What a difference an amp makes??!

[sleepyguy24]

Afternoon everyone. I hope everyone's Friday is going well.

A lot of you may have already experienced this but I'll put this out there anyway. Laugh away.

Ever just have change an amp and notice dramatic differences in sound when everything else is the same? I guess this can happen with any type of equipment but it happened to me last night when I changed amps.

Through the years I was able to get different kinds of amps. Amps that that piqued my curiosity.

Last night I was changing out my current set of Red Dragon M1000 Mk1 monoblocks to a very good condition Nakamichi Stasis 5 to try and compare sonic differences.

I kept everything the same in the system except for the ICs going from my preamp to amp. Digital sources are a EE Minimax DAC with a cryoed GE 6201 tube and a XS 728A tube buffer/preamp.

When I had the Red Dragon M1000 Class D monos in place my preference was for the EE Minimax DAC. It sounded a very different sonically and the difference was drastic vs the 728A. With the MiniMax DAC in place there was a wide soundstage with good bass. When I switched to the 728A the bass was good but the soundstage was laid back. Depending on the recording I go back and forth with the Red Dragons in place.

When I had the Nakamichi Stasis 5 Class A amp in place the sound was a lot better because with the 728A tube preamp/buffer. Sound was dull when I was using the EE MM DAC. With the 728A in place better mids and bass.

Previously when I put a my Jolida 502P tube amp in the system both sources sounded very similar that I was almost about the get rid of the EE MM DAC.

I guess the differences of each amp are interacting with my gear. Could this be the damping factor coming into play or the circuit designs of each? I have no idea this synergy thing is a funny thing sometimes.

Thanks

[steve]

Afternoon everyone. I hope everyone's Friday is going well.

A lot of you may have already experienced this but I'll put this out there anyway. Laugh away.

Ever just have change an amp and notice dramatic differences in sound when everything else is the same? I guess this can happen with any type of equipment but it happened to me last night when I changed amps.

Through the years I was able to get different kinds of amps. Amps that that piqued my curiosity.

Last night I was changing out my current set of Red Dragon M1000 Mk1 monoblocks to a very good condition Nakamichi Stasis 5 to try and compare sonic differences.

I kept everything the same in the system except for the ICs going from my preamp to amp. Digital sources are a EE Minimax DAC with a cryoed GE 6201 tube and a XS 728A tube buffer/preamp.

When I had the Red Dragon M1000 Class D monos in place my preference was for the EE Minimax DAC. It sounded a very different sonically and the difference was drastic vs the 728A. With the MiniMax DAC in place there was a wide soundstage with good bass. When I switched to the 728A the bass was good but the soundstage was laid back. Depending on the recording I go back and forth with the Red Dragons in place.

When I had the Nakamichi Stasis 5 Class A amp in place the sound was a lot better because with the 728A tube preamp/buffer. Sound was dull when I was using the EE MM DAC. With the 728A in place better mids and bass.

Previously when I put a my Jolida 502P tube amp in the system both sources sounded very similar that I was almost about the get rid of the EE MM DAC.

I guess the differences of each amp are interacting with my gear. Could this be the damping factor coming into play or the circuit designs of each? I have no idea this synergy thing is a funny thing sometimes.

Thanks

Hi Sleepy,

Could be a lot of things. Impedance matching, between pre and amp, and amp to speaker, which can determine the bass response, damping factor etc.

It could also include the inherent amplifier designs. It is quite possible that one can adjust one cap for better or more bass, while another cap location might alters the highs. Therefore, different brand and size caps could alter the sound even though the specs will claim the same.

Spab, from St. Louis, and I have been tweeking his particular system by adjusting values, brands, ICs, speaker cables etc.

Cheers and good fortune Sleepy.

Steve

[Werd]

It tells me alot of whats going on in my system.  Its a good base to see how well my speakers can accept changes, especially when moving up the same line in amps. There is a point where speakers can get left behind in resolution and I find this in amp changes.  If I stop hearing changes while improving amplification you know youve hit that point where speakers are no longer up for the job and begin to get left behind.

Once that point is found amps improvements are point less until speakers are better room suited or improved.

[richidoo]

Both are solid state amps so the damping factor will be good in both cases, probably not an audible factor.

