Regarding the power supply design... If I need roughly 25v for the lm1875, and 9v for the jfet preamp stage, what is the best way to design the power supply? I was thinking using an 18v transformer for the 25v power amp voltage, and then having a linear dc regulator that draws off of the filtered +/-25v dc and drops it down to about 9v and putting a capacitor filter network right after the linear regulator, which then goes to the preamp circuit... or i could use a 6.3v transformer for the preamp and keep both power supplies completely separate... any thoughts? 18v A/C rectified and smoothed is about 25v D/C and 6.3v A/C rectified and smoothed is about 9v D/C.

If I use a linear DC regulator, I could save on the amount of ironware I would have to buy, and also need only one rectifier. The main question I keep thinking of is: Will a linear DC regulator introduce noise into the circuit, even if I filter its voltage output with caps before connecting to the preamp circuit?

I'll add for reference the regulator type I'm thinking: http://www.ebay.com/itm/DC-DC-4-2-40V-to-3-3V-5V-6V-9V-12V-24V-Buck-Step-Down-Converter-Linear-Regulator-/322365124189?

I'm opting more now for a LM1875 type circuit...

The amp I first put a link up for is a class A mono-block, a circuit designed by Jean Hiraga. It is a "Hi-Fi" type circuit. However, I have since abandoned using this circuit because heat dissipation will be impractical, with the size restrictions I have to work with. I could use a fan, but this complicates things more than I wish to for this project. Also, from research I have since done, almost any power amp can be used for a guitar amp, as long as you implement a preamp stage that shapes the tone, and provides a correct input impedance for a guitar.

Would lug 1 go to ground?

Well... I have another question about the volume control of this pre-amp. If I use a pot in place of the 51k resistor in this pre-amp schematic, should I wire the pot with all the lugs as a voltage divider, or should I wire the pot with just lug 1 and the wiper, as a rheostat? for the purpose of volume control. schematic is pictured below.

So to remove this "notch" tone shaping circuit, Do I just have to put a spst switch right after the 4n7 capacitor that goes to ground?

by lifting the circuit from ground, will this allow the signal to pass through the circuit without being affected by it?

More thinking about the topology of this circuit has led to a few more questions:

1.Optimally, Where should the tone circuit stack or "notched mid" EQ circuit be... before or after the FET preamp stage?

2.Could a selector toggle switch be used to either apply the tone stack for a "notched" response in one position, and the other position, bypasses it and couples the FET preamp directly to the power stage?

Quote from: galaxiex on September 23, 2017, 03:20:14 PM
Cool project. 

May I suggest that you will need some kind of "tone shaping" in that amp.
Guitars just don't sound good played thru a "HiFi flat response" type of amp.

If you have a home stereo, try playing your guitar thru it,
possibly getting some adapter and using the phono input if it has one.

Of course the speaker will have a huge impact on the sound.
If you use a "real" guitar speaker that will help.

I have been playing around with this circuit...

http://www.muzique.com/lab/notch.htm

You can add this circuit inside and not even use a "tone" control.
It will give you a "notched mid" response which helps prevent the tone from being muddy.
A very useful circuit, I have added it to a couple of amps and played around with the values.
Made some crappy sounding amps sound great!

Cheers!

I'll add this circuit, it seems to be a logical thing to do...

Thanks!

thanks!!! this type of pre-amp circuit is exactly what i've been wandering around the internet looking for!  :lmao:

Hi folks,

New to this forum, and I have a question. I'm wanting to build a very simple SS guitar amp head of about 30 watts. I want it to have ONLY a single volume knob. I don't care about a pre-amp stage for distortion/overdrive at all. Essentially, that is the purpose of this project, to build a "hi-fi" head. I just want it to be an amplifier in its most simple form, zero coloration/modification of the input signal at all. This may seem like a silly or even pointless task to some... but its what I'm wanting to do.

More specifically my question pertains to matching the output impedance of an electric guitar to the input impedance of an amp kit specifically this one:

https://www.amazon.com/dp/B01F8RXXZI/ref=olp_product_details?_encoding=UTF8&me=

Can someone explain to me exactly how I would make the input stage for a guitar, and have around a 1Meg ohm input impedance, with a simple pot for the volume control. Exactly how would you design a simple input stage to be used with this power amp, for the purpose of plugging a electric guitar into it?


If someone has a better idea for what i'm trying to accomplish in general please share it with me, as i don't have to use a class A SS hi-fi amp, I just thought it would be a really cool unique project.

Thank you and looking forward to making some friends on here!