Author Topic: Newbie & Not-so Noob Thread: Questions (FAQ) on Receivers/Amplifiers (Read 190970 times)

akyatbundok · « **Reply #90 on:** Oct 24, 2003 at 03:56 PM »

thanks joan2, i'll forward the info to the supplier. actually its my friend's supplier. he works in purchasing dept. so medyo malakas friend ko sa supplier nila.

Leiko · « **Reply #91 on:** Oct 24, 2003 at 05:40 PM »

What specs (design, parts, data) to look at when evaluating a Power Amp? (Am currently in the hunt for HT setup but I consider going via the Power Amp route.)

The xFETS daze me and so are the publsihed numbers/data (which may not be true/reaslistic anyway).

H a n $ · « **Reply #92 on:** Oct 24, 2003 at 05:54 PM »

Read before that SS also needs warm up is this true and applicable for SS or tube gears lang?? forgot to unplug the cord will it damage or shorten the life of SS amp??

Thanks for your response.

joan2 · « **Reply #93 on:** Oct 24, 2003 at 08:07 PM »

i started this thread in another forum:http://www.diyaudio.com/forums/showthread.php?s=&threadid=21699 please read up and see for yourself.....if you leave your amp plugged in running continously, you may shorten the life of the electrolytic caps, and end up paying larger electricity bills....

joan2 · « **Reply #94 on:** Oct 25, 2003 at 08:14 PM »

for those who would like to learn more about capacitors, this link will fill you in:http://my.execpc.com/~endlr/index.html

Leiko · « **Reply #95 on:** Oct 27, 2003 at 03:07 PM »

i always get different answers (Y/N) whenever I ask if an integrated amp can still be played with a preamp. I have seen several integrated amps, with volume set to max, played and matched with a preamp. Is this made possible by a specific feature or technically speaking, can all integrated amps work with a preamp (with adj in volume control)?

homer · « **Reply #96 on:** Oct 27, 2003 at 03:37 PM »

imho, you can cascade as many analog preamps as you like. the problem is, each stage degrades the sound. so, the more stages you have ...

akyatbundok · « **Reply #97 on:** Oct 27, 2003 at 03:48 PM »

I've been wondering about this too since my old integrated amp did not have direct/main power amp inputs. So i ended up having 2 preamps in series - first my Denon receiver, then my Onkyo amp. I noticed that the sound was much clearer if i connect directly to the Onkyo amp.

Does the sound degrade even if the 2 preamps are good quality? What if i turn up the volume to maximum in one of the preamps, would it improve the overall S/N ratio?

Another related question: Is it easy to add direct/main power amp inputs to an integrated amp? I'm thinking of having mine modified so that one of the Tape inputs becomes a power amp input.

homer · « **Reply #98 on:** Oct 27, 2003 at 04:21 PM »

imho, high quality preamps usually have very low degradation (distortion), even if they are cascaded many times. an example of this is in recording studios wherein the signal passes through mic preamps, equalizers, effects processors, mixing consoles, and recorders.

to maintain good snr, the volume control nearest the power amp should be the master.

a direct input to the amp is possible.

Leiko · « **Reply #99 on:** Oct 27, 2003 at 04:34 PM »

Quote from: homer on Oct 27, 2003 at 03:37 PM

imho, you can cascade as many analog preamps as you like. the problem is, each stage degrades the sound. so, the more stages you have ...

Very interesting. So kahit receivers pala pwedeng lagyan ng preamp.

just a clarification... so this scenario possible: Power Amp + Pre AMp 1 + Preamp 2?

Another followup question: does that mean amps with pre-ins RCAs sound superior compared standard Aux RCA inputs if paired with Preamps? Am asking kasi some some integrated amps have provision for preamps and direct/integrated. Thanks!

homer · « **Reply #100 on:** Oct 27, 2003 at 04:58 PM »

Quote from: Leiko on Oct 27, 2003 at 04:34 PM

Very interesting. So kahit receivers pala pwedeng lagyan ng preamp.

just a clarification... so this scenario possible: Power Amp + Pre AMp 1 + Preamp 2?

