So i have to change the + and the – Loudspeakercable. Makes perfect sense. This is done with the unit open and sitting on a workbench. One of the best preamps McIntosh has ever made with three uncommon features: 1. The Hammond 269E doesn’t seem to be available anymore. Input signals are combined to the base of Q1 through the isolating capacitor C1 R1 suppresses the input impedance to the right value to match the specific input signal. To sum-up my understanding : Yes. So lets say the designers need 50W from a line level signal (i.e a standard power amp design). There was absolutely no problem with signal level or power. 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. Quad 606 Power Amplifier Specification If you don’t mind a well designed SS solution, the Boozhound RIAA preamplifier is also highly rated, easy to build, and has really been wrung out DIY-ers. However, in the real world, attempting to build a differential amp like this causes problems. Required fields are marked *. Using a resistive load (i.e. 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. 2. From the first moment I started playing music I was amazed at how the pair sounded together. My DAC has already a transformer output. So what they do is target the open loop distortion to a number they can achieve. The B+ required is + 250v. What would I need to do to enable the 4S Preamp to work with a Quad 606 Power Amp? The cookie settings on this website are set to "allow cookies" to give you the best browsing experience possible. The best way to correct for this is to insert a buffer stage between the 4S and the LM1875. If it was louder, would probably the circuit for ECC82 be optimized? In general, amplifier circuit testing or modeling with speakers is not done. Should a leakage resistor from the grid of the 12ax7 to the connection point of the new 2kOhm resistor and the cathode resistor be installed or is it unnecessary with the potentiometer at the input? Warranty dates from 29 January, 2020 and transfers entirely to the new owner. If connected, this pin should tie directly to the signal ground. microphones). If you continue to use this website without changing your cookie settings or you click "Accept" below then you are consenting to this. As such the full feedback factor ( |Aβ| ) will be large and the total gain of the amplifier can be reduced to the inverse of the feedback network gain 1/β. JLCPCB - Only $2 for PCB Prototype (Any Color). I’ve been intending to share my build outcomes with you since then (and will soon): the performance of that amp was and continues to be literally thrilling! I’d run the output of the RIAA to one of the selectable 4S inputs. Total harmonic distortion: 0.03%. 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. Thanks! This way you can see exactly what signal is feeding the preamp. 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. Just want to be sure that I am doing the right thing. I’ve also been considering a source selector switch as a possibly desirable feature, but with separate physical inputs for phone and “other”, so that cabling would not need to be changed when switching sources. This way a small amp can sit on a table next to a chair for easy volume control and the PS can sit below so there is still a place on a small side table for a mug and or a book. Or $113.00/month § for 24 months ... Single-channel Microphone and Instrument Preamplifier with Built-in Tube Tone Circuit $149.95. Any suggestions? Although the pure ‘electronics’ part of my full-time working days were spent in consumer-level repair, a considerably less elegant, professional or knowledgeable environment than yours, my perspective on tube audio has evolved in a somewhat parallel manner. Amazing, what you can twist with math. This FET preamplifier circuit is suitable for sending signals from the preamp to the amplifier circuit that uses long wiring. The most important thing to consider is that there is a voltage environment mismatch between a 4S and the BZ RIAA preamp. Profuse thanks for the fresh project inspiration. This is not anymore an 4S preamp , This is higly interresting as I measure the way to go before finding a solution. Oh, that’s good news. Wanted to rebuild the amplifier for a long time! Running it into a Pass Class A Amp Camp Amp modified, and use efficient open baffle speakers. 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. This circuit you can find in old amps, but it isn’t embedded in home cinema equipments or amplifiers can be obtained nowadays. Low distortion generators – Rohde & Schwarz has a few with THD at -120 dBv, but one problem – they cost more than a new car, a little rich for my blood. 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? I think this is what your are hearing with the basic 4S. Transparency is created through solid state electronics, but old preamplifiers used tube technology (just like cathode ray tube televisions did). Matt describes the design and construction of the 4S Universal Tube Preamplifier. Hope you can help. or is best to use the cap output. Thanks! The massive, well designed PT-9 universal power transformer used in the Kaiju 300B preamp was employed. It’s easy with which to work, provides great shielding, and can even be soldered. Most audio amplifier systems must have preamplifiers with many different characteristics. I love doing my own audio setup and i like to keep it simple, so your little project fit really well. The noise resistance is approximately 2.5/gm at the chosen operating point. The other place where I like to split things sometimes is in headphone amps. May I request the