100W HiFi MOSFET Amp

100W HiFi MOSFET Amp
100W HiFi MOSFET Amp
The neat thing about the series 5000 is that it was built around new (at the time) Hitachi lateral power MOSFETs. Most power MOSFETs (VMOS, trenchFETs, HexFETs etc) use a vertical structure, where the current flows vertically. This has the advantage of stunningly low Rds and hence high efficiency, but does nothing for linearity or capacitance. Lateral MOSFETs are a much simpler structure, where the gate oxide is formed on a flat substrate, and the current flows across the substrate. This results in well defined, controllable device parameters, good linearity, and relatively low gate capacitance. However, the Rds of lateral MOSFETs is nothing to write home about.

MOSFETs also have a high input impedance at low frequencies, and are capable (when driven by a suitable source) of extremely high slew-rates. Of course this very attribute makes them rather prone to HF oscillation when improperly compensated, but with careful design they're capable of impressive intermod performance.

LM3886 Power Amp with DIY Chassis

LM3886 Power Amp with DIY Chassis
This is a simple chassis using just 4 aluminum panels and 2 heatsinks. Designed around dimensions to tightly pack in a LM3886 chip amp kit. The top and bottom panels sit in ridges cut into the heatsinks with a table saw, and then the front and back panels just bolt into the end fins. Rear panel fixings are held with M3 nut and bolts, and panels that join to the heatsinks are held by M4 bolts tapped directly into the heatsinks so no additional brackets are required. Heatsinks are 75 x 160 x 50mm with a 10mm thick base.

VCO I

This is a very cool VCO of professional FM transmitter. I am sure the design itself gives some ideas to you as how to design VCOs.

Discuss this schematic in our Forum!

VCO II

Another VCO. It is originally made for 2m station, but is perfect for FM radio band as well. The mosfet serves as PLL mixer. If you want to use direct synthesis method, change this mosfet into buffer. Very clean signal, but it is narrowband. It has to be tuned every time you change frequency.Discuss this schematic in our Forum!

FET FM transmitter schematic

This FM transmitter makes for a nice project. No PLL, but stability is excellent. Does have spectral purity problems, though'. An additional filter is recommended. Giving some 400-1000mW.Discuss this FM transmitter schematic in our Forum!

World's simplest FM transmitter schematic, period.

If you cannot assemble this transmitter, then perhaps you should give up on assembling anything at all;-) Range and stability is not premium, but it works! Its a demonstration of what can be done with little to none resources. Please, don't bother asking how you could increase the power of this small FM transmitter.
Discuss this FM transmitter schematic in our Forum!

2W FM transmitter schematic

This is a bit more complicated transmitter, but gives a mile of range or so. You have to understand that it radiates god knows where, you will be making a lot of interference! This is probably the simplest 2W FM transmitter out there. Keep those two transistors cool, they can die quickly in this circuit. Don't forget that there is no such thing as a free lunch, stability and spectral purity suck. But range is significant (watch those feds).

1W PLL FM transmitter schematic

Cool little FM transmitter. Suitable for study purposes, you can use the RF part of this transmitter easily for your projects. However, unless you know how to build a serial data link and connect this LPFM transmitter to a PC or a microcontroller, you won't be able to use the PLL. All info about the PLL is available at Plessey's web page.

1.2 Watt Bullet Proof Amp For The FM-10 or FM-25

By Mycal
The follwing is a very easy to build amplifier that was designed to follow a Ramsey FM-10 and FM-25 transmitter. It is built on top of a simple PCB board surface style (all parts tacked on top, no holes in PCB.) The performance is excellent with power levels of up to 1.5 watts achevable and harmonic suppression greater than 50db. Using this amp in conjunction with an Ramsey FM-10/25 can provide you with the ideal micro power radio station with usable range of up to 2 miles or more. If you use this unit to amplify a Ramsey FM-25, build the FM-25 in the low power output configuration.
I feel this is a much better alternative than the Ramsey LPA-1 because it provides much lower harmonic output and it is relitivly bullet proof to antenna mismatches which has been known to destroy LPA-1s without the slightest warning.

The PCB board is a single sided copper board etched or grinded out to the shown layout. The board size is 3 3/8" x 1 3/8" but anything close that can accomidate the parts without any lengthing of the lead lengths is fine.