Another followup question: does that mean amps with pre-ins RCAs sound superior compared standard Aux RCA inputs if paired with Preamps? Am asking kasi some some integrated amps have provision for preamps and direct/integrated. Thanks!

i'm not so sure about receviers with external preamps. most receivers today have digital inputs and 6 channels.

yes, the 2 preamp setup is possible.

the performance will be superior if the external preamp is superior to the built-in preamp.

akyatbundok · « **Reply #101 on:** Oct 27, 2003 at 06:14 PM »

can i use an external preamp in a processor loop?

i know i can use an equalizer here, but im not sure if a preamp would apply. the processor loop in some amps seem no different from a tape loop. is that right?

homer · « **Reply #102 on:** Oct 27, 2003 at 06:25 PM »

Quote from: akyatbundok on Oct 27, 2003 at 06:14 PM

can i use an external preamp in a processor loop?

i know i can use an equalizer here, but im not sure if a preamp would apply. the processor loop in some amps seem no different from a tape loop. is that right?

i have a similar integra a819rs. i'll try to connect an external preamp across the tape loop, one of these days, and post the result.

joan2 · « **Reply #103 on:** Oct 27, 2003 at 06:50 PM »

Quote from: homer on Oct 27, 2003 at 03:37 PM

imho, you can cascade as many analog preamps as you like. the problem is, each stage degrades the sound. so, the more stages you have ...

i agree, that is why some serious audiophiles try to work with minimal number of stages, shortest signal path...etc...dirstortions, noise, is amplified by the next amp in line.....

just to give you some idea, a mc phono pickup generates about 0.8mV, so a phono preamp is used to convert(amplify) this to a line level of say, 150mV, then the tone control preamp converts this to about 2.5 volts say. then the power amp converts this to 28volts say, so into an 8ohm speaker load, this translates to 100watts.....

Quote

Another followup question: does that mean amps with pre-ins RCAs sound superior compared standard Aux RCA inputs if paired with Preamps? Am asking kasi some some integrated amps have provision for preamps and direct/integrated. Thanks!

not nescessesarily, a tuner fyi has a built in preamp, the output from the detector is so small thus nescessiting buffering, and this is also a preamp of sorts, even cd players have built-in preamps...a preamps role is to convert milivolt line level signal, about 150mV to over 2.+volts needed at the power amp input which in turn is needed to generate the desired output to the speakers....

Leiko · « **Reply #104 on:** Oct 28, 2003 at 05:09 AM »

Quote from: Leiko on Oct 24, 2003 at 05:40 PM

What specs (design, parts, data) to look at when evaluating a Power Amp? (Am currently in the hunt for HT setup but I consider going via the Power Amp route.)

The xFETS daze me and so are the publsihed numbers/data (which may not be true/reaslistic anyway).

Hi. joan2

I think i found the amp am looking for. Appreciate your inputs on the above before I finally part with my hard-earned funds for this amp. Just want to ensure I made a good decision on this. Thanks a lot!

joan2 · « **Reply #105 on:** Oct 28, 2003 at 06:43 AM »

leiko,
in the adio world jungle, there lurks many sellers feeding on the ignorance of potential buyers, regaling them with high falluting technical non-sense with the aim of stealing your hard earned money...that is why i take my time out to post here....

akyatbundok · « **Reply #106 on:** Oct 28, 2003 at 09:53 AM »

Re: choosing the right amp... since i became a junkyard dog (magbobote ng pier hehe), ive had to make decisions based on inspection only. Since there are no reviews whatsoever on junk amps, i rely on "heuristics". Heuristics are calculated guesses/estimates that are used as a substitute in the absence of a possible solution.

