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Messages - phatt

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31
Guitar News / Re: It's 2020, and Germanium Fuzz pedals still sound awesome
« on: February 08, 2020, 02:40:16 AM »
Thanks Joe,, Well not my thing and it sounds just like all the other fuzz boxes I've ever heard/Played. Always hated that sound as it just trashes an otherwise good sound.
The kids obviously love em and they are still getting rave reviews. The circuit has been rehashed many times over and it still sounds crap to me  xP
 but each to there own opinion. :tu:
Phil.

32
Amplifier Discussion / Re: Peavey Stereo Chorus NEW noise problem
« on: February 08, 2020, 02:32:03 AM »
My thoughts if useful,
Maybe post the schematic will help.
Sounds like you might have 1 or 2 issues.
The buzz behind the note might be *Crossover distortion*, the bias in the power stage might need adjustment. (or as Enzo said dodgy supply)
Re, Killing buzz by touching strings might be a grounding issue.
Schemo would be a huge help.
Phil.

33
Amplifier Discussion / Re: Marshall Lead 12 testing and repair questions.
« on: February 07, 2020, 03:13:08 AM »

If the bases of Tr1 & Tr2 are as stated then it's a fair bet the most likely problem is the Output Tr's.

but maybe check this first before you swap out parts willie nilly;

Lift (unsolder) the input side of C8 (it's the input to power amp) now use your walkman or any audio device that has line/headphone output.
You should hear a reasonable medium level CLEAN sound.
If the sound is severely distorted or very low volume then it's a fair bet the power transistors are shot or TR3 is dead.
Phil.

34
Amplifier Discussion / Re: marshall G30R CD clean channel volume problem
« on: February 07, 2020, 03:00:42 AM »
The most likely problem is the Volume pot is not grounded.
Several possibilities; the Volume pot itself might have cracked the ground pin,,or a cracked track,, a cracked or cold solder joint on the PCB.
Use plenty of light as these cracks are often hair thin and hard to see.
Phil.

35
Amplifier Discussion / Re: Vox Mini 3g2
« on: February 03, 2020, 07:54:35 PM »
Hello Max & welcome,
                Disconnect the speaker wires at the speaker and check with a meter it should read somewhere between 4 and 8 Ohms if it's working.
If you don't have a meter then tap the terminals of the speaker with a 9Volt battery,, you should hear a click/pop and the cone will move. if no sound then the speaker is likely blown.
Don't leave the battery connected for a long time.
Phil.

36
Amplifier Discussion / Re: Marshall Lead 12 testing and repair questions.
« on: January 31, 2020, 05:17:24 AM »
Wow...okay.   So my readings...


TR1
B to E = -.59 v
B to C = +19.73 v

TR2
B to E = -.56 v
B to C = +18.49 v
Test point voltages are referenced from Ground.
So black probe on Common/Ground/Chassis, then with Red probe check the test points.
Then post your readings.

*when probing TR2, B to C, it puts a hum to the speaker.  Sounds like 60hz.

Cannot determine "junction" of R15 and R16.

not important, just check the test points you can find.

Signal tracer?  Are we talking about inputting a low-level audio signal and testing for it at IC pin 1?

Yes you can inject a low signal into certain points on the circuit to find the offending part.
but I would be checking you have close to correct voltages at those test points on the poweramp first.
Phil.

37
Amplifier Discussion / Re: Marshall Lead 12 testing and repair questions.
« on: January 30, 2020, 12:10:52 AM »
Measure your DC supply voltages,,Might be a good place to start.
IF? the schematic I'm reading is the correct one,, then you should have ~20-0-20VDC for power amp and about ~15-0-15VDC for preamp.

The test point voltages are written on the schematic for the power amp section.
The Emitters of Tr1&Tr2 should be -.7Volts,, Collector of Tr1 should read +18Volts.
Junction of R15&R16 should read -9Volts.
If one of those readings is way off then that will help folks work out what'sup. :tu:
Phil.

38
Schematics and Layouts / Re: guitar amp diagram revision help
« on: January 26, 2020, 07:44:48 AM »
Thanks Joe, yes I was fairly certain that was the case. :tu:

Yeah I get your point about the fun of building your own rig,,,,but you have to buy and build everything. xP
Yes a kit is a good way to go, assuming you are talking just a power amp kit?
BUT you still have to pucha$e; a speaker, transformer, face plate, knobs, maybe some paint and vinyl covering,, add speaker cloth, a cab handle, rubber feet, corner caps.
Then you have to design a circuit from scratch that may end up no better than a $40 bargain from a second hand store. The circuit posted is a small 10/15Watt basic circuit and these can be found on landfill sites if you hunt around and you may even get lucky and pickup a whole amp for nicks. (well that depends on where you live I guess)
Having built a lot of amps from kits and from scratch,, I can tell you that the chance of success at first attempt is very low. Even worse if it's a first attempt. :-X

On the other hand ""IF"" *Watermelon33* has played an amplifier that uses this EXACT Design and it delivers the sound he wants,, then yes it then makes logical sense to build one because you have already heard the result.

