How do you know if your amp will work with a Passive preamp ??

[Akustic]

What am I missing ??

Why can't I use a passive preamp with a CD player as a source for this Aragon 4004 MKII ??

POWER OUPUT 8 200-watts by 2-channels
POWER OUTPUT 4 400-watts by 2-channels
THD 0.05% for 8 ohm loads
S/N RATIO 110dB A Weighted
INPUT SENSITIVITY 150 mV for 1-watt output
INPUT IMPEDANCE 22 kohms
POWER CONSUMPTION 1500-watts max

The amp just sounds thin and underfed unless I use an active preamp ..
Can't say that I understand the interactions of an amp and a preamp ..
The sensitivity spec confounds me ..

 

[Akustic]

The sensitivity specs seems like a fuzzy spec and pro equipment has adjustable gain ..they measure it and match it ..
How do we know with home gear ??

 

[lini]

Well, 150 mV for 1 Watt would mean ca. 2.1 V for the nominal maximum power output (200 W @ 8 Ohm). That would appear somewhat insensitive - most usually power-amps for hifi use rather have an input sensitivity of ca. 1 V for nominal maximum power output. So there'll be quite a few sources, which won't be able to mobilise the full power of that Aragon model.

Greetings from Munich!

Manfred / lini

 

[Akustic]

Well, 150 mV for 1 Watt would mean ca. 2.1 V for the nominal maximum power output (200 W @ 8 Ohm). That would appear somewhat insensitive - most usually power-amps for hifi use rather have an input sensitivity of ca. 1 V for nominal maximum power output. So there'll be quite a few sources, which won't be able to mobilise the full power of that Aragon model.

Greetings from Munich!

Manfred / lini

Thank you .. I need to study .. that whole gain matching thing has left me confounded for too many years ..
Doesn't help that the manufacturers quote differing specs .. hard enough already ..
Luckily I already have an active Wada preamp but it has way more gain than necessary ....
The steps on the volume knob are way too steep and it never makes it up to a quarter volume position ..
My other amps are just fine with Passive volume controls ..
Thanks for the help ..

 

[Akustic]

Still confuses me tho ..
If the CD is at 2 V .. why does the Aragon go all thin and anemic when it's getting a 2 V signal if it only requires 2.1 V for full output ??
My B&K is full bodied and fine with it's 1.3 V sensitivity ..
Is it impedance that I need to study ??

 

[fredgarvin]

The input impedance at 22k ohms is much too low. This is why some people find their amps with passive's to lack body, drive, sound thin etc.You could use a buffer to match it with the passive pre. An input impedance of 50k would be fine.

 

[E-Stat]

Is it impedance that I need to study ??

As fred already observed, its low input impedance could be a challenge even for some actives. I used attenuators between a GamuT CDP with 75 ohm output successfully for years with VTL amps having 132k ohm input Z.

 

[lini]

fg, E_S: Oh, come on, guys - 22 kOhm too low or a challenge even for some actives? Imo that's rather ridiculous - any half-decent line-level source should easily be able to digest that. However, it would be interesting, what pot resistance value the OP's passive pre has, provided it's pot-based...

Greetings from Munich!

Manfred / lini

 

[IPADave]

IME a passive pre works best feeding into a high impedance amp.

 

[E-Stat]

fg, E_S: Oh, come on, guys - 22 kOhm too low or a challenge even for some actives?

Such is quite common for tube designs with higher source impedance. It's not a question of better or worse. Rather the need for proper matching.

 

[WaynerN]

I use a plain old 4 input switch box to select sources for my volume controlled power amp. No need for a passive preamp, which in my opinion is an oxymoron. There is no amplification with the passive, only attenuation. The switch box is less complicated and lets the true sound of the source component come thru.

That is how I have my garage system anyway.

 

[pskaudio]

22K input is fine for a passive with a 10K attenuator. The only active preamps that might have a problem with 22K would be tube units with high output Z.

 

[sqlsavior]

It can depend on the type of attenuator, too. A magnetic attenuator, such as a transformer or auto-former volume control, will not be affected by impedance mis-matches.

 

[Akustic]

fg, E_S: Oh, come on, guys - 22 kOhm too low or a challenge even for some actives? Imo that's rather ridiculous - any half-decent line-level source should easily be able to digest that. However, it would be interesting, what pot resistance value the OP's passive pre has, provided it's pot-based...

Greetings from Munich!

Manfred / lini

Preamp is a Schiit SYS .. model SCH-13 .. I'll look on their website for info on the Pot . (HaHa, these names have to change, and it's too easy to call it the Little ****) ..
22 kOhm doesn't seem all that far from the 24 kOhms of the B&K ..but what do I know at this point .. I need a refresher course on impedance..
And my active tube preamp has no problem at all driving it ..

