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Messages - Katoda

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Tubes and Hybrids / Re: LND150 tube emulator attempt.
« on: December 22, 2017, 07:20:10 AM »
My guess would be that it's just easier to solder, but two diodes would conduct twice the current, so I'm not really sure.

The Newcomer's Forum / Re: First real build. LM386.
« on: December 20, 2017, 11:30:15 AM »
Cool, congrats!

The gain and volume pots are supposed to be logarithmic, if yours are linear, then they probably have an exponential curve effect to the ear, as we percieve the power vs volume logarithmically. You can simulate the log response by putting a resistor from the wiper to tje ground, but then you need a bigger pot or to decrease the impedance going into the pot.

Glad to see it works, cheers.

The Newcomer's Forum / Re: Pot switch replacement on gorilla amp
« on: December 17, 2017, 04:47:35 AM »
Maybe a push-pull potentiometer?

EDIT: Or maybe it's a simple potentiometer with on/off switch? I'll PM you both, as I'm not sure about the forums policy on store links... Gotta go read the terms...

Amplifier Discussion / Re: Capacitor conducting DC?
« on: December 14, 2017, 12:03:10 PM »
When tested with an ohm meter, every capacitor will conduct for a short period of time, depending on the RC charge time. R being the internal resistance of the ohm meter. If it conducts continuously, the cap went bad.

Amplifier Discussion / Re: Help with TDA2003 amp, a big project.
« on: December 03, 2017, 01:26:45 PM »
At 9V, the chip would have less than 2W of output with an 8 ohm speaker (isn't even on the datasheet), so it really cannot be than much louder than a LM386 based design. Also, the input sensitivity is in the 100mV range and your preamp probably delivers much more, so these two things explain the output and the distortion. Oscillations might then also be coming from long flying leads and high gain.

Amplifier Discussion / Re: KMG SS Poweramps
« on: November 26, 2017, 05:12:23 AM »
Well, you might as well search the internet for an EI core that can handle 100 watts, and then just use the winding ratios from KMG site. Should be close enough.

Amplifier Discussion / Re: KMG SS Poweramps
« on: November 23, 2017, 03:39:29 AM »
I think there is no way around winding the transformer for yourself. I built the 40 W version of it, and it is quite big with the windings and all. Just be careful to get a big enough core. All of the data is on the KMG site, I believe.

Software / Simple budget oscilloscope for Android
« on: November 04, 2017, 06:21:04 PM »
So I just wanted to share this with you, in case anybody needs to check some audio frequency waveforms and doesn't have the money (or is just cheap like me) to buy an actual oscilloscope.

First I disassembled and stripped the wires from an expired headphones set, the one with the microphone (TRRS), and soldered the wires to a piece of perfboard. Both of the headphone outputs were loaded by 1k resistors, one of them got connected to a 100nF capacitor for AC coupling. Than was the signal output / sine generator output. I loaded the mic input with a 20k resistor and put 3 header sockets onto the perfboard for an attenuator. The signal flow into the microphone input is as follows:
Probe wire -> Coupling capacitor -> one of the header sockets, where you can swap resistors to form a voltage divider -> microphone input.

I just put in a 100nF coupling cap, which together with a 20k resistor forms a high pass filter at 80Hz. Gotta upgrade that to extend the lower range of possible monitoring frequencies.

There are a lot of oscilloscope apps in Play store, I chose SmartScope.
I had a lot more problems finding an app that would continue to play sound when it was not in the foreground.  I ended up with an app called Note Fork from siliconfish, which is a nice little musical note generator, but you can still choose a note closest to the desired frequency. And, most importantly, it is the only app I found that continues to emit sound in the background, although if you have a better phone than I, chances are you will be luckier in finding a more suitable program.

Attached is a picture of a measurement I took to look into transformer distortion. The peak-to-peak value is not to be trusted, but the waveform is nicely visible. Depending on the phones sampling frequency, you can generally measure up to 20kHz.

So if anybody wants to analyze some clipping circuits on a budget, here you go. Hope somebody finds this useful.

Also, coaxial probe leads are quite beneficial in this application.

Preamps and Effects / Re: Designing that OP-Amp OR15-soundalike
« on: November 01, 2017, 06:50:01 AM »
So I did the calculations for the first gain stage, they might be a bit off, since i didn't print the load lines, but dragged a ruler over my laptop screen.  ::) The DC bias point is -1.8V on the grid, so it will clip the signal 1.8V in one direction and 2.2V in the other. This renders a quotient of 2.57, if you choose the lower clipping threshold to be a standard silicon 0.7V diode. So for the first gain stage, the gain should be 2.57 times smaller, the op amp output impedance should be around 38.5k, like in a tube. With the antiparallel diodes you should aim for Vf1=0.7V in one direction and Vf2=0.85V in the other.

There ya go, repeat the process for the rest of the circuit.


Preamps and Effects / Re: Designing that OP-Amp OR15-soundalike
« on: October 31, 2017, 06:11:40 PM »
Hey, I would say welcome to the forum, but your nice introduction makes me feel inadequate to do so, since I am usually mostly a visitor myself. So hi. :)
You transcribed the schematic nicely, but you have to take into account that you will be working with low voltage and different impedances, so you will have to scale either the op amps or the rest of the signal path accordingly. Also, antiparallel diodes will produse symmetrical soft clipping, while the tubes tend to have  a more asymmetrical character. If you want to get as close to the real deal as possible, you should add another inverting  op amp stage after every clipping stage, and only clip one half of the signal at a time. To determine how much to clip each stage, you will have to study tube datasheets and determine clipping points for each stage in relation to the signal. When all that is done, you will probably have the most sophisticated solid state distortion pedal, but it will probably also be incredibly close to the real deal.

