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    On Pre-Amps

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    Peter W.

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    On Pre-Amps

    Post by Peter W. on Thu Jul 26, 2018 10:39 am

    On active Pre-Amps (mini-rant warning):

    First, a few basics -

    A properly designed pre-amp will neither add nor remove artifacts. It will have no color, no shading, no ‘warm’, no ‘cold’, no ‘dry’ sound, and will do neither more nor less than reproduce what it is fed. Describing what it does (or does not) do in terms typically reserved for wine or truffles is pretty much a waste of time for both the victim and the perpetrator.

    The typical “Signal Source” will deliver +/- 2V out to the next-in-line component. For the purposes of this rant, all “sources” will be a generic 2V, and all “amps” will require this same generic 2V for full RMS output. This eliminates ‘refutation-by-exception’, one of the seven classical fallacies.

    The typical amp will accept a 100% modulated 2V signal and produce its full RMS output indefinitely. Feeding it an over-modulated 2V signal will not increase its output, just cause it to reproduce (faithfully) the trash it is fed. What this means is that transients (as noted previously: Rimshots, hand-claps, knocks and pings) will be over-modulated 2V signals. Distilling it down to its simplest terms: over-modulated signal from source is clipping at the source level as sources are not typically designed for transient-response capacity *BEYOND* the 2V level, but the signal source (vinyl, CD, Tape, Whatever) if well-engineered will have the transients at 2V – maximum modulation. Consider why, for a few moments.

    The typical active pre-amp will produce somewhere from about 5V out to as much as 15V out. Much as with amplifiers, call this “headroom”. NOTE: the source, typically at full volume, will produce 0 – 2V, and include the transients at the 2V level.

    A dynamic source will have many transients – and the amount of energy in the attack of that rimshot is immense – but momentary.

    Most well-designed amplifiers have an RMS capacity, and a transient capacity. The latter is typically defined in XX watts for YY seconds. Back in the day, this capacity was called many things and leveraged by less than scrupulous manufacturers to impute much greater power to their equipment than the reality. c.f. IPP – Instantaneous Peak Power. By comparison, the OEM Dynaco ST70 was rated at 35 wpc/rms with an 80-watt peak capacity, time not specified. My brute-force Citation 16 has an IPP of over 1,200 watts for one second. Generally, this IPP is a function of the power-supply and reserve capacitance. And with that in mind, consider that the VTA line has a much better power-supply than the OEM line.

    So, an active pre-amp will deliver transients to the amp at some level above 2V if so-set. This will allow *ACTUAL* signal already embedded in the source to be revealed where a passive attenuator will not. Those not familiar with the process may attribute these revelations to the pre-amp – they are not. They are already there, have always been there, but have been hidden or left below the noise floor for any number of reasons.

    Noise Floor: a passive attenuator has only the input signal to work with. There is no real adjustment between ‘too loud’ and ‘too soft’ for a dynamic source that makes everything comfortable at every level. And, if, like me, one is listening in a large room with highly inefficient speakers, it would simply not work. An active pre-amp solves all of those issues at once.
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    solderblob

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    Re: On Pre-Amps

    Post by solderblob on Thu Jul 26, 2018 10:34 pm

    Not sure if I follow all your analysis but you might agree with some of the following:

    In a phono-only system a phono preamp would/may produce 2V or less output.  The output is lower than desired to drive a power amp. This is what a line preamp would like to see as input.  In my case a DL=103 to SUT with 30 turns to phono pre with 44 dB gain provides 1.42V.  This might be considered a nominal 2V, similar to the output from a CD player.  But less than need for driving a power amp with respect to headroom for what you see happening with transients imposed upon steady state sinusoidal signals.

    So what I need is a phono preamp like the PH16 which includes an added stage of amplification to take a nominal 2V and amplify it to produce, when current demands, voltages well in excess of 2V, even for very short periods of time.  

    My evil mind wonders if this could be another PH16 (minus RIAA circuitry) all in one box.  For us phono-only extremists.  Or better it could be the PH-16 in the same box with an SP-14 minus switching, multiple inputs and volume control (I have a separate attenuator).  Why have two boxes and more interconnects...

    I've never seen a phono preamp that does this.  They all assume they'll drive a line preamp.

    It's late and I'm weary of editing this post.  Feel free to ignore.

    dave
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    Peter W.

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    Re: On Pre-Amps

    Post by Peter W. on Fri Jul 27, 2018 7:05 am

    Please excuse the odor of snarkiness in the following.

