Hello All,
I am in the process of building an 18 watt EL84PP amp using the minimalist schematic for low parts count, cost and simplicity. (see schematic attached)
I would like to integrate a simple passive tone stack but I am stuck on where to put it into the circuit...right after the input jack? After the first 12AX7? After the driver? I have seen tone stacks placed in all these locations but what are the advantages and drawbacks of each location or is it about the same?
Fire away. Inquiring minds want to know!
I am in the process of building an 18 watt EL84PP amp using the minimalist schematic for low parts count, cost and simplicity. (see schematic attached)
I would like to integrate a simple passive tone stack but I am stuck on where to put it into the circuit...right after the input jack? After the first 12AX7? After the driver? I have seen tone stacks placed in all these locations but what are the advantages and drawbacks of each location or is it about the same?
Fire away. Inquiring minds want to know!
Attachments
I would use the second half of V1 as the pre-amp and put the tone controls between that and the first half. That will keep the gain fairly constant and ensure you use the less noisy side of the valve as the pre-amp. The circuit is obviously just theory as preferred values for components have not been stipulated. Looks OK though. Don't forget the feedback loop to keep the unwanted noise down. There is none at present.
This thread should be moved to the Instruments "board".
JSE is correct. A tone stack has an insertion loss and additional gain is needed to compensate for the loss.
JSE is correct. A tone stack has an insertion loss and additional gain is needed to compensate for the loss.
@ JSE: I'm not sure I follow you when you say to put it between the first and second half of V1. V1 is connected completely parallel so how would I split it up? As far as the circuit being a concept as there are no stated values. The values are on the schem. or do you mean the tone circuit is a theory because cap values in a tone circuit are totally up to personal taste and picking the right roll-off for you.
You will need to separate the double triode into two separate amplifiers. Use no more than 100k anode load with a 2.2k cathode resistor that has a 47uF decoupling it.
The component values I was referring to meant that a 5nF cap is not a preferred value, I would select 4n7, etc.
If you want to use 820R as a cathode resistor the anode resistor will need to be 47k as the valves anode voltage will be too low otherwise. 2.2k is average with a 100k load.
The component values I was referring to meant that a 5nF cap is not a preferred value, I would select 4n7, etc.
If you want to use 820R as a cathode resistor the anode resistor will need to be 47k as the valves anode voltage will be too low otherwise. 2.2k is average with a 100k load.
Moved to I & A per forum policy. All MI amp threads belong here.not if you only need attenuation
or if you dont need it very loud
but yes, if this design originates from a hifi amp, you may need the additional gain stage
If the present design works, and he then wants to ADD a tine stack, the resulting loss of signal level will need to be compensated by the extra gain stage. In other words, his goal is NOT to have attenuation.
You have the two triodes in parallel, but as a minimalist parts saver, that is throwing away a perfectly useful triode. And that triode would be ideal for the gain recovery stage after the tone stack. A zillion Fender amps can serve as your model.
You have the two triodes in parallel, but as a minimalist parts saver, that is throwing away a perfectly useful triode. And that triode would be ideal for the gain recovery stage after the tone stack. A zillion Fender amps can serve as your model.
I've learned that Enzo (or you, probably) knows what he's talking about much more than I do...
Connecting your guitar directly to both grids in parallel might not be the ideal load for your guitar to drive, nor are you likely to need the current from both in parallel to drive a splitter that also uses both sides of a 12AX7 (and consider miller capacitance etc. make sure it won't cut your treble). Like Enzo says, it's kind of wasting half a 12AX7 unless you're trying to average the background noise or something. It will be interesting to find out how 'dirty' it will or won't get, being so minimalist. What is your tonal goal, on the clean/distorted scale? Where did you get that part of the circuit idea from?
And to barf up the same campaign drivel I'm always spouting in my personal opinion:
IMHO having seperate tone control over your distortion and seperate tone control over your guitar sound is very very valuable, if not 'control' at least some seperate 'fixed shaping' of the distortion. In order to accomplish that, you need some tone tweeking BEFORE distortion is generated and another tone 'control' or shaping AFTER distortion is generated. The idea is that your signal chain is: pre-emphasis-shaping/distortion/de-emphasis-shaping with the result that your guitar came thru with tone relatively unaltered because it went thru both pre-emphasis and de-empahasis, but your distortion only went thru the de-emphasis and was altered more. So you achieved a tone control over only your distortion...it just required two 'control' or shaping points. Which is great for a verastile amp. Most are not that versatile, but apply the same principle to boost treble early, generate distortion, then cut treble, resulting in a 'creamy' distortion without too much treble. Very common is some radical treble-boost like a 'bright' switch that puts a small cap across your volume pot (consider using a push/pull pot) on an early stage, then one to five additional voltage gain stages and loads between there and the splitter, just to add some rich harmonics, and finally a treble-cut in a very late stage to get rid of the buzzy irritating treble distortion and emphasize the lower-frequency beats and interesting effects on chords, that de-emphasis final tone control sometimes even really late via the feedback loop of the power amp or even in choice of output transformer and speaker. This generally ain't no hi-fi and there's bandwidth limiting and non-lineaar tone shaping all over the place, in almost every stage, inter-stage coupling, and every component.
