full details on creating good sound

Well, the first thing is for Enzy to verify and confirm there's a center tap. If there is a center tape, I definitely go with dual 12V supplies instead of single supply. Capacitor is not a good thing, unless you use all film caps, they can introduce distortion.

As for me, I just use a +/-15V dual switching supply https://www.ebay.com/itm/hot-sales-dual-output-switching-power-supply-50W-15v-1-2a-15v-1-2a-D-50F15-/321574148358?hash=item4adf501906:g:6HcAAOSwxH1T9bDn

I always use SMPS if I can help it. I use this on both the preamp I designed and it work like a champ. Quiet, light and cheap. no big filter cap, just series output inductor and make sure have 1000uF on the preamp pcb. Save the trouble of rectifier, more filter, more wiring and all.

Audioguru said:

Enzy, why do you have 2 preamp channels but both have the same mono input? Since you have two or more power amplifiers all with the same mono signal then you only need one preamp, not two. One preamp can feed many power amplifiers.
Do you need more than one preamp because each power amp needs its own volume control which has been decided works best at the input of the preamp since the power amp is far away and cable capacitance cuts high frequencies when fed from a volume control at the output of the preamp?

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Since Im feeding 2 mono amplifiers normally they would need separate controls since they would control 2 sets of speakers, most times one set of speaker isnt close by me so that section is turned up loader than the speakers close by.

Or I might be using one side to play tweeters and one side to play a low frequency mid range and I want to use 2 different controls.

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If I joined the output of one to the input section of the other would that be beneficial or would it work out to being just the same as using a single opamp or a single side of the dual opamp

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Ok I did the dual polarity version also and remove the bias stage.

Just a question. Why do you set the gain of the opamp to 34? For normal CD or DVD players, output is about 1 to 2Vpeak already, preamp doesn't need much if any gain. I only have gain of about 1.5 in my preamp to drive the power amp.

There is a school of people that don't even use any amplifier circuit, just straight from the source into a switching matrix to select one of the sources. Then drive the volume pot and the output of the volume pot drive the power amp. No active circuit in the signal path. I tried that, the sound is very natural. Problem is again, the capacitance of the coax to the power amp cut out some of the highs. But if you put the volume into the power amp, it will work.

I compare with and without opamp in the signal path, for music, total passive sound slightly better. But for tv and video, the opamp color the sound a little and add a little dramatic effect. I use it to watch tv most of the time, so I use an opamp buffer in my preamp.

Check why you arrive the gain of 34, only time you need gain is for phono( record player). But your amp won't work because you need equalization to compensate the frequency response of the magnetic phono cartridge.

It was recommended by Audioguru since he said the output needs to be 1v RMS to get full power from the amplifier.

this was the specs I gave him

- Power: 300W 8R (+ -75V), 600W 4R (+ -75V), 1000W 2R(+ -75V)
- Power supply voltage: DC+-60V~+-80V, (recommend voltage DC+ -75V)
- Distortion:0.07 % THD+N 600W 2 R
- Voltage gain:33 DB
- Loading resistance: 2Ohm
- Total Idle Power Consumption: 13.2W
- System Efficiency: 80% 600W 2R
- Dynamic Range : 99.4 DB
- Residual Noise: 290 UV
- Damping Factor:>70 (1K HZ ,2R)
- Frequency Response: 20Hz-20kHz + -1DB

Enzy said:

It was recommended by Audioguru since he said the output needs to be 1v RMS to get full power from the amplifier.

this was the specs I gave him

- Power: 300W 8R (+ -75V), 600W 4R (+ -75V), 1000W 2R(+ -75V)
- Power supply voltage: DC+-60V~+-80V, (recommend voltage DC+ -75V)
- Distortion:0.07 % THD+N 600W 2 R
- Voltage gain:33 DB
- Loading resistance: 2Ohm
- Total Idle Power Consumption: 13.2W
- System Efficiency: 80% 600W 2R
- Dynamic Range : 99.4 DB
- Residual Noise: 290 UV
- Damping Factor:>70 (1K HZ ,2R)
- Frequency Response: 20Hz-20kHz + -1DB

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Yes, like I wrote in the last post that that the output of the CD or DVD players is already about 1Vrms. Your particular amp has about 70V rail voltage and gain of 33db or gain of about 44.

Assuming your amp can swing to +/-65V with 70V rails, max input would be 65/44=1.47Vpeak without clipping. This mean you only need 1.47Vpeak or about 1Vrms to run the amp to max output. This is the output range of typical CD and DVD players. This mean you DON'T need to have any gain in the opamp..........Just like what I did in my preamp.

You only need a voltage follower. No gain.

