Guitar with built in amp and speaker

Status
Not open for further replies.
Jump to Latest
#22
i did see it, but those are some odd values, any reason for not making a 10k anode load and biasing accordingly? also i assume you're joining the 2 stages together and making a solid state power stage, with a 1M pot between the outputs/inputs? with higher cathode resistors i dont think you would need cathode caps that high (10uF for 2k, 20uF for 1K 4.7uF for 4.7k etc.) and if you want disortion too, dont make the coupling capacitors too big, 10nF-22nF should be fine.
 
#23
Yeah these values are odd as I haven't yet rounded them.
It's not 10k, so I can set a certain quiescent current, if I'm right it's mostly this resistor that sets the plate voltage, current,... the important stuff.

About your SS question: as far as i know I've made an amplifying circuit, so I'm not sure what you're talking about.

I'll make the caps smaller.

To make sure: I'd like to build an amplifying circuit (tubes) that uses a very low voltage (like 12V in this case) and is able to drive a small (some sort of PC-) speaker to a reasonable volume. Sadly I've looked around and couldn't really find the specs for a general speaker like this (current, voltage swings, watts, impedance,...)

BTW: the input comes directly from the pickups, so in the area of >100mV if I'm correct.

Thanks for the help razorrick
 
#24
ok, i would say you want around 2v p-p output at 4/8 ohms, so around 500mA of current, and about 1 watt, preamp tubes cant really supply that kind of current without a transformer, where as a power op amp (i.e. LM380) could easily drive a speaker of 4/8 ohm impedance. And yes, you have made an amplifying circuit, but its not all just about making a small input voltage a big output voltage.the output impedance would be closer to a few k ohms, (alot higher than a speaker impedance)

also, the plate resistor doesnt set the plate voltage/current, it determines how much maximum current can flow, and how much gain is in the stage, the cathode resistor is then chosen to set the quiesent current/ voltage.
 
#25
Google car tube radio. There's a list of "space charge" tubes. That 6GM8 has a max 20mA collector current, maybe other such tubes have greater current capability, which is what it would take to drive a speaker. Or maybe tube car radios didn't really work that way. Maybe someone can find a schematic of a car tube radio. I didn't look very hard, this is research the OP should do.
 
#26
i would guess a tube car radio would be powered by a 12k5, space charged pentode, or 12AL8 triode and tetrode. again using an output transformer 600ohms-8ohms. they can give around 100mA max, for max of 1/4 watt. of power, which probably wouldnt be far off of the 1 watt solid state power chip.
 
#27
either that a push pull config of BD139/140 or maybe IRF530/IRF9530 MOSFETs could give the power, and then put an opamp buffer around it to reduce the crossover distortion. (signal in to + terminal, connect output of opamp to gate/base of transistors, connect output of transistors to - terminal, run speaker off - terminal)
 
#28
mmm, seems like I have indeed a circuit that's not really of any help on such a low powerlevel. I'll try and find some other tubes otherwise I'll see if I can go SS (to start with as a first project).

For this circuit I thought of a PSU something like this (it's meant to be portable to I needed a stepup to 12V:
An externally hosted image should be here but it was not working when we last tested it.
 
#29
Ok, I found this schematic on the web around an LM380 as you said. It's supposed to be 2W and able to directly feed the guitar output to a 8ohm speaker.
I ahven't changed it as it is mostly just constructed using the LM380 datasheet.

I'll be able to maybe pick up the parts. I'll try playing with this and see what I can get out of it before continuing with tubes.

Good idea?

An externally hosted image should be here but it was not working when we last tested it.
 
#30
not sure about the power supply, or how well stepping up voltage would work for heater current, but for the LM380, that looks ok, i think there are also examples on datasheets, alternatively ive found there is an 8 pin version LM386 that is internally limited to a gain of 20, so a 47k pot to the - input would be the the only component you need, and then ground the + input. (i think the ruby tuby on the sopht site uses it) im also wondering if a PCF80 would work at a low voltage or a PCC84/88 would work (they have 9v heater filaments)
 
#33
razorrick1293 said:
really? i was told the first letter (E/P) corresponded to heater voltage? though thank you for correcting me.
Click to expand...

It refers to voltage OR current, depending on type.

E is 6.3V, P is 300mA, U is 100mA, D is 0.5V to 1.5V, G is 5.0V

Those are the common ones. also used have been:

A is 4.0V, C is 200mA, and K is 2.0V

Second and subsequent letters describe the valve, C for triode etc.
 
Status
Not open for further replies.
Top Bottom