Sometimes heuristics are based on the symptoms of a good solution. Applied to finding good quality amps, i look for the symptoms of a good amp. First the size & weight should be hefty. If you carry it and half the weight is on one side, it means it has a big trafo, which implies high power handling, which implies a good power amp section. Of course there are exceptions. NAD C20bee and luxman hybrids are relatively light but they sound very good.

If you look at the RCA jacks at the back, and some or all terminals are gold-plated, then there may be some hint of good sound quality. I make this assumption because the manufacturer spent money on something that won't be seen by majority of potential buyers (because its at the back). Its also possible that the designer took into account the small percentage of buyers who will inspect the rear portion of the amp. Then that means they were targeting discerning buyers, not your average joe.

If its a pre-owned or surplus amp, i also check the net for the prevailing market price. If it has a high selling price, then there must be high demand, which means it must be good. In yahoo auctions or ebay you will even see pictures & specs.

Finally, you have to listen to it using CDs you're familiar with. I also look at the brand/model of the speaker and the player used and estimate how different it is from mine. If i have bright speakers and they use laid back speakers in the audition then i'm aware that the treble chacteristics in my setup will be different. Same with the bass - if they use 12in woofers in the audition, then i would expect more bass in the audition than i normally hear in mine. If its about the same, then bass would be leaner in my setup.

If its possible to have it opened, i look at the parts used. This is where i would need an expert's help. I have an assumption that the more & bigger the power caps, then the higher the power handling? Is this correct?

av_phile · « **Reply #107 on:** Oct 28, 2003 at 10:54 AM »

Every gain stage will introduce phase shifts or high order harmonic distortions or both to the original signal. hence, it is important that the shortest possible route with the highest gain from the player to the speaker be used.

A CD player's analog output typically has an output RMS voltage of about 2 volts. It is theoretically capable of driving any Main power amp. Many audiophiles i know directly feed an excellent CD player's analog output (or CD transport + DAC/processor) directly to the main power amp considering that the player already has an output level control. This bypasses any tone control or pre-amp circuitry for purer sound through the shortest route at the expense of source seldction flexibility. (This is also equivalent to the DIRECT CD switch employed by some receiver or integrated for CD input if it bypasses the preamp section, not just the tone controls.)

With regards using pre-amps connected to receivers or integrated, it may be a good idea to remember that there are passive preamps and active preamps.

Passive preamps are generally preferred as these are essentially unity gain devices (x 1) that allow for volume control and input selection flexibility. Some use tone cntrols and loudness switches. No amplitude gain is done. Such devices can theoretically be cascaded or daisy-chained tik increase input flexibility en-route to a power amp.

Active preamps, the more common commercial ones, employ a gain stage to bring the player's output level (typically less than 1 volt (in tuners and turntables and tape decks) to a level needed to drive the main pwer amp - usually in the 3 volt RMS level.

It is also important to read the main power amplifier technical specification to know what input voltage is necessary to drive the amp to its Full rated power and at the THD levels indicated at that level. Some amps are specified to deliver 100 watts RMS at the input voltage of 3 vots RMS. Anything less than that will still drive the amp but at less than the rated power at full volume. Anything higher than that can overdirve the amp at full volume (with more intolerable THDs) though you can just use a lower volume setting on the preamp.

The audio route from player to speaker is like a chain. It is only as strong as the weakest link. Hence, the sound is only as good as the lousiest component along that chain. Necessarily, the distortion is as low as the highest distortion producing component on that chain. As such, the best active preamp will not solve any sonic problem if connected to a lousy receiver or integrated at the tape loop or input. That's because the receiver's or integrated's preamp distrotion will still be there. Only a passive preamp will do. And the only reason i could think of cascading a passive preamp is to increase the input flexibility of your exisitng receiver or integrated.

