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Messages - phatt

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Amplifier Discussion / Re: Rocktron Rampage R80 - No Sound problem
« on: January 21, 2021, 02:07:47 AM »
Don't forget to check you have continuity on each of the reverb cables.
Those plastic RCA plugs are a common fail point.  :trouble

Amplifier Discussion / Re: Rocktron Rampage R80 - No Sound problem
« on: January 17, 2021, 09:27:07 PM »
Plug a cord from Effects Send to Effects Return and see if it works. It could be the Effects Return jack switch.
Dmeek beat me to it,, Yep FX loop is the most likely culprit. they are *Switching sockets* the switch terminals corrode and give the symptoms you are describing. 
Also looks like it may have a Preamp out and Poweramp input,, which is another fail point. link them as well.

As to reverb not working,,pull the RCA plugs and clean the pins.
Also flip the tank and use a DMM to check you have continuity of the little transducers,, there are 2 of them. if no reading look close for broken wires.

As for the big difference in Volume between clean and dirty,, well that is how most of them work,, Normal. ;)

Amplifier Discussion / Re: Power supply/ power amp question
« on: January 17, 2021, 09:17:24 PM »
 If this is your first project I would suggest you do some reading first.
The power supply voltage you have is likely too high for a novice.
with 50VDC rails it's possible to end up dead,, the you accidentally touch both rails then it's 100Volts across your heart.  xP

You need a supply of around 35-0-35VDC would be a lot safer and far less chance of blowing up your circuit and dying as well. 8|

Working with anything over about 80Volts is a potential death trap. ???

Go here and do a lot of reading;

Look at Project27; It's a 100Watt guitar amp running from a
SAFE 35-0-35VDC. You can even purchase a PCB from Rod which will save you a lot of blood and sweat trying to make your own.

This is by far one of the best places for those wanting to DIY an amplifier,, tons of stuff and written for folks like you who do not have the skill to go it alone.
Cheers Phil.

Hum it might be a broken track.
What about,,
Wait till it's dark, (Really Dark) and just watch.

If it's a hairline crack with a high current it will flash when fault happens.
I have found that to save a whole lot of time wasting searching for that kind of fault.
I had one PCB that had cracked right under the edge of the solder pad and no way you could see it as the solder slightly overlapped the edge of copper trace. Worth a try.

Had something similar years back,, after much swearing turned out to be failing contacts in the main power switch. they were arching intermittently,,  Also had it happen to a Sansui hifi amp not so long back,  Rare but it can happen.

Tubes and Hybrids / Re: Help with Hybrid Design
« on: December 31, 2020, 12:58:56 AM »
OK thanks for the pics and explanation I now see how it has been done, i.e, the second primary is used inductively. (I kept thinking of Centre tapped primary :duh)
But still it's my understanding that most modern Mains Tx's are wound with extra isolation between Pri/Sec.
So are you aware there is normally extra insulation between Pri/Sec windings?

I do know that most IE type Tx's now use split bobbins so there is even better isolation than the old overlay winding system.

I'm not up to speed on the physical structure of Torids but I'm assuming something similar would be in place. If so that would put both primaries on the same stack with far less insulation which makes it a potential hazard if something ever shorts in the primary stack.
Tiss a fair bet that design concept would never pass most Electrical regulations that I'm aware of.  :-X

OK it will work but I still see it as a potential hazard and I would never build such a circuit based on that Tx trick.
When I build stuff I always think of the wotiffs?
What if your best mate uses this and he dies,,, how would you feel? xP

I have several muso mates who often use gear that I have built and I feel much better knowing that I have used as much safety margins as possible to ensure no one gets zapped.
Layout and wiring of Mains is often overlooked even in big name gear, often I find mains wires zip tied to secondary wires. OK it may never fail but if those wires did melt you have mains on the circuit,, of which you are directly connected to when holding an electric guitar or microphone. I choose to remove that possibility by keeping those mains wires well away from the working circuit wires. One less gotcha in the equation and it only takes a minute to layout a couple of wires to remove that danger.
In this case I can only assume the idea has inadvertently put the mains/secondaries dangerously close together.
Likely the person who designed it never realized the danger he created.

Tubes and Hybrids / Re: Help with Hybrid Design
« on: December 30, 2020, 03:38:23 AM »
Agree with G1, :dbtu:
Well the data sheet tells it as I suspected,, It's Not an *isolated 115v Tx*

It states very clearly it has 2x115v primaries and 2x 7V secondaries.

So unless I've lost it, :loco ,the only way one could get enough HT to run a valve is from one of the primary windings which means it's a death trap waiting to happen as the circuit runs off the primary. ARRRRGH!!!!
OK sure there are tons of old radio circuits that did indeed run direct from mains but most of those old units where bakalite cases and one would never come into contact with the circuit under normal use but this is an electric guitar amplifier and you ARE in direct contact with part of that circuit so if something fails you could end up Dead.
If you want to build it that is your call but I'm writing this to warm other non teck savvy folks that it's a death trap waiting to happen.

Be very careful grabbing ideas off the net some are really bad designs. 8|

To attain HT for a small valve amp there are much SAFER ways,, here is a better option for High voltage, uses back to back Tx's.

The added bonus is that it uses a 12Volt wall wart which keeps you a long way away from dangerous main voltages.
HTHelps, Phil.

