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 - dsmnoisemaker

#1
Amplifier Discussion / Re: Transformer output
February 19, 2010, 11:46:44 PM
Vrectified = 1.4 x Vsecondary
#2
Preamps and Effects / Re: DIY Rat Problem... HELP!
September 24, 2009, 12:38:55 PM
lm308 has the same pinout of most common single opamps..i have directly replaced lm308 for TL081 & 071´s and worked fine..even better IMHO.
check your board, resistor values, and check the fet.
#3
Amplifier Discussion / Re: Ohms question
September 24, 2009, 11:56:12 AM
A friend of mine bought one of those, and ask me to transform it into a guitar amp..
i totally dismantled it and build a 2 channel tube amp with reverb, fx loop, etc.
check it out here:
http://www.youtube.com/watch?v=2muKFCCx5l0&hl=es

i connected it to a 8ohm speaker with no issues..on tubes, impedance mismatch is not as a big deal as with SS.
#4
well, it is partially the same thing..but not.
speaker frecuency response graphs show the typical response of a speaker under a low impedance power source, that is, using a very linear amp..
Tube amps, being transformer- coupled to the speaker, have high output impedance, so the impedance curve of the speaker generate nonlinearities (apart from the natural freq response of it)..

picture a SS very linear amp hooked to a celestion speaker..the celestion speaker will respond like the curve (steep high rolloff at 3khz, bass cut from 100hz down)..we add the higher impedance simulator, and we have a boosted 100hz and enhanced highs, sounding more punchy and open. Try putting a graphic eq on the fx loop with a similar curve. sounds great!
#5
thank phatt, but looks like you didn't get what´s the objective of the circuit. It is not a cabsim..its a replica of what a high impedance amplifier output does to speakers..a cabsim may be added after that to simulate an actual speaker response.

#6
Thanks JM (gracias vecino!)
The advantages of using this on an amp are:
- you get this feature of tube amps without using mixed mode feedback. This means it is usefull for BTL configs and others that make MMF difficult to implement.
- You get the response fixed regardless of the speaker used (different speakers have different peaks)

i have to breadboard this to check clipping behaviour (on simulation looks ok, but on reality may be different)

next step is to get variable freq response like saturated transformers do. i have two plans:
- easy cheap one: using diodes to change frequency response by "stages"
- better, harder one: using envelope detector and LDR´s....
any ideas?
#7
OK..this is the version i did with cmos inverters:


upper inverter is a resonant peak filter tuned to ~110Hz with a gain of 10dB with a reasonably nice Q.
Lower inverter is a hi pass filter.
Both are mixed through resistors, balancing the response.. Probably will need a buffer after due to high output impedance (ironic, isn´t it?) of cmos inverters.
I like inverters because they are cheap, available, they auto bias, have nice clipping characteristics and need little extra components to make them work.

this is the frequency response:


i like it more than the marshall ckt, since the 110Hz peak is sharper, and nearer an actual speaker response..but i miss the "mix" capability of the marshall ckt..any idea how to implement it easily here?
also, i´d like to just use 1 inverter for this.. i tried using different feedback configurations, but the resonant peak eats everything else..
#8
thanks for the info JM, i´m now reading it..
Anyway, i managed to get a very similar response from 2 CMOS inverters in paralell (one as a peak filter at 100hz, the other as a high pass filter , and mixed back)..I like how it turned out, but is very, very component sensitive (well i´m dealing with 8dB 100hz peak, and 8db boost on high frequs above 2k, so, no wonder)

I simulated the response with my behringer eq after a distortion, and it gives nice "thump" and clarity..but i like the marshall solution cause it´s easy to control de "mix" of the effect (replacing the 56k resistor for a pot on the feedback loop of the upper opamp) with the eq bypassed, it sounded dull in comparison..

PS: I´m writing from Santiago, Chile..regards!
#9
thanks for your response teemuk.. btw, most of my projects get a lot of help from your book  8) , amazing info there, it´s my bible now...

I don´t think i´ll be able to compete with marshall or other commercial brand out there, i´m still a boutique builder doing this for fun on my free time..although maybe someday it will be my main occupation (if i ever loose my day job i´d give this a chance).

i think i´m going to insist on developing my own approach to this, i have a nice 3 CMOS inverters cabsim, and maybe i can use a couple more on getting the response/compression/dynamic frequency response.....
#10
Hi all:
I´m designing a tube power amp "approximaton", in which i simulate the trasnfer curve of tubes using a diode ladder, to get sucessive gain reduction versus output amplitude, like compression..

After that i added something similar to the marshall output impedance simulator (http://www.freepatentsonline.com/5467400.html), but instead of a opamp, i´m using a transistor as a gyrator, and some other values for components..

i tried to do the same thing with CMOS inverters and twin-t filters on feedback, but somehow i don´t get the same kind of response, looks like phase shifts don´t let me mix the treble boost with the bottom peak in a nice manner (like the marshall ckt does).

so, i decided to keed the marshall type simulator..but i´m worried about IP..maybe, eventually i could sell this things, and i wouldn´t like to get "cease and desist" letters from them..

a penny for your thoughs....
#11
haha, i mess with the chip number.. i meant TDA7293..
but still mensur, according to the datasheet, its maximum power is 100w at 4 ohms @ +-30v, but this thing has a fairly complicated current feedback ckt so its power sould be lower..

also, at 100W the THD is 10%..yikes!
#12
Amplifier Discussion / Re: LM3886 Spice model
September 01, 2009, 12:42:10 PM
 ;D this is more than 2 years old..

any guide how to use it with ltspice?
i create a .sub file and how i link it to a symbol?
#13
i couldn´t find a difference between the MG50DFX and the MG100DFX schems you posted..
i don´t think that the MG100DFX uses only 1 TDA2394..maybe 2 in BTL mode?

by the way i noticed that the power capacitors were only 1000uF?? isn´t that too small?
#14
Amplifier Discussion / Re: LM3886 Spice model
August 31, 2009, 09:15:26 PM
any idea how to add this to the ltspice library?
#15
my fav amp is my 90´s bandit..its clean channel is just superb, and the distortion chennel its very versatile (i use my own made distortions anyway)