Construction Practices

[Reeltarded]

I have an intern starting next week. Stop equalizing.

NO

[martin manning]

Being serious for a moment, the fundamental difference is that in Hi-Fi the intent is to reproduce a recording or broadcast as precisely as possible, whereas in an instrument (MI) amplifier the intent is to color the sound significantly with distortion. The pre amp, the power amp, and the speakers are all players in this. Both construction practices and circuit design features have been brought up, and both can contribute to the sound quality (or the lack thereof in the eyes of some). Operating at the edge of instability can be a good thing sonically. The observed practices may also be driven by economics. For example the Hi-Fi market will pay for minute improvements in S/N where buyers of MI amps will not. There are some special cases where more Hi-Fi-like practices are followed in MI amps, most often when a relatively clean high-power output section is desirable, such as for bass or steel guitar, but some of the most iconic guitar sounds were created with small, simple, and very over-driven amplifiers.

[VacuumVoodoo]

When asking about construction techniques in guitar amps and apparent non-optimality, one must remember the extremely fine lines between laziness, idiocy, and genius.

You just made me realize I'm walking in circles...

[Ken Moon]

Ned,

There are thousands of pictures of amps on here and other forums, or just by googling "amp guts" you can look at thousands more.

There are many ways to build an amp, from PCB to point-to-point to eyelet board to turret board, with a zilllion variations on each theme.

If you're looking for a "standard" or "most popular" way to build DIY amps, look at the pics on ceriatone.com or any of the sites that sell amp kits.

The turret board-based amp in an aluminum chassis with stand-up transformers is popular because all of the parts are available from multiple sources, there is a lot of reference material on amp forums such as this one, and they can be built without spending a fortune on tools.

If you don't know what some of these terms mean, spend more time searching and reading, then come back with specific questions, and there are plenty of nice people here who will help you understand. But asking open-ended questions with no sign that you've tried to figure it out yourself first, will get you the brush-off every time.

You should also know that the typical amp using good quality parts will cost about $600 plus the cost of an enclusure, and be prepared to spend at least a few months of studying to get up to speed, so don't go looking to build a nice DIY amp for less or in a hurry, you'll only be dissapointed.

I'd highly recommend getting Merlin Blencowe's books on power amps and power supplies to understand how guitar amps work, and how they're different from hi-fi amps. They are well worth the 50 bucks or so for the pair of books.

Cheers, Ken

[Phil_S]

...I am also wondering why there is very little use of drivers between the phase inverter and output pairs or quads in higher power versions using 6550s or similar.

I admit freely to my amateur status and there are things I encounter that I don't comprehend. This is one of them. The use of "drivers" is throwing me. Sometimes drivers refers to speakers, but this clearly isn't the case. Transformers, another tube, what? What is it? And, assuming it is some sort of buffer, why would we want such a thing? It seems that between the PI and the PA, we just want what we wrought. What am I missing? We certainly don't want to clean up the signal at that point.

[cbass]

I believe hes refering to amps like this with stages after the pi

[Ned]

Yes the Logo picture

[Reeltarded]

They aren't as long as you'd think by looking there. There is a 1/4" of leg or so. No melty booboos. The other ones are just routed to the turrets.

Leads are probably better than wire as far as RF and everything else I can think of at the moment.

[morcey2]

...I am also wondering why there is very little use of drivers between the phase inverter and output pairs or quads in higher power versions using 6550s or similar.

I admit freely to my amateur status and there are things I encounter that I don't comprehend. This is one of them. The use of "drivers" is throwing me. Sometimes drivers refers to speakers, but this clearly isn't the case. Transformers, another tube, what? What is it? And, assuming it is some sort of buffer, why would we want such a thing? It seems that between the PI and the PA, we just want what we wrought. What am I missing? We certainly don't want to clean up the signal at that point.

