That circuit will have a high output impedance, excessive gain, and a frequency response and distortion that depend on the load. You could probably do better.
I ordered the pcb (mainly because it + the tube are so cheap!) - what changes to the resistor values, etc, would you suggest for improvements?
The load will be a push pull tube amp with 100k input impedance...
The load will be a push pull tube amp with 100k input impedance...
Do you actually need a linestage with gain? What are your sources and your power amp's sensitivity?
Yes I need some gain, I'm using an ad1865 dac with only resistors for the i/v stage, so the output is only in mV. The push pull sensitivity is 3v (I had it made that way so it would work with variety of preamps and sources).
So what you really need is something like a mike preamp, i.e., 60dB or so of gain? The 6111 won't give you that much, more like 20-23dB. If it were me (and it will be, I have some 6111 awaiting my attention), I'd replace the biasing RC with a diode or LED, put a CCS as the plate load, then direct couple to a cathode follower. If I wanted to get 60dB of gain, I'd look at a cascode, either with a FET on the bottom and a 6111 on top, or a 6111 on the bottom and a higher voltage tube on top.
pcb has arrived - will populate as per the schematic and report back on the sound, any simple suggestions for improvement gladly taken (not quite up to the expertise level to implement SY's suggestions above!)
I’ve noticed that the filament section of the pcb (see schematic posted above) is very simple – it just sends 6VAC to the filament supplies. I have a dedicated 6.3v dc lab supply, would it be smarter to use this instead?
For the B+ (sourced from a transformer with 35VAC secondary) I am planning to use this transformer:
0 - 30V (Multi-tapped) @ 1A 30VA - Type 6672 Transformer - Jaycar Electronics
Forgive my ignorance, but on the PCB there are two soldering holes, underneath which it says "AC 35V", will it be possible to use this transformer?
The transformer has a solder lug for "0" and also solder lugs for each of the various secondaries, however the pcb appears to require 35v x2 (there is no '0' solder hole....)
0 - 30V (Multi-tapped) @ 1A 30VA - Type 6672 Transformer - Jaycar Electronics
Forgive my ignorance, but on the PCB there are two soldering holes, underneath which it says "AC 35V", will it be possible to use this transformer?
The transformer has a solder lug for "0" and also solder lugs for each of the various secondaries, however the pcb appears to require 35v x2 (there is no '0' solder hole....)
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Does anyone know how closely the Ebay circuit compares to the Quad QC-24 and Audio Note M-Zero preamps? Both use 1x 6111 and have high output impedances, so may be very similar (or not!)......
I am also interested in the answer to that question!
If this kit has an high output impedance it kinda renders itself useless doesn't it, the purpose of a buffer being offering a low output impedance? It will probably degrade my system (it will be after my 10 k passive pot and before my TA2021 amp's - vertikal bi-amping my speakers).
I am too much of a audio n00b to really judge it for what it's worth, but hearing this makes me choose impedance matching over added "tube warmth / better soundstaging"..aka not using the buffer. On the other hand, I could always try to get it working externally to see what it's like. Decisions decisions huh
If this kit has an high output impedance it kinda renders itself useless doesn't it, the purpose of a buffer being offering a low output impedance? It will probably degrade my system (it will be after my 10 k passive pot and before my TA2021 amp's - vertikal bi-amping my speakers).
I am too much of a audio n00b to really judge it for what it's worth, but hearing this makes me choose impedance matching over added "tube warmth / better soundstaging"..aka not using the buffer. On the other hand, I could always try to get it working externally to see what it's like. Decisions decisions huh
Finished building my preamp – will get around to putting up some pics. Sound is great – smooth for sure, not noisy. Need some time for it to burn in.
The pcb is so small – I wonder if it would be possible to get two of them, match the components and then build a balanced linestage?
The pcb is so small – I wonder if it would be possible to get two of them, match the components and then build a balanced linestage?
I’ve noticed a humming noise – can’t seem to work out where it is coming from. Has anyone else built the kit yet?
I’ve noticed a humming noise too... I'm using 6.3-0-6.3 transformer. May be heater needs to be separated...
Did you use 6 + 15 v or 6 + 30 v? Did you solve the humming? I still didn't get around to building mine 😱.
That circuit doesn't reject power supply hum, so maybe a better filtered supply would be needed.
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