I would recommend starting with a 12AU7 in the second stage until you get a feel for the drive levels required. Come to think of it I have seen a places on the net. As a follow up, would a stunted volume pot like this work? This will give you the opportunity to tailor the frequency response to your particular situation. Universal Pre-Amp - This is the universal pre amplifier circuit diagram that can be used for common input such us microphone, cd player, tape recorder or other electronic circuit which require pre-amp. This will probably not drive your LM1875 very well. Please excuse my ignorance, I am a newbie. …and more or less confirms my suspicion that it might not be a good idea to put both preamps in the same enclosure, though I was intending to pay attention to shielding the power sections of the two devices. My primary question involves how you are taking the THD measurements. Also, if you want to archive your vinyl LP’s inRead More Well, the theory of negative feedback says that the reduction in distortion is the same as the feedback factor. The ability to customize them gives you a unique opportunity to own a reference quality phono preamplifier that restores the sound of any recording to the way it was originally intended to be heard. One of the members had suggested building a Super Simple Single Stage Preamp (“4S” Preamp for short) and there was much discussion concerning various tubes, gain, noise, etc. This will significantly tame the overall gain when using the ECC83. The BHL RIAA preamp has a nominal gain of ≈40dB or 100v/v. If you are looking for an all tube design that supports MM cartridges and RIAA equalization, the best I can recommend is the “Grove Watt” preamplifier designed by Bruce Heran at Oddwatt audio. Hi Matt, is there a step-by-step type instruction for this pre-amp and what would it require to crank up the gain to line level? What can i do? The math doesn’t seem to add up. In that case, I might still use the 4S as a tidier destination for the cables from the RIAA, and place a selector switch on that chassis phono / tuner which essentially just bypasses the 4S when I’m using the turntable. Selling my McIntosh C40 preamp. On one other note, like all my other tube gear, it looks pretty good in the dark as well. 1. The signal generator allows me to test the unit at various frequencies and input levels, the oscilloscope shows me the input and output waveforms, and the volt meter allows me to directly calculate gain at any frequency without trying to get numbers off of the oscilloscope. interesting little preamp and so simple. This can lead to the capacitor destroying the tube if it fail in this manner. Or a resistor from the Cathode to the other Cathode. Things are fairly cramped inside. While this is a good preamp design, it really isn’t low noise enough to give good results with a microphone and it definitely lacks sufficient gain by a significant margin. For medium signal inputs, the frequency response offered by the design is just flat. But achieving and measuring that 0.001% distortion is very difficult. Probably comes from the grid of V1 to the output of the CF about 40kOhm resistance. Obtaining a nice clean B+ supply doesn’t seem too daunting, and I’m not sure yet whether I want to go the route of a big old honkin’ 5U4 and a double-pi-filter, or take the coward’s way out with one of these hybrid potted 250V PWM switch-mode widgets I’ve saved from various cannibalizing expeditions. Internally there is a metal shield between the two sections which is held in place by one of the card guides moulded into the cast chassis. Martin; The application of negative feedback in the 4S+CF circuit is a relatively simple matter. This is a 1:4 relationship. This avoids hum inducing ground loops when both chassises are grounded via the IEC connector. https://www.dropbox.com/sh/s9wt3acclrz5cjp/AACQ8tbk-rh5i86qDbSxPxN7a?dl=0. For this build all voltages were as calculated to within a reasonable margin of error. Thus was the 4S “Universal” preamp born. FREE Shipping. This is because speakers present a frequency dependent, complex impedance which tends to mask circuit operation. It will make the input signal is higher. Therefore, I would like to use the ECC83 in the first stage! Just be aware that if you are using the Hammond power transformer, it will increase core heating. Hi Matt, input voltage: 50mVrms And eliminate the 500kΩ grid resistor on the first stage. So you should have plenty of filament current available for the 12BH7. As for a step by step guide, I really don’t have one. When used in aircraft avionics we are required to place a fuse in-line with every tantalum capacitor just in case they fail shorted. The Universal Mono Phono Preamplifiers are all based on the same circuit board and only vary in their size, features, parts build, and power supplies. 