Schiit sys
Number of inputs: 2 (stereo RCA)
Number of outputs: 1 (stereo RCA)
Input impedance: 10k ohms
Output Impedance: 5k ohms maximum

 

[twiiii]

200 watts is 23 db above 1 watt. So whats 23 db above 150 MV. 20 db would be 1.5 volts and another 3 db would be about 2.4 volts. I don't have my calculator on this trip. So unless your input source can safely put out 3 volts with the internal losses of a passive pre-amp you are up the creek with out a paddle. Now if your amp had a sensitivity of around 1 volt or . 7 volts the passive pre-amp might work just fine. I like tone controls, mode selector switches, loudness controls and phono inputs, MM and MC. So a passive pre-amp was never a consideration.

 

[Akustic]

200 watts is 23 db above 1 watt. So whats 23 db above 150 MV. 20 db would be 1.5 volts and another 3 db would be about 2.4 volts. I don't have my calculator on this trip. So unless your input source can safely put out 3 volts with the internal losses of a passive pre-amp you are up the creek with out a paddle. Now if your amp had a sensitivity of around 1 volt or . 7 volts the passive pre-amp might work just fine. I like tone controls, mode selector switches, loudness controls and phono inputs, MM and MC. So a passive pre-amp was never a consideration.

Your math is shaky .. but your point is intact..
23x 150 = 3.45 V .. add in the loss .. I hear what you're saying ..
Luckily my paddle was sitting there in the shape of an active preamp... and this is close to double the CD player's output.
And obviously, some amps simply aren't candidates for a passive preamp ..

 

[Pio1980]

Sources should be able to drive more than 2.0 VRMS into 5k to work well with a random passive controller into a random amp.
Many sources can, some cannot.

 

[lini]

Akustic: Actually his math was fairly close, whereas yours is wrong. I.e., you can't simply multiply the dezibel value of the 200 to 1 power ratio with the input sensitivity for an output of 1 W to get the input sensitivity for 200 W. Instead you need to convert the 23 to a voltage ratio or respectively multiplier first: 10^(23 / 20) = ca. 14 (to 1). Then you can calculate 0.15 V x (ca.) 14, which is (ca.) 2.1 V.

For my first post above I've used a different approach to calculate the multiplier, though: I went with the formula P = U² / R, so U = (P x R)^0.5. So the voltage multiplier would be 1600^0.5 / 8^0.5, which again is ca. 14.

However, what I'd rather doubt, is twiii's guesstimation of the internal losses, which would seem rather high to me. And what really puzzles me is Shiit's output impedance spec: Why 5 kOhm max.? In my view that should rather vary between close to 0 (fully turned up) and 10 kOhm (fully turned down).

But in any case we can now determine the combined load impedance:

- fully turned up: (almost 0 Ohm +) 1 / ((1/10000 Ohm) + (1/22000 Ohm)) = ca. 6875 Ohm

- 90 % (in terms of resistance): 1000 Ohm + (1/((1/9000 Ohm) + (1/22000 Ohm))) = ca. 7387 Ohm

- "half way" (in term of resistance): 5000 Ohm + (1 /((1/5000 Ohm) + (1/22000 Ohm))) = ca. 9074 Ohm

So, as we can see, the "worst case" would be a bit less than 7 kOhm, which I'd still deem unproblematic for regular solid-state line-out stages. So which CD player model would we talk about in your case?

Greetings from Munich!

Manfred / lini

 

[Pio1980]

For a standard potentiometer configuration, the input resistance will vary somewhat with the shunt resistance of the pot and the amp's input.
10k seems a common value for the pot in a typical passive controller, amp can be anywhere between ca 10k and 250k.

 

[rothwellaudio]

However, what I'd rather doubt, is twiii's guesstimation of the internal losses, which would seem rather high to me. And what really puzzles me is Shiit's output impedance spec: Why 5 kOhm max.? In my view that should rather vary between close to 0 (fully turned up) and 10 kOhm (fully turned down).

But in any case we can now determine the combined load impedance:

- fully turned up: (almost 0 Ohm +) 1 / ((1/10000 Ohm) + (1/22000 Ohm)) = ca. 6875 Ohm

- 90 % (in terms of resistance): 1000 Ohm + (1/((1/9000 Ohm) + (1/22000 Ohm))) = ca. 7387 Ohm

- "half way" (in term of resistance): 5000 Ohm + (1 /((1/5000 Ohm) + (1/22000 Ohm))) = ca. 9074 Ohm

So, as we can see, the "worst case" would be a bit less than 7 kOhm, which I'd still deem unproblematic for regular solid-state line-out stages. So which CD player model would we talk about in your case?

Greetings from Munich!

Manfred / lini

Maybe I've missed something in this thread but the output impedance of a conventional pot is the same as the parallel combination of the resistance "above" the wiper and the resistance "below" the wiper, as seen in a typical diagram. That means any pot's output impedance is maximum when it's at the half way point - though "half way" means the same resistance on each side of the wiper, which isn't the same as half way round if the pot is logarithmic. A 10k pot's maximum output impedance is 2.5k, because there's 5k on each side of the wiper and 5k in parallel with 5k gives 2.5k. If the Schiit's max output impedance is 5k I suppose the pot is a 20k pot.

BTW, all the calculations on the thread above only explain if a passive preamp will allow a power amp to reach maximum output - they don't explain why one might sound thin. One possible explanation is that some power amps' distortion rises when driven by a high source impedance.