[mshan]

If you have a tape loop, maybe try an Yaqin Tube Buffer?

[Steve]

Good point re: the output capacitor.  Generally, to drive an SS load, you're looking at something in the 3.3-5 uf range.  If you're preamp uses an electrolytic (yucky but common) then they probably choose a plenty large enough size.  But, designers often like to keep film output caps as small as possible, given that large values like 3.3-5uf are physically very large and nicer types (polypro or better) and quite expensive.  If your output cap is undersized, it may lead you to blame a lack of bass on "tube sound," which isn't the problem at all!

Paul

Nice point Paul, blaming the tube preamplifier for lack of bass. What size preamplifier output cap that produces accurate bass with a 100k ohm input Z amp will lack bass when feeding an amp with a 20k ohm input Z.

----------------

On another note I wonder if Krell is referring to turn on/off thump. Otherwise the volume control will control the signal level so no damage should occur.

Cheers.

[motosapien]

Okay, I got the NAD amp manual out and here is what is listed on input impedance:

fixed - 10k + 200pf
variable - 100k + 100pf

For me this is like reading tea leaves. So, does my NAD amp limit my choice of tube preamps or will it be easy to find one that suits it?  My current NAD preamp has an output impedance of 75 which means it easily passes the 10:1 rule.   I will go to the Rogue Audio site and look at specs on their output impedance......


........and, for their Ninety Nine preamp the output impedance is listed at 350.  Should work just fine hugh?

[Steve]

What is the model number?

[opnly bafld]

What is the model number?

I've got NAD separates and heard that a tube preamp does nice things with a good SS amp ( C275BEE ).

[JakeJ]

Hi Motosapien,

I have been running hollow-state preamps into solid-state amps for most of the 30+ years I have been in this hobby.  To my ear there is something magical about the combo and I must be right as there are any number of mfrs that do the same, ie. Audible Illusions, Herron, Aranov, etc.

For instance, there is a Rogue Metis on Audiogon with remote and phono (if you need it) for $895 PP and shipping included.  A bit steep considering the website lists it as $1095 not the $1495 the seller claims.

There are plenty of options and maybe you should consider a speaker upgrade first.  I think a good rule of thumb is that the speakers should consume 50% of the total system price (+/- 10%).  I'll also say the used equipment market has been berry, berry good to me.

YMMV,
Jake

[Steve]

Thanks Opnly, but the specs only show 100k, 100pf input.
http://nadelectronics.com/products/hifi-amplifiers/C-275BEE-Stereo-Power-Amplifier/specs

I am wondering if it has been upgraded or modded?

Cheers.

[opnly bafld]

Okay, I got the NAD amp manual out and here is what is listed on input impedance:

fixed - 10k + 200pf
variable - 100k + 100pf

[JakeJ]

Let's see now...

Okay, I got the NAD amp manual out and here is what is listed on input impedance:

fixed - 10k + 200pf
variable - 100k + 100pf

For me this is like reading tea leaves. So, does my NAD amp limit my choice of tube preamps or will it be easy to find one that suits it?  My current NAD preamp has an output impedance of 75 which means it easily passes the 10:1 rule.   I will go to the Rogue Audio site and look at specs on their output impedance......


........and, for their Ninety Nine preamp the output impedance is listed at 350.  Should work just fine hugh?

And then you said...

Thanks Opnly, but the specs only show 100k, 100pf input.
http://nadelectronics.com/products/hifi-amplifiers/C-275BEE-Stereo-Power-Amplifier/specs

I am wondering if it has been upgraded or modded?

Cheers.

The spec you quotes are the exact specs the OP posted from the original manual.  What would make you think the amp has been modified?

Please note the amp has a switch on the back selecting between fixed and variable.  NAD doesn't seem to post both specs online but apparently the manual has both specs listed.

[JakeJ]

So, Motosapien, as long as you choose an amp that has a higher input impedance than the preamp's output impedance you'll get good sound.  If they are close it may not sound very nice.  This is an over simplified answer but it avoids a detailed primer on basic electronics.

One more thing, you should form a good habit of turning on the preamp before the amp and turn the amp off before turning off the preamp this way you'll always avoid a turn-on thump which could cause speaker damage.  I usually wait about 20-30 seconds for either situation.