0.50 Amps -15 VDC Current Out, Max. i think your hypthesis could be right. A couple of years ago, after much internet exploration, I found your site when looking for a tube amp design, and decided to build your Lacewood V2. You might get it to work, but it won’t work well. This could be accomplished with an 8kΩ and 2kΩ resistor in the divider network; the 8kΩ between the CF output and the 4S cathode resistor and the 2kΩ between the 4S cathode resistor and ground. First, with no input and both preamp and amp turned to max, the setup was dead silent. thanks in advance Phil Murray, Phil; COVID-19 quarantine gave me the insentive to get back into my audio hobby. what would happend if I use this configuration: iPod or a apple laptop – your S4 tube preamp – an ADCOM 545ii (100 WATTS p/ch) AMP – and a great pmc twenty.22 speakers? This is a little more complicated, but will also meet your balance requirements and provide good CMRR. I am interested in your thoughts about this approach. Thanks for the reply. Thanks Matt. . so your amp should have an input impedance greater than about 320kΩ. Values on the circuit diagram are subject to changes. Francis. Thanks for this great design. If you could go over to the diy audioprojects forum thread for this project (http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=4628) and post your question along with a schematic showing exactly which voltages you are measuring and what tube you are using, that would help a great deal. A small switch and a little LED would be all that you need to show with signal and power connections in the back. He is using Shure SM57 and 58s. You can get the 6CA4 data sheet,including pinout, at the following link: https://tubedata.altanatubes.com.br/sheets/093/6/6CA4.pdf. Maybe you can send me per Email? And the added effective dynamic range really let the amp open up. You can think about it this way: In a light load condition the first capacitor is going to discharge very little and the rectifier current waveform is going to approximate a square top pulsed waveform. I think i will add an input selector to. But the sound is very light. Is this with a 12AU7 or a 12AV7? You may need a preamplifier using IC. And don’t worry about the B+; 280v is fine. Input will be both Moving Magnet Stanton 500, and Denon High Output Moving Coil cartridges. Do you think it would sound better than thru the pioneer elite av rcvr ?. microphones). I think they call it RIAA. Thank you for the response. Thank you Matt, realy impressed with what you have done here. If connected, this pin should tie directly to the signal ground. It should make for a very nice sounding system. If it is well constructed, the dynamics should be improved by up to 4 dB and the anode current could even be reduced. DIY Audio Schematics Tube Linestage Preamplifiers. I am wondering how I could manage a lower gain… it’s loud even with a 12au7 at 8. Personally, I would build the 4S with selectable sources, but I would put the Boozhound unit in a small chassis with a switch and an LED and then use a good quality transformer based wall wart to power it. My first thought is to build a version with a tone stack and buffer. That some builders do say that the “real” distortion is actually the measured number minus the calculated reduction due to NFB. The connected 100k pot on the left and right input of the circuit will allow adjusting the input signal. AF0008 is an inline barrel adapter ensuring minimum influence on the sound field. A line level signal is +4dBu which is 1.228v rms. This means that the socket needs to be wired differently. Here in my office with a 12au6 in place the usable range of the volume control is between 6 and 7 o’clock. below the target of 0.6%). Furthermore, I assume that the output of this pre-amp is ok for the 6sN7 pre-amp stage of my amp (6SN7-300B SE). 1. too noisy, and, Circuit gain will be proportional, to the feedback resistor value. I purchased a Linn Sondek LP12 on eBay so I can listen to my vinyl collection I haven’t listened to in 30+ years. The B+ required is + 250v. As for your request to “crank up the gain to line level”, I’m not quite sure what you mean. Can this circuit be used for that? Universal Preamplifier using 741. Not with the sound mind you, but with the attainable power level from the amp. But the sound is very light. Hi Matt, I could have gone for a printed circuit board approach, but I really enjoy point-to-point build techniques for vacuum tube projects. One of the two oscilloscope channels should also be connected to the signal generator. Also, if by some manner it sinks enough current, the tantalum capacitor can catch fire and burn like a miniature road flare. I would like to be able to say yes but unfortunately, this