Baubericht Steel String Singer

Hallo Zusammen,

ich hatte das Projekt Steel String Singer auf Eis gelegt, da mir die Motivation dafür irgendwie fehlte. Nach längerem Hadern möchte ich die Sache jetzt doch angehen.

Boards und Chassis sind gerade eben angekommen:

Das Chassis geht bald wieder weg zum Lutz Kunz. Wird aber noch etwas dauern. Mein Budget ist erst mal aufgebraucht.

Ist ein ziemlich aufwändiges Design für einen Einkanaler mit "nur" einem Cleansound. Ich bin gespannt...

Gruß

Gerhard

Null Problemo. Unter #002 kucken.

Steel String Singer

Viel Spasssss

G.

Quote from simon.bethke

Gibt es unten links nen schalter für den Nord Deutschen Rundfunk, NDR?

LOL, ist mir noch gar nicht aufgefallen. 😂

Quote from MAD

Interessantes Projekt, steht bei mir auch auf der "muss ich mal bauen" Liste - aber da steht so viel drauf

Ja, der stand bei mir auch lange drauf. Es gibt auch mehr oder weniger abgespeckte Versionen davon. Z. b. ohne Kathodenfolger Phasendreher und einen Fender Standard Reverb. Dadurch spart man sich 2 Röhren. Dann ist aber genau das weg, was den Amp ausmacht. Das ist dann nur noch ein aufgebohrter Twin.

Moonshine

Hier eine Erklärung aus der Ampgarage, die für mich schlüssig klingt:

Quote

I was just thinking about what happens when you drive a grid from a low impedance.

The low impedance can charge and discharge the effective grid capacitance faster. The effective grid capacitance is the actual grid-to-ground capacitance plus the Miller capacitance - the grid to plate capacitance times the voltage gain. For pentodes and power beam tubes (EL34 and its ilk, and 6L6 respectively) the grid to plate capacitance is low - that's the reason there is a screen grid in the first place.But whatever the capacitance is, it has to be charged and discharged before the grid field can change the electron flow from cathode to plate. It's like rolling a rock over a garden hose to squeeze off the flow. Light rocks (low capacitance) are easy to roll, heavy rocks (high capacitance) are harder to roll. Hence, it needs more or less force to overcome the weight (capacitance) to modulate the flow. Using a higher-force rock mover (i.e. lower impedance drive) can speed things up. So using a low impedance follower can drive grids faster and ought to improve high frequency response >if< it's being slowed down by grid capacitance.

That only helps if the grid is operated below Vgk=0. When you make the grid positive with respect to the cathode, electrons are no longer repelled by the grid and some of them start sticking to it as the flow passes. This is grid current. To make the grid go more positive, you have to pull these sticking electrons off the grid by pulling them off with current. The effective grid impedance goes from the grid itself - near infinite impedance - paralleled by the grid leak resistor (which is there to pull off the odd sticking electron in the Vgk negative operations) down to as low as a few K ohms.

Most tubes will continue to increase plate current with the control grid driven modestly positive, as the positive grid sucks the electron flow from the cathode towards the plate. This is something that the screen grid does as well, and for the same reasons. But now even more electrons get sucked into the sticking to the grid itself, and you have to pull those electrons off the grid to keep it positive. That is, you have to supply grid current.

As long as you can supply enough current into the grid to pull the sticking electrons off and so long as the cathode can supply enough electrons, current increases.

What this does is stop the flat-topping distortion that happen when you can't supply enough current to the grid, and the grid stays flat at Vgk=0. When a high impedance driver lets Vgk stop at 0 because it can't supply the current, electron flow stays where it was at Vgk=0 (duuuh) so you get a flat, hard transition on the peaks that hit positive grid voltlages. This is quite different sounding from the compressed distortion of a tube nearly turning off.

This makes a difference in Class A amps, but not in Class AB, because the important parts of peaks in AB always involve the opposite-side tube being off. So supplying low impedance drive can make for a softer distortion in class AB output stages.

And it occurs to me that this is the answer. It's not whether you are in a 10W, 50W or 1000W amp stage. What matters is whether the amp (1) needs the extra high frequency capability that a follower can provide and (2) whether the output tubes clipping at Vgk=0 limits the output or not. If something else limits the output tube plate current before Vgk=0 does, you won't hear it. If you're banging on Vgk=0 with grid drive, a lower impedance drove as in a follower will soften the clipping.

A clearer form of the answer is that if you're driving output tubes with enough voltage on the grids to cause Vgk=0, and it would go more positive with more current drive, then followers will soften grid clipping distortion and provide a bit more power. Amp power doesn't matter so much as the size of the grid voltage drive relative to grid cutoff voltage.

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Quote from Hendrixianer

Das ist wohl Teil des Designs,ultra clean zu bleiben,gedacht für Amps mit mehreren parallelen Endstufen Röhren,der pi überteuert, zerrt hier halt nicht,so kannste die Kiste bis zum Arsch aufreissen,und die bleibt clean

Yeah, genau mein Ding, Baby...

Quote from Hendrixianer

Lothy: Was nimmst denn da jetzt für Trafos? TT? Dumble style? Oder die Hiwatt Teile von denen?Oder doch was anderes?

Ich nehme sehr wahrscheinlich die TT Dumbo Teile. Dafür ist das Chassis auch ausgelegt. Mit den SLO-Trafos von TT habe ich sehr gute Erfahrungen gemacht.

Hendrixianer gehts so mit dem Deppenhobel?