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  1. audioguru, could you explain what you mean by input impedance? i`m a bit unclear about it. sound as an ac wave enters the signal path (input of the amp) and from that point where is the other point(s) where you are measuring the resistance along the signal path to get the measurement of input impedance? is that the whole system? just to and through the first transistor? i`m a bit confused. impeding means hindering...de-energizing a bit, or slowing down...doesn`t it? how does that relate to ohms and a weak AC signal from a guitar microphone? i read you are a master of theory...perhaps you could enlighten me. where is the impedance being measured, what are the units, what happens when the impedance is low compared to when the impedance is high with a weak AC signal traveling through from one end to the other? is resistance the same as impedance? also, thanks everyone for the helpful and surely much easier solution to making a guitar amplifier. i`m dead set on making a transistor amp though. reconstructed a 50`s tube amp earlier this year and was a great experience. now i`m in the sixties. the specs for the transistors i found are above in my first post. if no one wants to look at them and audioguru`s schematic for the pre-amp...then ho-hum. but i`m going to do it anyways. tis a learning experience. at this rate i will have caught up with the modern technology for amplifiers (perhaps the ideas you folks are suggesting would be easier for me to implement) i reckon i`ll be in my 80`s. here`s to learning! (chink) sound of glass against monitor. glug glug.
  2. Hey folks. Am hoping to get some tips and advice regarding the next stage of a guitar amp I`m working on with a lot of help so far from this forum. Thanks very much! I`m getting set to build the power stage of the amplifier...the first stage is found from a schematic and design that audio guru made for me, combined with what i alread had onboard. theoretically it should work. great! i should note, i would like to use all found transistors in making all stages of the amp. currently the pre-amp is running from two bc109s i found in an old amplifier. For the other two transistors, the power amp ones, I was digging in a local electonic dumpster and found a seemingly rather hi-fi phonograph with two BD162s therein. I pulled em and have designed a non-working power amp...yipee!!!....ahm..or...rather--- would love to get it up and running and plug my guitar into it to hear the lo-fi madness. So. my question is-- if i follow the same principles from the schematic from audioguru, swap out the transistors to the BD162s and pump in 24 volts, will this puppy be basically a working power amp? are the principles the same for the both pre-amp and power-amp? Or perhaps I have to reverse the biasing and front loading of the transistors...so that the 100 ohm resistor shown first in audioguru`s schematic go to the second in the series of the power stage.......I`m a little confused about the two stages and their similarities and differences. basically the system is guitar--pre-amp--power amp(biulding while scratching head) -- speaker (found). can someone offer some guidance as to the similarities and differences between audioguru`s schematic for a pre-amp and what would be a good power amp with these transistors (BD162s) and advise with the schematic from audioguru as a reference? that would be really super. here`s the link to the pre-amp thread. audioguru`s schematic and my hand drawn one can be found there. http://www.electronics-lab.com/forum/index.php?topic=22032.0 and here are the specs on the transistor BD162 Transistor Datasheet. Parameters and Characteristics. Name: BD162 Material of BD162 transistor: Si Structure of BD162 transistor: npn Maximum collector power dissipation of BD162 transistor (Pc): 15W Maximum collector-base voltage of BD162 transistor (Ucb): 40V Maximum collector-emitter voltage of BD162 transistor (Uce): 20V Maximum emitter-base voltage of BD162 transistor (Ueb): 7V Maximum collector current of BD162 transistor (Ic max): 4A Maximum junction temperature of BD162 transistor (Tj): 175�C Transition frequency of BD162 transistor (ft): 1MHz Collector capacitance of BD162 transistor (Cc), Pf: - Forward current transfer ratio of BD162 transistor (hFE), min/max: 30MIN Manufacturer of BD162 transistor: STE Case of BD162 transistor: TO3 Application of BD162 transistor: Power, General Purpose
  3. audioguru asked "Yes, if the capacitors have correct values, have the correct polarity and the amplifier has an input impedance of 47k or more." well audioguru, here are the capacitors i`m using at present. numbers are based on the schematic i supplied (found above)...sorry, i don`t have the spice skills. or spice for that matter. easier for me to scribble by hand i reckon. so, here they are. C1 - mica B152 C2 - electrolytic 16v 1000uF C3 - electrolytic 16v 100uF C4 - electrolytic 16v 100uF C5 - propylene(?)(blue) B 472K 2KV C6 - electrolytic 16v 100uF C7 - electrolytic 16v 47uF i wasn`t able to hook up an active microphone today, but will get a chance soon. what do you think audioguru? are these suitable caps? ok, i think i get the hang of it now. posting on the forum i mean. electronics are still illusive to me i must admit. thank you all for your help so far. -ooops....how does one truncate a posting for a specific quote? seems like i have failed to do so.....
