Menu

Show posts

This section allows you to view all posts made by this member. Note that you can only see posts made in areas you currently have access to.

Show posts Menu

Messages - stormbringer

#1
Amplifier Discussion / Re: Preamp suggestions needed!
September 08, 2013, 02:52:14 AM
Emulator.
#2
I would not pre-regulate with a resistor, it will get really hot. Use the regulator instead, a preamp shouldnt need much power, so the 9V regulator with a small heatsink (not even sure you need one, but there are so many cheap ones) would be fine. I have read about pre-regulation quite a bit, but the only really good way in my opinion would be some sort of switching circuit, and with the small amount of power needed for a preamp it would be overkill. Also, leaving about 3V or more headroom for he regulator is a good thing for stability.

You could also regulate the 9V from the 12-rail, if you think the total power will exceed the maximum the 7812 can handle, google 7812 Pass transistor. That way you can put a bigger transistor, that can handle the additional power in the circuit, you will need to heatsink it anyway though.
#3
Amplifier Discussion / Re: Serious Blocking Distortion
August 24, 2013, 10:20:10 AM
I think it would work more as a treble/prescense control than gain, you could switch between 2 different source resistors instead and probably get a more satisfying result. The source bypass capacitor helps with the gain as it has a low impedance path to ground, but the size affects frequency rather than gain.
#4
Amplifier Discussion / Re: Serious Blocking Distortion
August 23, 2013, 05:01:53 PM
if you place the tone stack between your jfet and bjt and increase the bjt gain you have your recovery stage done.
#5
Amplifier Discussion / Re: Serious Blocking Distortion
August 20, 2013, 03:45:33 PM
You will Always lose signal level with a passive tone stack. So either add a recovery stage, or increase the level Before the tone stack.
#6
Amplifier Discussion / Re: Serious Blocking Distortion
August 07, 2013, 04:50:28 PM
In my opinion you can get quite warm distortion from jfets, i would suggest trying different types, and maybe make the gain adjustable.

There really isn't any magic about distortion, filtering Before and after to shape what frequencies get the majority of the distortion etc.

let's take a well known tube amp (analysis is from ltspice, not sure how accurate):

The first stage is a Clean amplifier stage that increases the signal level and rolls of frequencies below 70 hz.
the second stage clips the + side of the signal, filter after rolls of some of the highs
the third stage clips the - side of the signal, filter after increase high mids
fourth stage clips the entire signal, and drives the tone stack. which schoops out the mids and goes to a buffer stage.

This is a high gain amp, but as you can see, there is alot of filtering going on, not just bringing the signal up to clipping.

But also, as i said: try a different jfet aswell, mpf102 and 2n5457 are quite easy to obtain and used in lots of guitar effects, you will have to rebias them though.
#7
Amplifier Discussion / Re: Serious Blocking Distortion
August 01, 2013, 04:33:26 PM
Well, you changed the bias for the jfet, the question is if it clips now adding overdrive, as it is an input stage, i Think you would want it to stay Clean, but if you like the overdriven sound, maybe replace the bjt/diode stage with Another jfet stage.

Problem with overdriving the first stage and removing the clipping diodes will be that the 100k pot will not be a gain pot anymore, but Another volume pot. But as i said, maybe the jfet distortion is the sound you are looking for, and in that case you could just replace the clipping stage with a jfet instead.

You should probably check the level of the sound coming out of the jfet, and listen to it with the audio probe. Maybe the level is way too high, and hence the diodes clip no matter what level you turn the gain pot to? Or maybe the Bias on the BJT is incorrect? what's the DC level of the input/output signal?
#8
Amplifier Discussion / Re: Serious Blocking Distortion
August 01, 2013, 01:30:28 PM
I Think you got the 100k pot reversed if turning it down creates distortion. You could absolutely try different diodes, (Try leds, diodes in series etc). Nice to see you got it up and running! Good job. :)

#9


that is a simple, but awesome tool. you just connect it through any audio Equipment with a sound input, i usually use it through my Zoom R16 Sound card/portable studio, as it has LED VU-meters which will show me the signal level aswell as letting me hear the sound.

But also, i Think replacing that 220k resistor with a 1M or higher will be a good thing to test.
#10
Cool. :)

Actually the overdrive level might be volume related, have you made an audio probe? it's usually very helpful in finding out where the signal weakens.

The 220k Resistor does lower the input impedance, and might be what lowers the volume.
#11
I really dont intend to hijack the thread, but just for the sake of it, how would parallell caps act of used for DC blocking? :) I have been taught for example that often 2 smaller caps can be a better choise than one bigger for example as filter capacitors after the bridge rectifier in a Power supply, due to the lower ESR. What if you would use, let's say 2x470uF in parallell instead of 1x1000?
#12
It only affects the low cutoff according to the datasheet, and my calculation says 16 hz original, around 70hz with 220uF. You can try it, and if you later feel you lack low end you could increase the capacitor later.
#13
Hey. In my opinion i wouldnt say that building your own stuff gets much cheaper, atleast not while learning. It will definately be more fun though. :)

It depends alot on what type of amplifier and sound you are looking for. About where to start, how experienced in electronics are you? :)
#14
There's alot you can do with clipping diodes to experiment and find what suits you best. Right now you have "symmetric" clipping. it clips both positive and negative side equally, by putting one extra diode in series with one of them, or using for example 2 different diodes (maybe a LED and a standard Silicon diode) you might get interesting results. But start out easy, and then you can try out different configurations. :)
#15
Hm.. I dont think using the clipping diodes in the power amp is a good idea. They should be located in the preamp section, preferably followed by another gain stage to bring the level back up again.

Stage 1: the input stage, raise the level.
Stage 2: clipping stage
Stage 3: recovery stage.

With a gain pot before the clipping stage you get controllable distorsion, without the output volume being affected as you know the total voltage after the clipping stage depending on the diodes used. That way its easy calculating the optimal gain for the recovery stage.