V+(R)/GND= 25v, V-(R)/GND R= -25v. It also hasschematics for bridged and parallel amplifier circuits: Its also good to have the Overture Design Guide. Im trying to understand the origin of the mathematical formulas. Hi, I really enjoyed reading this ! Cheers. The Fc with a4.7 F capacitor would be: An Fc of 1.69 Hz is pretty close to my desired 1.5 Hz, so a 4.7F capacitor should be good. The right channel PCB is mounted upside down so that the input side of the board is close to the RCA and 3.5 mm input terminals. Heres one channel of my amplifier attached to a properly sized heat sink: Now that youve calculated the power supply and heat sink requirements, the next step isto find values for the components in the amplifier circuit. Talk to you next time. Due to the length of this post, I decided not to cover the power supply in detail, but I may do so in the future. Just about finished building the amp as described here. Ill be using the schematic below. On each amp board, on the signal input side , the SIG_GND connects to any of the SIG GND on the PS output side of the PS. Measure the mV output at the speaker out terminals. You can do this in two different ways- Build everything into the original amp housing or build the additional controls into a separate enclosure. To prevent interference between the inductors, they should be spaced apart or oriented at 90 angles to each other. But if you still want controls-knobs like I do, then researching in which way a controlscircuit is less likely to decrease/alter the soundquality could be the way to go from here. If you use an ALPS blue velvet pot there a small PCB boards available (Ebay or Amazon) that mount directly onto the pots pins and make wire attachment easier. Hi Pete and off course everyone. If aground loop protection circuitis used, all input and output terminals must be electrically isolated from the chassis. Im confused. Happy building! Hi. What a painless way of integrating theory, a bit of math, and circuit understanding to a fun project. Check the solder joint at Pin 8 of the LM3886. When you connect a powered audio source to your amplifier, magnetic fields fromthe sources transformer and power supply wires can be coupled intothe ground wires of the audio inputcables. Rodolfo, hi Military grade Silver Mica capacitors SSG2 0.1uf at 0.3% tolerance (possibly the best capacitor made) The power supply is all important and IS a part of the signal path, it controls it. Usually the trans that is stated to be 18V runs a little higher, maybe 19-20V so 19+19V = 38V then times 1.4 = 53V. Jrgen: the gerber PCB files are referenced all the way at the beginning of the article. I used 14 AWG, but anything larger than18 AWG shouldbe fine. After correct connection the. Wonderfully and informatively written. NASEOH, Chembur Maitrikunj Building Mumbai - 400071, Maharashtra, India, Carry Bags and Multiutility Bags & Pouches, Shop No. I am having a hard time finding X7R Ceramic resistors. and one from amp to receiver. Now that weve seenhow to calculate the component values, we can startdesigning the PCB layout and wiring scheme. I will definetly try a build on my own. Yes, and in addition to Johns advice, I would ask you to specifically try grounding the (-) side I the signal input as well, if that was not implied in his response. My power supply delivers + 34.5V 35.5 V to the amplifier end. Many thanks too for the fantastic links. Cc before Rb? To convert voltage gain to decibels (db) gain, use this formula: Higher value resistors create more Johnson-Nyquist noise, so its best to find an Rf1/ Riratio that providesyour target gainwith low resistor values. For the power supply circuit, how can I connect diodes and capacitors to safely give the required voltage and do away with the transformer. I was wondering the same thing. In my understanding there schould be an non polarised Cap, because there should be Years ago I made a very simple gainclone, cs: The thermal resistance of the gap between the chip case and the heat sink. ); This is 3u flight case for power amplifier. Thank you for your suggestion, Well done for a great article. If there nothing to do with the toroidal, do you think i can change the voltage rating of the caps with success? the rectifier I use other design , 50% more capsitor Does not matter, this is very silent when you change input, no hum, no noise. The bass is verydeep and clean. Simply adding some controls could decrease/alter the sound quality output, or not. Number of Elements per Chip 1 You seem to have calculated 10% of 110 as 1.1 when it should be 11? At least to me, but Ive been listening only to