Damn, I want to build something like that too. I'm going to if you're going to   :cheesy:


EDIT: Forgot to answer the question  :duh:
I think you should just appropriate the miller capacitance of the tubes in regards to the impedance driving it to form a low pass filter. In the op amp circuit, you would then calculate the cutoff frequency of the cap and the resistor to the VCC. And that cap isn't necessary, since you are decoupling the signal to the reference voltage. If you were to tie them to the ground, in your example, would create a different DC bias point for the op amp. Also, on the schematic, the input 1M resistor should be tied to the ground, as tou don't want half the supply voltage across your guitar. There should also be a buffer after the tone stack, then a coupling capacitor and a resistor to the ground. Again, you don't want any DC on the thing following your preamp.

Second EDIT: Just got an idea, but it would take quite some experimenting to get it right. To conserve some op amp stages while still retaining the asymmetrical clipping concept, one might experiment with using diodes with different threshold voltages, and/or diode biasing resistors. If you get the clipping right, you're 90% there. But it would still require a lot of research.
I'd start this way: Determine the clipping points for the tube stages,  they will most likely be around 1-2V. Then, compare this to the diode forward voltage drop, which is around 0.7V for silicon diodes, and adjust the gain of the op amps by this quotient. To achieve asymmetry when clipping, you might have to go through some different diodes, but you could also just connect two of them in series for a clipping threshold of 2*Vf. Or, you could calculate the signal current and add a resistor in series with each diode to adjust Vf ever so slightly. Once you have the gain adjusted to the diodes (so approximately 70% of the tube gain) and the diodes set to approximate tube clipping, you should scale the op amp feedback resistors to match the op amp output impedance to that of a tube gain stage, which is the plate resistor parallel to the tubes internal resistance.
Also consider using a higher supply voltage instead of the pedal-classic 9V. More voltage equals more headroom equals more precision when adjusting clipping points.
Good luck!

Amplifier Discussion / Re: Fender Frontman 15G
« on: January 29, 2016, 11:48:05 AM »
Most likely the TDA2030 burnt out. I had the same problem, instead of replacing the chip, I took all the guts out and built in some valve stuff  8)

Preamps and Effects / Re: EVH 5153 preamp with LND150
« on: January 13, 2016, 07:46:43 AM »
Thank you :)
I followed the lead channel of 5153 schematic (fender), with a basic gain stage like the one KMG came up with, using Bav99 and Bat54s diodes, from this post:
R3 was 180ohm, except on the third stage, where there is an unbypassed 39kohm source resistor, there its 270ohm. In the original schematic, the cathode resistors are mostly 1.8k with 1uF bypass and 2.2k, here the source resistors are mostly 2k2 with 1uF bypass and 2k7. Plate resistors are the same. The resistor before the 1uF capacitor is 680ohm.
For the power supply i have a 15V AC input, from which one path leads to a rectifier and 7812 regulator to get -12V for biasing the mosfets, and the other goes to an ugly 230-12V Ac transformer on top of the enclosure, which gives out about 340V.Filter caps are 2 680uF/200V in series, each in parallel with a 270kohm resistor.
The gain pot in 100kohm with 4.7nF treble bleed cap, as opposed to a 1M with 1nF.
And instead of the cathode follower on the 5153 version, the tone stack is plate-driven, as in 5150.

Sorry, I don't have a schematic, but this is pretty much it :)

Preamps and Effects / Re: EVH 5153 preamp with LND150
« on: January 11, 2016, 12:09:36 PM »
I didn't have a proper mic so I just turned the volume waaay down until the phone mic wasn't clipping and recorded a sample of the cleanup with the guitar volume knob.
Gain was on 11 o'clock, on the recording I gradually increase the guitar volume.

EDIT: Listening to it again, the gain was set kinda high, metal territory...

Preamps and Effects / Re: EVH 5153 preamp with LND150
« on: January 05, 2016, 04:14:06 AM »
Hello, thank you  :)
Yes, I only built the preamp, which is going to be played through the FX loop of my Fryette Deliverance project. I don't currently have the amp at home, but as soon as I get it I will post some clips. I am also anxious to try it with a real tube power amp, so far I have only played it through a small tda2030 based thingy.
The impulses are basically recorded speaker frequency response and behaviour, so a sort of fancy eq. It doesnt sound quite as good as a miced up cab, but at the time it was (and sort of still is) the only option. I have to ask a friend to borrow his mic again.  ::).  But kind of the reason I didnt play any actual riffs myself is that I've heard these DI tracks in many gear demos and I thought it might be a good comparison with the real thing. But I will put up something for sure, this little preamp is my favourite new toy :)
Also, perhaps it is worth the mention that this thing has waaay more distortion than I need, so I have already changed the 1M gain pot for a 100k one. Way better, now I can get it in the zone where it cleans up nicely with the guitar volume pot.

Preamps and Effects / EVH 5153 preamp with LND150
« on: January 03, 2016, 11:08:52 AM »
Just to see how it would have turned up, I attempted to recreate the preamp from the ultra-high-gain EVH 5153 (the Fender version) with the base of research being KMGs fantastic JCM800 preamp with LND150 mosfets, implementing the diode grid current limitation and therefore closely emulating the 12ax7 tubes. I ran out of space pretty quickly, because I was using two perfboards superglued together in a recycled enclosure from a 'true' tube Pittbull preamp project. It looks ugly as ****, but it cost me about 10€ (except the LND150, I had everything at home and/or at hands reach) and it sounds awesome. Having never played the original amp I cannot claim it sounds the same, but from what I heard on YT, its pretty close.


Some sound samples - Lasse Lammerts DI tracks reamped  through the thingy, with some impulses (Peavey 4x12, i think - or recto):

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