There shouldn’t be any differences in sound between the two versions. This is much appreciated. Does the value of B + apply with the tube inserted or without a tube? I did a voltage divider, it somewhat reduced the volume which I m happy. Any suggestions? Running it into a Pass Class A Amp Camp Amp modified, and use efficient open baffle speakers. In this preamp design you show a 250v supply being generated from a 190-0-190 transformer. Do you think this pre amp will be capable of driving my power amp (LM1875 based on non-inverting design of National Semiconductor datasheet which includes a 22K resistor to ground at the (+) input of the chip)? Now, my question tags on the March 15, 2014 post from Arturo. thanks for sharing this Project. Selling my McIntosh C40 preamp. I’m not sure what the final impedance is seen by the amplifier. Velleman K1803 Universal Mono Pre-Amplifier Kit, Multi-Colour. It will make the input signal is higher. 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. . Hi Matt, thanks for sharing this wonderful design, the circuit is fairly simple, and 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? Here is a picture of the unit as I was running it through its paces. From the first moment I started playing music I was amazed at how the pair sounded together. Hi, 1. Thanks for this great design. 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. And any additional feedback. Due to this the high frequencies can be boosted by a magnitude of 5 dB for high signal levels. Here is the circuit I implemented along with the tube rectified power supply. Therefore, I would like to use the ECC83 in the first stage! This is more than adequate for preamp operation. Hi Matt, 0.50 Amps -15 VDC Current Out, Max. UAD hardware owners can use the V76 Preamplifier on any mix, getting bold, rich colors, without going outside the box. Glad to hear you like the web page. Also, if by some manner it sinks enough current, the tantalum capacitor can catch fire and burn like a miniature road flare. You are listening to music. This will give you a -21dBv pad prior to amplification. If I use an Edcor XPWR177 transformer are there any changes that I need to make from the original schematics? It will make the input signal is higher. And the feedback factor (in our example) is 56dBv. For this build I wanted to go for two major themes: Utility & Compactness. I would like to add bass boost to this circuit for listening at lower volume. My son would like me to build a mic preamp. Any thoughts? Hello, Thanks for adding the 12bh7 option. As such they tend to add a pleasant “fullness” to the music. I was hoping you could explain the best way to go about correcting it. This is a line stage preamp and the output impedance is far too high for headphone use. It’s easy with which to work, provides great shielding, and can even be soldered. For this build all voltages were as calculated to within a reasonable margin of error. If you use a high impedance source, the a low noise active preamplifier stage is still required. Any music as we know is in the form of a consistently varying frequency, therefore when such a varying input is applied across the indicated C1 end terminals, the same is delivered across the base T1 and ground. Feb 5, 2018 - You have a good power amplifier and speaker. I believe what you are missing is the different loss in the rectifier and filter circuits of the two designs. I chose the 6V6 Lacewood amp. In this case -100dBv + 56dBv or -44dBv. For medium signal inputs, the frequency response offered by the design is just flat. But a word of warning. There are two conditions where I like separate power supplies. I primarily work with discrete transistors, but way back when I did build a few tube amps. I mean 4x 12AX7 tubes, 2 per channel to act as a preamp ? I would recommend starting with a 12AU7 in the second stage until you get a feel for the drive levels required. So once the unit was deemed technically acceptable, it was time to determine if it was sonically acceptable. Personally, if I run the 4S in front of one of my amps, I almost exclusively use a 12AU7. The volume pot brings me in trouble, because i use class D amps with a input impedance from 10k and 100k. Basically a high-gain linear amplifier, its characteristics can be altered by switching alternative resistor filter networks into its feedback system. If I use an 6H30PI Sovtek are there any changes that I need to make from the original schematics? Best regards, On the 6H30PI pin 9 is an internal shield. And choose the biggest chassis you can, and then buy one half again larger. M032N | Amplifier 12 W, universal) and a weak signal source (e.g. Matt describes the design and construction of the 4S Universal Tube Preamplifier. Matt, For headphones you need a much lower matched output impedance. If it is not possible then can you recommend a good quality preamp tube circuit to build instead? If the preamp is built as mono-blocks, please advise which connection is better: How do you like the sound? The massive, well designed PT-9 universal power transformer used in the Kaiju 300B preamp was employed. And the added effective dynamic range really let the amp open up. Crosstalk: -100db (100hz), -85db (1 khz) and -65db (10khz) Thanks for your reply! Is there any mods to this circuit which would limit the gain some. One of the two oscilloscope channels should also be connected to the signal generator. 