The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Dynaco VTA tube amp kits, all Tubes4hifi.com products and all Dynakitparts.com products


    Any rule for pairing pre-amp and power amp

    Share

    maninmac771

    Posts : 30
    Join date : 2011-03-07

    Any rule for pairing pre-amp and power amp

    Post by maninmac771 on Tue Mar 15, 2011 8:23 pm

    Hi. Can anyone tell me if there is any golden rule for pairing pre-amp and power amp? What I mean is should solid state be paired with solid state, and tube with tube? Can a tubed one be paired with a solid-state one? I am now pairing the Dynaco ST70 with a Counterpoint Dual Channel Hybrid Pre-amp SA1000. Thanks in advance for views.

    j beede

    Posts : 328
    Join date : 2011-02-07
    Location : California

    Re: Any rule for pairing pre-amp and power amp

    Post by j beede on Tue Mar 15, 2011 9:01 pm

    Good question. Tube amplifiers often have a higher input impedance that do solid state amplifiers. Driving a tube amp input with a solid state preamp or a preamp with a solid state output driver is ordinarily no problem--though some people are uncomfortable with the more sensitive feeling volume control that this arrangement can produce. I am listening to Miles Davis right now with a solid state preamp driving my freshly finished Mark IIIs. The volume knob is at "8 o'clock" position where 7 o-clock is "off" and I use failrly inefficeint speakers. Driving the input of a solid state amplifier with a tube preamp could raise some less tolerable issues. If the amplifier has a particularly low input impedance and the preamp's output is relatively high impedance (PAS) there could be noise issues as the preamp's volume setting may be higher than usual to drive the solid state amplifer's input. In the 1970s and 1980s when may PAS preamps were being discovered/recycled it was not uncommon to add a unity gain drive stage to the PAS to circumvent address this. Bottom line, if you have a big solid state amp and like your music with lots of dynamic range you may not enjoy using an old style tube preamp.
    ...j

    GP49

    Posts : 735
    Join date : 2009-04-30
    Location : East of the sun and west of the moon

    Re: Any rule for pairing pre-amp and power amp

    Post by GP49 on Wed Mar 16, 2011 12:30 pm

    j beede wrote:If the amplifier has a particularly low input impedance and the preamp's output is relatively high impedance (PAS) there could be noise issues as the preamp's volume setting may be higher than usual to drive the solid state amplifier's input.
    ...j

    The BIGGEST issue isn't the higher volume control setting. It's the inability of the stock PAS linestage to drive a low-impedance load, and the bass rolloff due to the value of the output coupling capacitor. You can offset the latter by increasing that capacitor's value but can only go so far; and that still does not address the first issue.

    The volume control setting is a matter of GAIN and sensitivity, not the ability of the circuit to drive a load. Parallel illustration: in the early 1990s, some Japanese cars felt peppier than their American competition. Yet in side-by-side maximum acceleration tests they were not any quicker; in many cases they were slower. What the Japanese did was to contour their throttle position sensors to act "faster" in the first increments of motion, while the Americans designed theirs to be more linear. So the Japanese ones FELT quicker but their sensors would run nearly to maximum early, and the last increments of motion hardly did anything. That was scary when you would try to overtake another vehicle, realize you had to go faster and STOMPED on it...and almost nothing happened.

    By 1993 or so, the Americans caught on (Chrysler, I believe, was the first to do it).


    Last edited by GP49 on Wed Mar 16, 2011 5:31 pm; edited 1 time in total

    j beede

    Posts : 328
    Join date : 2011-02-07
    Location : California

    Re: Any rule for pairing pre-amp and power amp

    Post by j beede on Wed Mar 16, 2011 3:47 pm

    GP49 wrote: The BIGGEST issue isn't the higher volume control setting. It's the inability of the stock PAS linestage to drive a low-impedance load

    I thought that's what I said. How do real users compensate for the low drive? Same way they do with their high impedance mp3 players when used as a source: turn it up. Here comes the noise and there goes the usable dynamic headroom.

    Hence the addition of unity gain stages as I pointed out. Overly sensitive volume controls are no more of a problem than overly sensitive bias pots--more an inconvenience or annoyance rather than an electrical problem. This is never (never say never) the case when a high impedeance tube output stage drives a low impedance solid state amplifier input so why is it even mentioned? Driving a low impedance input with a high impedance source is not an inconvenience, it represents an electrical mismatch that Mssrs. Thevinen and Norton have described nicely and has been addressed in the past with unity gain cathode followers, for example. Don't most people simply bypass the output cap anyway?

    GP49

    Posts : 735
    Join date : 2009-04-30
    Location : East of the sun and west of the moon

    Re: Any rule for pairing pre-amp and power amp

    Post by GP49 on Wed Mar 16, 2011 5:41 pm

    Bypassing the output capacitor on a PAS causes scratchy noises on the tone control pots due to DC on them; and even if those are bypassed, DC on the output jack. Some amplifiers are direct-coupled and DC on the output jack with those amps would be a big mistake because that voltage goes straight to the grid on the input tube or the base/gate of the input transistor.

    Such amplifiers with direct-coupled inputs are not rare. Name one? The Dynaco Stereo 70 (though not the Stereo 70 Mk II: Panor stole a bandpass filter design from somebody else, and it includes an input capacitor)

    Casual users may not even be aware of the inadequate drive issue. Put enough gain into the linestage and enough sensitivity into the power amp and the volume may still be loud at low volume control settings; but with inadequate drive, the distortion will be high, with early onset of overload in the linestage.

    LOTS of people have tried driving low impedance solid state amplifiers with a stock PAS, and then complain about the results, more often in terms of the sound sounding strangely odd (distortion) although it is plenty loud ("I only have to turn it up to nine o'clock to drive my family out of the house"). Some upgraded their tube systems with transistor amps, all the while believing the oft-repeated untruths from major audio magazines of the time, that all components are compatible with all others.

    maninmac771

    Posts : 30
    Join date : 2011-03-07

    Re: Any rule for pairing pre-amp and power amp

    Post by maninmac771 on Thu Mar 17, 2011 1:50 am

    So, basically I guess it would be logically good to drive tube amps with either tube or solid-state pre-amp and it would be a different situation if solid-state amp is driven by tube amp. The Coungerpoint SA1000 I'm using has 2 x 12AX7 for phono and 1 x 6DJ8 and MOSFET for line stage and therefore is not a pure tubed machine. I wonder if this is appropriate for the ST70.

    GP49

    Posts : 735
    Join date : 2009-04-30
    Location : East of the sun and west of the moon

    Re: Any rule for pairing pre-amp and power amp

    Post by GP49 on Thu Mar 17, 2011 3:01 am

    maninmac771 wrote:So, basically I guess it would be logically good to drive tube amps with either tube or solid-state pre-amp and it would be a different situation if solid-state amp is driven by tube amp. The Coungerpoint SA1000 I'm using has 2 x 12AX7 for phono and 1 x 6DJ8 and MOSFET for line stage and therefore is not a pure tubed machine. I wonder if this is appropriate for the ST70.

    Yes. Smile

    Sponsored content

    Re: Any rule for pairing pre-amp and power amp

    Post by Sponsored content Today at 1:43 am


      Current date/time is Fri Dec 09, 2016 1:43 am