Well I have a mix of different DIY amps. From Pass A40, HB, PassAB, and a Tube AB 80W/CH. Doesnt this design have poor CMRR? Would be nice if Broskies boards were still available.
The question is, what signal level do you need on the output? A typical tube amp will be happy with 1~2 volts, therefore you need a pre-amp that does amp 🙂
Maybe introducing negative FB to reduce gain? But then there is the question, why do you need the pre-amp for? You could connect your CD player directly to your amps...
Maybe introducing negative FB to reduce gain? But then there is the question, why do you need the pre-amp for? You could connect your CD player directly to your amps...
Augmenting upon what jcalvarez and vinylkid58 are asking, here is how I go about it. Just sharing my thoughts.
What is your source? DAC or Phonostage or both? What outputs on the source do you use? RCA or XLR? What is the output voltage in RMS of your sources?
We know the various gains of your amplifiers, we can measure them and we can figure out how much voltage on the input is needed for 2.83V RMS (assuming 8 ohm speakers) and how much voltage on the input will clip the amplifier, yes? You want to have an idea of these things so you don't end up with excessive gain.
What are your speakers? What is their overall sensitivity from 100Hz to 5khz or so? How far away are you sitting from your speakers?
Going through these questions will help dial in if you 1) need a preamp or not and 2) if you want the tube/2nd harmonic sound if using just a tube buffer is enough versus a preamp which typically has gain. Let's be honest, it's all about entertainment!
In example, in my room that is 26 feet deep, 12 feet high and 16 feet wide with me situated roughly 12 feet from my speakers that are 96dB sensitive @ 2.83V at 1m, and with a voltage source from my dac which is 2.9V RMS (DSD 512 from XLR outputs), I need an amplifier/preamp combined gain of ~20-26dB for all my recordings and all my SPL levels that I care to listen to. Since most of my amps are 20dB to 26dB in overall gain, I do add a tube buffer of about 0-3dB gain whenever I want to do the second harmonic game. Staying within this region, helps keep my signal to noise ratios high. So I hear more music with a background of silence. Since my speakers are fairly sensitive, I can get away with smaller amps (i.e. 15 watts minimum) but I do like to listen loud on occasion so 100 watts RMS/8 ohms isn't out of the question.
Hope this helps.
Best,
Anand.
Last edited:
@Freecrowder are you familiar with the 12AU7 Color Preamp from CascadeAudio.com ? It's a tube buffer project that has unity gain and easy to wire by hand, no PCB needed.
I'm looking for a preamp thhat can provide higher drive for a SET amp with a single stage driver.
I'm looking for a preamp thhat can provide higher drive for a SET amp with a single stage driver.
I see a gain stage in front of a CF. Doesn't look much different that what you're building.
jeff
The through write-up in the web page seems to indicate that putting the volume control at the end of the circuit changes the output impedance, which may be suitable for the amps @Freecrowder is trying to drive.