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Messages - phatt

Amplifier Discussion / Re: 12w Marshall
January 27, 2023, 07:23:46 AM
Quote from here;

Under, The limitations of Class D
(near the bottom of page)

"Thirdly — not finally, but enough for now — a Class-D amplifier has a **relatively poor damping factor.** The damping factor is the ratio of the impedance of the loudspeaker to the output impedance of the amplifier (it's a little more complex than that, but let's not get bogged down with details). In simple terms, it's a measure of how well the amplifier can control the movement of the diaphragm of the loudspeaker. A good amplifier doesn't just give it a push and hope for the best; it senses where the diaphragm is from moment to moment and controls its position. To do that, a high damping factor is desirable, and, as mentioned above, a simple Class-D amplifier has a low damping factor."

I think of this much like a Valve Amp where the same power output is delivered to  4,8 or 16 ohm speakers partly because most Valve amps have *Low damping factor*.

So even if you drive an 8 ohm speaker from the 4 ohm tap the power is much the same but freq suffers a little.

Better minds may explain this better but there is obviously a connection.
Amplifier Discussion / Re: 12w Marshall
January 26, 2023, 06:29:02 AM
In answer to Guzzis3 previous Q, Class D  are a switching amplifiers which use a Pulse Width Modulation system.
 They switch so fast that very little heat is generated thanks to mosfet teck, so no need for big heat sinks. 

C0mplikated to ezplain but some info here might help;

The Hotone circuit tricks, after a little bit of analog at input the rest is most likely all done in the digital realm using IR's  (Google *Impulse Response* for clues on that)
Hence each one is programed with a different flavor. ALL the shape and grit is done in the digital chip while the D class output would run clean.

The one I liked most was the "Mojo Diamond" gives a good balance between clean and drive but I've only heard them on the tube.
I'd be waiting till they realise they can make a unit with 4 or more different modes in the one unit but the Diamond would work well with my existing pedal setup.
hope that helps, Phil.
I've heard these at gigs and not so impressed,, very sharp and too much bandwidth to really nail the classic sounds but the young ones seem to like this stuff.
I guess I'm showing my age here  ;)
I have noticed a lot of these Kats come up for sale on gumtree in my part of the world,, humm which suggests to me that they sell on novelty which wares off in a short time.
Amplifier Discussion / Re: 12w Marshall
January 23, 2023, 06:21:47 AM
All good, Just throwing in some observations from my experience sorry if you think it's off topic.
Amplifier Discussion / Re: Add effect loop to jc120
January 23, 2023, 06:19:05 AM
Hi Tassie,
          All good, like you I've not ever been inside a JC amp and just looking at Schematics tiss easy to miss things. I had to scratch my head for a bit to work it out. :-\

Thanks for the info on Enzo, yeah a great mind who was always helping us lesser minds learn from his wealth of knowledge. He will be missed.
Amplifier Discussion / Re: 12w Marshall
January 22, 2023, 01:32:36 AM
Go here for real in depth insight into guitar amp tones.
The end will likely make you wonder why no one ever researched this before.
I've been quietly babbling on about this for years but this chap pretty much puts it all together well.

I'm not a marshall fan mainly because they only have one trick and the tone controls are pathetic. (though I'm sure many will argue) lol

I use an old Laney Keyboard amp which is super clean.
Everything else is done with my pedal circuits, half of those are my own designs

I can produce Hank clean all the way to ZZ top at the press of a button or 2.
If you have built amp/pedal circuits then it will not be hard to work out how it's done when you see the end of the video  8)

The game of guitar tone is in understanding the frequency range the guitar needs. most gear today has insanely wide bandwidth and it totally destroys your tone (Especially for hard driven OD tones).
You have to dramatically limit the bandwidth for rock guitar sounds otherwise it's just one clangorous mush of eFd up noise.
which is why I steer clear of all in one pedal like Boss GT's as they have way too much hi freq crud and tonal adjustment is limited.
Go build some pedals and save a fortune and your back ,,,winky Phil
Amplifier Discussion / Re: 12w Marshall
January 21, 2023, 07:29:07 AM
Hey Guzz,
I assume when you say *Terrible Freq response and then Boss GT8 in the next sentence* then you are maybe chasing the old sweet magic of limited bandwidth valve gear.
This can be done with SS gear but you have to in a different manner than you do with Valves.
Amplifier Discussion / Re: Add effect loop to jc120
January 21, 2023, 07:22:34 AM
Also the Fet pair phase splitter Q1 and Q20 form a limiter circuit so inserting after that may (or may not) cause strange things to happen.

