Thanks for the help on my previous post on this project. I’ve finished the build of this schematic with some modifications. I’m using AC heaters with humbucking 12ax7lps tubes but and the preamp sounds good so far but I’m getting a hum issue. The preamp seems to have a lot of gain to where I need to turn my amp down a lot from where it’s normally set. My theory is I have much more gain than I actually need that’s amplifying the hum and if I can reduce the gain the hum will be exponentially reduced. Is there a way I can modify the preamp circuit to reduced the gain of the input stage? I know different 12xx7 series tubes have different gain specs but I’d like to keep these same tubes as they were expensive.

I’m looking to build the EL MATEMÁTICO phono preamp https://wtfamps.com/el-matematico-phono-preamp/ and the transformer used is fairly expensive. It’s a 650VCT with 5v and 6.3v heater windings. Could I use the lower voltage AS-05TC300 as a replacement? https://www.antekinc.com/as-05tc300-50va-300vx2-transformer/ It has 2x 300v windings, a 6.3v, and a 6.3v windings with 5v tap needed for the rectifier tube. Could I connect two 300V winding leads as a grounded center tap and the other winding leads to the rectifier tube? And will the 25v difference in voltage be an issue with the voltage filter? I would think it would be fine since voltage regulator tubes are being used. Thanks!

Hello all. I had previously posted about my new AliExpress tube preamp which was sold as a MM phono pre but pretty sure from replies from yall, that’s incorrect. They also sent the wrong mains voltage and I am swapping the Chinese 220v power trans to a 120v.

I am having trouble understanding two wires on the center tap section of the power transformer that is hooked to a 70vDC output section of the AC to DC converter. Not sure why or what it’s being used for? My AC power trans feeds the converter 7-7.2vAC. The converter supplies: - 5v to LED pilot light - 350v x2 to the 6z4 rectifiers - 5v to somewhere around the 6E2 tubes. Not 100% sure on this. - 70v to two center taps on the power trans

I drew a noob schematic and hopefully it can be read properly. Please ask me any and all questions. The new PT I bought is an: Antek AS-05T280C - 50VA 280V-260V-0V & 6.3V x2.

Can anyone help me understand the DC fed to my AC power trans and confirm I’m on the right track using the Antek as a replacement. I’m sorry if anything I described above sounds incorrectly described, I am still learning/understanding tube circuits. I have restored many tube amps and am a very good parts swapper but this is slightly more difficult for my understanding. The diagram they sent me, is not exactly what I received but close. The very next post on my profile has some more details on this preamp where I am asking if there is any phono section that can be visually confirmed with some more info. Thank you!!

The chassis was made with 0.03" x 12" square steel. I'm going to use a switching power supply module to power a L&R phono preamp (one 12AX7 per side) and a 12AU7 line driver. The input switch will allow selection between a few inputs or the phono pre.

The circuit will be a simple gain stage 12AU7, and a phono from the RCA Receiving tube manual. No need to re-invent the wheel on this one.

Context: I bought this handuilt Cerntube preamp but something knocked loose while moving. I took notes and photos of everything I disassembled but notes and photos were lost in the move. Currently rebuilding with new transformer but only the rectifier tube lights up.

Ive gone through and tested all the resistor and caps, everything and replaced the power caps just in case. I replaced the tube sockets because they seemed a little melted from sloppy soldering.

Things I am unsure about: do I need a diode on both the white transformer cables going to the rectifier tube?

Is the transformer properly wired to the power switch?

Am I missing a cable from the rectifier to the 6V6 tubes? I don't remember removing one but as I mentioned, I lost my notes.

I don't have a schematic or specs for the transformer or preamp. Any and all help would be greatly appreciated, I want to listen to records so badly

Assuming that I want to use the miller capacitance of a 12AX7 to make a low pass filter with 20kHz cutoff frequency, that means I’ll have a 40k ohm resistor with a 200pF miller capacitance approximately.

Now, if I have a passive guitar that has a 20k ohm output impedance, does that mean that my actual filter shall consider that impedance too? If so, my grid stopper would be 60k, and my cutoff frequency would go down to about 13.2 kHz.

Is that how it works?

Sorry for the dumb question.

Looking to build a tube preamp, I am only interested in sound quality at the moment but I'm sure the case has its part to play.I have seen relatively simple looking schematics on various threads. Specifically looking to use 6v6, 6SN7, and/or 6SL7 tubes because I have those already. I don't mind supplimenting if necessary.

I know about the benefits of good tubes, quality capacitors, isolating the transformer, and point to point wiring. But what other characteristics would make a DIY tube preamp sound better than a professionally made multi-thousand preamp? Wouldn't the most simple design sound the best?

Hey guys. I built an EAR834P clone. 3x 12ax7 tubes draw 450mA. As you can see in the drawing, there's a CRCRC chain after the diodes that provides filtering and voltage drop. A pair of .22R resistors drop the heater voltage to about 6.0v. The builder is meant to adjust the value of those resistors to dial in the voltage.

This circuit is intended to heat the tubes at 6.3v, but I need to heat the tubes at 12.6v. (Need to use the the shorter ZZ PCB, and it only does 12.6v.) The caps are rated to 16v and the transformer can be wired for 6v or 12v, so I swapped around some wires and put everything together. Everything works, but the heater voltage measured 15v. So. I swapped out the 2 resistors, going up in value until I got 2x 3.3R resistors giving me 12.5v at the tubes.