Lots of bass amps with quads or sextets of KT88s or 6550s have driver tubes after the PI. cbass's post is a good example. One reason that lots of Marshall-ish amps don't have post-PI drivers is that they were designed for a quad of EL34s which don't generally require them. When they started importing them to the US, Marshall was having trouble sourcing EL34s in the US so they started using 6550s, which probably should have had a driver tube, but seemed to do OK without it. At least that's what I've heard from several reputable sources.

Matt

[Reeltarded]

It was all about the BVA, turns out.

The tube mob made Marshalls suck caulk.

[overtone]

Hello Ned,

from here it looks like the caps were mounted with proper regard to the fragility of the leads in this type. The legs are bent out to the turrets after strain-relief-kink in the lead and not right where the it exits the body. That and that the lead seems to be mounted towards the top of the turret makes it look like it has "tall legs" or longer than, say on a pcb mount.

I understand your concern about ruggedness, but this image comes from an amp type that would usually not get into the hands of a high roadie or UPS without a proper flight case, if at all. I think it is fair to say that it has some unusual component mountings, but it is just one representative image of one amp type that most here know well. There are lots of others and individual hand signatures here to see.

As said previously a guitar amp for us like a musical instrument and has a different specification to that of an amp for a different purpose. I am interested in your experience especially as in guitar amps we are often working on the edge of stability, I guess to push to the limits of a system. This has a long tradition going back to when guitarists found how great certain circuits sounded and reacted to types of playing when pushed beyond what was intended. It is a fine line between this "sweet" zone and instability.

Hope that I did not muddy anything. Constructive and left-field thoughts are extremely welcome here.

tony

[Structo]

That Logo picture is pretty small to make any observations from.

Ned, can you upload a better resolution picture as a example of what you are talking about?

[Reeltarded]

In years of torturous traveling without cases I never lost a non-pcb amp to the road. Keep the amps off the dance floor of the truck and no trouble. I have had stacks fall forward onto the stage and when the output selectors are found and reinserted the show goes on. Tubes and all. Miracles? Nah. It just isn't that fragile.

PCB amps handle shocks very poorly in my experience.

[dave g]

I am also wondering why there is very little use of drivers between the phase inverter and output pairs or quads in higher power versions using 6550s or similar.

Most guitar amps don't use drivers because grid clamping on the output tubes is desirable. People typically call it "power tube distortion" and is the holy-grail of electric guitar sound for a lot of people.

[Ned]

No I am not trying to pick a fight or irritate anyone. (Probably will though) I am trying to get an education. So far from the responses I have deduced that (1) when building a guitar amp one should not attempt to amplify what the pickup (acoustic, coil or microphone) is producing with any degree of accuracy. (2) If any stage in the amplifier does provide distortion free amplification it should immediately be hunted down and killed like the misfit it is..
OK.. thanks to whoever put up the schematic with the 7591s and 6EU7 driver. That is a very cool amp, probably low distortion and able to produce a real 30 watt output. I always wanted to Tip my hat to those manufacturers who can provide a 150 watt amplifier fused with a one amp fuse. Thats another story for the power supply section.

So after reading up on grid clamping.....a term unknown in engineering of my day since it would operate a tube outside of its specifications.... I am asking why drive a control grid so hard it draws appreciable current. It has a hard enough life being so close to the cathode and its wires warp so easily. Wouldn't a simple diode like a 6AL5 or silicon javascript:emoticon(':x') (wash my mouth out) provide the same distortion? I'll wait for the answer for that one.

Oh by the way for the gentleman with the driver fetish. Technically the magnet,vc, spider, cone, surround and basket make up a conventional loudspeaker...shortened to speaker. A driver is the magnet and coil structure screwed or bolted on the back of a horn shaped loudspeaker. Drivers are also seen on highways and in golf bags.

Thanks guys. I appreciate your attempts to educate this old Hi Fi guy who actually played with radios with 01A tubes. Watch it I didnt say I built them.

Ned