Question about matching pre-amp/processor to power amplifier.

S

sirpouncealot

Audiophyte
Hi guys,

I would like some advice regarding power amplifier input sensitivity and pre-amp output voltage:

Power amplifier is Cayin D1205.1A, basically five separated monoblocks in one chassis, each with their own transformer and circuitry.
Specs are:
-5 x 120W @ 6 Ohms.
-SNR 91dB.
-Input sensitivity: 250mV

I understand that to drive this amp to full power, I will need to feed it a signal of 250mV. The question is that many pre/pros I'm looking at are having output voltage FAR, FAR higher than the input sensitivity of my power amplifier. For example: Outlaw Model 975 listed pre out at 2V, Emotiva UMC-200 has 4V pre out, other AVRs are listed from 1.5V to 4.6V and with some, even 7V!!!

a. My first question is: what will happen if a pre out signal of 2000mV (4600-7000mV) is feeded to a power amp with only 250mV input sensitivity? Would the pre amp volume knob never go pass the 9 o'clock position? Or stuffs will simply go out with a bang?

b. The 5-channel amplifier can be bridge into a 3-channel configuration (FR+SR and FL+SL). In this case, it's specced at 2 x 300W @ 6 Omhs, and here is my second question: Will the input sensitivity of a bridged channel still be 250mV, or it's doubled/halved?

Thank you all and good day to you guys.
 
P

PENG

Audioholic Slumlord
Hi guys,

I would like some advice regarding power amplifier input sensitivity and pre-amp output voltage:

Power amplifier is Cayin D1205.1A, basically five separated monoblocks in one chassis, each with their own transformer and circuitry.
Specs are:
-5 x 120W @ 6 Ohms.
-SNR 91dB.
-Input sensitivity: 250mV

I understand that to drive this amp to full power, I will need to feed it a signal of 250mV. The question is that many pre/pros I'm looking at are having output voltage FAR, FAR higher than the input sensitivity of my power amplifier. For example: Outlaw Model 975 listed pre out at 2V, Emotiva UMC-200 has 4V pre out, other AVRs are listed from 1.5V to 4.6V and with some, even 7V!!!

a. My first question is: what will happen if a pre out signal of 2000mV (4600-7000mV) is feeded to a power amp with only 250mV input sensitivity? Would the pre amp volume knob never go pass the 9 o'clock position? Or stuffs will simply go out with a bang?

b. The 5-channel amplifier can be bridge into a 3-channel configuration (FR+SR and FL+SL). In this case, it's specced at 2 x 300W @ 6 Omhs, and here is my second question: Will the input sensitivity of a bridged channel still be 250mV, or it's doubled/halved?

Thank you all and good day to you guys.
The D1205.1A is an integrated amp. If you pair it with a prepro you should bypass the preamp section. Take a look of the manual to see if it has inputs for preamps/prepros.
 
S

sirpouncealot

Audiophyte
The D1205.1A is an integrated amp. If you pair it with a prepro you should bypass the preamp section. Take a look of the manual to see if it has inputs for preamps/prepros.
The Cayin D1205.1A is labeled a "5.1 channel hi-end transistor power amplifier" FWIW, I got it secondhanded at a very good price but unfortunately no manual. Yes it has three knobs on the front plate but two of them Center and Rear Volume are for small adjustments +/- 6dB only. I failed to see how the Main Volume control can be bypassed, it has two bridge switches on the backplate but that's it. From its rated power I calculated the Cayin voltage gain at 26.8dB.

Just played around with the other gears on hand, a Sony AVR DA3400ES and a NAD C320BEE, an integrated with user replaceable link for preamp and power amp section. The manufacturer provided the following specs:
NAD Pre-amp section:
Line level inputs:
Input sensitivity 220mV -->only 220mV to full power of pre-amp
No line level output voltage provided, I presume it the same as power amp section's input sensitivity?

