The preamp thread

[watchdog]

To me, the preamp has always been the heart of an audio setup. This is despite the fact that for most people using line-level sources, it may actually be unnecessary to use a preamp. This is especially the case for people using DACs that have built-in volume control, whether this is done in the digital domain, or via an analog attenuator.

Let's have a look at the some of the common preamp types around. For simplicity of discussion, let's only include line level preamps.

1. Active preamp

You have a gain stage(s) and volume control. The gain could be handled by solid state, tubes or a combination of both. Sounds simple and shouldn't cost too much right ? If you think you can find a really top notch active preamp for a budget price, let me know - I'll be real interested.

2. Passive preamp

No gain here. Just a volume control. Since the voltage from your source (nominally 2V from a CD player) is usually enough to drive your power amp to full levels, why need gain ? Why not just attenuate ? Passive preamps are simplicity personified.

Of course there is no free lunch. A passive preamp has quite high output impedance and you need to keep your cabling short and capacitance low. You need to rely on your source to drive the whole chain up to the power amp. Your source could be up to the task, or not.

A passive preamp could cost a couple of bucks to make, or big money if you start shelling out for a premium potentiometer and other parts.

3. Transformer based preamp

A variation of #2. But volume control is achieved using a multi-tap transformer. This design has a trick up it's sleeve. Since you are using a transformer, you can step up as well as step down. So you can also incorporate a bit of gain too. Secondly, by stepping down you are decreasing voltage but increasing current, and decreasing output impedance. All very desirable things. Why doesn't everyone do this for passive designs ? Cost ! A resistive potentiometer starts from a few dollars upwards. A pair of transformers ain't cheap, especially for the premium names in the industry.

4. Other unusual designs

Unity gain buffered preamp - Enough voltage but problems with high output impedance, or driving long interconnects ? Why not make a passive preamp with a buffer stage ? There you have it. Have a look at the very popular DIY design published ages ago by Corey Greenberg in Stereophile. http://www.stereophile.com/solidpreamps/54

Another very popular buffered preamp design is the Nelson Pass B1. This is available in both kit version and as a finished product. https://www.passdiy.com/project/preamplifiers/b1-buffer-preamp

#2 and #3 combined - Take a transformer and step up the voltage to have some gain, and then let your potentiometer handle the rest. This is the approach taken by Amtrans of Japan in their APCG-01S.

[WildRain]

To me, the preamp has always been the heart of an audio setup. This is despite the fact that for most people using line-level sources, it may actually be unnecessary to use a preamp. This is especially the case for people using DACs that have built-in volume control, whether this is done in the digital domain, or via an analog attenuator.


3. Transformer based preamp

A variation of #2. But volume control is achieved using a multi-tap transformer. This design has a trick up it's sleeve. Since you are using a transformer, you can step up as well as step down. So you can also incorporate a bit of gain too. Secondly, by stepping down you are decreasing voltage but increasing current, and decreasing output impedance. All very desirable things. Why doesn't everyone do this for passive designs ? Cost ! A resistive potentiometer starts from a few dollars upwards. A pair of transformers ain't cheap, especially for the premium names in the industry.

Happen to hear on a couple of occasions and they had a very fluid (?) character to them.

Wondering if nortel and other reputed brands would be have models that can meet the specs for this design. Someone could try for an MO if there's sufficient interest and the supplier agrees

[watchdog]

Not sure which preamp you heard, but my Promitheus TVC had a very airy and fluid character too.

I don't think conventional transformer manufacturers would be interested in this as this is a very niche product.

The transformer manufacturers I know that produce models for this purpose are,

1. Sowter
2. Stevens & Billington

Closer to home, you have,

1. Promitheus Audio of Malaysia, and
2. Silk of Thailand

[shadowmoses]

If you think you can find a really top notch active preamp for a budget price, let me know - I'll be real interested.

I'd be real interested too. Finding the right preamp turned out to be the most difficult step in my setup. Tube or SS? SE or Balanced (ok no contest, the answer is always balanced for me). Is the preamp a true balanced design? How is the volume control done (balanced requires a 4-channel volume control. Is it LDR, resister ladder, TVC, volume pot ...)? and finally, how many outputs does it have (The more the merrier. My current pre has 2 variable and 1 fixed outputs. i use all 3)? This is on top of the usual features of preamps such as channel balance etc.

At one point, the pre turned out to be my most expensive component for something that doesn't seem to have much functionality... As Watchdog puts it, just a gain stage and volume control..
Must say it turned out to be a pretty interesting and rewarding journey though. 

[watchdog]

If you think you can find a really top notch active preamp for a budget price, let me know - I'll be real interested.

