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evengravy

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1. Help with voltage conversion

Hi I am creating a project with the new arduino due and I need to convert the voltage output (0.55v to 2.75v) from the DAC into a range that is linear from -5v to +5v I have looked through national semi app note 31 and in the upper right corner of page 6 there is a circuit for voltage conversion but I'm really stuck of where to go from here, I have no idea how to calculate the offset I need and the gain required. http://www.ti.com/ww/en/bobpease/assets/AN-31.pdf I have an accurate and stable +10v and -10v supply to work with, Can anyone help? I'd really appreciate any input, Thanks and r
2. Help with a Tube EQ circuit

Hi, I have been given a circuit diagram of a tube based EQ unit and I need some help if anyone could help me I'd be gratefull. Basically the circuit is in two parts a Tube base amplification stage and a "passive" inductor based EQ circuit that "appears to me" to be in the feedback path of the Tube amplification stage allowing for both boost's and cuts to be applied at the set frequency ranges. The EQ section is fairly well understood and I have worked out the multi tapped inductor values based on the given frequencies and capacitor values. I am having some issue understanding the Tube top
3. hv transformer wiring

hero, thanks very much, even
4. hv transformer wiring

Thanks hero, I've been working with hv dc ozone up until now so sorry for the confusion, just so I'm clear could you check my wiring diagram? Thanks, even
5. hv transformer wiring

thanks hero, one question, does it matter which wire of the secondary is grounded? there are no markings on the secondary wires at all, and they are both the same colour. am I correct in thinking one secondary wire is + and one - that should be grounded? if so how would I identify which is +? my thinking is that the turns ratio is 1:13 so if I apply mains voltage to the secondary side and measure the primary side as it produces a safer measurable voltage this way, I can determine the + and - wires on the secondary. Not sure if this is even necessary? Thanks, even
6. hv transformer wiring

My current thinking is to wire the secondary to the electrode like the image attached, Since one side of the secondary is contained within a sealed pyrex tube I am presuming this is correct but I would appreciate input/corrections, thanks.
7. hv transformer wiring

hi, I am building an ozone generator using a high voltage neon sign transformer and I am a little unsure of wiring. The transformer I have is brand new and runs off 230v and produces [email protected] I want to be 100% sure of how to wire this safely for obvious reason so I would appreciate your assistance guys/gals. Basically the nst that I have bought is like in the image attached. The ozone generator electrodes will consist of a scroll of stainless steel mesh that is pushed into a Pyrex test-tube where it unfurls against the walls and a lug on the end makes connection to the circuit through a nu

"A mic preamp used an input transformer about 30 years ago but now they use an electronic circuit." Yea, I understand what you mean but there is a certain tonal advantage to using a transformer also, I see what you are saying about the impedance, adding a transformer would be wasting the high input impedance of the Jfet, If I were to choose a transformer however what specs would be suitable? impedance in/out and ratio however, in order to achieve the electrical balancing, could I use similar spec matched jfet pair (2SK-369) and the same circuit doubled, one circuit for positive input and o

audioguru: "its input impedance is 10M ohms so why ruin it with an input transformer" I really need to make this ciruit balanced and add to add phantom power, which is why I thought of adding a transformer, is there another simple way of achieving these functions without the input transformer? I know that it is possible to add dc blocking caps to allow phantom power to be blocked from entering the input, but is there a way to work with the balanced input that emulates the transformer function. even.

thanks again hero999, even

I think I may have been wrong with the output impedance values that I posted, basically the circuit (well two in series will make up the mic pre) will need to be suitable for connection to a line level mixer, after some more reading it seems as if "The impedance of the line input is high -- about 10K to 1 Meg ohms" http://www.tape.com/resource/impedance.html

so, if i understand what you're saying correctly I need to increase current through q4 such that it can drive the low impedance load but such that it is low enough so as it wont overheat. Is this correct? I have no idea how to go about running output impedance simulation, I am using multisim. also in regard to the input transformer, I understand that the input impedance is high with the jfet input, but i'm unsure how to add phantom power using dc blocking capacitors, this is why I thought a transformer would be easier, but i'll scratch that idea. thanks guys.