    My PAS 3X has a perfectly good MM phono pre-amp on board.
    My PAT 4 has a perfectly good MM phono pre-amp on board.
    My PAT 5 has a perfectly good MM phono pre-amp on board that will handle some MC devices
    My Citation 17 has two (2) perfectly good phono pre-amps on board.
    My Hafler DH110 as above
    My Revox A720 has two, one focused on MM, one focused on MC - but both are adjustable.
    I keep an Ortophon MC head-amp (not a transformer) which will make any MC cartridge compatible with any phono pre-amp.

    Back in the day, MM phono pre-amps were available at about every level of audio device, and were considered trivial exercises in basic electronics - which, for the most part, they are. I see the transformation of these most basic devices to be following the lead of esoteric cables - now that "Vinyl" is considered exotic and special rather than the cheapest means of producing, transporting and reproducing signal of the day, may as well make the phono pre-amp into something special, exotic and non-trivial. Just like cables, interconnects and power cords.

    William of Occam suggested we eschew needless complexity. Find a good active pre-amp with a good phono pre-amp already on board and go with that. You will be happier for it - as well as less broke.

    I had better stop here.
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    solderblob

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    Re: On Pre-Amps

    Post by solderblob on Fri Jul 27, 2018 9:39 pm

    Peter W. wrote:Please excuse the odor of snarkiness in the following.

    My PAS 3X has a perfectly good MM phono pre-amp on board.
    My PAT 4 has a perfectly good MM phono pre-amp on board.
    My PAT 5 has a perfectly good MM phono pre-amp on board that will handle some MC devices
    My Citation 17 has two (2) perfectly good phono pre-amps on board.
    My Hafler DH110 as above
    My Revox A720 has two, one focused on MM, one focused on MC - but both are adjustable.
    I keep an Ortophon MC head-amp (not a transformer) which will make any MC cartridge compatible with any phono pre-amp.  

    Back in the day, MM phono pre-amps were available at about every level of audio device, and were considered trivial exercises in basic electronics - which, for the most part, they are. I see the transformation of these most basic devices to be following the lead of esoteric cables - now that "Vinyl" is considered exotic and special rather than the cheapest means of producing, transporting and reproducing signal of the day, may as well make the phono pre-amp into something special, exotic and non-trivial. Just like cables, interconnects and power cords.

    William of Occam suggested we eschew needless complexity. Find a good active pre-amp with a good phono pre-amp already on board and go with that. You will be happier for it - as well as less broke.

    I had better stop here.

    I also have an Adcom preamp with MM/MC phono stage and a Mcintosh integrated amp with built in MM phono stage.  Neither sound near as good as my current Hagerman phono preamp/stepped attenuator setup -- it sounds magnificent.  The Adcom and Mac sound flat and lack transparency.

    The first stage of amplification of small signals would seem to be the most beneficial of excellent circuitry and not an afterthought.  Not saying anything, but I don't believe your (or mine) preamp/integrated amp phono stages were a high priority and thus were not designed and built as excellent phono stages even though phono/records/LPs was state of the art at the time.  I think Mcintosh favored a mellow, laid back, warm sound.  That's not what I want.

    Besides. this is a hobby -- try new stuff. build things, modify things.  Get some maggies!

    dave
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    Captain Coconut

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    Re: On Pre-Amps

    Post by Captain Coconut on Sat Jul 28, 2018 1:16 pm

    solderblob wrote:So what I need is a phono preamp like the PH16 which includes an added stage of amplification to take a nominal 2V and amplify it to produce, when current demands, voltages well in excess of 2V, even for very short periods of time.  dave

    Is there enough gain in the PH16 to drive a Dynaco amp directly, using let’s say, a mm cartridge with a 3.5 mV output?
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    solderblob

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    Re: On Pre-Amps

    Post by solderblob on Sat Jul 28, 2018 2:36 pm

    Captain Coconut wrote:

    Is there enough gain in the PH16 to drive a Dynaco  amp directly, using let’s say, a mm cartridge with a 3.5 mV output?

    Probably but it could depend.  There are two other recent threads below that discuss the pros/cons of driving amps directly without a line preamp.  Here's one:  ...any-benefit-to-a-preamp

    I used a MM cartridge with 5 mV output into a Hagerman phono preamp which has 44 dB gain.  It drove my VTA ST70 with no problem.  Currently using an MC cartridge with 0.3 mV with a step-up transformer tapped to 30 turns and with the Hagerman it works great with my Mk3 VTAs.

    I will note that both situations don't exactly match your 3.5 mV cart.  And also that if I use my MC step up transformer on the 15 turn tap, I occasionally get ringing/clinking transients on things like a high/loud piano note.  This is probably an indication of insufficient voltage headroom provided to the amp.  