Mesa and Peavey sometimes add a treble-boost between your guitar and that first grid, a cap across a resistor, or between first and second stages. Fender's 'bright' switch is economical (for Fender anyway) and lets you use the gain you throw away in the volume knob to add treble-boost. Peavey sometimes boosts treble by undersizing an inter-stage coupling cap (which also has other objectives in minimizing problems when overdriving the next stage).
An Alembic preamp jacked in series, essentially two Fender-like channels in series, is one of my favorites, having two tone stacks and generating distortion in between them.
If you're going for a clean tone, it doesn't make much difference where you put the tone controls, except how it affects the tone of background noise (hum and hiss etc.). If it's all clean you can have tone controls really early like a guitar...caps and inductors for high-cut and low-cut...at the very input to your amp. You can have tone controls at the opopsite end, at speaker-level if you don't mind the component cost; if you turn down the treble in a cross-over-like circuit it will also cut the treble on any noise generated anywhere in the amp, including the power amp output stage. Or you can put them between any stages, or in a feedback loop. IMHO it really doesn't matter that much if everything is 'clean'...not even to the noise, because most of it is generated really early in the chain anyway, so on a clean amp a pre-gain knob or master volume has about the same effect.
If you really want EL84 'chime' you might look at some Vox circuits.
Have fun! Adding more stages doesn't necessarily make a guitar amp dirty, though it certainly can. The guitar input is already pretty noisy. Even for 'clean' sometimes I like radical treble boost in several clean stages with none overloaded and achieving some real dynamic range rather than a minimalist circuit that sounds lifeless like plugging into a low-gain hi-fi. Then again, sometimes a simple single-ended champ can be amazing when each of the non-linear parts work together to make magic. So good luck, and enjoy tweeking the drive levels and tone at various points! With a push/pull you might have fun tweeking the sag touch response compression too. Great fun, I'm jealous LOL.
Connecting your guitar directly to both grids in parallel might not be the ideal load for your guitar to drive, nor are you likely to need the current from both in parallel to drive a splitter that also uses both sides of a 12AX7 (and consider miller capacitance etc. make sure it won't cut your treble). Like Enzo says, it's kind of wasting half a 12AX7 unless you're trying to average the background noise or something. It will be interesting to find out how 'dirty' it will or won't get, being so minimalist. What is your tonal goal, on the clean/distorted scale? Where did you get that part of the circuit idea from?
And to barf up the same campaign drivel I'm always spouting in my personal opinion:
IMHO having seperate tone control over your distortion and seperate tone control over your guitar sound is very very valuable, if not 'control' at least some seperate 'fixed shaping' of the distortion. In order to accomplish that, you need some tone tweeking BEFORE distortion is generated and another tone 'control' or shaping AFTER distortion is generated. The idea is that your signal chain is: pre-emphasis-shaping/distortion/de-emphasis-shaping with the result that your guitar came thru with tone relatively unaltered because it went thru both pre-emphasis and de-empahasis, but your distortion only went thru the de-emphasis and was altered more. So you achieved a tone control over only your distortion...it just required two 'control' or shaping points. Which is great for a verastile amp. Most are not that versatile, but apply the same principle to boost treble early, generate distortion, then cut treble, resulting in a 'creamy' distortion without too much treble. Very common is some radical treble-boost like a 'bright' switch that puts a small cap across your volume pot (consider using a push/pull pot) on an early stage, then one to five additional voltage gain stages and loads between there and the splitter, just to add some rich harmonics, and finally a treble-cut in a very late stage to get rid of the buzzy irritating treble distortion and emphasize the lower-frequency beats and interesting effects on chords, that de-emphasis final tone control sometimes even really late via the feedback loop of the power amp or even in choice of output transformer and speaker. This generally ain't no hi-fi and there's bandwidth limiting and non-lineaar tone shaping all over the place, in almost every stage, inter-stage coupling, and every component.
Mesa and Peavey sometimes add a treble-boost between your guitar and that first grid, a cap across a resistor, or between first and second stages. Fender's 'bright' switch is economical (for Fender anyway) and lets you use the gain you throw away in the volume knob to add treble-boost. Peavey sometimes boosts treble by undersizing an inter-stage coupling cap (which also has other objectives in minimizing problems when overdriving the next stage).
An Alembic preamp jacked in series, essentially two Fender-like channels in series, is one of my favorites, having two tone stacks and generating distortion in between them.
