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February 06, 2023, 10:30:06 AM

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#21
Amplifier Discussion / Re: Add effect loop to jc120
Last post by Psc - January 21, 2023, 09:31:42 PM
Thanks for the input. Yes, I want to be able to have a mono input that would go to both power amps if possible.

Phatt, you're correct, the in/out between board 1 and 2 is exactly like that in the amp, very easy spot to access, very reversible. I think I'll try it there when I get a chance. Free time is hard to come by these days, but thinking at work I can manage!
#22
Amplifier Discussion / Re: 12w Marshall
Last post by phatt - January 21, 2023, 07:29:07 AM
Hey Guzz,
I assume when you say *Terrible Freq response and then Boss GT8 in the next sentence* then you are maybe chasing the old sweet magic of limited bandwidth valve gear.
This can be done with SS gear but you have to in a different manner than you do with Valves.
Phil.
#23
Amplifier Discussion / Re: Add effect loop to jc120
Last post by phatt - January 21, 2023, 07:22:34 AM
Also the Fet pair phase splitter Q1 and Q20 form a limiter circuit so inserting after that may (or may not) cause strange things to happen.

Teemu mentions this limiter but I'm still not sure how it works.
A note,
Sadly Teemu along with Enzo and J M Fhaey don't post much these days but they have a wealth of knowledge if you go searching for older posts. plus a few others, whose names I can't recall right now.
These wonderful members have helped me many times when I've been stuck. 8)
Phil.
#24
Amplifier Discussion / Re: Add effect loop to jc120
Last post by phatt - January 21, 2023, 07:03:02 AM
Hi Tassie,
Note;
Vr4 And VR10 is the mix point for the 2 power stages, trying to insert a loop at C26/C126 means you will only be able to use one power section. (I'm assuming a mono FX loop is being asked for?)
I think you will find the 84 schematic is a single channel circuit which makes your idea possible but this one is a different setup.
 I assume by the schematic the in/out wires are easy to lift on the unit posted so less chance of stuff up.

For a full run down on all the JC models try this page;
https://www.ssguitar.com/index.php?topic=2243.0
Thanks to Teemu ;)
Phil.
#25
Amplifier Discussion / Re: Add effect loop to jc120
Last post by Tassieviking - January 21, 2023, 04:14:00 AM
I had a look through my files and found a 84 JC120 schematic with an effects loop,
if you compare the circuit after the return jack you will understand what I meant above.

Never mind, that's a single channel head only.  (Thanks Phil)
#26
Amplifier Discussion / Re: Add effect loop to jc120
Last post by Tassieviking - January 21, 2023, 03:48:34 AM
You can also remove those resistors and use the holes for wires to run to the send/return jacks, just replace the resistor along the wires so it goes back in the circuit.
I would solder the resistor to the send jack and then add the wire to the resistor.
If it works ok then put a bit of heat-shrink tubing over the resistor.

I would have thought that the place to insert the send/return would be at C26/C126, or just before C26/C126.
I think it looks like the circuit between R19 and C26 is where the effects and distortion might enter into the circuit.
I might be wrong as I am not familiar with this amp.
#27
Amplifier Discussion / Re: Add effect loop to jc120
Last post by Psc - January 20, 2023, 11:31:27 PM
Thanks for the confirmation. I'll update when I get around to doing it.
#28
Amplifier Discussion / Re: 12w Marshall
Last post by guzzis3 - January 20, 2023, 10:01:58 PM
Thank you for the replies.

Morayfield! Goodness it's a small world. I'm at Mt Crosby.

Yes I now unfortunately am on the pension. Humiliating but I'd run out of options. The blindness is one of several problems.

I found your thread on the 100W models also. I assume all these generate clipping in the preamp and you can dial it in at different volumes ? Maybe I'll build one of those instead. I have developed an interest in stereo setups though. Some of the effects sound a lot better on 2 channels. I could hang on to the 8008 and build a preamp to feed it. Another option.

A PCB would be helpful though. I've built on..tag strips ? before. I forget what they are called. When you get a lot of components that can get messy. Building a pair of preamps though should be manageable.

Limited component availability is disappointing.

I'm not looking for distortion, just an amp with terrible frequency response :D I've got a Boss GT8 and of course if I want a singing sound I've any number of valve amps to play with.

I have grabbed an 8020 and VS15 at very good prices but it's surprising how disappointing both are. The VS15 oddly seems to be the nicer clean amp. The 8020 need a bit of help. Reverb seems not to work and I suspect other problems. Perhaps there is a mouse living in there.

I have a plexi marshall major. Bought it when I was young and dumb. There was a super lead, lead and major second hand. The lead and major were the same money, the super lead was out of my price range. It would have been better had I bought the lead but I figured if I couldn't be good I'd be loud :D Oh to be young again.
#29
Amplifier Discussion / Re: Add effect loop to jc120
Last post by phatt - January 20, 2023, 08:27:41 PM
Yes output of VR10, cut before R19 and R121.
Should work and easy to reverse if it does not work.
Phil.
#30
Amplifier Discussion / Re: 12w Marshall
Last post by phatt - January 20, 2023, 08:05:38 PM
Quote from: guzzis3 on January 18, 2023, 09:05:19 PMHi,

If you had to order extra PCBs that you want to sell I'd be very happy to buy them from you. I am in Brisbane,

This is my first post to this forum. I was pointed to this thread by a person on the marshall forum. I've been building electronic stuff since I was a kid but while I have built quite a few valve guitar amps I've not built a SS one.

 Have you determined if the 5005 etc develop their distortion in the preamp, power section or both ?

I realise you haven't finished your design, and there may be problems, but starting even with a flawed PCB is probably easier than laying it out on tag strips or breadboard.

Thank you for reading.
Hello Guzz, just note on SS rigs,
Most do not respond to power stage distortion, some rare ones try to do that but likely not as convincing as a full Valve powerstage.

With SS Amps all the dirt, grit, compression and like attributes of Valve amps needs to be done in the preamp stages.

My main rig is just a basic SS amp and all the magic is done with my pedal board. Most of the pedals are my own design, some of my schematics are posted on this site.

40 plus years back I wanted to build an amp that did it all in one rig.
Took me many years to realize that I was just building land fill.
I now  have draws full of failed ideas (other wise called spare parts 8) )
I have built both Glass and Sand designs and although I like Valves there many benefits to SS designs.

If you are lucky enough to find an amplifier (Glass or Sand) that works for you then lucky you, sadly more often than not you'll spend a fortune trying to find it.

BTW I'm up the road in Morayfield if you want to make contact I'm happy to help with my years of researching. Just pm me for my phone number.
Phil.