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Marshall Clean Channel

Started by askwho69, July 29, 2011, 02:06:17 PM

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askwho69

Hello all ! I've been busy doing some eagle "practicing" be cause its fun so i tried to copy and make a PCB out from Marshall Clean channel "8080 Valvestate" i need an advice too how can i make it to single supply? :D is my schematic corrert? from here http://www.drtube.com/schematics/marshall/pc0689.pdf

teemuk

#1
Quotei need an advice too how can i make it to single supply?

This topic has been discussed ad nauseum. Run a search.

In essence, you want to bias the OpAmps to idle at half of the supply voltage. With bipolar supply this comes down to zero volts (ground) but with eg. 30V single supply it comes down to 15V (half of 30V). So, you need a voltage source generating that potential (typically a resitive divider with a filter cap), then you reference the OpAmps to that DC reference instead of ground (0V). AC coupled references (such as those typically found from feedback loop dividers) can be hooked to either ground or to the half supply reference, as the DC levels do not matter due to capacitive coupling.

Naturally, because the signal's "zero crossing point" is at DC voltage you need to AC couple inputs and outputs. Most designs do that anyway but it's something you need to ensure.

askwho69

woooh to 30 v? mmmhh i rather make it to bipolar :D im gonna make a lm1875 amp this days with this preamp "clean" and thor for dist.. is this ok setup?

Thanks man for the advice need to search then about single supplies :D

joecool85

Quote from: askwho69 on July 29, 2011, 10:37:37 PM
woooh to 30 v? mmmhh i rather make it to bipolar :D im gonna make a lm1875 amp this days with this preamp "clean" and thor for dist.. is this ok setup?

Thanks man for the advice need to search then about single supplies :D

Sounds good to me.  Nothing wrong with having two separate circuits for clean and OD.
Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com

J M Fahey

If you build a split supply LM1875 amp (or any other split supply chip amp, which means *all* of them over 15W), you can easily pull +/-15V out of them for your Marshall preamps.
And from one of them you can also easily pull +9V for your Boogeyman or whatever.
You can have your cake and eat it  ;)

polo16mi

Quote from: J M Fahey on August 01, 2011, 01:42:44 PM
If you build a split supply LM1875 amp (or any other split supply chip amp, which means *all* of them over 15W), you can easily pull +/-15V out of them for your Marshall preamps.
And from one of them you can also easily pull +9V for your Boogeyman or whatever.
You can have your cake and eat it  ;)

I thinking about this since a long time. How you can do that? Maybe a voltage divider? LM7815 a LM7915  is other way, but datasheet of these says that no more of 23V of input for sure..... What you think?



J M Fahey

Do what *all* manufacturers do: dropping resistors + Zener diodes.
Look at any Marshall/Fender/Laney/Crate/Peavey schematic.
Using 3 leg regulators, expensive Op Amps such as OP27, etc., usually means experimenter or n00b designer; commercial factories are happy with resistors+zeners, TL072, etc.
Nothing wrong with using "improved" parts or technology, quite the contrary,  it´s just that in massive, commercial production, 1$ extra you spend at the factory may mean $10 extra at the Music Shop, breaking a deal.
And money is much better spent on Advertising/Looks/Packaging than on the product itself.
Sad but true. :duh

Alexius II

If he is doing an amp for himself, he might as well go with a "more expensive" regulator  ;)
Actually, not all LM7815 are the same. In my local store I found one that went from 17V to 35V (input voltage). I'm sure you can find some similar somewhere (online?).

How high will the voltage to LM1875 be?