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Messages - phatt

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Amplifier Discussion / Re: Z-MATCHER 100W IMPEDANCE MATCHER
« on: September 13, 2019, 09:12:11 PM »
I'm not the expert but logic suggests that as there is no HV & Hi Z primary (as in Valve output Tx) then the Z matcher would not need to be as big.
I would assume it's just a low Z matching Tx with switching taps.

Have a look here not quite the same thing but obviously uses rather small Tx but still rated at 100Watt and only $30. Before you ask,,I have no idea if this would work for Valve guitar Amps. :-\

Maybe check the trim and pot wipers are actually in contact with tracks.
That can stop it from working.

The Newcomer's Forum / Re: Lab Series L5 settings please?
« on: September 01, 2019, 10:40:36 PM »
Welcome to SS guitar. :tu:
I don't know the amp but too many variables to give meaningful answers.
Type of pickup SC or HB, Speakers used, pedals you might use. Many things need to be in place to make it happen.
You can try an eq pedal in front,, maybe even a Treble booster.

Be aware that one persons idea of *sounding like a Fender twin* might be very different to your idea. :-X

Schematic shows this amp has 2 inputs, top one has a passive type tone circuit which might prove to be more useful that the second input which runs an active tone with sweep EQ as well as that multi filter. (which I don't fully understand??)

The original Fender twins normally had a lot of bass at V1 & V2 while the input to power stages had a big bass roll off.
Change that cap from 1nF up to a 22nF and it will no longer sound like A Fender Twin.
It will just fart :lmao:
I use pedals to get my sound/tone/breakup and can run that into 3 quite different amps and still get a similar tonal outcome.
As much as I hate pedal boards I've realized that it's easier than trying to mod amps. (Sand or Glass)

On my Pedal board,
I use a tone circuit, a Treble booster and a compressor along with a simple OD setup.
This covers most of the classic rock/pop styles I play. If you are into heavy metal grunge then this would not work.
The tone circuit and Tboost are my own designs.
If you are into building pedals I can post them here?

You have to experiment a lot before you find what works.
And for bedroom players don't assume the fantastic sound you hear at low SPL will equate to stage stardom,, At high volume it most likely will turn to crud.

Amplifier Discussion / Re: Zener vs IC regulator for the preamp section
« on: August 30, 2019, 11:41:58 PM »
Who told you zeners are unstable?   A zillion guitar amps use zener regulated supplies for the op amps.
Maybe i should have said that generally IC regs are more reliable?
I don't recall having to replace any IC reg circuits I've worked on. But you have many more years of experience than myself.
In my limited experience I've had to fix a few Zener regulated circuits.
Maybe not so much the fault of the Zener but the way it's implimented.
I can't recall exacts now but I recall a couple of SS Amps where the zeners have run so hot it delamed the copper track,,Overheating and killing the Electro beside it.
If only a little more thought went into layout and stand off the zener from the PCB it would have been ok?

Also after replacing the Zeners in my old faithful SS Laney twice in the first~5 years I ripped them out, replaced with ICreg and has given no issues in the last 10+ years.

Amplifier Discussion / Re: Zener vs IC regulator for the preamp section
« on: August 30, 2019, 10:22:48 AM »
Zener or IC reg will make no difference to any *Organic mojo*
These are SS amps and without any form of OD the amp will have no feel.
these trick have to be done in the preamp stages.
to get power stage rattle in SS power amps you need to have years of practice at building gear.
I use an old Laney keyboard amp which is rather basic and *Sterile* by itself but all the tricks are in the pedals I use, easier and cheaper than trying to reinvent the wheel of Valve power stage compression and all the other mojo that goes into that.

I have 6 pedals on my board 3 are brand names and 3 are my own designs.
This covers all my needs from clean to heavy OD. I don't play metal or like so I only need the classic rock which is often just a bit of compression and rattle. Some call this the edge of break up.

as to regs,, IC regs are trouble free and would have better regulation.

OK good to hear you are ok with it.  :tu: sorry i missed the point but I did have one young chap who almost blew himself up assuming the circuit did not need a transformer and wanted to plug it directly to mains. xP

The Headphones might be powered from the preamp hence it works ok to that point.
Sounds like a power stage problem.
Things to try;
number one, with meter set to DC Volts check if there is any DC voltage on th output,, report the result,, it should be very close to Zero DC.
Look for hairline cracks in the solder pads, use a magnifying glass in sunlight to find them.

It may have a Zobel network on the output (google it if not sure),, normally a cap and resistor across the output.

check for any overheating caps or resistors on the power amp as these parts can drift after years of service.

pock around with a wooden chop stick and gently wiggle parts and see if you can get the sound to change.
That may give clues as to what parts are failing.
Sorry We can't be much help.
Maybe take pics of the guts and post ,, that may give clues for folks here to help.