Tubes and Hybrids / Re: Help with Hybrid Design
« on: December 28, 2020, 08:14:57 PM »
Hang on I just reread the 1st post and as this is your first build,, I'll assume you don't have a lot of teck skill.

Warning!!! RE this;
"The power supply for the amp I'm trying to build features an inexpensive 7-volt Antec Toroid transformer with the 120-volt coils split, making it a small isolation transformer.  The 7-volt side is used for the tube filament."

Unless I've missed something in translation,,,that tells me it is a 120/120 split *Primary* so something sounds wrong :loco

Also the way in which the power Tx is drawn up in that schematic seems strange.
Others here may know more but meantime be careful cause if I'm right as it could kill you. :police: :police:

Normally when a Tx states 120/120 split primary that means it can be wired up to either 120 mains ans 240 mains. It is most likely NOT an isolation Tx :-\
Maybe post a picture of the Tx you wish to use ideally showing the label.

Tubes and Hybrids / Re: Help with Hybrid Design
« on: December 16, 2020, 07:15:38 AM »
Yes my tone circuit draw little current.
Well you need to research another Fet stage to run a tone section.
Sorry but beyond my scope to design something from scratch like that but you can always just add another stage in front with enough gain to pickup the loss from a tone circuit. I assume it's doable,, outcome unknown??
My thoughts ,, not worth it for such a tiny amp. xP

Tubes and Hybrids / Re: Help with Hybrid Design
« on: December 13, 2020, 04:59:36 AM »
Go here , Schematic is on the 2nd post.
Yes I know it does not have a preamp  :o and some think it strange but this does not need a preamp just plug your guitar into it.
I've lost count of how many of these I have built for players and No one has yet complained.
Just make sure you you use a Log pot for the Bass. I doubt you will ever need more treble but if so just lower the value of C8.  will run on 9V or up to the limit of the opamp and cap voltages used.
I run mine on 18V
Have fun, Phil.

Tubes and Hybrids / Re: Help with Hybrid Design
« on: December 11, 2020, 07:02:57 AM »
The problem with tone stacks (assuming a normal Hiz fender type tone circuit)
is that they suck a lot of energy from the signal level (often termed insertion loss)
You can loose as much as 70% of the signal that way and you would need another gain stage otherwise the Amp will be very low on output. xP

A better option might be to add a separate tone circuit in front.
I have a circuit for such situations if you are interested I can post it?

Or maybe just use an EQ type pedal to give you an idea of how well that works.

Amplifier Discussion / Re: Acoustic G120-112
« on: December 06, 2020, 06:49:49 AM »
It's likely you have a ground loop or non grounded part of the circuit. You may need to research where the ground paths run. Generally you only want one Chassis to circuit Common point.
Normally schematics use an arrow head of horizontal lines for circuit Com and angled lines for Chassis Com,, but not always.

If you can trace the Circuit Com all the way from Power Com node through to preamp input com you may find there is more than one Com connection which could be the issue. i.e. a com point is wired back to chassis by mistake creating a ground loop.

Ground is always a problem because Schematics assume com and Chassis and are not usually shown. which makes it a tricky thing to get your head around.

Amplifier Discussion / Re: Coxx GG-30 with low volume issue
« on: December 05, 2020, 07:33:37 PM »
OK if the speaker contacts are intact then I can see you have 2 likely fail points the *power chip and the relay*.
You need to find the path of the main signal, if it goes through the relay then that may not be passing signal. I'm assuming the OD switch activates a control voltage to the relay so that may have failed.

(I'm guessing, The Reverb path is likely a separate path to dry signal and not passing through the relay ,, hence you can faintly hear it)

As Mr Jazz has mentioned you really need to isolate the input on that LM1875 power chip then hot wire a signal into it to see if it works. I'd test that first because it's a common fail point and not too hard to test out.
If that works then you need to find the signal path in the preamps/relay/reverb.

Maybe wise to spend some time to draw out the circuit,, or at least part of it.
When I'm stuck this is how I work out a schematic.
Most single side PCB's are semi translucent so with a strong light under the PCB you can follow the tracks from the component side. and draw them out. often requires several attempts and lots of waste paper.
It might seem hard and does take time but it's a good way to get the brain to connect how it all works.

Older PCB's are laid out in (human) logical format while some later pcb's use computer lodgik and they can be a real challenge to back engineer.

Amplifier Discussion / Re: Coxx GG-30 with low volume issue
« on: December 04, 2020, 02:03:29 AM »
If the amp worked before and then started to loose volume it could be a corroded contact sw.
As the amp has an External speaker output socket then check that tab on the socket. These elcheapo sockets are a common issue for fading volume loss. :trouble
The external speaker likely disconnects the internal speaker when used so wise to check.

Insert a guitar plug in and out a few times or just clean the contact points,, if you have an external speaker maybe try that as well.
It's a long shot but the amp might be working just speaker fading out due to a bad contact in that socket.

That relay has got me puzzled Any clue as to what it switches? xP

You have lost the neg rail so the power supply is the issue. with TP4 dead none of the other TP's will read correct.
so first check the filter Caps and Bridge rectifier.
  Suspect parts are D13,14,15,16. and C36.  (If C36 is dead then I would replace C35 as well)
Once those are fixed the rest of the circuit TP's will likely be normal,, but check them after PSU is fixed just in case something else has been stressed.

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