Yamahas for the past 10 plus years. The lower limit of human hearing is 20 Hz, so theFcshould be well below that to prevent attenuation of bass frequencies. I have a set . To hold individual components in place while soldering, use a putty likeSticky-Tac on the top side of the PCB. I have just been testing only one board. A bit much perhaps? This is know as a ground loop, and it can createhum in your amplifiers output. We havemore tips and tricks on designing PCBsin ourHow to Make a Custom PCBarticle, so check that out if youre interested. This is what you posted to me just before with how I suggested to hook up the tranny to the PS input. Thank you! The combination of bulk caps should provide low impedance current throughout the frequency band for the load. I recently did some comparisons with some other amps, and I find my gainclone is quite slow in the deep bass, not very dynamic, so Im trying to improve it. Anyone has any idea on how to be qualified in order to build this amplifier without major mistakes ? The 20K resistor shows up in the Stability Components Rf2 & Cf section. Heres how I installed everything inside mychassis. The video at the beginning of the post will give you an idea of what it sounds like. The individual ground networks are connected to the main system ground so thathigher current grounds arecloser to the reservoir capacitors. Therefore, smaller values ofRsnmake the Zobel network more efficient at filtering radio frequencies, but it also increases the cutoff frequency, which in turn reduces its effectiveness. most likely its a ground fault. I learn a lot, specially about grounding. Im thankful of an Answer if I missunderstand something. Thanks. Alternatively, can we purchase the finished CBs (not stuffed) from you? I put some changes in Powe supply A pop up box asks for an email address.
I was using this project for almost a year without any problem. Wery nice article! Awesome writeup, many thanks! Fusing both AC line input and power rails are the best but more work and expense. The design is definitely not the best looking :-) , more so as I purposely made a design that should be small enough to have 2 PCBs on a 100mmx100mm board. I have the same ground for both signal input and output, signal ground, which is then connected at one point with the power ground. I needed to have learned many things from reading this article, and building this amp, before I tackled the My_Ref amp. And I have a few questions: Is there any reason why the input capacitor C1 has such a huge voltage rating well above the theoretical maximum of 60.4V from the positive to the negative rail of the power supply? The main system ground is located as close as possible the reservoir capacitors on the power supply. No Alessandro, thats not what I said if Im reading your response correctly. Also, some airflow spacing is needed around the caps. On the PS out side of the board are (from one side to the other) V- (L), V- (R), Earth, V+(R) and then V+ (L). Relay contacts sometimes get worn/coated over time but youll only be having pre-amplified signal going through (not like relays for speaker protection). Hello! Some designs used only these parts For input: I will add a comment to this post: I calculated the total cost of accuiring these exact components in The Netherlands (europe): 80 (mouser) + 180 (hificollective) + 120 (modushop enclosure including heatsinks) + 50 (ebay/amazon/other) = 430, in total without pcbs. https://www.indiamart.com/stagelineelectronics. I would also like to see a follow up post with details on the power supply. Ive learned a lot from your detailed sections on build and theory. Can you provide more details about your power supply circuit. thanks man. (This is where you find air flow holes across the entire top and bottom of enclosure.) These calculations will tell youthe correctvoltage and VA ratings for thetransformer youll use to power youramp. No electrical contact exits. Realistically. Only one thing- why the pcb ordering link wont work anymore? If the muting circuit is not getting its necessary current to shut off no sound will be generated. Rb and Cc form a low pass RC filter that sets the upper limit of the amplifiers bandwidth at the non-inverting input: In the datasheet, Cc is shown connected betweenthe non-inverting input andthe inverting input. Is it isolated from touching the case ? 2. However, as I mentioned before, the hum only exists when the input is left open (without any connection to it). You can really feel it. The way you explained all the design papameters was very useful to me. Posted by Scott Campbell | DIY Electronics | 247.