It is unwise to casacde active preamps to a receiver or integrated via the input or tape loop points Unless the built-in preamp of the receiver or itnegrated is BYPASSED. That means, taking out the jumpers at the back connecting the pre-out to the main-in of a receiver or integrated and putting a new preamp to the main-in terminal. For all practical purposes that renders the inout, volume and tone sections of the receiver or integrated sonically uselsss. And the external premap takes over that function.

Equalizers and DAC processors are unity gain devices that do not generally have amplification stages at their output. So they can be safely inserted in the tape toop or fed directly to receivers and integrateds at the input level.

Connecting an active preamp directly to the inout of a receiver or integrated may increase the apparent loudness of that receiver or integrated. That's because the input to the receiver/integrated, rather than being less than 1 volt, can acutally go as high as 3 volts or more. And anything loud alwys gives the impression of being sonically better.

av_phile · « **Reply #108 on:** Oct 28, 2003 at 11:20 AM »

Quote from: akyatbundok on Oct 28, 2003 at 09:53 AM

First the size & weight should be hefty. If you carry it and half the weight is on one side, it means it has a big trafo, which implies high power handling, which implies a good power amp section. Of course there are exceptions. NAD C20bee and luxman hybrids are relatively light but they sound very good.

Weight is always a good indication. Either employing "materiales fuertes" or heavy transformers or both. Especially if you''re talking about a 100 watt RMS class AB gear to begin with. Class A amps would be even heavier.

One other indication is to check electrical power consumption. It should be a lot higher than the combined power output of all channels. A stereo amp that consumes only 250 watts of electricity cannot be expected to spew out 150 watts per channel. A Rotel class AB 5-ch amp I've seen only gives out 60 watts RMS per channel with a power consumption of 700 watts! Now that's high-current headroom.

Quote

If you look at the RCA jacks at the back, and some or all terminals are gold-plated, then there may be some hint of good sound quality. I make this assumption because the manufacturer spent money on something that won't be seen by majority of potential buyers (because its at the back). Its also possible that the designer took into account the small percentage of buyers who will inspect the rear portion of the amp. Then that means they were targeting discerning buyers, not your average joe.

I remember an ad sometime ago where the back of an amp was pictured, not the front. The ad says, or words to this effect" "We're not ashamed to turn our back..."

A good amo will always sport gold-plated terminals at the back and properly organized and labeled so as to make them "user-friendly" or "iidiot-proof."

Let me add: they should sport gold-plated 5-way binding or banana terminals for speakers as well. Not spring-loaded types.

The big and heavy amps I've seen lately have detachable power cords. That would be good if you plan to use those exotic power cords out there. But also check that any power cord is thick enough to handle high current loads.

Quote

If its a pre-owned or surplus amp, i also check the net for the prevailing market price. If it has a high selling price, then there must be high demand, which means it must be good. In yahoo auctions or ebay you will even see pictures & specs.

After checking the net, baka nabili na yung target amp sa pier. It may be a good idea to bring a notebook PC connected to your cellphone when visiting the pier and check right there and then in your car or van.

Quote

If its possible to have it opened, i look at the parts used. This is where i would need an expert's help. I have an assumption that the more & bigger the power caps, then the higher the power handling? Is this correct?

In general, yes. But also bear in mind that smaller capacitor values using multiple capacitors in parallel yield the same and provide faster instantaneous current handling. Some slim but powerful amps i've seen uses four 6,800microfarad caps per channel.

joan2 · « **Reply #109 on:** Oct 28, 2003 at 11:32 AM »

Quote

If its possible to have it opened, i look at the parts used. This is where i would need an expert's help. I have an assumption that the more & bigger the power caps, then the higher the power handling? Is this correct?

