I am planning a Class A amplifier build. I'm leaning towards a version of JLH.
I notice that most pictures showing members' class A builds do not have volume pots. This makes me assume that most people are either using a pre-amp (active or passive) or are using a digital source where there is volume control (e.g. software based media player).
Given that the classic Class A designs come from a time before CD players and home PCs I'm wondering whether a 2V input still requires the use of a pre-amp to increase gain.
Some people insist that amps sound better with pre-amps. Some even claim that passive pre-amps improve the sound (how can adding a pot in a box and using a longer signal path improve things??). I don't really understand this even for an active pre-amp. I would imagine that this would only be the case if the pre-amp is very carefully designed to complement the power amp, which then removes any flexibility offered by having a device with volume and selector control that could be used for muliple power amps, meaning simpler and cheaper power amp builds. An active pre-amp then also need its own power supply and cord etc.
To me a pre-amp (active or passive) it is just adding another layer of potential degradation and/or a deviation from the character of the power amp. I feel like I must be missing something. By the way I have never owned a pre-amp, but like the idea of adding a (good) volume pot to active amps even if there is digital volume control at the source. Sometimes its just more convenient to twist a knob.
I notice that most pictures showing members' class A builds do not have volume pots. This makes me assume that most people are either using a pre-amp (active or passive) or are using a digital source where there is volume control (e.g. software based media player).
Given that the classic Class A designs come from a time before CD players and home PCs I'm wondering whether a 2V input still requires the use of a pre-amp to increase gain.
Some people insist that amps sound better with pre-amps. Some even claim that passive pre-amps improve the sound (how can adding a pot in a box and using a longer signal path improve things??). I don't really understand this even for an active pre-amp. I would imagine that this would only be the case if the pre-amp is very carefully designed to complement the power amp, which then removes any flexibility offered by having a device with volume and selector control that could be used for muliple power amps, meaning simpler and cheaper power amp builds. An active pre-amp then also need its own power supply and cord etc.
To me a pre-amp (active or passive) it is just adding another layer of potential degradation and/or a deviation from the character of the power amp. I feel like I must be missing something. By the way I have never owned a pre-amp, but like the idea of adding a (good) volume pot to active amps even if there is digital volume control at the source. Sometimes its just more convenient to twist a knob.
If your source has enough maximum output to drive your power amp to full output, then
a preamp isn't required, just a way to control the volume. Locating the volume control in
the power amp is optimal electrically (but perhaps not the most convenient place).
Size the resistance of the volume control as low as possible, but still an easy load for the source.
Often a 10k pot is fine.
a preamp isn't required, just a way to control the volume. Locating the volume control in
the power amp is optimal electrically (but perhaps not the most convenient place).
Size the resistance of the volume control as low as possible, but still an easy load for the source.
Often a 10k pot is fine.
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So do you reclon that 2V is likely to be enough for a typical Class A power amp?
Yes I was planning on trying a 10k stepped attenuator style pot initially.
You've obviously got to have a volume pot somewhere, as a minimum. Personally I feel a 4 section Baxadall tone control circuit (active) is way worth it, to dial in just the right loudness comp, and deal with room acoustics to some extent (that's what I've been using for decades). But apparently many people think that's evil... As if the tonal mix is always just right... Any well designed circuit should be fine, and not even close to the weak link of the system. If the music source is a smartphone using bluetooth (apparently the latest trend ?), there are apps that can give you preamp control, which could be good. I haven't personally done that, but I believe that's out there.
It will be close enough for most amplifiers. Remember to compare like voltages;
the typical 2V digital output level is Vrms, so compare that with the maximum Vrms
amplifier output voltage divided by the amplifier's gain (not the peak output voltage).
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Is your amp tube or Solid State?
If SS most are made with a sensitivity about 1V RMS or less ; IF your digital source output can reach 2V RMS. you're done.
A few Tube amps may have less sensitivity, say around 2V RMS , and may be on the edge.
So what´s the brand and model of your power amp?
If SS most are made with a sensitivity about 1V RMS or less ; IF your digital source output can reach 2V RMS. you're done.
A few Tube amps may have less sensitivity, say around 2V RMS , and may be on the edge.
So what´s the brand and model of your power amp?
To reduce the input signal, you can use ALPS at the input. You can change the negative feedback resistor.
To increase sensitivity or vinyl you need a preamp
#6594 Table 1
JLH 10 Watt class A amplifier
To increase sensitivity or vinyl you need a preamp
#6594 Table 1
JLH 10 Watt class A amplifier
An active preamp has never been a requirement in the digital age. Certainly not technically.
In practice, however, the vast majority of audiophiles, having tried the minimalist direct connection, eventually go back to using an active pre. Yes, it is a mystery, but a fact.
Perhaps the culprit are the digital sources and the extra layer of filtering/decoupling/noise a preamp introduces is essential for a degree of musicality.
Certainly lower quality digital seems to benefit more from the additional box, but many owners of even the MSB Select II, after a period of enchantment with the transparency of a direct connection and digital VC go back to an active preamp.
My position is that provided you are not prepared to make an extreme effort in constructing an active pre it is much more sensible to use a direct connection between dac and amp.
In practice, however, the vast majority of audiophiles, having tried the minimalist direct connection, eventually go back to using an active pre. Yes, it is a mystery, but a fact.
Perhaps the culprit are the digital sources and the extra layer of filtering/decoupling/noise a preamp introduces is essential for a degree of musicality.
Certainly lower quality digital seems to benefit more from the additional box, but many owners of even the MSB Select II, after a period of enchantment with the transparency of a direct connection and digital VC go back to an active preamp.
My position is that provided you are not prepared to make an extreme effort in constructing an active pre it is much more sensible to use a direct connection between dac and amp.
The class has nothing to do with voltage gain or input impedance. There haven't been any enforced standards in this area for many years. A power amp can have a voltage gain of unity or of 40. Input impedance of 2k or of 1M.
JLH has high sensitivity, you can drive it directly by your smartphone. If you have the intention of adding volume control, as digital outputs are now low impedance you can use down to 1k potentiometer. If 10k or above is to be used, A buffer is recommended , JLH proposes one with jfet.
I have built a JLH, the 2003 model, using pcbs from Jim's audio on ebay.
I have no analog volum control. My source is a Raspberry pi with Hifiberry DAC+ Pro as source. Works very good. I use it in my workshop. No problems with the level. The Hifiberry DAC has a builtin volum control.
I have no analog volum control. My source is a Raspberry pi with Hifiberry DAC+ Pro as source. Works very good. I use it in my workshop. No problems with the level. The Hifiberry DAC has a builtin volum control.