I recommend that if you don't have a good way to make the PCB that you buy the Radio Shack PCB Etching Kit, this kit works very well for this type of application. We've used laser printer iron ons for this board, but we've found that electrical tape or the resist pens work fine.


Design and Schematic:
The amplifier is a 2 stage design. The first stage uses a high gain microwave transistor amplifier running class-A to boost a 10mw signal to about 150mw.
In the first stage the resistor R1 (1.5K) gives Q1 (mpf-901 or mrf-901) and the Ramsey transmitter a nice stable input/output load to look at that should smooth out missmatches between the transmitter and the amp (note that this type of matching is only workable at flea power levels.. < 50mw.) R2 (20K) provides the bias voltage making the amp class-A. Current is fed to the stage through R3 (300ohms) with a ferrite bead on the power side to help keep RF out of the power grid. An inductor of 1uh or better can be substituted if a ferrite bead cannot be found (use only small resistor type inductors, not giant monsters from Radio Shack). The first stage is isolated from the interstage maching circuit by C12 (.001).

Intra-stage matching is done by C1, C2, and L1. This network trys to match the output impeadance of the first stage with the input impeadance of the second stage. It also provides a little bit of filtering. It should be noted here that the power output of the first stage affects it's output impeadance which is effected by the input power level. Any change in power outputs of the transmitter (most likly from frequency or power supply change) will require re-tuning of this amplifier.

The second amplifier is running Class-C pushing it's output into the output matching circuit made up of C3,C4 and L2. The output is fairly clean and can drive an antenna or another stage.

PCB board:

3 3/8" x 1 3/8"


Construction Tips:
Solder all the small low lying parts first; resistors, L3, L4, L5, L6. Then mount all the small capacitors; C5-C10, and C12. Next Q1, C1,C2,C3,C4, followed by L1, L2 and Q2. Finally add C11 and attache the input and output with coax to the connectors and/or transmitter.

Part's Layout:


for maximum output. This amplifier doesn't like to ocsillate, but this is always a possiblility. You can check for oscillation by tuning a FM radio up and down the FM radio band, if you hear multiple images of your broadcast your amplifier is in oscillation (not good).

Updates and Modifications
I would change the design slightly if I were to build more of these amplifiers. The input is not DC isolated. I would add a .001uh cap between the input and Q1. This is a must do mod if the amp is to be used as a stand alone device (ie not hardwared ont a FM-10).
I would get rid of C12, it is not necessary since C2 blocks the DC between stages. I would move C1 to the other side of C3, this allows C2 to be adjusted without effecting the C1/L1 low pass filter. I would add another 5-50pf cap from the input side of L2 to ground, thus adding an extra element and more flexibility to the output/matching filter (I would and have done this addition on every amp that I have built with an output power of under ~3 watts, cannot get -50db down on harmonics without it.)

The modifications listed above can easly be made to the existing circuit board if done during the assembly stage. Basically you would shift Q1 and its associated parts one pad to the right on the circuit board (since C12 is no longer necessary), and add a .001uf cap between the first pad and the base of Q1 pad. C1 can easly be moved to the pad on the output side of C2. And another 5-50pf variable cap fits nicely on the input side of L2.

L6 mostlikly can be optimized, but is most likely not that critical to the overall performace of the amp.

Updated Schematic

Parts List
Resistors
R1 1.5K ohms
R2 20K ohms
R3 300 ohms



Caps
C1, C2, C3, C4, (C14) ~5-50pf
C12,(C13) .001uh
C5, C7, C9 .01uf
C6, C8, C10 .1uf
C11 10uf



Inductors
L1 .2uh adjustable digikey...
L2 .2uh fixed coil...
L3,L4,L6 10uh Moulded Inductor
L5 3 turns of #22 enamal wire through Ferrite
Bead.

Transistors
Q1 mpf901 -or- mrf901
Q2 2sc1970

Schematics - FM amplifiers

Hook this one to any above VCO and voila, you have a 4W FM LPFM transmitter.

Schematics - Stereo encoders 2

another cool stereo encoder schematic. Looks better than the above model. It has a bit of noise, filtering is not sufficient, but otherwise it can be made to work extremely nicely. Substitute XR2208!
Cyber Max 15W

Schematics - Stereo encoders

Stereo encoders 1