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. In the past, when driving this amp with just my iPod, I was disappointed with the overall performance. As you indicated, the input potentiometer does this function just fine. Hope you can help. Thanx again 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…. I don’t think you’ll need the series combination to get the level of color you desire. The 4S performs just fine with B+ anywhere between about 250v and 310v dc. I just checked and the hammond 269EX is still listed on their website. Unless the switch itself is a potential weak spot in the chain? In triode stages, the distortion (color) is roughly proportional to the drive level as a function of its total distortion. Thank you for the info. To get good tube color with the 4S, stick with the 12AU7 with the volume control on the output. You might get it to work, but it won’t work well. Francis. I would like to connect the cd player thru this little preamp of yours directly to the yamaha. It is inexpensive, easy to build, and sounds great. You may need a preamplifier using IC. Den Foulk One very important feature of this build is the ground lift switch. So the actual end to end gain they need is 20*log(20/1.228) or ≈24dBv. Your comment about the secondary waveforms differing and their effect on harmonic generation; I’ve never heard this discussed. The best way to correct for this is to insert a buffer stage between the 4S and the LM1875. This is very good performance. 2. If not, post a request on that forum thread. So what they do, is design a high gain ≈80dBv but narrow band amplifier with a distortion factor of <0.6%. This entailed hooking up the preamp to one of my other units. Keep working, you got an another “suscriber”! This is because speakers present a frequency dependent, complex impedance which tends to mask circuit operation. Hi Matt, Can you describe me please the difference in Sound between the original 4S and the 4S with Cathode Follower. As such, it suffers asymmetry problems and has zero CMRR response. Thanks, i build it around this schematic, i’m building a wood box and a aluminuim top plate for the retro look, will it be ok to drive a 10k ohm SS amp input? And eliminate the 500kΩ grid resistor on the first stage. It will work ok with a 6H30PI Sovtek ? Is there any modification to your 4S Universal Preamp that would suit this application? If you only want one channel, just wire up one of the triodes and leave the other disconnected. Here in my office with a 12au6 in place the usable range of the volume control is between 6 and 7 o’clock. So it really depends on what the input of your amp looks like. And my Precision E-310 vacuum tube signal generator is specified at <1%. I came across your 4S preamp, and made one up in an old Conrad Johnson chassis. And don’t worry about the B+; 280v is fine. A little better filtering even. 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. This measured distortion equates to -44.9dBv. One of the best preamps McIntosh has ever made with three uncommon features: 1. The Hammond 269E doesn’t seem to be available anymore. One is very low noise, the second is a gain of between 50 and 60dBv. Matt describes the design and construction of the 4S Universal Tube Preamplifier. To sum-up my understanding : I would like to build a phono preamplifier. http://www.world-designs.co.uk/forum/showthread.php?t=5795. Modern engineering combined with advanced semiconductor processes allow performance which cannot realistically be achieved in discrete-component designs. Just starting a preamp project to feed my power amp. 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. But in a heaver load condition, the cap discharges more and the waveform starts to look more like a sawtooth waveform. This is not something I do regularly. 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. Regarding noise wouldn’t input and output transformers take care of that? I simply showed only one channel in the schematic.I’m not sure how duplicating the components would allow you to make a P-P version. http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=3545. 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. I built one of these and it sounds great. But the sound is very light. This should work great. So could you please tell me the difference in Sound with and without CF and maybe sjow me the circuit from that 6.5k preamp? i see you only used 1 side of bottle , i was thinking ,i could just duplicate the components and use the other side of the tube ,to make a push pull version. The higher performance of the tantalum is not required and the risk to your amplifier is not worth it, in my opinion. I think this is what your are hearing with the basic 4S. – The design I had in mind is driving me to a no properly working system. Hi, So how did the unit do? 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! Basically used the power supply, but regulated the heater supply. Only 8 left in stock - order soon. One 12AU7, a few resistors, a couple of caps, and you’re good to go. You can get the 6CA4 data sheet,including pinout, at the following link: https://tubedata.altanatubes.com.br/sheets/093/6/6CA4.pdf. I’d run the output of the RIAA to one of the selectable 4S inputs. A line level signal is +4dBu which is 1.228v rms. Excuse me, I am a newbie On the output (of the same channel, left or right), you need to connect the other channel of the oscilloscope. Then, You will listen […] I am just curious as to how others with a “basic” basement lab are getting their THD measurements. The most important thing to consider is that there is a voltage environment mismatch between a 4S and the BZ RIAA preamp. Amazing, what you can twist with math. The noise resistance is approximately 2.5/gm at the chosen operating point. The filament voltage is a little high. FREE Shipping. I now have a preamp that can be adapted to the task at hand simply by swapping tubes. The 545ii is a nice amp. An additional resistor with 2 kOhm between ground and cathode resistance of the 1st stage so the 12ax7. Regarding the second part of your response, it sounds like you don’t think the BHL RIAA preamp needs any additional gain, and already will provide a suitable input to the Lacewood amplifier? E. That’s fine. If you have a microphone that is relatively low impedance, you can use a step up transformer that reflects the microphone impedance to the grid input at about 4 times the vacuum tube equivalent noise resistance. Simple and clean sounding. BR Martin. I used a 50K volume pot, and around 330K to ground on the input. 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.
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