New Power Amp Build

[silverfox]

Okay so the last power amp I built, the Carvin, I didn't really like the sound of it after all. It seemed to have too much distortion, as in mushy fuzzy sound; too bassy. In addition, being a first build it didn't really fit well in the chassis after it was done. Since I reused the parts from the Carvin PC board it was no loss and a good experience.

Now I'm starting on another.

The power amp and supply portion of this circuit: http://www.projetg5.com/Projets/MI60/MI60_EVO_beta3.pdf

Most of the supply is done but I'm having some questions. The bill of materials calls for 2 watt resistors in many locations where I've seen 1/2 watt in those positions on other schematics.

Bill of Materials: http://www.projetg5.com/Projets/MI60/BOM.xls

Here is my request: Based on the fact that I'm using 35 Watt Iron- Does this schematic look right and are the resistors over kill.

Would the forum suggest a different power amp that uses similar voltage levels. I can't say why but my intuition tells me this is a good design for a power amp and supply. The reason I've selected this particular build is the Master Volume option if I want it. I've heard a couple videos and I don't think the preamp section has much metal. But then again, this is part of the dual preamp- October build I'm working on. Again, the OT and PT are 35 Watt.

Also, please understand this is part of the original project to build Sluckeys dual preamp build. This will be the power amp section for that build so don't think I'm a project flake... At least no yet...

Thanks again everyone,

Silverfox.

[HotBluePlates]

The bill of materials calls for 2 watt resistors in many locations where I've seen 1/2 watt in those positions on other schematics.
... are the resistors over kill.

Guy must have had a bunch of 2w resistors on hand... or wanted to buy some special brand that was only available in 2w parts. Yes, 1/2w is fine for probably everything except some of the power supply positions.

Note also, the BOM is incomplete, includes a couple parts (but not all) for the master volume, and doesn't have any of the power supply resistors listed... It's just half-done.

... good design for a power amp and supply.

I don't recall form the other build... do you already have a preamp or some other source you're using to drive this power amp? If so, this thing has 2 preamp stages you don't need, as well as a tone stack.

To my mind, a power amp would have an input jack and then C7 and the phase inverter, etc. All the preamplification is done in whatever is driving it.

Well, let's say you are like some golden age hi-fi companies... you might assume the preamp doesn't have sufficient gain, and so you add a single triode stage after the input jack, then a volume control, then phase inverter input.

To me, a post-phase inverter master doesn't make a lot of sense but because I would use the power amp to cleanly amplify whatever my preamp, etc was feeding it. A volume control just before the phase inverter helps ensure the source doesn't blast the power amp if you choose to stay clean (I've used 50's monoblock power amps fed directly from a CD player, which has a high output level).

But maybe someone else has experience with a split preamp/power amp setup they'd like to share. I've only had split components like this in a tube home stereo situation.

[silverfox]

In reference to the question regarding what I need the power amp for: It is for a build of an amp. At this point a Marshall style preamp. Just thought I'd build the power amp first and then put together a preamp.

Still thinking things through. I'll test my power supply today.

Fox.

[silverfox]

In the study of common push pullpower amp designs, (Marshall, Dumble, etc.) I've notice the netwok of resistors between the driver tubes, (phase splitter?) and the power tubes have different values. Bias tap can be 100K or 220K and the resistors connected to the grid can be 3.3k or 5.6k. Sometimes a network consisting of 82K in series with 100k.

From what I've read, these are balancing resistors. Perhaps one network is for balancing and the other is for bias? Different balancing schemes?

How do I determine which network to use, what are the reasons for these different values of resistors. There are designs that do not have both networks.

Fox.

[tubenit]

I'd suggest lowering the post LTPI coupling caps from .1 to .047 or .033 to help eliminate too much boomyness or mush.

With respect, Tubenit

[silverfox]

I may be starting to understand this now. In my last post, this topic I mentioned the balancing network. Huss in his 6v6 Plexi puts a cap in conjunction with a resistor across the output of the LT-pair for balancing.

What your saying tubnit is these cap values you suggested, are filter caps for the input to the driver tubes the values you suggest will improve the tone. I'm looking at several schematics and basically arriving at the same destination as previous wheel designers. But I think I'm understanding wheel design in the process and that's good.

Fox.

[HotBluePlates]

From what I've read, these are balancing resistors.

I don't know which resistors you're referring to.

Huss in his 6v6 Plexi puts a cap in conjunction with a resistor across the output of the LT-pair for balancing.

Not for balance.

You know the real reason he does it? Cause the plexi Marshall amps had that cap.

You know why Marshall used it? Cause the Fender 5F6-A Bassman that they copied used it.

Fender used the cap because it cancels very high frequency output at the phase inverter; -1 + 1 = 0.

Fender supposedly noticed some issues with oscillation in the output stages in some of their Bassman amps (and perhaps others). Rather than test/troubleshoot every amp coming off the assembly line, they installed the cap to kill the frequency range where oscillation tended to happen.