    Consideration should also be given to your speakers, room, etc. and how loud you listen.  My speakers are old Maggies and they tend to like a decent amount of current from the amp.

    I don't know what gain the PH16 has but it's most likely more than 44 dB.  My current plan is to build a PH16 and see how it works.  Maybe later build a preamp like the SP-14.

    Roy has said that the PH16 should work with my setup but that he is a staunch advocate of using active preamps.  Of course he has the things just layin' around Very Happy

    dave
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    Peter W.

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    Re: On Pre-Amps

    Post by Peter W. on Sun Jul 29, 2018 5:22 pm

    I have been sitting on my fingers until the nasty-juice subsided. "Back in the day" - pre-amps, integrated amps and receivers from decent manufacturers took the phono-stage _Very_ seriously, often discussing their various choices at considerable length in their literature. Many discussed how interconnect capacitance could be modified to match the cartridge chosen, and a number gave a list. Consider those who owned vinyl at the time had far more $$ in their records than in their system in many cases and took this very seriously.

    That vinyl has the veneer of the exotic today does not make it anything other than settled technology, with the RIAA curve very well understood. Those who would suggest otherwise are either sheep to be shorn, or those doing the shearing. That is not to suggest that there is not a lot of junk out there - and that such junk at 40 or 50 years of age is no better than it was when new. Nor is it to suggest that age and wear do not cause problems such that maintenance and upgrades must be considered. But! I would suggest that the phono stages in my Revox A720 are as fine as anything available as present-day manufacture, very probably better than most of it - the Swiss do not screw around with these things. The analysis of a properly maintained PAS 3X phono stage suggests that was no slouch either.

    Do keep in mind that an active pre-amp will reveal much that was otherwise hidden - if properly applied. And if what is revealed is not very appealing - that would be the fault of the source, not the electronics.

    McIntosh Labs, back in the day, cut no corners and left nothing to chance. They were, then, one of the few manufacturers - even more-so than Revox - that justified every penny of their prices. But they were not for everyone, and I have often heard their 'sound' described as "clinical" - I would more suggest the term "uncompromising". A bad source remained a bad source, and a good one could shine.

    Need I go on?
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    Captain Coconut

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    Re: On Pre-Amps

    Post by Captain Coconut on Sun Jul 29, 2018 5:32 pm

    Why the persistent condescending attitude? It’s getting a little tiresome.
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    Bob Latino
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    Re: On Pre-Amps

    Post by Bob Latino on Sun Jul 29, 2018 8:50 pm

    Captain Coconut wrote:

    Is there enough gain in the PH16 to drive a Dynaco amp directly, using let’s say, a mm cartridge with a 3.5 mV output?

    Yes ... I have a few people with VTA ST-70 or ST-120's with an attenuator that use one of Roy's PH16's directly into their amp and use the VTA stepped attenuator to control volume. It's a simple set up >  turntable with cartridge > PH16 > ST-70 or ST-120 with attenuator > speakers. This would be sort of a dedicated vinyl system. and Yes > An active preamp will give you more flexibility .. (Selector switch, tone controls, tape loops, loudness control etc.).

    Bob
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    solderblob

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    Re: On Pre-Amps

    Post by solderblob on Mon Jul 30, 2018 10:57 pm

    Peter W. wrote:

    McIntosh Labs, back in the day, cut no corners and left nothing to chance. They were, then, one of the few manufacturers - even more-so than Revox - that justified every penny of their prices. But they were not for everyone, and I have often heard their 'sound' described as "clinical" - I would more suggest the term "uncompromising". A bad source remained a bad source, and a good one could shine.

    Need I go on?

    I'm in the process of ressurecting some of my equipment.  My main system is downstairs as a dedicated stereo listening room.  Phono only, tube only in a room filled with LPs.  It sounds good.  Real good.

    Upstairs I'm now setting up what might be considered a more family-friendly stereo.  It consists of  my old JVC QL-A7 turntable with the factory-supplied tonearm and Ortofon 2M Bronze cartridge (replaced by my newer DL-103 in the basement system and acts as a backup for the DL-103).  Amplification is a Mcintosh MA-6100 integrated amp with MM phono stage.  There is also a Jolida CD player and a Mcintosh MR-74 tuner.  Speakers are Vandersteen 2Cis which I recently re-socked and inspected the drivers for degradation.

    I'll update on how this goes and how this system sounds, vis-a-vis a comparison of sound quality of the phono playback.  I'm sure you're on pins and needles...

    dave
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    aguaazul

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    Re: On Pre-Amps

    Post by aguaazul on Tue Jul 31, 2018 12:23 am

    Hey Dave,

    Sounds like some good comparison systems we'd like to hear about.

    Aguaazul

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