If you bypassed the Mains transformer and you are STILL ALIVE to talk about it then consider yourself very VERY lucky.
NEVER bypass the transformer of an amplifier. :trouble :trouble :trouble :trouble

I doubt the amp has been as lucky as you,, as the much higher voltage would have most likely destroyed the circuit and likely not worth fixing. :'(

I'd advise you to get help from a qualified tech shop to check out if it's worth fixing.

If you have 20VDC across the speaker terminals then (as Enzo has already noted) the chip is likely fried.

Disconnect that speaker until you get zero volts on the output otherwise you could burn up the voice coil.

Check to see if the Zobel network on the chip output has signs of over heating, a sign there is instability,, possibly bad layout, circuit design.
If so then others here may know what is wrong.
The Zobel is the series resistor and cap across the output.  It should be as close as possible to the output terminals of the Power chip.
If there are signs of discoloration (overheating) then check that resistor is within tolerance.

To the best of my understanding the LM1875 will work,, though you may have to replace the zobel.
TDA2050 data shows 2R2/2Watt and 470nF,, while the data for LM1875 shows 1R and 220nF.

I just did a search on TDA2050 and spider 2 and 3 seem to have a habit of blowing.
so maybe bad design or maybe counterfeit chips.  :-X
hope that helps,, Phil.

Amplifier Discussion / Re: Gallien Krueger 800RB
« on: August 20, 2019, 02:22:45 AM »
Well have you checked the voltages on the schematic?

If that 5 Ohm resistor at R57 is running hot then I believe that is a sign that there is Hi Freq instability.

What is the DC reading at idle?
Then how much does it drift as you increase power?
I'd haz za guess the issue is early in the signal path.
If C11 is stuffed that may send it into oscillation.
A scope here would be the best way to tell you what is going wrong.

Also don't forget to keep a keen eye on simple things like dried /cracked solder pads.

Amplifier Discussion / Re: Kay 708 amp repair
« on: August 19, 2019, 05:29:54 AM »
Yes I could not load your posting before  :loco
Seems to be working now.
So post the schematic and other pics :tu:

Amplifier Discussion / Re: Pedal into TPA3116, impedance problems?
« on: August 14, 2019, 07:56:55 PM »
It's a digital power module and most will have way tooooo much bass for guitar use.
Just insert a capacitor between the pedal and power amp to roll off some bass.
At a guess start at 22nF and then go down to 10nF,, keep trying different values until you find a balance. :tu:


BTW, Thermal Paste although not conductive does not Isolate.
Never rely on it as an insulator, you need the washer.

Re the pic,,The tab of U1 is still grounded because the screw is not insulated.
But don't try to insulate it as that will break the link with C26 and D10.

Amplifier Discussion / Re: Peavy Rage 158 no sound after 1-5 mins
« on: August 08, 2019, 01:44:09 AM »
AGND1 has a circle around it in the circuit diagram AGND does not (and input jack ground actually says "CHAS", what does that indicate?

Update: Circled Ground No. 5018 Noiseless (clean) earth (ground): To identify a noiseless (clean) earth (ground) terminal, e.g. of a specially designed earthing (grounding) system to avoid causing malfunction of the equipment.

Yes the circle obviously means it's isolated or ground lifted from chassis.
Basic logic suggests that U1 is directly coupled to heat sink (no washer) but the heat sink MUST be isolated from Chassis for that to work.

Amplifier Discussion / Re: Peavy Rage 158 no sound after 1-5 mins
« on: August 07, 2019, 11:45:35 PM »
The best I can make out between the schematic and pcb layout at the bottom of PDF is that the tab of the power chip needs to be grounded to the heat sink but the heat sink should be isolated from Chassis.  So I think you are on the right track.

That pcb pic shows D10 and a wire link connected to a copper pad (right side of U1) which connects to the heat sink when bolted down.

I can only assume the 2 screws should be insulated from the heat sink and the heat sink is then isolated from case via a mica washer.
But the screws would need to pass through a plastic sleeve so as not to make contact with the heat sink.

Maybe parts were lost when someone fiddled with the amp before you got it.

Amplifier Discussion / Re: Peavy Rage 158 no sound after 1-5 mins
« on: August 07, 2019, 03:40:18 AM »
*Chas* would obviously mean Chassis/Case.

I can only assume that input socket is meant to be grounded to Chassis and therefore the Power chip needs to be isolated with a mica washer or silicon pad.

The break between the 2 grounds can also be seen at R49 / C32 of the power supply.

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