The input impedance of the class D is advertised as "high, for use with exotic tube preamps." That means >100kOhm, easy for the tube buffer to drive with low distortion. I can't find the input impedance for the discreet input stage Statis, but I would guess it is a more standard 10kOhms (or lower) that was common for SS amps in that era, and now. Even though the tube buffer output impedance spec says 600 ohms, that is an industry standard figure which may or may not be actually true. Assuming it is true, the tube buffer will still make more distortion driving 10k than 100k.  You may or may not like the higher distortion the tubes make with the harder load.

The tube in the EE DAC is not actually driving the amp's loads, it is driving a high impedance opamp buffer stage on the output of the EE so the tube will have low distortion compared to the pure tube buffer.

You can add another tuning option by turning off the tube in the EE. I liked it better off. Then it's just the opamp. Maybe that's enough when using the Stasis.

[Bill O'Connell]

Try pulling the tube out of the DAC and just run the SS instead of the tube output. I like it that way.

[steve]

Both are solid state amps so the damping factor will be good in both cases, probably not an audible factor.

The input impedance of the class D is advertised as "high, for use with exotic tube preamps." That means >100kOhm, easy for the tube buffer to drive with low distortion. I can't find the input impedance for the discreet input stage Statis, but I would guess it is a more standard 10kOhms (or lower) that was common for SS amps in that era, and now. Even though the tube buffer output impedance spec says 600 ohms, that is an industry standard figure which may or may not be actually true. Assuming it is true, the tube buffer will still make more distortion driving 10k than 100k.  You may or may not like the higher distortion the tubes make with the harder load.

The tube in the EE DAC is not actually driving the amp's loads, it is driving a high impedance opamp buffer stage on the output of the EE so the tube will have low distortion compared to the pure tube buffer.

You can add another tuning option by turning off the tube in the EE. I liked it better off. Then it's just the opamp. Maybe that's enough when using the Stasis.

Hi Rich,

The problem with 10k ohm input Z, as you state can be a real problem, especially with output capacitively coupled preamplifiers and lack of bass. Distortion is not quite the problem, assuming a descent plate current.

Here is a quote from my article concerning some measurements that I hope helps. I edited the quote, one can find more information at:

http://www.sasaudiolabs.com/sasaudio.htm

This section deals with impedance "mismatch", distortion and frequency response changes.

What is the effect of amplifier input impedance VS active preamplifier/source output impedance. To be more precise, the input impedance (Z) of the amplifier verses the output Z of the preamplifier or source. (The specifications of both impedances can be found in the owner's manuals.) Most recomment a 10:1 ratio.

I also recommend a 10:1 ratio to be safe. (The RCA Radiotron Designers Handbook recommends a 5:1 ratio.) Using a 10:1 ratio, the amplifier input impedance should be 20,000 ohms (20k ohms) with the preamplifier output

Understand that teaching the 100:1 ratio attempts to legitimize the use of a buffer stage while inferring that those who use a 10:1 ratio are inferior. Not only does adding a buffer stage not significantly reduce distortion, but deteriorates the musical quality, increases the complexity, increases "crosstalk" problems between channels, and adds to the cost (which increases the profit margin). Let's check out an example.

We have an amplifier with 20k ohms input impedance (Z). Let's compare a preamplifier with a 100 ohm output Z to a 2000 (2K) ohm output Z. As such, we are decreasing the ratio from 200:1 to 10:1.

The total harmonic distortion of a JJ E88cc tube, at 2v rms output measures approximately 0,01% (-80db) using the 200:1 ratio. changing the ratio to 10:1 raises the distortion by approximately 0,0012% to -79db. So the distortion rises from -80db to -79db.

How about frequency response changes.

This section deals with the high frequency response of our active preamplifier with and without a buffer stage. We will use a 50pf IC vs 250pf IC. The output impedance with buffer stage is 100 ohms. Without is 2,000 (2k) ohms.

First, the high capacitance 250pf interconnect cable and the buffer stage, 100 ohms. The high frequency response drops approx 100udb at 100 khz, and approximately 6udb at 20 khz. With output Z of 2khz, the drop is 0,045db at 100khz and 0,002db at 20khz. Not much is it.

