Park G10 by Marshall - guitar amp question

[flintan]

I have this small guitar amp Park G10 wich i really like the sound of. I'm thinking of modding it to have an effects send/return because i would like to be able to use reverb and delay after the distortion section at the input.

Anyone have or know where to find the schematic? Maybe someone else also have experience from messing with this nice little amp?

I have sent a mail asking for the schematic to Marshall but no reply yet..

 

[MartyMart]

I rebuilt one a few years ago, needed all new pots and PSU was shot.
I modified it a little with all new IC's and sweetened up the OD section, with
a diode change and a few caps.
I thought it was still sounding like a cheap overdrive pedal !
Gutted it, fitted a nice "amp sim" front end from www.runoffgroove.com
I think I went with the "English Channel" ( AC30 type ) and then built a new
power amp using a TDA2050, which gave me about 15 watts running it on
a single "beefy" 18v supply - more if you use +/- 15 or so.
It's a cool sounding little amp now, great tone and quite loud enough for a
small rehearsal room / gig !
I looked hard but didn't find a schem for the G10 ..... you could build something
much better in about 4 hrs

Marty.

 

[flintan]

Well, i like it for what it is. But it seems almost impossible to get a schematic. Got a reply from marshall, they redirected it to the swedish agent and they just pointed me for support to where i bought the amp... I bought it used so..

 

[isophase]

Hi,
i know this is an OLD thread, but if it can help anyone in the futur...
Here is the schematic (found on the internet, hope its ok to post it here)

 

[isophase]

I have a question regarding the value of resistor R30 (on the very right side of the schematic under the headphone output jack)
its not very clear on the schematic but seems this is a 0.1 ohm 1/2 watt ?
It is connected in series from the center tap of the power transformer to the common/ground terminal of the headphone output jack.
Can someone please confirm this is the correct value ?
Also what is the role of this resistor ?
Thank you

 

[CJ]

"In order to write Ohm values easily in schematics, R is used for sub 1000 Ohm values, as 0R1 = 0.1 Ohm"

snipped it out of my G10R just to make sure

it is probably a fake fuse, or a soft ground, or a F/B resistor, no time to analyze,e, shop is closing, gotta go bar b que a NY steak which id better than new york city, mo offense,

yes it is an amazing amp for a POS.

 

[Gus]

It looks like it is for mixed feedback

 

[Khron]

Also what is the role of this resistor ?

Very likely this: https://sound-au.com/project56.htm

 

[Slindybug]

I'm trying to figure out what R16 is? On the schematic it has the numbers: 330 1/2 next to it. Whatever it is, it looks kinda burnt out on my PCB. I changed the volume pot due to excessive crackling & dropout, but since fitting the new 50k pot, the amp is still a bit crackly. I then spotted that R16 looked overheated & burnt, so wondering if replacing this part will make a difference?
Just need to figure out what it is so I can order a replacement

 

[fallout]

330 Ohm 1/2W Resistor

 

[Slindybug]

 

[Slindybug]

Thanks fallout

 

[ccaudle]

Whatever it is, it looks kinda burnt out on my PCB

Check the voltage drop across that resistor when you have the new one installed. Should only be a few V, it is just filtering the power supply for the op-amps. From a quick look I'd guess around 0.1W to 0.2W dissipation, so shouldn't get too cooked. Just make sure nothing downstream is pulling more current than it should be.

 

[NoisyIndividual]

This is a simple Zener power supply circuit.

Usually the Zener is faulty.

 

[Brian Roth]

This is a simple Zener power supply circuit.

Usually the Zener is faulty.

Could also be the lytic after that resistor....or slight chance of a faulty IC. Just saying! <g>

@Slindybug Resistors don't just start overheating because....unlike people....they are in a bad mood. Something is causing that fault and needs to be corrected.

Bri

 

[NoisyIndividual]

Yes I am well aware of that.

It is usually the Zener.

Just saying.

 

[CJ]

Thanks! Mine crackles now and then, I wrote it off as adding to the funk.

Anybody put a different speaker in?

 

[Slindybug]

Check the voltage drop across that resistor when you have the new one installed. Should only be a few V, it is just filtering the power supply for the op-amps. From a quick look I'd guess around 0.1W to 0.2W dissipation, so shouldn't get too cooked. Just make sure nothing downstream is pulling more current than it should be.

Thank you for this suggestion. I will check that. Aiming to replace that resistor later today.

 

[Slindybug]

Thanks Brian & Khron for all of these pointers. In truth I'm a novice when it comes to amp repairs. Not dabbled with PCB stuff in years, but I have a couple of ENGL Screamers that I might attempt to start looking at myself, through frustration of paying a previous repair person to not fully repair. I have these two smaller transistor amps to practice on first. One was an old Laney which was just a simple EGEN 603 switchable pot, but this little Park G10 is proving a little more interesting in the fault finding area. I will keep you posted with the progress (once R16 is replaced), I will check the Zener & the IC, but please keep the suggestions coming - as it all helps