great, thanks so much, you just made my day! Just a question: if I want to use a volume control, how should I set the input resistor to limit dc offset due to input bias current? Use low ESR bulk storage caps and minimize inductance lengths. Also, at the same time provide IC centric decoupling of the supply. Use the metal tab version of the part. I do not care particular brands of capacitors or any other components as long as their specs meet requirements. Thanks. Thanks for replying and giving me at least the first hints on where to start troubleshooting. My guess is that the fault lies with the amp chips. Set the Low Frequency Cutoff at the Feedback Loop the diagram under that title I think needs the 20k resistor between output and neg input. You already found a value for Rf1when youset the gain of the amplifier. How did you obatin electrical continuity between the front, back, side, top and bottom panels? Thanks. Although its a bit more work, I prefer the T version for the 0.8 C/W increase over the other. The power ground and signal ground are the only ground networks on the PCB. Hello John, do you have any more boards left over? I have built 98db sensitive speakers, without physically large speakers its a little difficult to achieve sensitivity
and always thanks for your support. I also added the decoupling capacitor, 1) I am just starting to get into DIY audio and while this amp seems like a great quality amp and the article is very in depth I am wondering if this is too complicated for a first amp build? It will ask you to save the file first so do that. These values came from the original LM3886 data sheet as I remember. What kind of transformer are you using btw? Second is to place fuse at the output end of the lytics. I have built a couple of the Peter Daniels Audiosector Gainclones before. Like all the other, simple LM3886 or LM3875 gainclones Ive built the soundstage was magnificent, airy and brought detail to the music Ive never realized before with my regular amps & DAC combinations (nothing high end). It turned out after a week of troubleshooting that it was the zener diode in the mute circuit that was the reason for the distortion. It will then give you a download box for the gerber file. Ci is still bypassed, because I cant find good quality capacitors around, and I was able to get very little DC at the output. Use thisSingle-Layer Air Coil Calculatorto find out how many turns you need for a particular wire diameter and coil diameter. Hi.. very interesting reading, enjoyed every moment of it. Thats why it blew. I did build my own enclosure with about $25 in material and I cut back on the high priced input coupling capacitors to another high grade film type. i burned the 2 caps in 2 different times, the 22uF first, then i made a new board and the 1000uF blew. My opinions are based on listening judgements and not electronic measurements. Rich: I think the author only wanted to show the two components of the high pass filter in that diagram. EasyEDA is a full suite schematic and PCB design software/manufacturing service thats free to use and offers great prices on custom PCB manufacturing. Start soldering the smallest components first, andwork yourway up to the larger components. That wayCcstill filtersradio frequencies, but italso acts as a low pass filter that willset the upper limit of the amplifiers bandwidth. I am now in the process of building 3 way active speakers, initially with crossovers then with dsps fed through a preamp. Heres one of the PCBs: High currents flowing through the power supply and output traces will createmagnetic fieldsthat can generate currents in the feedback loop and input traces if theyre routed parallel to each other. I second the request for component details, such as the voltages of the caps that cant be read, if possible. I have just finish the buikt This is an Excel spreadsheet that calculates output power, heat sink size, gain, and other useful parameters: Since this is a rather long article, here are links to the differentsections: You can also check out this video to see a quick overview of the design process. of the build guide. So with Rf1at 20 k, thevalue of Rinthat balances the input bias currentfor my amplifier is: Youll probably be able to find a 19 k resistor available with the type of resistors youre using, but 20 k is the closest value I could find with Vishay-Dale PTF resistors so Ill have to settle withthat. V+(L) / GND L = 25v , V-(L)/GND L =-25v Tambis the ambient temperature inC that the amplifier will be operated at. I started with 1.5 Hz, but you can use higher or lower values if you want. Nice project, good explanations, etc. Since the inductor will be carrying the full output current of the amplifier, the wire should be heavy gauge. 2-Cim,Rb,Rin PS schematic https://drive.google.com/file/d/1pk3knK2XnM-miUWUE3pPuHc-KMmIOE6N/view. As an electrical engineering student, I love getting the chance to truly understand the process of creating the design. A complete schematic, as well as components values for the power supply will be greatly appreciated, Thank you so much in advance. I still dont understand where the 50VDC is being measured. When you convert the transformers AC voltage to DC on the power supply, the voltage actually increases to about 25V due to the bridge rectifier. Its also well above the upper 20 kHz frequency of human hearing, so higher audio frequencies wont be attenuated. A single chip for each tweeter and a parallel pair for the woofers. What do you think of these changes?
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