Tex Houston said:
Tex, the value of pot it is right by anyway. Simply the most common place of it is after the main amplification IC, the AD797 in your case. This IC it is formed as noninverting op. amp. and the number of paralleled caps around it place me in thoughts. The quality of caps it is good? Why so many caps paralleled? You may search about this to the present and we will see furthermore. It is so strong heared the hiss?
Fotios
Hi,
this pre-amp has the opamps wired for unity gain.
The 5534 are not suitable for unity gain. They should have the comp cap soldered in.
Change them for something more suitable.
It would take just one of these to oscillate and all subsequent opamps would do their best to amplify that noise and it will affect the final sound.
Who told you to fit 5534s here?
this pre-amp has the opamps wired for unity gain.
The 5534 are not suitable for unity gain. They should have the comp cap soldered in.
Change them for something more suitable.
It would take just one of these to oscillate and all subsequent opamps would do their best to amplify that noise and it will affect the final sound.
Who told you to fit 5534s here?
Alternatives?
Thanks again - the NE5534 was on the circuit diagram when I bought the PCB. Can you suggest an alternative or should I just solder the cap on the underside of the board. Do I have to do this on all the IC's? What about OPA134? The AD797's are very expensive.
The hiss I have at low levels is only audible when close to the speakers - but hey! it shouldn't be there at all should it! The preamp seems to sound very good apart from this.
One more question - what is the advantage of having more than one input buffer, when one could just switch signals beforehand and just use one? I notice there is a slight difference in component value for the Tuner input , but the DAC and CD are the same.
Thanks again - the NE5534 was on the circuit diagram when I bought the PCB. Can you suggest an alternative or should I just solder the cap on the underside of the board. Do I have to do this on all the IC's? What about OPA134? The AD797's are very expensive.
The hiss I have at low levels is only audible when close to the speakers - but hey! it shouldn't be there at all should it! The preamp seems to sound very good apart from this.
One more question - what is the advantage of having more than one input buffer, when one could just switch signals beforehand and just use one? I notice there is a slight difference in component value for the Tuner input , but the DAC and CD are the same.
Hi fotios,
For a preamp, the use of dual power supplies is a little silly. Your grounds will be commoned at every source and the power amp. You must take a systems approach to these designs. There isn't enough power draw to even warrant considering a dual mono design here.
Hi Tex,
Glad you found the problem. I would now try the proper op amps in this unit. It's worth the money in your application.
A buffer for each input would drive the volume control better, but you could use only one after your selector switch. This achieves the same thing. If you install a tape out, buffer this output also.
-Chris
For a preamp, the use of dual power supplies is a little silly. Your grounds will be commoned at every source and the power amp. You must take a systems approach to these designs. There isn't enough power draw to even warrant considering a dual mono design here.
Hi Tex,
Glad you found the problem. I would now try the proper op amps in this unit. It's worth the money in your application.
A buffer for each input would drive the volume control better, but you could use only one after your selector switch. This achieves the same thing. If you install a tape out, buffer this output also.
-Chris
Hi Chrisanatech said:
Generally the use of individual power supplies in preamplifiers it is not commonly used but it is a rule in expensive Hi-End devices. And the reason is that: If we have a source with individual ground conductor for each channel such as the phono cartridge, there is no problem of ground loop from a preamplifier with common supply - and thus a single ground node - for the two channels. Also if the source it is a very expensive SACD with individual supplies for each channel, again there is no problem with the same preamplifier. But in the case of the majority of CD or DVD etc. players where only one supply exists for the two channels simmultaneously, only one ground node exists common for the two outputs. If the preamplifier has a single supply for the two channels and thus again a single ground node for the inputs, the two shields of the stereo signal cable arriving from the source outputs they are in position to create a nice ground loop. According to the total gain of preamplifier this can heared louder or quiter. For this reason i thing the use of individual supplies for each channel - and thus seperate ground nodes - in the preamplifier it is the better solution.
Fotios
To understand you better my thought, i quote bellow a schematic diagram with the two cases.
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Hi Fotios,
a group of posters laughed at my suggestion for keeping the grounds between the channels in a pre-amp completely separate.
Were you reading that thread?
I would keep the channels separate, including the power supplies.
I have only built one passive pre-amp. It's only big downfall was hum at low levels, once I had optimised all the compromises that a passive inflicts.
That was nearly thirty years ago and I have never tried a dual mono.
a group of posters laughed at my suggestion for keeping the grounds between the channels in a pre-amp completely separate.
Were you reading that thread?
I would keep the channels separate, including the power supplies.