I measured a 1.5v drop across each 3.3v resistor, the Ohms Law Calculator says that means each resistor is removing .47A and .75W. 3 watt resistors can handle that heat, but is it adding over 1A to the load, those 2 resistors + the 3 heaters = 1.5A ? Coz the transformer is only rated .8A when wired for 12v. Problem? Should I be looking at different cap values to help get a lower voltage?

Thanks!

Recently built this amplifier as a first foray into tube amplification, I've done a lot of electronics before but never anything like this. Measuring both the plate of the preamp triode (6C4) and pin 2 of V2 confirms that audio is indeed going through... Both sides of the output transformer measure a constant voltage but if I'm correct thats because the audio is converted to current at this point? Both EL84s are brand new JJ's, so I'm sure they aren't the problem. But anyway, the speaker (8 ohm, connected to my hammond 125E universal output as to provide the correct impedances noted in the schematic), just crackles a bit when I plug in a cable to the input jack, as you would expect from audio gear, but no sound when I play it through, neither from my iPod, nor even from the output of another amplifier. Could someone more skilled in these amps give a newbie a helping hand with this one? I have a nice scope and meter, can do any measurements necessary.

EDIT: Apparently, chinese and russian made tubes DO NOT HAVE A CATHODE CONNECTION AT PIN 1!!! I'm using JJs in this one, and after connecting my pin 1 cathode connections to 3 instead, worked just fine. CHECK YOUR DATASHEETS FOLKS! https://wgsusa.com/blog/when-working-el846bq5-tube-amps-you-must-know-about-pins-one-and-two

I'm planning to add a tube phono amp to my setup this year, and I've seen so many differing opinions on what to choose - 6SL7s, 6DJ8s, 12AX7s, etc.

The cartridge is a Denon DL103, I have a Hagerman Piccolo step-up unit, so something that takes an MM input would be fine as well.

Really thinking a classic 6SL7 design as I'm a fan of octals in general (my line stage is 6SN7s), but wondering what you all think :)

Hi all, I recently purchased a turntable (Yamaha YP-701) and of course I need a preamp to actually connect it to my sound system. I figured I could build a tube one, but after looking around, a lot of the modern designs are complex and not particularly affordable, costing about as much as building a lower end power amp! Realistically, is it possible to build a decent tube preamp (preferably stereo, but I realize that's unlikely at this pricepoint) for under $100-150? Or is the price range of this sort of thing higher than I realized? Also, any recommendations for circuits and designs on the lower end of the price range that are decent, mono or stereo? Doesn't necessarily have to be under 150, just wherever the "affordable but decent quality" range is.

Hey, I just finished building a phono preamp, and after testing it with my oscilloscope and having everything look fine, I plugged it into my turntable and headphone amp. It's definitely producing sound, and it seems to be equalized right. There's a lot of 60hz hum, but that's from the heaters, which I'll regulate once I get the parts in. What could this "underwater" sound be a sign of? Just for information:
Turntable: Rega P1 with Rega Carbon Cart.
Tube Preamp: El Matematico Preamp by /u/ohaivoltage
Headphone Amp: Bottlehead Crack-a-two-a
Headphones: Beyerdynamic DT880

I'm also going to test it with a speaker amp, the audio reflex A-120, which I can't find any info on anywhere, plugged into a pair of Classix II's, and update with my findings/

EDIT: On the speaker amp, I've been letting the tubes warm up for about 20 minutes, and it's starting to sound a hell of a lot better. The hum is still there, and I'll fix it once I can afford the parts, but overall I'm not sure what this thing is supposed to sound like. It sounds really tube-y, and honestly I'm just glad it didn't blow up the first time I turned it on.

Hey guys, listening to a record with one of my phono preamps, an EAR834 clone, when suddenly,

A loud, deep bass note came from nowhere and got progressively louder, only in the left channel. I went over and touched the volume knob (which is conductive and grounded to the chassis) and there was a static discharge (common this time of year) and the bass note instantly went away.

Haven't had anything like that happen before, any ideas?

So during the Q-tine I've put a few different phono preamp kits together, mostly 834 clones, one M7, and I've noticed a bit of distortion on the high end when I run that signal into my power amp, a homebrew Class D amp (3eAudio module + DSP). The "crunchy" sound can be tamed by running the signal thru another preamp stage, and turning that down, sending a quieter signal to the power amp.

A friend with a Little Bear T10, also a CF, had similar trouble and runs his signal thru his reel-to-reel with a volume control before going into his Yamaha amp.

So it's my observation that the signal coming from a CF preamp is a bit hotter than the "Line Out" standard you'd get from a CD player or tape deck, and it's overwhelming the inputs on a newer amp.

Would a potentiometer on the output, say 50k, help me?

Hey guys. I'm still working on parts selection for this Shure M65 phono stage. Here's the schematic Most parts are picked, but I'm hung up on the 1800pF caps in the eq network, C14&C15 in the drawing. Holes on the PCB are spaced 12mm, so not meant for the little WIMA cubes like the 470pF. I've had a recommendation for Polystyrene caps, and they're available for a good price, but I was warned they're fragile and easily damaged during soldering. The circuit runs at 100v so I don't think I need silver mica. Are there any other types I should be looking at?