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What makes for a good clean channel?

Started by edvard, February 15, 2021, 05:10:37 AM

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One of my favorite stories is about Ken Bran, a designer for Marshall.  He went on to design his own line of amps, the NARB amps.   He reported once that he had a set of Fender transformers on his shelf and decided to put them in one of his amps instead of the Marshall ones.  he said it still sounded like a MArshall.


Can the same be said about some of the more recent Marshalls ? A couple of threads about JCM2000's over at MEF right now. Seems like the quality of transformers used by Marshall has gone down. Has just the reliability changed, or has the sound changed also.


Quote from: joecool85 on February 17, 2021, 11:17:29 AM
Quote from: phatt on February 17, 2021, 01:00:58 AM
Quote from: joecool85 on February 16, 2021, 08:53:42 AM
For me the short of it is yes, sparkly clean but with tone shaping.  Normally a -10db dip in mids, centered around 600hz.  After that it is up to preference if you drop lows or highs.
Hi Joe, Your observation is correct but sadly it is only one piece of a much larger jigsaw puzzle.
If you insert that tone curve into a generic SS amp it won't sound like it's valve equivalent.

He asked for a clean channel, I figured he meant just preamp.  If that is the case, I stand by my argument.  Of course, taste/preference is relative.

I do agree about what you said though.  I've not tried using a transformer for speaker output, but I've thought about it because I constantly hear about it's magical properties.

Per my (admittedly limited) knowledge, since it's SS, much of the "magic" has to happen in the preamp.  If one wants to mimic power supply 'sag', or speaker reactance, it's gotta go before the power amp because that thing is linear all the way, toots... 

Transformer output is particularly intriguing, because in my mind, it promises to deliver just a little of that non-linear "magic" we hear so much about with tubes.  I am leaning toward a MOSFET power amp due to MOSFET designs being relatively simple to build, but I think it might also be a little easier to design around a transformer output.  However, I don't doubt I may be plenty wrong about that.  Searching around the internet, the general consensus reaction to the idea of transformer output on a Solid State amp is "But why?", and I guess they kinda have a point, I mean why use a transformer if the chips can drive a speaker directly?  MOJO, that's why!   :trouble

That said, if anybody has any MOSFET-with-transformer circuits, send them my way, especially if it uses one of those 70-volt PA system transformers; I have one, and they are pretty cheap as far as audio transformers go if I want another.


IM Experience, the easiest way to get close to what a transformer output can do is a Compression and Cab
sim circuits.
A cab sim is not hard to make as anyone who has built 9volt pedals can do it. It's a whole lot easier to do that than trying to work on the hardest part of the Amp where there are high currents and any mistakes can be expensive. A SS driven OTx won't give you the distorted PI like a real Valve circuit and SS PA uses Very stiff Power rails while Valves PSU is loose,, Hence the SAG/Compression.
And remember this;; Valve amps only really sound good when driven at higher volumes as that is when all the mojo they talk about really happens, at lower volumes it's not so obvious. No SAG. A lot of Valve rigs now come with a master volume but many will tell you that it tends kill off the magic of the power valves and OT compression magic.

Here is the circuit for my Phatt Box which is the mictester Compressor and a cab sim all
in one box. Cab sim is loosely based on the Nobels SST1 which is similar to the old Rockman.
If I was to build this again I would change a few things so feel free to experiment.

Without the Cab sim the guitar sound is ok but you will never be able to cut through (as they say) when you need it. This is where relying on your tone controls is not enough.
Even a bright switch will add way too much hi freq hash,, especially if the bandwidth is already too wide for OD guitar sound. Yeah you might cut through but you will sound like crap.  :-X
Listen to some Santana,,, 90% of that magic smooth sound is actually under 1khZ

I worked out long ago that if you insert a compressor after distortion then you get close to what happens inside a Valve Power stage. Run that through a limited bandwidth (Cab sim) then even into an average guitar amp can sound quite slick.   

I have a few Valve amps and yes they are very good at the magic compression at high volumes but my  setup is light and can do a fairly convincing impression of an overdriven guitar sound,, as well as crystal cleans. And it's the same at any level.
I play with other people who might want to sing ballads then next up someone wants to play ZZTop.
Not a problem for me. 8|

There are plenty of proven SS power amp circuits that will do the job and super clean PAmps can be an advantage.
Take EVH as example, early on he used a Valve head driving a power resistor then tapped a line signal from that into a couple of 400Watt SS power amps which drove the massive speakers. So if you analyze that for a while it's really the same as an OD pedal driving into a SS power amp. The advantage with EVH idea is that ALL the tone/Bwidth/compression is done by design in the Valve head, he just needed a clean power stage at the end.

All I have done is used pedal circuits to replicate the Valve head dynamics,, It won't win prizes but does a good job.   

Doing the tricks in preamp circuits can give you much more feel at lower volumes even with the most basic SS power chip Amp.

Also a pic of my main rig the pedal board is mostly DIY as runs from a Computer PSU which gives me 18V and regulated down for 9V. Although the Lappy PSU is not Earthed I've added an earth to the Secondary output as I've found that does help keep the humbugs away.
This whole setup is extremely quite even with all 3 dirt pedals on, helped by the fact that I don't use Dirt pedals with the Gain up high. 
You could build this all in a head if you don't like pedals,, but you will still need a control pedal,, winky ;)