I have only built one passive pre-amp. It's only big downfall was hum at low levels, once I had optimised all the compromises that a passive inflicts.
That was nearly thirty years ago and I have never tried a dual mono.
Hi Fotios,
a group of posters laughed at my suggestion for keeping the grounds between the channels in a pre-amp completely separate.
Were you reading that thread?
I would keep the channels separate, including the power supplies.
I have only built one passive pre-amp. It's only big downfall was hum at low levels, once I had optimised all the compromises that a passive inflicts.
That was nearly thirty years ago and I have never tried a dual mono.
a group of posters laughed at my suggestion for keeping the grounds between the channels in a pre-amp completely separate.
Were you reading that thread?
I would keep the channels separate, including the power supplies.
I have only built one passive pre-amp. It's only big downfall was hum at low levels, once I had optimised all the compromises that a passive inflicts.
That was nearly thirty years ago and I have never tried a dual mono.
Hi AndrewAndrewT said:
First of all i am very glad to meet you again after a long time. I haven't read any thread about this. Simply i had distressed very hard in the past - before 20 years i think - when i was tried to build my first power amplifier a monster with +/-70Vdc supply. I have yet in my stock the transformer with the single secondary winding of 49,5-0-49,5 Vac which of i had tried the use in the common supply with the single ground node for the 2 channels. What a buzz! What a pity! This 800VA nicefull xformer in my shelf! You can understand furthermore why our thougts coincide.
Regards
Fotios
Hi Fotios,
A couple of thoughts.
In your first example, the designer of such a source must assume the signal grounds will be common in the preamp. Therefore, if there is a problem, the design is defective (no matter what the name plate says!). I have seen many design errors in almost every brand out there, and this is getting worse. It is silly to blame the fault of a source on an industry standard design for a preamp.
Now, what do you do with the tuner ground? Tape deck (R-R, DAT or Cassette)? It seems that you now have an enormous problem if you wish to keep all grounds separate (as you must for your approach). Not only do all your sources use common signal grounds, but some may also use a mains ground (that would be a fault if the connection is direct). So you are going to switch all signal grounds along with the signals. Connecting and disconnecting your sources in this manner will product a "pop" most probably.
-Chris
A couple of thoughts.
In your first example, the designer of such a source must assume the signal grounds will be common in the preamp. Therefore, if there is a problem, the design is defective (no matter what the name plate says!). I have seen many design errors in almost every brand out there, and this is getting worse. It is silly to blame the fault of a source on an industry standard design for a preamp.
I do not agree with you. The loop area is very small and signal cables ought to be routed away from radiating areas. Also, the problem of a loop is easily solved by using some small resistance in series with each ground. In any event, I haven't seen this as a problem in any equipment I have worked on. It's a non-issue unless someone has done something very silly elsewhere. Solve the problem at it's source.
Now, what do you do with the tuner ground? Tape deck (R-R, DAT or Cassette)? It seems that you now have an enormous problem if you wish to keep all grounds separate (as you must for your approach). Not only do all your sources use common signal grounds, but some may also use a mains ground (that would be a fault if the connection is direct). So you are going to switch all signal grounds along with the signals. Connecting and disconnecting your sources in this manner will product a "pop" most probably.
This is only done in higher dollar units where the advertising copy can be used to differentiate this unit over others for a supposed improvement. I do not even begin to buy it.
-Chris
Re: Alternatives?
I don't understand why NE5534 are not so good and they can produce noise. I remembered my own designed preamplifier with a PCB made from myself in my home. Ths device it is a simple microphone preamplifier with extremelly high gain of +54dBV max (much more from the Tex preamp) and builded with the worse NE5532s in cheap DIL8 sockets and cheap pots, and the power supply in the same board. This preamp produce unaudible hiss and zero buzz in his output. To prove this i quote below a scope picture of output with the input open and the pots in full CW place (for max gain). Thus i believe that maybe the complexity in circuitry of Tex's preamp, the wrong cabling, the wrong position of pcbs may cause the hiss heared.
Tex, for you i quote below photos of my construction to take an idea from what i wrote in my replies.
Tex Houston said:
Hi again Tex and Chrisanatech said:
I don't understand why NE5534 are not so good and they can produce noise. I remembered my own designed preamplifier with a PCB made from myself in my home. Ths device it is a simple microphone preamplifier with extremelly high gain of +54dBV max (much more from the Tex preamp) and builded with the worse NE5532s in cheap DIL8 sockets and cheap pots, and the power supply in the same board. This preamp produce unaudible hiss and zero buzz in his output. To prove this i quote below a scope picture of output with the input open and the pots in full CW place (for max gain). Thus i believe that maybe the complexity in circuitry of Tex's preamp, the wrong cabling, the wrong position of pcbs may cause the hiss heared.