preamp just doesn’t have sufficient gain to serve as a microphone preamp. Description. I have a silly question about this pre-Amp. Leaving its imprint on countless classic recordings from Ray Charles and Frank Sinatra, to iconic titles like Van Halen and the Beach Boys’ Pet Sounds, the 610’s tube-powered mic preamp and EQ gave anything … So back to it. If you’re using the 6SN7 you might want to consider this circuit. But that doesn't keep the manufacturers from publishing it. Instead of trying to run wires from the top plate to components mounted inside (which would make working on the box and sealing it up problematic) I decided to mount all of the components to the top plate. Velleman K1803 Universal Mono Pre-Amplifier Kit, Multi-Colour. The simplest way to do this is a restive pad behind the preamp. Take a look at my blog post here Sizing up a new Power Triode and you’ll see that I use a resistive load (the unit with finned heat sinks in the back) so that I can accurately determine how the tube is performing. Why not parallel? This is not anymore an 4S preamp , This is higly interresting as I measure the way to go before finding a solution. Crosstalk: -100db (100hz), -85db (1 khz) and -65db (10khz) The real question is how much gain do you need? Maybe in Kobination with a positive feedback! You need to make sure that you really want that much gain. My contempt for thermionic emission grew over the years due to the self-destructive and generally cruddy, temperamental nature of tube TVs, so I happily embraced silicon for all it was worth. So lets say that the amplifier as designed has an open loop distortion of 0.57% (i.e. I’d run the output of the RIAA to one of the selectable 4S inputs. I think this is also ok for my 33k classD amp. This is much appreciated. Total harmonic distortion: 0.03%. So the actual end to end gain they need is 20*log(20/1.228) or ≈24dBv. Or i got a little problem where the b+ split to plate, one got 60vdc and 80vdc on the other. Personally, if you want to use tubes, I would suggest the preamp from the old 1975 RCA manual. To meet this broad requirement, most amplifier designers include a single universal preamplifier circuit. 24 Hours fast turnaround, Excellent quality & Unbeatable prices, $18 Welcome Bonus for new registrations Now https://jlcpcb.com, © Electronics-lab.com – 2021, WORK IS LICENCED UNDER CC BY SA 4.0, By continuing to use the site, you agree to the use of cookies. As such they tend to add a pleasant “fullness” to the music. And it has the added benefit that you can add another layer of vibration isolation to the turntable by choosing the proper feet. So lets say the designers need 50W from a line level signal (i.e a standard power amp design). The 4S Universal preamp is a super simple single stage line level Hi-Fi preamplifier that will work with any of the 9-pin miniature 12A*7 twin triode tubes (12AU7 12AV7 12AY7 12AT7/12AZ7 12AX7). And this is only for speaker testing and not amplifier testing. There are two conditions where I like separate power supplies. Interesting note about the bizarre Fosgate device: the filaments were evidently operated at partial voltage, didn’t visibly glow, and the tubes were lit from underneath by orange LEDs! A simple voltage divider with a 24.9kΩ resistor in-line and a 10kΩ shunt to ground should give a -10.8dB reduction in output level. The cap following the power tube is shown as 33uF@450v. I have only done point to point versions of this preamp. In this picture, the iPod line out is driving the preamp, the preamp is directly connected to the Lacewood amp and it’s volume is at max. This entailed hooking up the preamp to one of my other units. Does this one delivers enough gain to get Line level (+4dBu) from mic level (-40dBu aprox)? You may need a preamplifier using IC. The first step is to simply power up the unit and check all the major voltage points in the circuit. Said unit croaked again a few days ago, and because I wasn’t impressed with the design and build quality, rather than overhaul the stupid thing again, I decided to strip it down to a bare chassis, rummage around on the web for a nice simple preamp schematic, and what should pop up but your lovely design, which I’d like to insert into the pre-out/main in loop of my Yamaha receiver. 