I have recently been poking inside a small guitar amp. It's a VOX pathfinder 10.
I am currently experimenting by adding some good practice parts, like proper psu, proper bypassing etc.
What I am curious about is its output circuit.
I assume that C22 is the zobel, expecting the pcb lines to form the 1R resistor (or I could be wrong)
What is the purpose of the 10R/1W resistor in series with the speaker. Does it just reduce the volume making the speaker appear like an 18R one? Or does it have some other interaction with the rest of the parts?
And what is the purpose of R23 and c23? Are they simply there to work when the headphones are plugged in?
Here is the relevant part of the schematic
I measured the speaker at 100Hz giving 235mH. Impedance is 10R at 100Hz and 8,3R at 1KHz. Rdc is 7,5R
Thanks in advance for your help and time
I am currently experimenting by adding some good practice parts, like proper psu, proper bypassing etc.
What I am curious about is its output circuit.
I assume that C22 is the zobel, expecting the pcb lines to form the 1R resistor (or I could be wrong)
What is the purpose of the 10R/1W resistor in series with the speaker. Does it just reduce the volume making the speaker appear like an 18R one? Or does it have some other interaction with the rest of the parts?
And what is the purpose of R23 and c23? Are they simply there to work when the headphones are plugged in?
Here is the relevant part of the schematic
I measured the speaker at 100Hz giving 235mH. Impedance is 10R at 100Hz and 8,3R at 1KHz. Rdc is 7,5R
Thanks in advance for your help and time
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I just checked the actual amp, and the schematic seems to be wrong. R22 is the zobel resistor and is in series with the cap. Not in series with the speaker
Well, assuming the schematic is correct... I can tell you why I put a resistor between the LM386 output and speaker in my silly little guitar amp. Apparently it make the sound more 'tube'-like by decreasing output impedance and allowing speaker impedance to influence things. Mr. Pass wrote a good article about this some while ago, but I can't seem to find it now.
--Christian
--Christian
Yes, My first thought as well, watch what happens to a drivers FR in winlsd when you add resistance to it it flattens out the resonant peak caused by the drivers Qts. 😉
IIRC it changes the HF slope slightly as well, been a while,I guess I am gonna have to fire it up and play with it for a while, cause you know that is what is gonna happen and I won't be able to re edit this post because i'll be over the time limit.
Not mention it is running a rather high supply voltage there fore much like my Park Amp if run that thin Wide Open what you get is a Huge High power Square wave of 40Vp-p in to the speaker as it is a Guitar amp right!!
Well that chip amp is not gonna supply enough current to drive that load in the First Place, it is a LM386!! 😉
So the resistor is there to limit the current else that IC chip amp would go Pew after awhile after such abuse (I know I play Guitar Too!) thus helping to protect the driver until its final demise as well as warming up its sound a bit because they used such Cheezy High Frequency peaked High Q drivers in the First place !!! 😉
😀
FWIW
jer 🙂
IIRC it changes the HF slope slightly as well, been a while,I guess I am gonna have to fire it up and play with it for a while, cause you know that is what is gonna happen and I won't be able to re edit this post because i'll be over the time limit.
Not mention it is running a rather high supply voltage there fore much like my Park Amp if run that thin Wide Open what you get is a Huge High power Square wave of 40Vp-p in to the speaker as it is a Guitar amp right!!
Well that chip amp is not gonna supply enough current to drive that load in the First Place, it is a LM386!! 😉
So the resistor is there to limit the current else that IC chip amp would go Pew after awhile after such abuse (I know I play Guitar Too!) thus helping to protect the driver until its final demise as well as warming up its sound a bit because they used such Cheezy High Frequency peaked High Q drivers in the First place !!! 😉
😀
FWIW
jer 🙂
Hi, I post here my two cents on this amp, which I have too.
If you remove the two diodes in the preamp, the ones just after the tl071 op-amp, you will get a wonderful Neil Young distortion, not unlike his classic tone heard on Rust never sleeps.
My explanation is that, by this mod, you will get rid of preamp distortion, and get loads of power amp distortion, which sounds way better.
Keep on modding an playing!
Dimitrij
If you remove the two diodes in the preamp, the ones just after the tl071 op-amp, you will get a wonderful Neil Young distortion, not unlike his classic tone heard on Rust never sleeps.
My explanation is that, by this mod, you will get rid of preamp distortion, and get loads of power amp distortion, which sounds way better.
Keep on modding an playing!
Dimitrij
On my phone I thought the output jack was for an external speaker.
Being a line / headphone out that is NOT what R22 is for.
My apologies.
Yep, that was the first thing that I did when I got it. The high gain "channel" was unbearable with those LEDs.
By the way, as I said above the schematic is wrong. R22 is in series with C22 in the actual amp. It's the zobel resistor.