I know it has been a while since I posted on this circuit but I have been flat out with other projects until now, so, I have modified the circuit to include diodes between the base of Q4 and ground as you suggested and this has reduced the current to just below 6ma, I'm not sure how to simulate for output impedence, It will need to drive a 600ohm load max (i think around 75Ω @1kHz) how would I go about simulating for this, I have been searching online for answers but I can't seem to find any relative info. any help is greatly appreciated, also the ac coupling hasn't been added as I inten

thanks a lot for this i'm glad i have at least biased correctly and i will work on the current draw on Q4 and post updates as/if required, you've been a massive help cheers

im simulating with multisim 10 with a specific 2sk117gr model, which are the ones I have. some voltages of circuit in no signal condition Q1 drain voltage is around 17.3V. gate sits at 20.2mV source 133mV Q4 base 17.3V collector 36v emitter 16v Q3 base 7.5v collector 16v emitter 6.81v i've took a print screen of probe measurements from throughout the circuit. I wonder if the multimeter in multisim draws current? im using a probe this time and seem to be getting different values.

I thought you calculated current by the following: (I = Current/V=Voltage/R(t)=Resistance Total) I = V / R(t) I = 36/(8.5 + .060) I = 36/8.56 I = 4.2(mA) this is close to the value i'm measuring in the simulation also, so now i'm really confused.

"Why have you insisted on a non-standard value for R1" basically I am a little confused as to bias the fet correctly, my take on it from my reading was to aim for a figure close to the measured Idss of the measured device (gate and source connected and voltage applied with no signal) with a 50ohm source resistor the drain resistor value to bias close to 0v just happened to be 8.5k. I think I can choose a standard resistor value close to this value without significant change to the bias. "4.332mA through Q1 seems too high" maybe i'm measuring the current incorrectly. I'm measuring from Q1 drai

"I'm not sure if you understood when I talked about E96 and E24 values" oh i understood ok, just wondering whether metal film E24 values are superior to carbon E24 values in terms of noise. "You have sketched a class-A heater.." haha, might be usefull its freezing here in ireland ok, heres the full first stage with part numbers, Q4 is a Darlington which was chosen merely due to its voltage rating and I was under the impression that using a darlington would minimise loading on the jfet (higher input impedance) the bc635 is a generic npn, again chosen due to its voltage rating suiting my su

"What does the xlr grounding pin do?" Not sure to be brutally honest, I'll have to look into this, although it is on almost every preamp schematic that I have seen so far. "What load is the pre-amplifier driving?" Hmmm........well it will be driving a professional line level sound card, impedance is approx 20kΩ balanced and 10k unbalanced. "An ordinary silicon diode connected between the input and 0V will clamp the voltage at -0.6V" thanks for this, will the orientation be the other way round to the zener currently in the circuit? "It needs to have a significantly higher impedance than 4.

"think Mr Evengravy records electric guitars so he likes the even harmonics distortion caused by Jfets and vacuum tubes. He also likes overdrive but not the severe clipping distortion produced by opamps. " pretty much spot on, the pre will have DI input for guitar plus a transformer to allow mic input/phantom power and pad switch on secondary of transformer. He is lucky that the Japanese Jfets are binned into fairly low ranges of conductance. I bought so many of the toshiba parts for this very reason, shame they don't make them any more. :( "The gates of both transistors are biased at 0V

The overload characteristics are exactly why I want jfet, I can design an opamp preamp quite easily and don't want to go down this road again as I already own some very low noise opamp pre's, some based on the ina217 which I built recently, these are very very good but opamp designs from a personal sonic perspective always sound somewhat clinical. Clean sound is not always what is required during a recording session. Although in electronics design you aim to reduce distortion as much as possible, in my case the distortion characteristics of the jfet, which are similar in respect to tube desig

Firstly thanks for the responses guys, Audioguru: "Why use Jfets? Why not use an audio opamp instead?" i am looking to avoid opamp designs for personal reasons, I hate the fact the signal goes through so many stages, i love the sound of jfets and their gracefull distortion/overload characteristics. "Why use an expensive condenser mic that needs a 48V supply?" well... I work in a professional recording studio as an engineer and working with phantom powered mic's is completely unavoidable. "A resistor from the source to ground will add negative feedback to reduce the effect of the wide range