I'd be real interested too. Finding the right preamp turned out to be the most difficult step in my setup. Tube or SS? SE or Balanced (ok no contest, the answer is always balanced for me). Is the preamp a true balanced design? How is the volume control done (balanced requires a 4-channel volume control. Is it LDR, resister ladder, TVC, volume pot ...)? and finally, how many outputs does it have (The more the merrier. My current pre has 2 variable and 1 fixed outputs. i use all 3)? This is on top of the usual features of preamps such as channel balance etc.

At one point, the pre turned out to be my most expensive component for something that doesn't seem to have much functionality... As Watchdog puts it, just a gain stage and volume control..
Must say it turned out to be a pretty interesting and rewarding journey though. 

One point about preamp outputs. Most preamps with two sets of outputs are simply two pairs of sockets wired up in parallel. That means that if you are driving two power amps with 50 K input impedance, your preamp is effectively driving a 25 K load. Now, you do have preamps with independently buffered outputs, but its not a common practice.

[jb]

Sometime I also wonder whether a preamp is needed in the chain, since most high end CDP can output about 2V, and power amp only need 1v input to output max power. But in actual audition, having a preamp will make the system sound better as have more dynamic range and better bass.

When using CDP source, the preamp actually only giving buffer gain and there is not much stage gain, my conclusion is that with preamp, it has a more stable quiet power supply, the preamp gain stage has some reverse isolation gain so that any junk noise from power amp will be attenuated before reaching the CDP source, and preamp able to output more current and voltage to drive long interconnect cable. All this characteristic make using a preamp sound better than without.

[greatsound]

for years, i hv been happy with just cdp / integrated amp in the chain.
only earlier this year i began to explore separates and what a difference it made
preamp / power give me a sound that i never knew was there.. haha...
then there is the issue, tube or non tube preamp, until someone suggested why not the best of both world
tube preamp n SS power n tats exactly what i did with no regrets
my current setup -

preamp - Conrard Johnson PV11
power - Classe CA 400
source - DIY Philips Pro II transport / Project Box S FL (non filter) DAC with a custom build LPS
speakers - PMC OB1s

loving the sound to bits... infact there is so much emotion from jus playing CDs that i hardly play LPs since.. haha...

[sydney1128]

loving the sound to bits... infact there is so much emotion from jus playing CDs that i hardly play LPs since.. haha...

Please don't "say that"....
I'm just about to start my vinyl journey 😅

[greatsound]

lol.......

analogue playback will always hv its place in my heart
at 17, i started hifi with a JVC cassette deck n Marantz TT as source
even now, i m keeping my RP6 (heavily modded with Groove Tracer add ons)
the only thing i sold off was the Graham Slee phono preamp as the CJ PV11 comes
with a built in phono stage running 1x12AX7, 1x5751, 1x 12AU7 n $$ was spent getting Amperex n RCA tubes
to ensure a good decent playback for LPs

the only thing about LPs is tat it takes time n mood to listen to and its very hands on all the way, from the removing of the LP from cover to the dropping of the needle and the flipping at 25mins.  if i m in a rush n feeling lazy, plonking a CD onto the transport is much less work.... 

[watchdog]

Sometime I also wonder whether a preamp is needed in the chain, since most high end CDP can output about 2V, and power amp only need 1v input to output max power. But in actual audition, having a preamp will make the system sound better as have more dynamic range and better bass.

When using CDP source, the preamp actually only giving buffer gain and there is not much stage gain, my conclusion is that with preamp, it has a more stable quiet power supply, the preamp gain stage has some reverse isolation gain so that any junk noise from power amp will be attenuated before reaching the CDP source, and preamp able to output more current and voltage to drive long interconnect cable. All this characteristic make using a preamp sound better than without.

Yep. Somehow, adding an active preamp (a good one that is) brings the guts and glory that is commonly lacking in the passive preamp approach.

[greatsound]

yep, hv to agreed on that.  no offence to those using passive preamps but i hv been to 2 home demos where passive preamps (one setup with a Krell power amp and the other a tube power amp) were used and based on what i hear its like "something is missing", like eating mee rebus somehow the garnishing dun hv or the fried shrimps missing like that.... 

[Wizardofoz]

Personally my experience is where amps are low gain and/or source out is low then there will often be a need to have some gain option in the pre. I have an LDR Lighternote and Lightspeed passive pre's and to be honest, as open as they are you need the right combination of amp gain and source drive levels without having to sacrifice headroom. I seldom use them now as the flexibility of a pre with gain is just so much better. Not all res are created equal of course and some will not cut the mustard.