My advice would be buy something cheap and back engineer it, you will learn a lot faster and avoid the eternal frustration of building a circuit only only to find it sounds nothing like what you hoped for.
cheers, Phil.

39
Schematics and Layouts / Re: guitar amp diagram revision help
« on: January 24, 2020, 07:39:05 PM »
BTW, X1 is NOT a buffer. As for distortion, just adding diodes won't work well, you would need to add an extra stage to get a reasonable outcome.
You could add an input buffer stage and alter X1 to work like the link *Joecool* noted above.

Also, I believe the TDA2050 is no longer made, though you could use LM1875, others here will know more.

The reality of this is that you it would work out a lot cheaper and many times easier to just purchase a small amp. xP
Phil.

40
That would be a waste of a good malt whisky.
Your tone would sound a lot better if you drank the whole bottle. ;)
Phil.

41
Tubes and Hybrids / Re: 12 v tube preamp
« on: January 17, 2020, 08:59:30 PM »
hi Flester,
AFAIK, Tiny Terror is all valve running on high voltage.
I have no doubt that running Valves on low voltages will work but I doubt you will do much better than SS pedals.
The big thing with Valve rigs is the High voltage and the way in which the supply is delivered to each stage.
I think the term is  High Impedance supply, these sag as power is increased giving the classic compression feel. There are of course many other things that make all valve amps do the magic but just altering the values of the drop resistors in the supply chain changes the way the whole amp responds to how you play.
I doubt that will happen if running an AX7 at 12Volts.
Phil.

42
Amplifier Discussion / Re: Crate CR112 tone stack
« on: January 10, 2020, 07:33:11 AM »
Hi Jopy, Your amp circuit is an oddball and I doubt it will ever be ideal.
The Treb & Bass are Passive while Mid is Active, (mid similar to TS9 tone control).
I've just done a quick simulation of the preamp and it looks like it might be a design hickup. :loco
Sims are not perfect but handy for giving clues as to what might be wrong. 8|

The first thing I noticed is p2 (Level) is not grounded in clean mode causing a wacky tone curve and your bass starts with a 5dB hump at 5hZ,,, WTF? no guitar amp will work well with a response curve that low. :duh
That might explain why you have to back off the bass so much.
In clean mode p1&p2 are not in circuit but if I ground p2 while in clean mode then IC1 works in a normal manner, bass rolls off at ~100hz. Though you would then need to lower the value of C3. try 50pF.

The best I can make out is p2 needs to be grounded all the time otherwise IC1 works more like a notch boost at 5hZ.  :crazy2:

I've noted the area of schematic in question, see pic. maybe check that on the pcb as schematics are not always correct.
Of course when the OD is engaged the response curve is closer to what I would consider a normal curve. but then the diodes conduct and you might have more diode fizz to deal with.
It's complicated to explain as there would be a lot to do to make it work the way you want.
Hope that helps, Phil.

43
Tubes and Hybrids / Re: JTM60 Combo rectified diodes fried
« on: January 03, 2020, 07:38:20 AM »
Do you have the schematic? That will help you decipher which is which.
The pcb will likely have the reference numbers printed on the pcb.
Maybe post a pic as that will help us. 8|
I'm guessing you have about 8 secondary wires, 2 for HT, 3 for Filaments and another 3 for the opamps.
HT will be ~ 300 ish VAC,  Filaments will be around 3v5-0-3v5 AC and the opamps will be ~ around 12-0-12 VAC.

not sure about the bias,, might be tapped off the HT?
Others here will know more.

You will need to build your self a limiter before you turn it on other wise you might just blow up more parts.
See here for details on how to make one;
https://www.ssguitar.com/index.php?board=2.0
3rd post down.

Phil.

44
Tubes and Hybrids / Re: Laney VC30 Output Transformer
« on: December 13, 2019, 12:03:26 AM »
1760J looks like it would be close.

Generally a pair of 6V6 use ~6k pp
while a pair of EL84 would be ~8k pp

The reality is,
there are many OT parameters that effect the final outcome.
Phil

45
Tubes and Hybrids / Re: Laney VC30 Output Transformer
« on: December 12, 2019, 09:01:56 AM »
The links are mostly for 6V6, you need a Tx for EL84.
IIRC a quad of EL84 needs a primary winding plate to plate of 4k.  Pri Z is usually just written as (4k pp) on data sheets.
Others here might know places in your location to find a Tx that will work well for that amp.
Phil.

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