Tex, for you i quote below photos of my construction to take an idea from what i wrote in my replies.
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Sorry Chris for the confusion. Our replies are simultaneous and i tried to shrink the schematic to not failed the size of page. Now you can see a pair of voltage followers (a NE5532) used in output and the filtering around these. One resistor of 10K and one cap of 100pf in parallel to improve the bandwidth.
Fotios
Fotios
Because as i understand we are of the same occupation instead words, i quote below some pictures to see you from alone the performance of this preamp.anatech said:
1. Square wave response 10KHz
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2. Typical setup for measuring the reproduction of a Mission780 with a Behringer ECM8000.
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3. Three sinus and one triangle curve. The top red waveform it is the output of the function generator. The blue bottom waveform it is the output of preamplifier (the reproduction chain is in this row: generator>amplifier>speaker>mic>preamp>scope)
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Chris because i am engaged for 20 years with the service of Peavey electronics, i know very well the 4558 which used in the vast majority of his signal processing devices. I remembered a suggestion of factory: you can replace RC4558s with NE5532s but there is the risk of presentation of d.c. offset. Thus the RC4558 (the only nearest alternative is LM833) it is better from NE5532 in this property but worse as for the noise and slew rate. It is usually used in the output sections. Sure the OP275 it is better from NE5532 but not so in the noise figure, maybe in the slewing; i don't know at all because i never tried this IC. But i am based many times in the old trasty NE5532-NE5534. As for the Tex's preamplifier, i think that it is bad designed. I have many plans as you understand with NE5534 in inputs of phono, CD, line but with different filters in input and around the op. amp.anatech said:
Fotios
Chris in the following block diagram a reply to your query. Suppose that the source it is a tuner, CD, tape deck etc. and except its case all the other cases are earthed. But the gnd node it is connected to earth (as usually) only in the source. The preamp and the power amp does not have the same shorted gnd to earth. And voila the benefit of the individual power supplies and the rule of not earthing the supply gnd. A nice star connection from source to P.A. Also through the shield of signal cables it is achived a safety earthing of the PCBs of all devices exist in the chain, by the gnd earthing of the sourceanatech said:
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Hi fotios,
I have no problem with the NE5532. It is at it's best in lower impedance circuits whereas in higher impedance circuits, a FET input op amp usually will have lower noise and DC offset. So it's a case of "it depends" on what you are doing with it. The OP275 is a nice little dual op amp. Not expensive either.
In your conceptual diagram, you are presenting a nice view of a perfect world. Life isn't like that. Personally, I don't care too much for the RCA connection system. What might be better is something based on a shielded L, R and common conductors. The shields only connected to the source side. In this way you can have common signal grounds and proper shields. A new system for this type of signal flow would differentiate it from the more common RCA system. A five conductor or three conductor XLR plug would work. I find the five conductor DIN too light for most cables. The three conductor DIN is pretty much reserved for power connections (at least that is what I think when I see one).
In short, without changing the connector type, you are stuck with common grounds at each connection. That is the standard.
-Chris
I have no problem with the NE5532. It is at it's best in lower impedance circuits whereas in higher impedance circuits, a FET input op amp usually will have lower noise and DC offset. So it's a case of "it depends" on what you are doing with it. The OP275 is a nice little dual op amp. Not expensive either.
In your conceptual diagram, you are presenting a nice view of a perfect world. Life isn't like that. Personally, I don't care too much for the RCA connection system. What might be better is something based on a shielded L, R and common conductors. The shields only connected to the source side. In this way you can have common signal grounds and proper shields. A new system for this type of signal flow would differentiate it from the more common RCA system. A five conductor or three conductor XLR plug would work. I find the five conductor DIN too light for most cables. The three conductor DIN is pretty much reserved for power connections (at least that is what I think when I see one).
In short, without changing the connector type, you are stuck with common grounds at each connection. That is the standard.
-Chris
Chris, do you know how many times i have seen this resistor of 10Ù which connect the gnd to earth (yet of fireproof type) burned? And how many speakers destroyed from the loud buzz caused in such a case? It is a phobia to me personally the use of such resistor. I prefer to spend a little more euros (the difference in price between a Xformer with single secondary from another with double secondaries it is only 3 euros, the cost exist mainly in the power of core, the copper wire for the windings it is almost the same for the two cases) to be calm when i am sleeping.anatech said:
Regards
Fotios
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