rectifier tube pin schematics? A little better filtering even. Tantalum capacitors have a very bad failure mode where they fail shorted. I know that at first glance it doesn’t look like it makes sense, but this is why I wrote the power supply design paper in the first place. I just don’t think that it’s worth the extra effort. A small switch and a little LED would be all that you need to show with signal and power connections in the back. Is this with a 12AU7 or a 12AV7? However, the filament of the 6H30PI is on pins 4 and 5 ONLY. Just leave pin 9 of the 6H30PI disconnected. The basis for this amp started out as a post in a thread on the DIY Audio Projects Forum site. http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=3545. Thats -100dBv in all one harmonic (i.e. Input will be both Moving Magnet Stanton 500, and Denon High Output Moving Coil cartridges. I posted a good design for this over at the DIYAudioProjects website (Link – Baxandall circuit). This will allow you to see the output waveform. 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? If you look at the calculated performance table you’ll see that the 4S has a varying output impedance with peaks ranging from ≈65kΩ to ≈80kΩ. Dual-channel tube preamp based on the legendary UA 610 modular console. Here is a picture of the setup. I would however suggest that you look over the “Super simple single stage tube preamp” thread over at the DIY Audio Project vacuum tube forum. I think that a sub-base for the turntable to house the RIAA preamp is a great idea. Specifications. Lovely sound, I love it. The even order harmonics (especially the 2nd) are called the choral harmonics because they are prevalent in music and reinforce the natural hearing process. This circuit is designed as a stereo preamp. Most audio amplifier systems must have preamplifiers with many different characteristics. This type of mathematical masturbation has been accepted practice in the audio equipment industry for decades. Why not parallel? Francis. input voltage: 50mVrms In this case -100dBv + 56dBv or -44dBv. DIY Audio Schematics Tube Linestage Preamplifiers. So once the unit was deemed technically acceptable, it was time to determine if it was sonically acceptable. Only 8 left in stock - order soon. The 4S with the cathode follower output buffer has an output impedance of 575Ω. Would it still be compatible with different tube types? The discussion of the 4S starts here “Super Simple Single Stage Tube Preamp – Post 109”. Thanks for the interesting insight on THD measurement and calculation. My power amp is better behaving with balanced signal. I’d like to read up on it. These include high-gain linear response for magnetic microphones, low-gain linear response for tuners, and high-gain RIAA equalization for magnetic phone cartridges. Could I use copper chassis to build this pre-amp? For those measurements your talking conditioned lab power, Faraday cages, and high end equipment. 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. Cathode follower output stage. 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. Thanks for the design and the knowhow. They are theoritical numbers or very controlled lab tests under very clean conditions, not real world operation. My hypothesis is that the low input impedance of the class D amp coupled with the action of the 4S drove up the 2nd order harmonic distortion and this is what you are hearing. All functions tested and passed, face plate cleaned and presents very well. Crosstalk: -100db (100hz), -85db (1 khz) and -65db (10khz) I would be interested in building one of these as i have always wanted to see if I like the sound of a valve system. 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. In my case I don’t have an audio analyzer, but use “clean” recorded tones from an iPod or from Audacity on my laptop. Is this even close to your instructions above? This is much appreciated. Can this circuit be used for that? I could have gone for a printed circuit board approach, but I really enjoy point-to-point build techniques for vacuum tube projects. The first is to use center tapped transformers on the input and output. This means that with the 12AU7 in the preamp, you’ll get approximately unity gain with the volume at full. Yes, that’s clear, thanks. I am getting 123v from the wall. The input impedance is only 10kΩ and the preamp would not function properly with this control. I currently use a 10K potentiometer in front of the amp as my volume control and it works well instead of higher potentiometer (I tried 50K and 100K and they sounded worse). Copper makes a great choice for chassis material. Thank you Matt, realy impressed with what you have done here. This project was a great success. In triode stages, the distortion (color) is roughly proportional to the drive level as a function of its total distortion. Is there any mods to this circuit which would limit the gain some. In the past, when driving this amp with just my iPod, I was disappointed with the overall performance. I’m thinking about building this preamp but I’m new at this. Potentially. Otherwise it will unduly load the output and distort the waveform. See here: http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=5186. For medium signal inputs, the frequency response offered by the design is just flat. Brinson, Ga. Hi Matt, No. This is because speakers present a frequency dependent, complex impedance which tends to mask circuit operation. To answer your second question, as for the PGA2311, this is not an appropriate volume control for this preamp. I have used this amplifier (actually the “Rebuild” version) five days a week, eight hours a day for a couple of years and it still is performing flawlessly. I have built a simple op amp and that is as much I know about building an amp. This could be done with a vacuum tube cathode follower, a transistor emitter follower, or a solid state op amp properly configured for buffer operations. With the tube inserted the B+ is at 280V, at the anode 80V and at cathode of the preamp stage 2,4V. 