Now we use the 50pf interconnect cable. The result is less than 0,150udb drop at 100 khz, and 0,05udb at 20 khz. With output Z of 2khz, the drop is 0,002db at 100khz and 75udb at 20khz. (Rarely, a longer IC with higher capacitance is neccessary as there is no choice.)

Capacitively output coupling is a real challenge at lower amp input Z.

Hope this testing helps.

Steve

[Response Audio]

All this is a perfect example of is meant when people mention "system synergy". Too many people don't look at impedance differences when combining components which sometimes leads to bad or incorrect consumer reviews.

From what I have read in forums, a LOT of Class D based amps are getting wrongful bad feedback due to improper matching of a preamp. I saw one consumer bad mouth a Class D amp (6k ohm input) and after checking further, his tube preamp had an output impedance of 2,500 ohms and a gain of 26dB. Simply not a fair evaluation. That preamp is meant more for a tube amp with high input Z and very low gain.

In most cases, a preamp (any output stage) with an output impedance of under 1k ohms does not pose a problem with [most] tube amplifiers and many solid state amps.

However, I have seen solid state/Class D amps all over the replace when it comes to inputs. I have used a Class D amp at my place for a couple years now with only a 7k ohm input. So going by the 10:1 ratio, this requires a minimum 700 ohm output from a preamp. The lower input of many of today's amps, especially Class D/Ice,  is what lead to the design of our single ended preamps having a very low output impedance. One of our full size LeAnna models and out Segue tube buffer has an output of <90 ohms and the other LeAnna models no higher than 630 ohms.

[steve]

author=Response Audio link=topic=5079.msg65278#msg65278 date=1408814160]
All this is a perfect example of is meant when people mention "system synergy". Too many people don't look at impedance differences when combining components which sometimes leads to bad or incorrect consumer reviews.

From what I have read in forums, a LOT of Class D based amps are getting wrongful bad feedback due to improper matching of a preamp. I saw one consumer bad mouth a Class D amp (6k ohm input) and after checking further, his tube preamp had an output impedance of 2,500 ohms and a gain of 26dB. Simply not a fair evaluation. That preamp is meant more for a tube amp with high input Z and very low gain.

The impedance matching itself is not a problem as is the coupling method (see below). IF capacitance output coupled, the bass response will definitely suffer. I have seen some components use a poor size .67uf output coupling capacitor (see below).

If transformer coupled, one then has to worry about ringing, +/- frequency response besides tilting of the frequency response.

In most cases, a preamp (any output stage) with an output impedance of under 1k ohms does not pose a problem with [most] tube amplifiers and many solid state amps.

Preamplifier output Z is the main determining factor of high frequency response in most amplifiers. 20k, 50k, 100k amp input Zs. However, most preamps already have tremendous FR as per my quote above.
 
With about 2k preamplifier output Z and 100pf, the FR is somewhere around 300khz or higher, minus 3db. As one can see, less than 2k means little except another stage, unless if one has very high interconnect cable capacitance.

My whole article is at:

http://www.sasaudiolabs.com/sasaudio.htm

The vast loss in FR in a preamplifier is due to volume control to input device, whether tube or SS.

So going by the 10:1 ratio, this requires a minimum 700 ohm output from a preamp. The lower input of many of today's amps, especially Class D/Ice,  is what lead to the design of our single ended preamps having a very low output impedance. One of our full size LeAnna models and out Segue tube buffer has an output of <90 ohms and the other LeAnna models no higher than 630 ohms.

It is too bad that class D amp designers do not raise the input impedance because with 6k, 7k, a huge, gigantic output capacitor is necessary to not heavily skew the overall response, the lower the more deviation from accuracy.

A 1uf capacitor has 8k reactance at 20hz, 2uf has 4k of reactance at 20hz. Either small value will negatively influence the response into midband. 8k will be at least 6db down at 20hz. That means approximately minus .25db at 320hz, and some even at 640hz. (Of the top of my head.)

Either a huge output cap is needed, or transformer, or dc coupled. But they also have their problems. 

I agree that with 26db of gain, a low gain amplifier would work nicely as one has more volume control rotation to work with.

Cheers

Steve

[rollo]

   Some do. Our Arion HS500 hybrid has a 100K input. The RS500 non hybrid has a 10K. Soon to be revised to 100K.
    I have found that a passive can work very well with the 10K crowd as well.
     

charles