Teemu mentions this limiter but I'm still not sure how it works.
A note,
Sadly Teemu along with Enzo and J M Fhaey don't post much these days but they have a wealth of knowledge if you go searching for older posts. plus a few others, whose names I can't recall right now.
These wonderful members have helped me many times when I've been stuck. 8)
Amplifier Discussion / Re: Add effect loop to jc120
January 21, 2023, 07:03:02 AM
Hi Tassie,
Vr4 And VR10 is the mix point for the 2 power stages, trying to insert a loop at C26/C126 means you will only be able to use one power section. (I'm assuming a mono FX loop is being asked for?)
I think you will find the 84 schematic is a single channel circuit which makes your idea possible but this one is a different setup.
 I assume by the schematic the in/out wires are easy to lift on the unit posted so less chance of stuff up.

For a full run down on all the JC models try this page;
Thanks to Teemu ;)
Amplifier Discussion / Re: Add effect loop to jc120
January 20, 2023, 08:27:41 PM
Yes output of VR10, cut before R19 and R121.
Should work and easy to reverse if it does not work.
Amplifier Discussion / Re: 12w Marshall
January 20, 2023, 08:05:38 PM
Quote from: guzzis3 on January 18, 2023, 09:05:19 PMHi,

If you had to order extra PCBs that you want to sell I'd be very happy to buy them from you. I am in Brisbane,

This is my first post to this forum. I was pointed to this thread by a person on the marshall forum. I've been building electronic stuff since I was a kid but while I have built quite a few valve guitar amps I've not built a SS one.

 Have you determined if the 5005 etc develop their distortion in the preamp, power section or both ?

I realise you haven't finished your design, and there may be problems, but starting even with a flawed PCB is probably easier than laying it out on tag strips or breadboard.

Thank you for reading.
Hello Guzz, just note on SS rigs,
Most do not respond to power stage distortion, some rare ones try to do that but likely not as convincing as a full Valve powerstage.

With SS Amps all the dirt, grit, compression and like attributes of Valve amps needs to be done in the preamp stages.

My main rig is just a basic SS amp and all the magic is done with my pedal board. Most of the pedals are my own design, some of my schematics are posted on this site.

40 plus years back I wanted to build an amp that did it all in one rig.
Took me many years to realize that I was just building land fill.
I now  have draws full of failed ideas (other wise called spare parts 8) )
I have built both Glass and Sand designs and although I like Valves there many benefits to SS designs.

If you are lucky enough to find an amplifier (Glass or Sand) that works for you then lucky you, sadly more often than not you'll spend a fortune trying to find it.

BTW I'm up the road in Morayfield if you want to make contact I'm happy to help with my years of researching. Just pm me for my phone number.
The Newcomer's Forum / Re: Shorted IEC line filter
January 02, 2023, 04:56:33 AM
Looks like Ukraine shot it down ;D
Hi TassieV,
           I guess it depends on what the High/Low is referring to?
The size of the source signal or the sensitivity of the input, take your pick ;)

In the case of the Lab circuit
The LOW input would be much louder than the HIGH input for a given voltage.

But as the Lab uses *Inverting* inputs then yes the Hi input is HiZ  but with much less gain.

BTW The Lab input design is not an ideal setup, there are better ways.
Hi Joe, Yep can be confusing.
My understanding, it's about the Z (impedance) of the input.
A low Z input on guitar amps is for big signals or even line input.
While a Hi-Z input is very sensitive so as to pickup very small signals.
In the early days guitar PU's were low output and needed a very sensitive input to amplify well. (Hence the 1Meg grid resistor on the old Valve gear)
These days even the cheapest guitars have much bigger outputs than the 40's 50's era so the preamps will redline much earlier on the dial using the pu's around nowadays.

The old Fender circuits used 68k resistors on the Grids of V1 for LOW input. while the HIGH input switched the input Z to 1Meg. far more sensitive.

With super hot pickups you are likely better served by limiting the input Z to about 220k.
I've noticed this with some of the hotrod boutique Amps.
A Carvin Legacy is an Example of this where in put grid R is 220k.
With multi stage preamps this keeps thing from going stupid and also helps keep circuit noise lower.
Agree, Mr Thud
If it has master volume then likely it has a gain pot as well
Try turning the master to full then turn down the gain pot.