Enzy said:

Since Im feeding 2 mono amplifiers normally they would need separate controls since they would control 2 sets of speakers, most times one set of speaker isnt close by me so that section is turned up loader than the speakers close by.

Or I might be using one side to play tweeters and one side to play a low frequency mid range and I want to use 2 different controls.

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If I joined the output of one to the input section of the other would that be beneficial or would it work out to being just the same as using a single opamp or a single side of the dual opamp

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Ok I did the dual polarity version also and remove the bias stage.

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If you do two rails, you don't need C1, C2, C3 and C7. I drew the circuit for you before already. You can get rid of the gain like this.



I really suggest you to study up on opamp circuits and get to know the common audio spec. You are really guessing.

yes I am guessing no doubt Audioguru is aware of me not understanding creating circuits, as I said I normally make circuits just never created any for myself since I dont have the knowledge.

So giving him my specs he recommended the preamp this would be my second preamp circuit.

SO you recommend a voltage follower and since I lack the knowledge it sounds ok to me but why wouldnt someone else suggest that. I normally state that my signals only come from phones, laptops professional mixers and cd players.

Ok I made this update

Enzy said:

yes I am guessing no doubt Audioguru is aware of me not understanding creating circuits, as I said I normally make circuits just never created any for myself since I dont have the knowledge.

So giving him my specs he recommended the preamp this would be my second preamp circuit.

SO you recommend a voltage follower and since I lack the knowledge it sounds ok to me but why wouldnt someone else suggest that. I normally state that my signals only come from phones, laptops professional mixers and cd players.

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The last question is whether your source is a CD or DVD player? If so, I am pretty sure I am right on this. If you want to play is safe, keep the R3, R4, R7 and R8 in the pcb layout, you can just not putting R3 and R7, then put a jumper for R4 and R8 to get a buffer out of them. Or if you decide to get a little more gain, you can set the gain accordingly.

OK so the gain would be unity, so of my input is 316mv would that make my output 316mv also which wouldn't be able to give me full power to my amplifier even if the nob is at maximum.

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I tested it with another small amp I made, I herd a small hum coming from the speaker I attached I'll need to check where it's coming from first though.

I think i would need more gain though it seems low but once I test everything fully I'll post on that

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What are your thoughts on speaker protection circuits and applying then to the amplifier

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is the caps to gnd necessary for the feedback stage?

First all, you have not answer my question whether you are using CD/DVD players as a source. That is you are only using as standard line input like other preamps. There is a standard people follow. The signal is about 1Vrms. I don't know where you get the 316mV. The other question is whether the 316mV is RMS. You have to specify this.

One thing I learn is you don't want to have too much gain. You want to design so you normal listening level is when the volume know is at about 1/3 way of the turn on the volume knob. If you set the gain too high, the volume is going to be very touchy. I use remote motorized volume in my preamp, it is much easier to control the volume if you set the normal listening level at about 1/3. My gain is about 1.5.

Whether you need the AC grounding cap at the feedback all depends on the gain of your circuit. The output offset voltage depends on the DC gain of the opamp. That is if your opamp specified the input offset voltage of 1mV, if you DC gain is 34 like your original circuit, then the output will have offset of 34mV. Some opamp is worst than 1mV, so you can get like 50 to 80mV at the output, that's way too much. The cap is to provide an AC ground so you get the gain of 34 at audio frequency, BUT at DC, the cap is an open circuit, so your amp has DC gain of only 1, so the output offset is 1mV as the input of the opamp.

Therefore if you have high gain, you need the cap. If you have gain less than 3 or so, you don't need the cap.


I am new on this forum, I come here to ask a specific question of getting suggestion for a SMPS book only. I frequent AudioKarma forum where I have detail on my amplifier. This is the link of the Thread:**broken link removed**

You can join the discussion if you like. As I said before, the real forum for expert design is diyaudio.com where there are experts there talking about design. But it might be a little too advance. You might want to join audiokarma.

If you are interested in building your own power amp, I strongly suggest you to study up transistor basics and get the book by Bob Cordell. You need more knowledge to build the power amp, that's where the challenge and fun is. It is very involved, a lot more complicated than most people think....that it's only a slow audio circuit that works only to 20KHz. As I said before, for high end amplifier, you design to at least over 200KHz, better to be 300KHz and over. Think of a circuit that produce 100W power that can run as fast as 300KHz!!! You run into all sort ( I repeat, all sorts) of stability problem. I have been a design engineer for 30+years design all different type of discrete transistor circuits, RF even IC design. I though it will be a piece of cake designing audio amps, I was wrong, took me over a year to study and build my first amp successfully. For audio amp, I am still quite new, no where an expert by a long shot. I only successfully designed and build an ultra low distortion amp. I yet to venture into some of those that has no global feedback type and tube audiophile amps. Still have a lot more to learn.

for now my signal is coming from a laptop but for longer plays it would be coming from a crossover which would get its signal from a mixer which would be fed by cd players. Its a regular dj set up.