5 band program equalizer 3. As a new person to the tube world, the last option sounds interresting but I am far away from being able to calculate all values needed : capacitors, resistors, biais, gain, HV rails…. The PGA is 100k in and < 1k out. But in a heaver load condition, the cap discharges more and the waveform starts to look more like a sawtooth waveform. First, my %THD measurements are made much like yours. My Leader LAG-1208 has distortion specs between .05% and 1.5% (-66dBv and -36dBv) depending on settings, but getting down to below -60dBv is finicky on this particular unit. In pure tone testing I use the FFT function on my digital oscilloscope to determine the dBv levels of the harmonics, I then convert to absolute, and RSS them to get a total. Universal Audio 6176 Tube Channel Strip Analog Channel Strip with 610 Tube Microphone Preamp and 1176LN Compressor $2,699.00. It uses a reasonably sized grid stopper to control clipping and bias excursions, a pure restive load, and a high impedance grid resistor to avoid loading virtually any driving device. Microphone preamps have two basic requirements. I have built it before, it works well and is easy to assemble. As can be seen from the table, the peak gain can be varied considerably by choice of tube and the distortion (virtually all second harmonic) is very well controlled. Appreciate you taking the time, learning a lot from this site. You also talk in the diy forum about a circuit with the 12au7 and a output impedance of about 6,5k. My answer was to design a universal stage that would work well with an entire range of tubes. The power supply design in the paper for the “Ghost Amp” has a peak rectifier current of 260mA. The natural output impedance of the stage can be as high as 39kΩ meaning that any volume control used should have an input impedance of at least 156kΩ. e. Hi Matt, I have sent you an email. Switchable with a switch? Have a 2.0uf MIT coupling Caps, and used a couple 12AT7’s, but paralleled the 2 sections to have 1 tube per channel, so compensated on the resistors because of paralleling the 2 sections. However, it has a very high gain and therefore I would like to incorporate a negative feedback. I’ve got some 47uF, will that be ok ? 20W low-distortion monitor amplifier (if you use horns the C40 actually makes a fantastic integrated amp!) Just want to be sure that I am doing the right thing. Basically a high-gain linear amplifier, its characteristics can be altered by switching alternative resistor filter networks into its feedback system. I retired from my business, Kandel Electronics, where we sold and repaired (NIST calibration lab) industrial electronic test equipment. Of course, you only need one channel, or you can just build a two channel unit with separate volume controls. Because i can not hear in direct competition but i build first the 4S+CF and then the 4S original with pot at front (100k) and like the 4S without CF much more but don‘t know if it is the sound or the not perfect match with the classD amplifier with a impedance of 33k. Hello As such +4dBu (1.228 vrms) is no big deal. The only down side is cost. The 4S performs just fine with B+ anywhere between about 250v and 310v dc. 2. insufficient gain Transparency is created through solid state electronics, but old preamplifiers used tube technology (just like cathode ray tube televisions did). Hi Matt, Then the proverbial gauntlet was thrown down with the phrase “switch from 12AU7 to 12AX7“. I think the answer to your question is that it should sound good. Thanks, Then use the preamp volume as your main volume. The discussion of the 4S starts here “Super Simple Single Stage Tube Preamp – Post 109”. Would it still be compatible with different tube types? I have recently started utilizing Ltspice to try some modeling in order to learn how various component values may effect an amplifier response. With the V76 Preamplifier's complete circuit emulation, you can craft your projects with the same rich flavor heard on countless classics. On the 6H30PI pin 9 is an internal shield. The other place where I like to split things sometimes is in headphone amps. These include high-gain linear response for magnetic microphones, low-gain linear response for tuners, and high-gain RIAA equalization for magnetic phone cartridges. Universal Preamp/ Mixer - A small and versatile mixer and preamp, suitable for many uses __ Designed by Rod Elliott ESP What would I need to do to enable the 4S Preamp to work with a Quad 606 Power Amp? However, in the real world, attempting to build a differential amp like this causes problems. The rectifier drop in this design is around 28v (Er≈0.74) and the filter loss (with a 130mA dc load current) is over 40v. This will give you constant color and about unity gain with the volume control set to 50% (i.e. So 269v is the B+ voltage? Hi Matt, How do you connect the oscilloscope, the voltmeter and the signal generator to the preamp to do the testing? You would probably be ok if your input volume control is 250kΩ or greater. Can you describe me please the difference in Sound between the original 4S and the 4S with Cathode Follower. Also do you have any opinions on external power supplies, where the power supply is in one box and the line stage is in another box? could