If you're going for a clean tone, it doesn't make much difference where you put the tone controls, except how it affects the tone of background noise (hum and hiss etc.). If it's all clean you can have tone controls really early like a guitar...caps and inductors for high-cut and low-cut...at the very input to your amp. You can have tone controls at the opopsite end, at speaker-level if you don't mind the component cost; if you turn down the treble in a cross-over-like circuit it will also cut the treble on any noise generated anywhere in the amp, including the power amp output stage. Or you can put them between any stages, or in a feedback loop. IMHO it really doesn't matter that much if everything is 'clean'...not even to the noise, because most of it is generated really early in the chain anyway, so on a clean amp a pre-gain knob or master volume has about the same effect.
If you really want EL84 'chime' you might look at some Vox circuits.
Have fun! Adding more stages doesn't necessarily make a guitar amp dirty, though it certainly can. The guitar input is already pretty noisy. Even for 'clean' sometimes I like radical treble boost in several clean stages with none overloaded and achieving some real dynamic range rather than a minimalist circuit that sounds lifeless like plugging into a low-gain hi-fi. Then again, sometimes a simple single-ended champ can be amazing when each of the non-linear parts work together to make magic. So good luck, and enjoy tweeking the drive levels and tone at various points! With a push/pull you might have fun tweeking the sag touch response compression too. Great fun, I'm jealous LOL.
the signal loss is adjustable, and frequency limited, depending on choice of component values
playing bass guitar, I only need attenuation/cut
a lift option is not on my wishlist at the moment
but for guitar I dont know what will work best
that said, I do have plenty of gain for my home practice
besides, I have lots of amp power/wattage to spare
but with just 18watt you may not want to loose too much of it
does not look like it has any gain stage for guitar pickup
maybe it have been intended as power amp, for use with guitar/effects preamp
(if at all designed for guitar)
so basicly you could already be low on gain, even without passive tonestack
looks like you would be better suited looking at something more 'finished' and ready to build as is ?
If you have a look at 18 Watt Lite IIb, there are a bunch of variations to the circuit. You can put 2 input jacks and switch between single stage or parallel stage for V1. You will see tone stack position on the circuit. If you want to go real minimalist then a single pot tone control like an early fender Champ would work. I am in agreement that using V1 only in parallel is limiting gain wise but it has a different sound, people used to parallel early marshalls that way. 2 separate stages would be better using a simple switch to go from parallel to 2 stage IMO. Have a look at Mod 102 amp kit schematic, that one is 2 preamp stages, treb/bass control and a fixed mid. More fendery sound. Note that V3 is 12 AX7 type and not AT7 which picks up more gain at the Phase inverter.
The schem should work as is, but just offering up a couple of simple mod options you can do with what you have already. I have a feeling this type of design is going for more power amp overdrive than preamp overdrive. Which is of course real nice!
The schem should work as is, but just offering up a couple of simple mod options you can do with what you have already. I have a feeling this type of design is going for more power amp overdrive than preamp overdrive. Which is of course real nice!
Well there you go, that's the obvious answer to the original question. One sentence & .gif more directly relevant than all my drivel.
😛 ... sometimes we have to poke the thing to see what happens 😉 😀
shanx deserves the credit for this one
Hey guys,
It is just as important to explain the way you see it, and what the reasoning is behind the suggestions. Words matter a lot, so that schem was merely one possible way to go. The single tone control there is not very lossy on the signal, but a full TMB tone stack has the potential to drop a lot, so a second gain stage is going to work better.
It is just as important to explain the way you see it, and what the reasoning is behind the suggestions. Words matter a lot, so that schem was merely one possible way to go. The single tone control there is not very lossy on the signal, but a full TMB tone stack has the potential to drop a lot, so a second gain stage is going to work better.
This is another version, top channel Superlite with the TMB tone stack and split V1 into 2 separate stages. The insertion loss of the TMB stack is substantial so 2 gain stages required to recover that loss. You could try the top channel preamp alone and as cyclecamper suggested try a bright switch across the ''gain'' pot as a bit of treble pre-emphesis. I just want to note that the TMB stack will give you a mid scoop, and depending on how you like your sound, an increase in resistance on the mid pot will give you less inherent scoop. Try using the tone stack calculator from Duncan amp pages, if you want to play with the stack values.
To keep the minamilist approach AND the parallel triode input stage simply replace the volume control with volume/tone control from the Fender Princton.
See here:
http://www.webphix.com/schematic heaven/www.schematicheaven.com/fenderamps/princeton_5c2_schem.pdf
This same arrangement was used in early AMPEG Amps and works well. Want something a little more sophisticated - lookup "TILT" Control.
Cheers,
Ian
See here:
http://www.webphix.com/schematic heaven/www.schematicheaven.com/fenderamps/princeton_5c2_schem.pdf
This same arrangement was used in early AMPEG Amps and works well. Want something a little more sophisticated - lookup "TILT" Control.
Cheers,
Ian
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