, and they work wonderfully well in a lot of applications. An almost-perfect linear amplifier in a tiny package for a buck or two - what a gift!
Unfortunately, IMO, there is one place where they do not perform well. Op-amps, in standard textbook configurations, are just not well suited to guitar amplifiers.
A discrete design is much more complicated that dropping an off-the-shelf op-amp into a schematic. Parts count will be much higher, and you actually have to know about things like biasing and operating points, and how to calculate them.
Looking at the crudely slapped-together Sidegig schematic, with its plethora of blunders, I wonder what percentage of EEs today have any idea how to design an audio gain stage without using an op-amp. Many of them will never have seen any semiconductor device other than a microcontroller or microprocessor. Never mind an entire discrete analogue audio amplifier.
The good news is that DSP simulations (tube amp models) are getting really good, and starting to become really affordable. Microprocessor simplicity with discrete-device sound quality is a winning combination for manufacturers, and for musicians too.
The little Flamma preamp has opened up a whole world of new guitar playing techniques for me to study and work on. Now I can finally dial up Gary Moore guitar sounds at apartment-friendly volume levels, which I've never been able to do with actual tube amps.
-Gnobuddy
It can be as complicated or as simple as necessary, IMHO. A discrete design would involve a bit more work, but for DIY purposes, there's less of an issue dealing with component tolerance spread compared to a design for mass production. For example a single channel discrete preamp that sounds good both cleanish right up until overdriven would be useful and simplify the circuitry a lot.
Hey, what´s the problem? Easy-peasy. 🙂
Oh! .... you said today 🙁
(Instantly feeling like old Pawnshop or Salvation Army store material) 🙁 🙁 🙁