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. These voltages are in the ballpark. Ok..thanks a lot.i am looking forward to the build. Then use the preamp volume as your main volume. The other option, if you want to avoid transformers, is to use a mixer tube (like the 6J6) on the input, tap one load to drive the preamp tube, then couple to the output with a concertina phase splitter. it is advisable ? You don’t need much gain since 1.2vrms drives the amp to 93W output. Basically a high-gain linear amplifier, its characteristics can be altered by switching alternative resistor filter networks into its feedback system. Speaker impedance is also very difficult to model correctly due to the variables involved. Although small, I was sure I could fit the entire PS and stereo preamp in this box. Designed by Bill Putnam Sr., the UA 610 modular console is arguably the “Holy Grail” of vintage tube desks. ... GRAS 26AB 1/4''-1/2'' Universal Preamplifier with Integrated Connector. It's the same reason that the advertised THD of most SS amplifiers is total hooey. The AC voltmeter needs to have a relatively high input impedance (>100kΩ). Thanks a million for your efforts and sharing of the 4S. Here is the circuit I implemented along with the tube rectified power supply. The specs are below. After carrefully reading this post and its twin on DIYAudioProjects, I wonder if a simple 4 multiplication will fit my need ? The 545ii is a nice amp. Basically a high-gain linear amplifier, its characteristics can be altered by switching alternative resistor filter networks into its feedback system. And don’t worry about the B+; 280v is fine. In general the input impedance of the amp should be more than four times the driving impedance. Maybe in Kobination with a positive feedback! its a preamplifier with balanced output signals will be provided. 1. The cables you use are dependent on the test equipment you’re using. (7.4-6.3)/(1.0+0.3)≈0.8Ω; (1.3^2)*0.8≈2.1W so use a 0.8, 5W power resistor like this one: ACS 5s R8 K T&R, And yes the 269v is my B+ Is it possible to use it as a headphone amplifier? But in a heaver load condition, the cap discharges more and the waveform starts to look more like a sawtooth waveform. Regarding noise wouldn’t input and output transformers take care of that? I also occasionally use a PC oscilloscope with a built in function generator to perform this measurement also – the one I have can give a direct %THD readout, but it is “suspect” – the function generator running in sine mode in and of itself has a THD of almost 0.5%, and I know to be truly accurate, a good audio generator with something like .001% THD or less is really required to get a good THD reading. Of course, the V76 Preamplifier plug-in isn’t just for UA Audio Interface owners. If it’s going into a consumer amp, this may be just fine. It will work ok with a 6H30PI Sovtek ? I am really happy and I am sure it has some more burn in to go. 1. too noisy, and, Now, my question tags on the March 15, 2014 post from Arturo. To meet this broad requirement, most amplifier designers include a single universal preamplifier circuit. But the sound is very light. If I use an 6H30PI Sovtek are there any changes that I need to make from the original schematics? That some builders do say that the “real” distortion is actually the measured number minus the calculated reduction due to NFB. Basically a high-gain linear amplifier, its characteristics can be altered by switching alternative resistor filter networks into its feedback system. Do you have any schematic or something to build it in PCB? Right? 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. Does this one delivers enough gain to get Line level (+4dBu) from mic level (-40dBu aprox)? As you mentioned, your testing is done with an oscilloscope and a.c. voltmeter. Also, he may occasionally want put his electric guitar signal through it. There is likely insufficient gain or phase margin in the feedback loop. The problem is that it’s not really a differential amp, it’s just two separate amps, one for each side of the signal. You really don’t need an additional grid resistor on the 12AX7. Use one section only, or The NBS Universal Preamplifier uses absolutely state-of-the art monolithic circuits throughout. Then the approach is to use 56dB of negative feedback to get back to 24dBv end-to-end gain. If not, post a request on that forum thread. This will give you a -21dBv pad prior to amplification. Regarding using the 12BH7 tube if your heater supply is capable of putting out a full 600 mA into the filament- If I built my preamp using the Hammond transformer per your schematic- then I should be able to use 12BH7 tubes? Besides this, I’m not sure I could have designed a PCB that would work with all the bulky items protruding into the case (inductor, IEC connector, tube socket, potentiometer, RCA jacks, etc.). It has been a pleasure to construct this. There are two conditions where I like separate power supplies. I checked the frequency response and you should be fine with the ADCOM 545ii’s 50kΩ input impedance. Can I use this circuit to modify the 4s universal pre-amp? I would like to add bass boost to this circuit