akyat,
i like your heuristics approach, by more, you are reffering to higher ufd(capacity) and by bigger, you are reffering to not only the physical size, but the voltage rating on the capacitor, a higher voltage rating means a higher rail voltages, also higher power output. you may add also the size/quantity of the output transistors. lets take the case of your luxman amp for example, it has a rating of 71volts dc, so i would hazard a guess that it has a rail voltage of about 55 to 65volts, and your mosfet output transistor has a drain breakdown voltage rating of 160volts, so that the sum of the rail which is about 130volts in absolute values is just right for your output devices...so if you have other amps that you would like to consider buying, then you can post its vital statistics here and i can give more or less a simple engineering evaluation as to its capabilities

av_phile,
by passive preamp, are you reffering to this:http://www.diyaudio.com/forums/showthread.php?s=7a453682bc3900b92be901b60d877bf2&threadid=21795

av_phile · « **Reply #110 on:** Oct 28, 2003 at 11:43 AM »

Quote from: joan2 on Oct 28, 2003 at 11:32 AM

av_phile,
by passive preamp, are you reffering to this:http://www.diyaudio.com/forums/showthread.php?s=7a453682bc3900b92be901b60d877bf2&threadid=21795

Yes, (though it has a selector fo a 6db gain) but they don't necessarily have to look exotic. Any circuit between a player and an amp that allows at least for volume control and input selection flexibility is a passive preamp. They can also have tone controls or loudnesses switches that use passive RC circuits, Add a separate record selector. Some would also have some form of DAC processing as well for DD/DTS, etc. For as long as no signal mplification gain is emploed. Input signal = output signal at full volume.

akyatbundok · « **Reply #111 on:** Oct 28, 2003 at 03:59 PM »

wow... thanks for the preamp link. how does peter daniel do that? the eye-candy casing i mean.

joan2 · « **Reply #112 on:** Oct 28, 2003 at 05:06 PM »

peter daniel in continuation of this gainclone line....

Leiko · « **Reply #113 on:** Oct 29, 2003 at 05:42 AM »

thank you guys on your discussions on preamps and amps selection. Parang nag-crash course ako sa electronics (1 or 2 chapters lang)

seriously, very enlightening!

joan2 · « **Reply #114 on:** Oct 29, 2003 at 07:49 AM »

keep your questions coming and we'll try to answer them best as we could.....

joan2 · « **Reply #115 on:** Oct 29, 2003 at 07:51 AM »

Quote from: akyatbundok on Oct 28, 2003 at 03:59 PM

wow... thanks for the preamp link. how does peter daniel do that? the eye-candy casing i mean.

peter daniel has a complete array of tools for his use, and easy access to materials that he needs, but most of all the imagination to go with it......

marty_e · « **Reply #116 on:** Oct 29, 2003 at 11:47 AM »

Hi, although I've leaned towards valve gear in the past few mos, I have a B&K ST140 that I still like to use from time to time. This is an old amp, maybe manufactured in the late 80's to early 90's. Since I've got no schematics nor a spec sheet, what sort of upgrade path can this amp go through to breath new life into it? Any inputs would be appreciated. Thanks!

joan2 · « **Reply #117 on:** Oct 29, 2003 at 01:17 PM »

your amp can benefit from replacement of electrolytic caps to nerw ones, the mains rects you can replace with mur860, you can bypass the coupling caps with polypropylene caps, where possible or practical, you can replace it altogether with polypropylene caps....

RU9 · « **Reply #118 on:** Oct 29, 2003 at 01:32 PM »

What is difference between a passive attenuator and a passive preamp?

Thanks.

akyatbundok · « **Reply #119 on:** Oct 29, 2003 at 01:38 PM »

Is it possible to convert the AUX input of my integrated amp into a power amp direct input?

I was hoping to use my old integrated amp as a separate power amp for my receiver but unfortunately it did not have main ins. This way i could use both the digital & analog outputs of my DVD player for playing movies & music respectively. When watching movies i switch to AUX to bypass the integrated preamp and use my receiver as the external preamp. When playing music i just switch to CD input to use the integrated preamp. I dont have to power up my receiver when playing music. I also dont have to switch speaker cables.