Question regarding Merlin Blencowe's Tube Premp Book- Ch. 14 Topologies Opinions??

[silverfox]

Just wondering if anyone has ever built or if there are any commercial amps out there with tones similar to the ones listed in Chapter 14 of the Designing Tube Preamps 2nd edition; Generally speaking of course.

I'm trying to settle on two channel designs for for a build. Right now I'm considering a Train Wreck for the high gain and a Fender Bassman as the clean channel.

I would like to get an idea as to the tone character of those listed in the Preamp book though... Guess you would need to have read the book or able to look at Ch. 14....

Silverfox.

[wyatt]

I don't have the 2nd edition (and the 1st doesn't have a Chap 14), but multiple channel amps work best when...

A) The rely most heavily on the preamp for tone and overdrive (dedicated master volume amp designs like Mesa, modern Marshall, etc.)

OR...

B) The channels can easily share a common PI and power amp.

Neither of your amps fit these categories. While I have to make some assumptions (you didn't say which era or circuit your were considering for the Bassman), you've picked too amps where the PI design and as a result power amp design have a MASSIVE impact on the final amp tone. I can't see a Bassman...or any amp...being able to match up well with a good Trainwreck circuit, the latter is designed right to the edge of stability and can run away real easy if everything isn't *just* right.

Though, depending on the Bassman circuit, you could probably find some pair-able preamps. I believe you want to focus on a high-gain channel is more "modern" and preamp-centric....Mesa, Soldano, JCM or any of the dozens of modern high-gain amps.

[eschertron]

+1 to what Wyatt says.

I gave a look-through at ch14 last night, and if you compare the 'low gain' example to a Fender Champ you'll see right away it's the same circuit. Pretty much all the classic Fender designs are the same up to the PI and power stage. This is exactly what Wyatt is talking about. The character of a Bassman is not in the preamp. It's in how the output is overdriven. Without the characteristic distortion - and by distortion I mean the slightest nudge into the output headroom that starts generating harmonics - and without the characteristic sound of those early under-rated OTs, any amp you build with the basic 'low gain' input is just going to sound anemic.

If you desire to see the evolution of amp design, then look at as many schematics as you can get your eyes on - Fender, Marshall, Soldano (for examples) are related to each other, as later designs evolved from earlier designs. And yes, they match up pretty well against Merlin's 'archetypal' preamps shown in his book. Then find recordings of the amps that you've identified as fitting into the types that Merlin discusses.

Analyzing preamp topologies by looking at schems is a great way to intellectualize designs<->tones. Be aware of the timeline and the evolutionary path these designs took.

As far as pairing preamps in a gigging amp, keep in mind that the book you mentioned is a preamp book. Power stage distortion and tone was not mentioned because it was outside the scope of the chapter.

The other part of the amp evolution is that as amp designs became "uber" gain, the power amp became less relevant. Wyatt's comments about matching a low-gain design with a high-gain design hits the mark here. Contrary to a Bassman (or similar design) that depends on the output to provide color, a super-distorted preamp wants the power section out of the way; a big SS output section that provides wide bandwidth is the way to get all that sound out into the open.

So consider the whole amp when you design.

[pdf64]

'without the characteristic sound of those early under-rated OTs'
I agree with the main thrust of the advice to consider the system as a whole but the above doesn't seem to sit happily with my (limited!) understanding - the bassman type OTs seem suitably specified, at least for guitar frequencies.
41Hz at full power may result in saturation of the magnetic circuit though.
Which of their specs / aspects are thought to be under-rated?
Pete

[eschertron]

'without the characteristic sound of those early under-rated OTs'
I agree with the main thrust of the advice to consider the system as a whole but the above doesn't seem to sit happily with my (limited!) understanding - the bassman type OTs seem suitably specified, at least for guitar frequencies.
41Hz at full power may result in saturation of the magnetic circuit though.
Which of their specs / aspects are thought to be under-rated?
Pete

Ah, Pete. You caught me happily spewing unconfirmed and generalized claptrap.

WRT the Bassman, I will concede that the OT aught to be sized appropriately for design amplitude signals into the bass guitar range (after all, it's a Bassman, innit?). My personal familiarity with Fender's OTs ends with a few Champ-type circuits, and beyond that, only what I've gleaned from the internet. I think the point I was trying to make was that drop-tuned seven-string death metal is going to sound unconventional through a Fender power section. I hope I'm not too far off with that.