for listening at lower volume. But the sound is very light. Best regards, Everything went well until I put a model of a speaker on the output of the preamp circuit during simulation. Whether the whole in the hearing test is good or bad I will like to report next week. You may need a preamplifier using IC. I am attempting to build this amp using a Stancor 235-0-235 117v transformer. I chose the 6V6 Lacewood amp. I have built the preamp. This would mean that the 12AU7 would give about 9dB of gain at full volume. The simplest way to do this is a restive pad behind the preamp. The power supply design in the paper for the “Ghost Amp” has a peak rectifier current of 260mA. The iPod output simply wasn’t enough to drive it to full power. The tube input capacitance is at least an order of magnitude smaller and is swamped by the test equipment and the nest of wires on the table. Does the value of B + apply with the tube inserted or without a tube? It is my first build and I have played out the power supply and one channel on a breadboard. 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 … Your email address will not be published. The real question is how much gain do you need? COVID-19 quarantine gave me the insentive to get back into my audio hobby. 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. – The design I had in mind is driving me to a no properly working system. Right? My first thought is to build a version with a tone stack and buffer. and several designs were presented using various dual triode tubes. This will take a -40dBu level to approximately -5.5dBu. He is using Shure SM57 and 58s. 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). Or i got a little problem where the b+ split to plate, one got 60vdc and 80vdc on the other. I think that in an integrated setup, I would fully encase the RIAA stage in a µ-metal shield. 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. When a signal flows to AF in through C1 and R1 to pin 2 of IC1. 4.2 out of 5 stars 54. To meet this broad requirement, most amplifier designers include a single universal preamplifier circuit. On the output (of the same channel, left or right), you need to connect the other channel of the oscilloscope. Now in addition they want really low low distortion, like the 0.001% figure you mentioned above. The signal generator should be connected directly to a single input (left or right). Sounds like I’ll continue with the CF version of this circuit for hi fi and find a schematic for one that’s mic specific. I would like to connect the cd player thru this little preamp of yours directly to the yamaha. Forget 0.001% THD. The volume control is on the output to help ensure that the noise figure for this preamp … The higher performance of the tantalum is not required and the risk to your amplifier is not worth it, in my opinion. . Feb 4, 2018 - You have a good power amplifier and speaker. I think i will add an input selector to. Hi Matt How do you connect the oscilloscope, the voltmeter and the signal generator to the preamp to do the testing? 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. We can change the resistance of R3 from 1.5K to 4.7K when using low voltage power supply. Universal Preamplifier using 741. This can be done, but it can be finicky to get a good result. I rebuilt 2 Acrosound ULii’s which are driving rebuilt IMF RSPM Mkiv speakers. So it really depends on what the input of your amp looks like. 2. So what they do, is design a high gain ≈80dBv but narrow band amplifier with a distortion factor of <0.6%. To get good tube color with the 4S, stick with the 12AU7 with the volume control on the output. Make the series resistance 100kΩ and the resistance to ground 10kΩ. If you have a stand alone AC voltmeter, you can connect it to the signal generator as well. I primarily work with discrete transistors, but way back when I did build a few tube amps. so your amp should have an input impedance greater than about 320kΩ. Thanks, David. – The third option, if I understand properly, is using a 6J6 tube per channel to mix the 2 phases, using half a 12AX7 to act as preamp and use a concertina phase splitter to get back the 2 phases. This means that the socket needs to be wired differently. I want to use it as a phono preamp. thanks for sharing this Project. The first step is to simply power up the unit and check all the major voltage points in the circuit. Or how about configuring the first stage in the manner you suggested to Scott Bartholomew, with the higher-value grid resistor and extra input load resistor? 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. The circuit is a simple two transistor pre-amplifier using a feedback loop for enhancing the amplification. Unfortunately, no. This is why a 250kΩ control is used in this design. The problem has many reasons. The universal pre-amplifier circuit has a top cut filter using R7 and c8, which allows an attenuation of around 5 dB with 10 kHz frequencies. Just remember that the buffer input impedance should be at least 250kΩ for proper 4S operation. 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…. There are really two ways to go. I’m amazed at how much can be achieved with so little in valve amps. My fallback idea, again aimed at eliminating one more separate chassis on the shelf along with the main amp, fm tuner and turntable, is to build a sub-base for the turntable, perhaps of the same wood I’ve used for the amp (and will use also use for the preamp) and install the RIAA preamp inside that… I would be grateful for your thoughts on that approach!
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