i use in the Power Supply a Hammond 156M (3H, 100mA, 86 Ohm, 400V) instead the 154M? Ideally you want to keep a 6.3V filament between about 5.7 and 6.9 volts. Hope you can help. Yup. Now, my question tags on the March 15, 2014 post from Arturo. the dominant harmonic). I am interested in this circuit. If you use a high impedance source, the a low noise active preamplifier stage is still required. In the preamp design, the peak rectifier current is about 11mA with a drop of around 3.6v (Er≈0.96) and the filter loss is about a third of a volt. Hi Matt, thanks for sharing this wonderful design, the circuit is fairly simple, and I got a little question again, when verifying the voltage, do i need to put a load resistor? This means that at a sound pressure level of about 94dB it has an output of -56dBv. can i use a tantalum 33uf 35V bypass cathode capacitor? This would require a buffer stage (ss or tube) to properly match the impedances. The only reason you need to think about the phase inversion is if you are embedding the preamp inside of a feedback loop. Those feedback resistor values are selected between 10 kilo ohms and 10 megohms to suit individual listener tastes. And THAT is the number they publish even though the real measured distortion was about 1/2%. Thanks for the reply, I’m glad to hear that the FFT and RSS method is being used others. Your email address will not be published. I am getting 123v from the wall. However, I would hazard a guess that the CD player fed through the 4S with a 12AU7 in the preamp should sound pretty good. And thanks for the schematic , I am assuming that the voltages you are quoting are with the breadboard. I recommend you read up on these two solutions and decide if one meets your needs. I’m writing here because I am now preparing to build the 4S/Universal preamp, but am considering modifying the design to include the Boozhound Labs RIAA preamp in a semi-integrated manner. Most audio amplifier systems must have preamplifiers with many different characteristics. For example, microphone, tuner, CD and AUX. Only 8 left in stock - order soon. You really don’t need an additional grid resistor on the 12AX7. I then use the FFT function on my oscilloscope to view and measure harmonic content, then plug the numbers into some math and come up with a %THD number. This will give you a -21dBv pad prior to amplification. Here is a picture of the unit as I was running it through its paces. I would avoid daisy chaining two of these simply because that’s something for which it was not designed and the gain would likely be excessive. In the circuit above, IC741 is set into inverting amplifier mode. This is done with the unit open and sitting on a workbench. Hey Matt, thanks for sharing that desing with the community. 2 Specifications: Power supply: 10 - 30V DC maximum, stabilized. Preamplifier GRAS 26AB is provided with an integrated 7-pin LEMO connector. About the only time I do testing with speakers is when I am measuring SPLs. And, I think the reality of harmonic distortion is that it is impossible to hear <1%, most of us can't hear 5% in music or speech, and through some unscientific testing, I really can't hear anything wrong with the sound until I see clipping of music or speech on my scope. It is one to which I listen often. Which it can use with various inputs. So i have to change the + and the – Loudspeakercable. I now have a preamp that can be adapted to the task at hand simply by swapping tubes. For a project like this, it is so small already, I would not even consider splitting the chassis. There is no phase coherency in recorded music. Just remember that the buffer input impedance should be at least 250kΩ for proper 4S operation. Lets start with the input. I am going to build this version. I’m curious if this preamp would provid the necessary equalization for records. Any help is greatly appreciated. I primarily work with discrete transistors, but way back when I did build a few tube amps. – The second option is to unbalance the signal though transformers. Technically, the design you drew could be considered a differential preamp, if the tubes were perfectly matched, and all the load and bias components were perfectly matched. Yes. Dual-channel tube preamp based on the legendary UA 610 modular console. It will work ok with a 12BZ7? Have you ever looked at results utilizing a speaker as a load? For one harmonic this would be about -46dBv down from carrier which would be right in the ballpark for a lot of wien-bridge oscillator signal generators. The input impedance is only 10kΩ and the preamp would not function properly with this control. So I started with a stock enclosure from Pomona, the 4226. Hi! Thank you for the circuit! In your excellent write-up on power supply design you go through a