I am not sure how far I will bring the gain ill have to test it out at probably about 10 but in other words using a voltage follower the signal will be pure and there shouldnt be much distortion or hum so ill finish the rest of the testing.

I really want to build a power amplifier I plan to learn the proper way and buy some books I can buy the books as yet though im looking about 2 months time before I can attempt buying 1 or 2.

I would like to start working on an amplifier now but not sure how to even start, alot of the amplifier boards I use seem to use IRAUD2000, Irs2092, Irs2110 looking at the datasheet the basic design seems to work however I would like to understand more about the operation so I could amplify power rating.

A volume control should normally be set at about halfway so it can be adjusted up and down. A volume control is supposed to have a logarithmic taper then halfway it cuts the signal to about 1/10th. I calculated that the Chinese power amplifier does not have enough gain for a normal line level (about 316mV) to produce full output so I gave the preamp a little more gain than just 10 times.

This preamp has a DC-coupled output so if the capacitor is missing in the feedback to ground then the preamp amplifies its max of 10mV input offset voltage causing a DC voltage at the output. If the source to the power amp is switched to another signal source or from another signal source to this preamp then the DC at the output of this preamp would cause a POP sound.

@Audioguru What is your thoughts on using a voltage follower instead of the preamp that was first designed

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If I add the gain resistors and increase it to 34 then I could add the 10uf capacitor c9 and c10 to gnd what are your thoughts on that.

If you make the preamp opamp a voltage follower then you don't need it. Simply connect the volume control to the input signal and to the Chinese power amplifier. The gain of the power amp is not enough to produce full output when the volume control is set to max. Doesn't your music have a dynamic range of levels and sometimes don't you want to turn up the lower levels? Then you need gain to do it.

C9 and C10 prevent the preamp from amplifying the input DC offset of the opamp which is a max of 10mV. But with a dual polarity power supply and reduced values on the feedback resistors then the C9 and C10 capacitors must be non-polarized (hard to find) electrolytic types (low frequency distortion). But maybe your circuit will be on a solderless breadboard or have a poor pcb layout causing stability problems when the higher value feedback resistors I recommended and/or your subwoofer speaker produces much more distortion than an electrolytic capacitor. Therefore I like fairly high value feedback resistors so I can use film capacitors that have no distortion and/or I use a single polarity supply so that electrolytic coupling capacitors do not need to be non-polarized.

The idea would be using the high value resistors in the feedback circuit while still using the 10uf electrolytic capacitor.

I'm not grate at pcb making since I just freelance while making them, do u have any tips on making gold pcb boards

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The idea would be using the high value resistors in the feedback circuit while still using the 10uf electrolytic capacitor.

I'm not grate at pcb making since I just freelance while making them, do u have any tips on making gold pcb boards

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I have all versions on the schematics drawn so I'll make and test each one (preamp).

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Do you have any type of power amplifer that you would recommend for bass.

I want to power 4 15" blastking 1500w speakers 8ohms each

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I think 2 more will be added soon also

You can use 33k and 1k resistors with a 100uF capacitor or 330k and 10k resistors with a 10uF capacitor.
Blastking lies about the power rating of their speakers by saying 1500W power handling but then they say it has 500W program power. What are they? Momentary peak power? Audio speakers should be rated in continuous undistorted power at a certain frequency.
I have never seen amplifiers and speakers with the extreme power ratings you need.

That's probably true, since it doesn't require that amount of power to drive them hard.

But I would still like a high power amplifier design though

Forget all my comments on power amp, you are using it for DJ, it's very different from home audiophile amplifier. What I am talking about is audiophile amp with ultra low distortion, not necessary high power. My amp is only about 180W into 4ohm or 90W into 8ohm. It's a puny amp for what you want. A lot of people use class D amp which I have no knowledge.....and don't even want to know about it, for high power, low power dissipation and not necessary high sound quality. Diyaudio has a section on class D amp also.

Of cause you can still use normal class AB amp. Since it's for DJ that always play loud, you don't need high quality design. It's actually much easier to design and cheaper. Most amp sounds a lot better when you crank it up, only the high end amp sounds good at low volume. My little amp ( not the size) use 9 pairs of output transistors each channel to produce only 180W into 8ohms. I am only concentrate in the first 10W. I use a huge 12"X7" heatsink for each channel just to get the first few sweet watts. For just high power, you can get away with a lot less, smaller cheaper chassis, less transistors to get 400W or even higher.

That's alot of transistor for 180W, what about using some high powered fets