Hope this helps,
Jake

[opnly bafld]

If you don't have a (good) subwoofer I would suggest that as the first step.
Epos makes fine speakers but the M8 is only rated down to 60 hz (since it was designed to be a center channel).

Lin

[Steve]

Let's see now...

And then you said...

The spec you quotes are the exact specs the OP posted from the original manual.  What would make you think the amp has been modified?

Please note the amp has a switch on the back selecting between fixed and variable.  NAD doesn't seem to post both specs online but apparently the manual has both specs listed.

Hi Jake.

As you probably know, I don't have a manual, so I went to the website listed above:
http://nadelectronics.com/products/hifi-amplifiers/C-275BEE-Stereo-Power-Amplifier/specs

Input impedance R and C 100 kΩ + 100 pF
Input sensitivity (for rated output into 8 ohms) 1-2v (ref. rated power)

As one can see only one input spec is listed and nothing about switchable nor another active stage, either gain or buffer. 1-2 volts can't be relied on to tell in absolute terms.

I am going to have to assume either the active stage is gainstage in which an external preamplifier is not needed, redundant to some extent, or simply a buffer and an active line preamplifier might work nicely. However, 100pf seems to me rather high if one is going to use a passive preamp.

The 10k input is rather low for any capacitive coupled preamplifier (low bass output) while the 100k is nice, but I doubt any external preamplifier is necessary, esp if the input sensitivity is 1volt rms. DC coupled preamplifier output would be a different story when it comes to 10k amp input impedance (Z).

Cheers.

[JakeJ]

Hi Steve,

I didn't mean to cause consternation.  I clicked on the you link you kindly provided and sure enough only one spec is given....online.  I noticed the photos and clicked on the one of the back of he amp and one can plainly see the input RCA jacks, the switch for fixed or variable, and the potentiometer to adjust said input signal.  I just figured that specs Motosapien quoted from his original manual offered the additional information.

So, if an owner switched it to variable they would have the benefit of the higher impedance and an easier match to a larger selection of preamps be they tubed or SS.

Again, sorry for any confusion I may have caused.

Jake

[Steve]

Hi Steve,

I didn't mean to cause consternation.  I clicked on the you link you kindly provided and sure enough only one spec is given....online.  I noticed the photos and clicked on the one of the back of he amp and one can plainly see the input RCA jacks, the switch for fixed or variable, and the potentiometer to adjust said input signal.  I just figured that specs Motosapien quoted from his original manual offered the additional information.

So, if an owner switched it to variable they would have the benefit of the higher impedance and an easier match to a larger selection of preamps be they tubed or SS.

Again, sorry for any confusion I may have caused.

Jake

No problem Jake. I did see that the input sensitivity is stated as 1-2 volts, which probably means another gainstage for the 100k ohm input Z and 100pf input capacitance input, although I cannot state such as fact. I would estimate there is probably no need of an external  gainstage preamplifier without going hyper sensitive.

Of course contacting NAD is the only sure way of obtaining all the facts.

Cheers.

[motosapien]

I could have provided a bit more info on the fixed/ variable setting.  I use the variable.  Based on the helpful posts in this thread, I'd say I'm good to go when I want the tube preamp upgrade.  I ordered a NX2 speaker kit this morning from GR Research ( sealed 2 way with a ribbon tweet and quality crossover components ).  Hoping for a noticeable improvement from my ported Epos ELS8's which are somewhat lack luster.

Maybe I can find a tube preamp kit to build as well?

Thanks for all the info guys!

[Steve]

I could have provided a bit more info on the fixed/ variable setting.  I use the variable.  Based on the helpful posts in this thread, I'd say I'm good to go when I want the tube preamp upgrade.  I ordered a NX2 speaker kit this morning from GR Research ( sealed 2 way with a ribbon tweet and quality crossover components ).  Hoping for a noticeable improvement from my ported Epos ELS8's which are somewhat lack luster.

Maybe I can find a tube preamp kit to build as well?

Thanks for all the info guys!

Well, if the NX-2 sounds anything like the A/V-3 (tower with transmission line), you are in for a treat. I have a pair of 3 here on loan.

Cheers.