Valveking 212 has no sound when fx loop on

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Lebowski717
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Valveking 212 has no sound when fx loop on

Post by Lebowski717 » Mon Sep 27, 2021 9:06 pm

First hello all I'm new to the forum, so cheers to everyone out there.
So I own a heavy modded Valveking 212 converted into a head by now with the most common mods done on the valveking mod site.
Sounds like a common more expensive sibling by now but the last mod I´ve done consisted in buffering the fx loop which comes on that Valveking mod site. So adding a 10nf capacitor jumping the right leg of r174 to the right leg of r169 and then I added a 5k pot with a cable from the wiper to both righ leg of r174 and the capacitor in conjunction. So I got it to work at first and actually creamed the fizziness natural to the valveking fx loop, so by increasing the pot the smoother and bass heavier I got out of it and the clean with delay was kind of pink floydish. So now when I connect to send jack I still get sound, but once I connect to return then goes almost bypassed with some AM kinda low sound. I also tried with a patch cable with nothing in the loop and still nothing.
Hopefully, someone can give some insight, before I go back into it just, don't want to fry anything since this mods are not either certain 100 per cent, but yeah it was Fxloop buffering mod as described in ultimate-guitar-valveking-amp-mods-electronics.com

Some pics of the amp
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https://www.facebook.com/photo/?fbid=10 ... 1130756660

Lebowski717
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Re: Valveking 212 has no sound when fx loop on

Post by Lebowski717 » Mon Oct 04, 2021 9:36 am

Hi, there if anyone has an idea of what could be bypassing the fx return when a patch cable is connected, I get sound if I only connect to fx send. Also if plugged directly into fx return it will get that pristine clean sound. I really like that filter knob on the fx loop it smooths out that fizziness that makes people dislike the amp.
I will give you guys some sound clips of the amp without anything in the signal.
Just would like to recover the fx loop otherwise it sounds killer now. Caps used orange caps, wima mks and red mylar. The tonestacks mod was what really opened up the amp, the bias mod made it more focused.

rogue777
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Re: Valveking 212 has no sound when fx loop on

Post by rogue777 » Mon Oct 04, 2021 6:09 pm

The normal internal signal (labeled sig) goes thru R166 and out through C139. The FX loop is not enabled until there is something plugged into the Return jack breaking the connection at J115. Q102 is only used to send a signal out the Send jack.
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Peavey-Valveking-112-Schematic.pdf
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Lebowski717
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Re: Valveking 212 has no sound when fx loop on

Post by Lebowski717 » Tue Oct 05, 2021 2:33 pm

Thanks for the answer, so actually that section had been modded by the previous owner, I'm not sure since I bought it from pawnshop dirt cheap also 200e. So c139 is jumping into r176 and from there is a wire jumping all the way to the power board to 2nd pin (sig) ground of p311. I noticed that the c139 cap is a bit loose since it's standing in one leg with the other side jumping into r176, could that lead to not having any sound when the loop is engaged? It worked before maybe cos I was adding that filter knob to r174 jumped into r169, I might have moved that cap slightly and it might have come a bit loose. Just to recapture does the conjunction of c139 a r176 affect the fx return signal?

rogue777
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Re: Valveking 212 has no sound when fx loop on

Post by rogue777 » Tue Oct 05, 2021 4:07 pm

C139 should not be loose. Both legs of the component should be soldered in its place in the PC bd.
When you put a signal into the Return jack, the voltage is developed across R176 (3.9M ohms) and then the signal goes thru C139 and on to the Power Amp, connector P301/311 pin2. So Yes, R176 and C139 are the main components for the FX Return signal.
I hope your mods work the way you want.

