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Messages - Tassieviking

I have seen multimeters that physically block the holes when you turn the knob so it is only possible to use the volt probe when volt is selected and only amp plug when amps is selected, but it was many years ago.
I wonder if you can still get some like that anymore, maybe it was just a temporary fad that went for a while.
megatrav: I would really love to build my own hybrid amp with a tube preamp and solid state power amp for gigging.

Have you considered building / getting a valve stompbox from Sushi Box ?
He has valve pre-amps in stompboxes, add a DI and you could go straight to FOH.
Get a class D pedal amp and a speaker cab and you are ready to rock.
Crap !!!!
I just went and pulled apart 2 of my Flukes and I have weird fuses as well, I think I have replaced some a long time ago as well but the company I worked for had a draw full of them.
I wish I had kept some spares with the meters now.

No wonder I have some cheap Uni-T meters on the workshop bench, I think they cost around $30 when I bought them. (Many years ago). I know they use cheap fuses as I blew one working on my car.

You can get some fairly decent meters on Ebay for under $20 ($10 up) that are ok if you are only working on low voltage stuff at home for yourself. I would only get Cat3 rated stuff at least.

I will leave my Flukes to have a rest unless I decide to start working for a living again.
I do not need a good meter anymore as the highest voltage I work with now will be  240v mains in my own gear.
EDIT: maybe a bit more in valve amps (a lot more).
Any Cat3 meters should be enough for any private use I think.
That is too much for a normal fuse, what type is it ?
Photo ?
It is usually a M205 fuse that costs cents, sometimes a ceramic type but still cheap.
I love your dedication to learn electronics, not many people would take it upon themself to do it so thoroughly with textbooks and lessons.
By the end of this year I think you will be good enough to really get into pedal designs and even amplifiers.
It won't be long before you can start designing your own PCB's and have them fabricated so you can build your own projects.
It is great fun when you want a pedal that is no longer made and the old ones are costing a fortune, make them yourself really cheap.
Keep up the great work.
That was a good find, I once read a post when someone preheated an oven to 400F and placed the DSP PCB in there for 15 minutes as a last hope to reflow the solder, it restored it back to working condition.
I think it was a Fender where the DSP PCB's are no longer available anymore and they had a reputation of bad solder joints, you have to love the lead free solder that always gives people trouble.
To get asymmetric clipping like that makes me wonder if the input to the OP-Amp is biased at 1/2 voltage.
Can you measure the voltage across pin 4 to 3 on IC1, also across pin 4 to 7 and pin 3-7, all with no guitar plugged in.
If it is not set at 1/2 you might be able to tweak the value of R16 and R17 until you get exactly 1/2v at the input at pin 3 on IC1.
You might even have to change the bias slightly off to make IC1 clip evenly.

This is just my thinking and i could be wrong, I think the bias on the input to the OP-Amp determines how the output hits the power rails and flattens out.

If you have a spare 20k pot (or bigger) then connect it to 0v-22v and lift the leg on R20 that goes to the +11v and connect it to the viper on the pot, then you can adjust the bias voltage you have created to see what happens to the clipping on the input stage. (If you can understand my crazy way of explaining it)

Rail to rail clipping is used to produce distortion in some amps just like people use diodes or leds to clip the waveform to produce distortion, it might have been intentional on the amp just to make the sound you don't like but the designer wanted.

EDIT: I did a quick trace of the preamp to see what I got, I used the values already quoted and also the references.(I haven't double checked it or anything)
It looks like a basic baxandall tone stack for Bass & Treble and then the Mid is just like the active Mid in a Lab Series L4 Bass Amp.

I think it might be a line out since it is not variable, the one marked Pre Out has a volume pot.
Headphones would also need a level/volume pot.
The output might also be for the VU-leds so you can see if you are over-driving the gain stages before the master volume ?
I can't find any info on the old Randall R-412 DXT cab neither, are there any more markings on the speakers ?
Look at the back of the speaker cones and on the metal frames, sometimes there is information with speaker dates and builds etc.

The amp is 300 watts output but it uses 500 watts to make the 300 watts for the speaker. Some valve amps are much worse then that.
I would place the effect in/out between the Post Gain pot and C20.
It might be easiest to remove C20 and run 2 wires to the new jacks from there, place a C20 cap between the return jack and PCB. (Solder one leg to the jack and the other to the wire)
Looking at a WT300 PCB (R74, R75) it shows that location as a 22k and 47k resistor at the 12AX7, bottom left of the WT300 schematic.
Looking at the WT400 schematic it shows the same thing just different component numbers.(R81, R82)

I presume they used a WT400 Preamp PCB to build that WT300 amp.
You might not need a heatsink for that module unless you are going to run it hard, just try it and see what happens.
You can get stick on heatsinks from a lot of places, you will have to see how much room you have and order one that fits if you want/need one. I think you will just have to peel the tape of and press the heatsink down to attach it, they are really easy to use.
Google stick on heatsink and you will find lots of them, and they are cheap to buy as well.

Read the spec sheet on the 3118 chip and see what it says.

Personally I would get a MeanWell 24V power supply that is rated around 100VA to get plenty of headroom for one of those modules.

The biggest question would be what size heatsink is sitting on the TPA3118 chips, and are they 3118 or 3118-D2 chips on those modules of yours.

To run at full power the chips should have a heatsink on them, but most often they don't have any installed on the Ebay amps.

I went with the TPA3116-D2 mono 100 watt boards from Ebay a long time ago when I tried them, they had a nice heatsink on the modules so I got them.
I think I used a 24V 120VA MeanWell supply to run one for a home practice amp, it worked fine but it never got run hard.
The ICE power modules are well priced for what you get, you can get cheaper modules from China but often you have to buy a power supply and an amplifier and put them together.(And most likely not run them anywhere near the advertised power without dropping out from overheating)

The  Straight Ahead Amplification power amps seems like someone is just putting pre-bought modules into a cheap box and selling them from home, I could be wrong but I would not buy one unless they have been fully certified for public use like that.

If you want and need a really powerful amp then it is best to buy a good quality made one as it will be certified with all the various agencies required nowadays.
I don't think that it would be worth the effort to build an amp from scratch if you want to truly be able to gig with it, I believe some venues might not allow non-certified gear to be used due to insurance reasons.
If an arena was to burn down because of a musos homemade amp caught fire there could be serious problems with the insurance companies as well as with the legal implications if someone got hurt or worse.

If you want your own sound then build a preamp in a stomp-box and run that into the return jack on a commercial amplifier, proper Class-D Bass amps are not that expensive and deliver a lot of power. Certification  can cost $20,000-$50,000 to get through for a single amplifier model and that has to be included in the final cost of a proper amp you can buy in the shop.

If you just want it for home use then get/make whatever you want and go for it.
Have you read Teemu Kyttälä's Book about solid-state guitar amplifiers ?
There is more in it then most people will ever need.
I would not recommend plugging the effect send into the input of another amp, however if you measure the voltage from the guitar itself and then turn the volume of the amp down until the send signal is the same or lower level as from the bare guitar it might be ok.
The output of a guitar is very low so you do not want any signal you put in to be much higher then that or you risk damaging the pre-amp of the other amp.

Make sure you turn the level of both channels right down if you are going to try this.