  4. so, if i`m to understand correctly -- this pre-amp could quite possibly be functional at this point? hmmm...that would be great actually. that means i can start working on the speaker driving portion. am i right in my understanding....that these voltages i posted as "measured" from the made version of audioguru`s schematic are in the "ok range"? should i proceed to the next step? ahhhmmmmm....and i`m not seeing a modify button here....i`m simply replying to my post...should i be looking somewhere else to keep a dialogue going? not simply click on reply? audioguru, to answer your question -- til now it has been simply a 1/4 inch jack. i`ve been touching the end of the cable to see if i can get a hum/pop/or rattle of any kind to show up on the other side. i have, at one point, plugged my 50`s silvertone guitar into it....but it produced no sound through the amp. i was thinking i would hear something through the amp before putting a microphone into it as you suggested. do you think with those voltage readings i posted on your schematic that it is worth my while at this point to "hook it up" and do a microphone test?
  5. still trying to work with the help from the forum. another day of no progress...the amp still isn`t producing any sound. any ideas what i can do from here? i have put in the resistors on this drawing as audioguru suggested, measured the voltages and noted the readings.... scratching my head today. um.... what`s wrong? hopefully it isn`t frowned upon to post the same topic at more than one forum online. having read audioguru`s posting on the other forum where i posted this topic...it seems perhaps i shouldn`t be hearing a sound coming from the output side of this preamp. is that correct? someone on the other forum mentioned that i should set the bias of the transistors to get a voltage of substantially over .7 volts from the base to emitter. i`m really a newbie to building my own transistor sound amplifier....i`m not sure if this is accurate about the VBE. is it? is perhaps my preamp as posted, with the voltages i measured in blue, working? boy am i confused. not sure if it matters...but i should also note that both transistors are now bc109 thought perhaps the other transistor was bad.....but not really sure how to tell if a transistor is good....i get the diode readings from the base in both directions to determine that the flow is unidirectional, but should the readings vary somewhat...? and if so, by how much? how do you determine from the readings if the transistor is "healthy"?
  6. I`ve tried a few different things with this amp....changed the resistors a bit on the collectors and emitters....and biased the base and am getting a BE voltage of .75 seems like it should now work....at least some sound should be coming out right? but still nothing. any suggestions?
  7. Hey folks. This is my first posting in the forum. I have been working on making my own solid state amp from scratch...having some problems i guess understanding some basic concepts. in short, this is what i have built .... it doesn`t seem to put out any sound. I`m hoping someone will have the time, knowledge and the grace to guide me in the right direction with it. that would be super.. I`m thinking of this little thing as a pre-amp. I`ve also been working on the secondary stage of the amp, but perhaps think it would be best to get the preamp up and running first. Is there anything that sticks out as "could be changed and then it should work". I`m hoping whoever answers is a friendly sort. I`m not shooting for the Nobel prize with this design, just something to plug my guitar into and get a bit of sound and tone out the other end. Any help is greatly appreciated. Image shouold be attached of the hand drawn schematic. Thanks!
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