Lebowski717
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Re: Valveking 212 has no sound when fx loop on

Post by Lebowski717 » Sun Oct 10, 2021 8:53 am

Hello again so I tried to put back c139 both legs in the circuit and removed the jumper coax cable that was connecting to the sig line on the PA. When I did that the sound dropped and sounded fizzy. I'm sure that that mod was there for a reason maybe the sig line track got compromised or so. Like I said when I bought the amp that mod was already in the amp. So I checked about that mod and instead of plugging to the jumper on the sig line, the mod says to solder the wire to the cap and resistor closer to the v3 grid. I also grounded through r176, so that made it work again and now better cos I also lifted one of the jumper legs from sig line to v3 grid. That cleared all noise that was still heard when the cable was soldered to the jumper(sig line) on the PA. The fx loop still has the same issue though even when I put that cap back in the problem is still there.
I'm thinking the issue might be at r174 since when the fx loop is engaged the resistor should work instead of r166 like you said. I replaced r174 already twice since I added that buffering mod cos it caused too much heat while soldering. I will check if those resistors are faulty.

Lebowski717
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Re: Valveking 212 has no sound when fx loop on

Post by Lebowski717 » Thu Oct 14, 2021 12:52 pm

So since the last time I rechecked r174 r169 r168 and they are ok the question is if the connections in this section got compromised. I´ve bridge all that should be with solder in a way to fix some loose sockets, and when I jumped the fx loop still no sound almost, there is signal but almost inaudible.
So could it be, that q102 might be faulty, and if so does it affect when the loop is engaged? I mean would it still be signal if q102 is removed? I also heard how it affects the hiZ which makes it much brighter than it should.

Lebowski717
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Re: Valveking 212 has no sound when fx loop on

Post by Lebowski717 » Mon Oct 18, 2021 7:58 am

If someone can give me a hint about q102, cos I'm not sure where the problem is. I still have sound when plugged straight into fx return so that is also not the problem, must be the components that bridge the loop. I just don't where to start. Everything was fine until I added the buffer mod described above.

Lebowski717
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Re: Valveking 212 has no sound when fx loop on

Post by Lebowski717 » Mon Oct 18, 2021 8:19 am

That's the only thing really left to complete this modded beast, just need some info about this issue, I've searched through the web about this specific problem on the Valveking, but nothing related to the same issue. I´ve sent it to an amp tech to repair, but he just checked it and denied doing any repair on it, since it's a PCB mounted headache for those old school amp techs, that just want to work on old stuff. Since I'm living in a small country in Europe there is no support for more modern amp types. I've been fixing it myself since.

rogue777
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Re: Valveking 212 has no sound when fx loop on

Post by rogue777 » Mon Oct 18, 2021 1:18 pm

I tried to lookup info about your effects loop mod, ultimate-guitar mods but I couldn't find anything. So I don't really understand what your doing.

>>>>>>>>>>>>>>>>>>>>>>>

Thats good, you plugged your guitar into the "return" input and got sound. That means the problem is in the "send" signal. And you say everything was fine before you added your mod as described, so there's a good chance there is nothing wrong with Q102.

If you liffed any original component leads from the board while doing your mod you broke the original signal path. You stopped (opened) the "send" signal path. Either that or you grounded the "send" signal putting in your mod. Then the FX loop will not work.
You have to backstep your mod (remove it) step by step to see what caused the issue.

One end of the 1k ohm resistor R174 must be connected to the pc bd to route the signal to the "send" jack.

Lebowski717
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Re: Valveking 212 has no sound when fx loop on

Post by Lebowski717 » Tue Oct 19, 2021 6:56 am

Hi there, so yeah I did bridge the right leg of r169 to the right leg of r174 with a .010uf capacitor and added a 5k pot to the right leg of r174 to fine adjust the brightness of the fx loop. I left the resistor's right legs on the PCB and just soldered the cap to both legs, I don't know if it's correct they don't precise it on the mod pdf. It was working until the cap came loose from r169 after I soldered a second cap cos the first one was charred and it worked again. That second one came loose also probably too much heat broke the solder joints. At some point after soldering multiple times in the same spot something must have fried. I tested the resistors R174 R169 R168 because after all that soldering I decided to replace those and make a more stable connection with that second cap and I think that's when the fx loop got no sound when hooked up.
The mod was intended to smooth the high frequencies and add more low frequencies by increasing the potentiometer more filtering was added. It was working but after multiple tries to solder that cap back in place something must have gone wrong. Could be one of those 3 resistors, I didn't change anything on the r166 lane so most likely it could be there the problem of the PCB lines or resistors not making enough contact(r174,r169,r168)
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