[silverfox]

Output section Design

Thanks for the comments and information. As for searching schematics and tones, I've done that so much I probably now suffer from information overload. Too many conflicting thoughts and must consider all the data. This is most helpful.

I have some older Iron and upon disassembly have noted the quality of construction as well as understand the influence material composition has on the tone. I have also read an article discussing improvements on Fender power supplies that resulted in a loss of Mojo. That being taken into consideration:

Is it possible to use relays to switch out components in the output section, influencing power stage harmonics for each channel, or is impracticable?

Silverfox.

[eschertron]

Is it possible to...

Anything is possible! Beyond the engineering nightmare of hooking an array of different devices together and making them all compatible, The sheer weight of an amplifier containing multiple output sections would make it unwieldy unless the artist has a road crew high on steroids.

To sidetrack a little, this thread is starting to sound like the stereo amp thread that you commented on recently, In which you pointed out that many well-known players feed their guitar signal into multiple different amps at the same time, switching between or combining the sounds for the effect that they want.

There's no shame in collecting (or building!) the amps that you want, and setting them all up to play through singly or in combination. And the modularity of the system makes it easy to modify, not to mention carry it around!

[loudthud]

Take a look at the Kendrick Joyzee amp, there is a pdf floating around. It combines a Trainwreck and a Fender type preamp with reverb.

[silverfox]

Composting a final output.

...this thread is starting to sound like the stereo amp thread that you commented on recently, In which you pointed out that many well-known players feed their guitar signal into multiple different amps at the same time,...

I'll clear up some details but first, I will definitely check out the Joyzee amp.

First, I'm not a purist on this particular amp design. Which is to say, if using a Train Wreck preamp design into an AB763 power amp sounds great, that is all I need. In this instance I don't need the power amp distortion. I only play for my own entertainment and not out at all. Perhaps some day.

Ultimately what I'm going to end up doing is bringing the pre amp outputs to separate lines out. From there I'll process them through a mixer and then bring them back into the power amp. This also give the ability to add effects from the mixer which tend to create an electronic hall environment; my opinion...

This should give me the ability to try different effects and gain settings simultaneously on the two channels, then blend them. I don't need the stereo out but for the ability to mix composites into a final tone.

As for lugging heavy Iron, I don't think I've mentioned yet that I've replaced the transformer set from the 160 watt Road Master with a 40 watt version of a Fender power transformer and the 6L6 output transformer from a Univox 1221. With the effects unit I have driving the Fender style power amp it sounds very good and weighs much less than originally. It will also get loud enough for me to enjoy.

That's where I'm going with the project. Off to search out the Joyzee...

Silverfox.

[silverfox]

Joyzee as in New Joyzee

Found the schematic over on Amp Garage. Couple of different pdf's. Thanks for the direction...

Silverfox.

[pdf64]

A key thing regarding tonal balance and power amps is global negative feedback.
Without it there tends to be significant interaction between the amp and speaker, mainly due to speaker impedance varying with frequency.
The effect of this is more bass and treble.
The pre-amp may require tweaking to compensate for this, or a presence control adding to the power amp.
Pete

[Beefcake]

I wonder if it would be possible to change an output stage's topology using relays. I guess that would make it possible to have a Trainwreck and Bassman in one amp.

[kg]

I wonder if it would be possible to change an output stage's topology using relays. I guess that would make it possible to have a Trainwreck and Bassman in one amp.

nearly impossible to do without switching noise. you're going to have to add a lot of housekeeping circuitry...

ldrs are a lot easier to do noiselessly but they have lousy characteristics (on isn't really on, off isn't really off).

[printer2]

Late to the party again. Been wallowing around in the acoustic guitar building end of this wonderful guitar world and guitar amps have taken the back seat. Hope you don'y mind me throwing in a schematic I drew up a while back crossing a Marshall Plexi with a Train Wreck. Of course there are a number of different TW schematics out there and a Plexi is just a modded Bassman, so view this as just a design exercise, I do this kind of stuff when I need to distract my mind.



I have some mini four pole toggle switches that are commonly available and limit the schematics to them. Whether you can practically lay out a design with them, especially a high gain amp, well I have not tried it yet. Actually looking at it, doing a Bassman might allow you to drop one switch for the input cathode, and not use one pole to put some distance between two signals.

[silverfox]

I see the Light- LDR's

I don't have extensive experience with this however, the Peavey Road Master I played through prior to donating to scientific purposes seemed to switch very nicely using LDR's. With all due respect, what are your thoughts on that?

Silverfox.