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Messages - teemuk

The maximum 68 watts RMS of LM3886 is not my idea of transparency unless you happen to have a very efficient speaker system. Even my 2 x 75W amplifier starts to distort notably when i turn it to a point where it can compete with a drummer. Besides that LM3886 is equipped with protection circuitry (SPiKe) that isn't very ear-pleasing when it happens to kick on. I have heard several comments on LM3886's trasparency and i do not doubt them but the truth is that those comments have come from people who use their amps at "normal" listening levels. Granted that with a good and efficient speaker cabinet 60 watts might be adequate for stage use, but transparent? No way.
I think it's quite impossible to find such thing as a "transparent SS amplifier" - it's actually impossible to find a transparent amplifier whether it's SS or not. I mean, it's possible to have something very close to one with either highly sensitive speakers, low listening levels or hundreds of watts of power but an average musician probably has neither one of these in a real-life situation. When you have to play with a drummer and use your amplifier as a monitor it will surely distort in some way. This is where the major difference between tube and transistor amplifier's really starts to matter.
I think reading the Russell O. Hamm's article is worthwhile too. Both articles are quite old which leaves lot to argument about, still i think that the authors have nailed the main issues quite right. Now, today's transistor amplifiers are indeed more developed but (unfortunately) a huge part of that development has been happening on audio reproduction area: Numerous ways to lower the distortion in transistor amplifiers have been developed and as a side effect the clipping's "knee" has become harder and circuits more complicated. Opamps are a good example of this - actually many of todays power amplifiers are mainly like high power opamps. It could be different.

What's concerning is that Biggest guitar amp manufacturers still tend to make their designs based on the principles of audio reproduction when they should concentrate on the character of guitar signal instead: To avoid clipping, increase sustain and "psychoacustical power" the solid state guitar power amplifiers really should have a built-in limiter circuit. It really should be mandatory and how many of them have one: I can come up with only few and there are thousands of amplifier models out there? Bass amplifier designers seem to have noted this shortcome but they are lightyears ahead in some other issues anyway: They exploit crossovers and biamping while guitar amps still rely on principles developed on 50's or even earlier. I hate the modern attitude that selling an amplifier actually means selling a complicated preamplifier hooked to a mediocre power amp and cheap speaker system. This is cheap for manufacturers and makes a lot of profit so why change it - the pro consumers are not the main source of their income.

It's quite strange that the article mentions the power response issue to a frequency dependant resistance (impedance) since it really isn't that big deal and mixed-mode-feedback amplifier design has been around for few decades. Rod Elliott has made a nice article about it, which is definitely more worthy reading than articles about transistors vs. tubes:
Other way around the poor impedance matching would be to use an output transformer's or chokes but it is quite expensive and people are used to design based on "modern" transistor guidelines.

Teemu K
Quote from: joecool85 on March 28, 2006, 07:48:33 AM
I'd have to double check, but from what I remember, the first half of the TL072 is a buffer.

No it's not: TL072 Contains two separate opamps that share the same supply. The first stage of an opamp is always a differential amplifier not a buffer - unless we are talking about a special IC, which TL072 definitely isn't. Note that all TL07x IC's are packed in a standard opamp DIL package: Following this logic, TL071 contains one opamp and TL074 four. The first half is a buffer only if you connect it to be one, see:

The input impedance of K-20X seems quite small (220k) for a guitar use. (The common rule of today is that the impedance should be more than 1 Meg). I have never tried K-20X so i don't have experience of it's tone but i seriously doubt the need of separate buffer. The guitar signal can hit opamp directly as well as it can hit a buffer if the input impedance is set correctly and all "safety precautions" are taken into consideration. Placing the buffer before the guitar cord is a different matter. As far as i see it, this preamp should be good as is.

Sorry for being off-topic.

Teemu K
Amplifier Discussion / Re: What have you guys built?
March 28, 2006, 07:23:20 PM
Be careful not to focus on one thing [preamp] too much when you really should see the whole picture. Basically, i feel that the things that have an impact to the tone of a (solid state) amplifier are: a) the voicing of the preamplifier, b) the amount of distortion (and it's spectrum) in the poweramplifier and c) the speaker system. Mess up one of these three parts and you have an amp that sounds crappy no matter how good the rest of the design is.

Teemu K
Schematics and Layouts / Re: Several SS Amps
March 28, 2006, 06:58:24 PM
Some solid state schematics here too:

SLM (Crate and Ampeg) schematics here:

Despite the name Dr. Tube page contains some solid state schematics:

Standel schematics and service manuals:

B.B. King used Lab series amplifier and Wes Montgomery used a Standel amplifier. Lab series amps are considered as one of the best SS amplifiers and they were used by many other big name acts too (unfortunately I can't remeber who). Standel was basically a huge innovator of all SS guitar stuff. (If i recall correctly they were the first company that manufactured a solid state guitar amplifier).
Then the SS Vox gear: Beatles used it at a time since it was "hip" and Status Quo used SS Vox AC30's.
I also quite often see some SS stuff from Crate used by metalheads.

Teemu K