NAD Power amp section:
Input sensitivity 630mV --> needs 630mV input to attain full rated power.
Voltage gain 29dB.
So why is NAD pre-amp input sensitivity is only 220mV while Redbook CD line level output is 2V?

The Sony 3400ES has pre-out voltage rated at a meagre 150mV and a digital volume knob going from -92dB to +23dB. I connect the Sony to NAD power amp (bypass the NAD preamp). In theory it should not be able to drive the NAD power amp section to full power but my KEF Q300 was drived to a VERY loud (read: uncomfortable) level at 0dB. Didn't go further than that for fear of disturbing neighbors.

I'd like to know how to calculate the digitalized volume in dB units to AVR pre-out voltage to Voltage gain at the power amp output?

Thank you guys.
 
P

PENG

Audioholic Slumlord
The Cayin D1205.1A is labeled a "5.1 channel hi-end transistor power amplifier" FWIW, I got it secondhanded at a very good price but unfortunately no manual. Yes it has three knobs on the front plate but two of them Center and Rear Volume are for small adjustments +/- 6dB only. I failed to see how the Main Volume control can be bypassed, it has two bridge switches on the backplate but that's it. From its rated power I calculated the Cayin voltage gain at 26.8dB.



Their website says it is an integrated amp.
http://en.cayin.cn/product_view.asp?id=718
 
Last edited:
S

sirpouncealot

Audiophyte
Their website says it is an integrated amp.
Oh yes, that explained the unusual specs. I checked specs of other popular multi channel power amps and their input sensitivity are all above 1V. Thank you, guys.
Yet my question remains, what will happen if I use a pre/pro with pre-out voltage far exceed the input sensitivity of my integrated amp (250mV)? For example, 4Vrms of the Emotiva UMC-200. At which position should I set the integrated amp volume knob?
 
M

markw

Audioholic Overlord
At which position should I set the integrated amp volume knob?
At whatever position that produces the sound level you prefer but you really shouldn't be feeding a pre/pro output into the input of an integrated amp.
 
P

PENG

Audioholic Slumlord
I agree with markw. Unfortunately that amp does not seem to have provision for bypassing the pre-amp stage. It may be easy to modify it if you know how to do it or know someone who can do it for you. Depending on how good the Cayin's power amp really is, it may or may not be worth doing anything else with it other than using it for it is designed for.
 
TLS Guy

TLS Guy

Seriously, I have no life.
I agree with markw. Unfortunately that amp does not seem to have provision for bypassing the pre-amp stage. It may be easy to modify it if you know how to do it or know someone who can do it for you. Depending on how good the Cayin's power amp really is, it may or may not be worth doing anything else with it other than using it for it is designed for.
It all depends.

There is a proliferation of a multitude of all manor of types of Chinese amps around. Details are hard to come by.

I have found those Cayin amps are particularly popular in Germany for some reason. My German is not that good, but I have picked it a little from watching German Opera, especially Wagner.

Those amps are technically integrated. There is a discrete transformer and power supply for each channel. How they do this all for under $500 I have no idea.

Now there are three volume controls on the front one controls the front two amps, one the center and one the two rears. There is also a remote control. My German was good enough to determine that the inputs connect directly to chip opamp input amps. Then the levels are set between these opamps and the power amp stage.

Now the question, which is vital, that I can't find the answer to is how the volume controls work. If I were designing this unit, I would put the volume control not between the stages, but in the feedback loop of the op amp chips. This has these advantages.

As gain is lowered, input voltage head room is increased and signal to noise improves as gain is reduced. This is very simple design. What a Chinese designer of unknown experience would do, I have no idea.

Whether the OP can find this out from the importer VAS Audio, I have no idea. The website is not promising, a lot of eight year old kids could do better.

However, if the amp is designed as I would do it, he will be fine, as the volume knobs will reduce gain and increase headroom.

If the amp is not deigned like that, then he needs to find out the headroom of the input stage. If it is adequate he can still go ahead, and set the volume knobs appropriately.
 
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