calculation and arrive at a 250v DC supply output from a 275-0-275 transformer. In this preamp design you show a 250v supply being generated from a 190-0-190 transformer. Lovely sound, I love it. Forget 0.001% THD. However, If you contact the author of this post (http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=3266&start=256) then he should be able to help. Hi, Let’s see. As such, it suffers asymmetry problems and has zero CMRR response. The best way to correct for this is to insert a buffer stage between the 4S and the LM1875. Very cool build! Provided you make this translation it should sound great. http://diyaudioprojects.com/Solid/JFET-Phono-Preamplifier-Kit/. Right? I tried it that way and it does not work the amplifier starts to oscillate. After carrefully reading this post and its twin on DIYAudioProjects, I wonder if a simple 4 multiplication will fit my need ? Here is a setup scheme: https://www.dropbox.com/s/v4llkgp1r7miq37/4S-Universal-Tube-Phono-Preamplifier-Schematic-Riaa.png?dl=0. Audio Preamp Circuit Diagram Pdf Posted by Margaret Byrd Posted on February 14, 2021 Universal preamplifier electronics audio preamp circuit diagrams la3161 stereo for car simple preamplifiers low noise pre tone control class a bass mid treble circuits diagram pdf … $16.79 $ 16. One reason for the problem is the input signal is too low. I want to build this one and have some Questions: 1) this is a single stage pre amp, so the absolute Phase is 180° inverted, isn`t it? So, the ghost amp design has about 68v of loss whereas the preamp loss is only about 4v. My question, other than if this configuration is posible, is that if the final sound would be nice. The RIAA stage you also want as quiet as possible so just putting it in the same chassis with the 4S makes that difficult. This mini module is simply connected between a power amplifier (e.g. Make the series resistance 100kΩ and the resistance to ground 10kΩ. So they design an amplifier with an open loop gain of something large; like 80dB. Can you point me to a reference? I would like to build a phono preamplifier. The input structure of the LM1875 is such that the input impedance is simply too low for effective 4S drive. If the preamp is built as mono-blocks, please advise which connection is better: I am really happy and I am sure it has some more burn in to go. The even order harmonics (especially the 2nd) are called the choral harmonics because they are prevalent in music and reinforce the natural hearing process. More Buying Choices $11.95 (4 new offers) HiFi Preamp NE5532 Pre-Amplifier Volume Tone Control Board … Do not wire the triodes in parallel as this would require all different component values. As always, I greatly appreciate your time and consideration towards the DIY community. Brinson, Ga. Hi Matt, If so, are there component separation and/or shielding issues needing careful consideration? its a preamplifier with balanced output signals will be provided. M032N | Amplifier 12 W, universal) and a weak signal source (e.g. Input Impedence: 20Kohm But once you understand what's actually going on, all those super small distortion numbers become just so much advertising foolishness. This is an “E” size (8.3″ x 4.2″ x  1.74″) die cast aluminum enclosure with a sheet aluminum cover and internal card guides. If you have a modern digital oscilloscope, you can dispense with the AC voltmeter and just allow the oscilloscope to measure the voltage. http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=3545. I’m in the part scavenging to build one of these, but i chosen to use a 5y3GT and a 6sn7 from and old 6v6 GE monoblock, so i guess i remove the universal but keep the 4S. The preamp has gain figures from 19.9dBv to 34.6dBv depending on configuration and output voltage swings in the range of tens of volts. My DAC has already a transformer output. Required fields are marked *. http://diyaudioprojects.com/Tubes/RIAA-Phono-Preamp/, http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=3545, https://boozhoundlabs.com/collections/all/products/bhl-audio-jfet-phono-preamplifier-kit-2sk170-riaa, http://diyaudioprojects.com/Solid/JFET-Phono-Preamplifier-Kit/, 4S Tube Preamp with 12AU7 Cathode-Follower, http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=5186, https://tubedata.altanatubes.com.br/sheets/093/6/6CA4.pdf, https://drive.google.com/open?id=1OnnT65jnonsf9zSDV3NhKnjpsSavQcqV, High Voltage (Plate) & Filament 200 Series, http://www.world-designs.co.uk/forum/showthread.php?t=5795, http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=4628, http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=3266&start=256, Super Simple Single Stage Tube Preamp – Post 109. You'll likely never get there and any signal generator advertising such a value is blowing smoke.