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Old 29th June 2012, 08:34 AM   #411
owdeo is offline owdeo  Australia
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A fair call Jan but obviously not practical for a hobbyist.

I've done some blind testing in the past between preamps where I used a remote controlled relay and didn't know which device was operating on each switch position. I could switch the devices back and forth as much as I liked and took notes on the sound on each position with each track I listened to. I wrote down my vote for which position I preferred overall for each track and then after many many tracks took the final score for each.

I learnt from this that the differences I previously thought were great bewteen the two preamps were actually pretty marginal, but after I worked out which switch position was which preamp I found I still preferred overall the same one I did before the blind testing.

I know this is not double-blind testing, but I still think it was extremely useful and could even be more relevant since it removes the confusion in that you know you are comparing two devices all the time. As you can see I don't know much about the science behind pschoacoustics, but what I was doing seemed sensible at the time.
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Old 29th June 2012, 09:46 AM   #412
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A fair call Jan but obviously not practical for a hobbyist.
Hi owdeo,

It might be an interesting exercise to temporarily bypass the active volume control stage to see if that is influencing the sound as you describe. If your amplifier's input impedance isn't too low, you could take the pre-amplifier outputs from IC9B/7 and IC18A/1 via 47 ohm and 220uF NP capacitors in series. A 10K-20K pot at the output would serve as a volume control.
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Old 29th June 2012, 10:19 AM   #413
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Originally Posted by owdeo View Post
A fair call Jan but obviously not practical for a hobbyist.[snip]
Maybe not. But it does put a lot of statements here as to what is heard into a different perspective.

In effect you say: it's too cumbersome to find out if I really hear a difference, so lets just assume I do and then go on a chase as to what it might be, how to 'fix' it, spend money and time on it, etc.

jan
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Old 29th June 2012, 10:38 AM   #414
owdeo is offline owdeo  Australia
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Originally Posted by currentflow View Post
It might be an interesting exercise to temporarily bypass the active volume control stage to see if that is influencing the sound as you describe. If your amplifier's input impedance isn't too low, you could take the pre-amplifier outputs from IC9B/7 and IC18A/1 via 47 ohm and 220uF NP capacitors in series. A 10K-20K pot at the output would serve as a volume control.
Hi currentflow,

Good idea, but it would leave me with no gain in the preamp and reversed phase. I also don't like using a pot on the output as the higher output impedance could have an effect, so overall I'm not sure the comparison would be that worthwhile done that way.

The only way I can see to really compare apples with apples is to desolder the volume pot and short between the input and wiper pins on the board, and use a 10k log pot at the input before the input buffer. This leaves the max gain and phase the same and every opamp still in circuit, but will be a pain and I will risk damaging the pot and or PCB.

I'll sleep on it and see how keen I feel in the morning...
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Old 29th June 2012, 10:58 AM   #415
owdeo is offline owdeo  Australia
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In effect you say: it's too cumbersome to find out if I really hear a difference, so lets just assume I do and then go on a chase as to what it might be, how to 'fix' it, spend money and time on it, etc.
A fine point Jan, and very hard to argue with if I was trying to improve the sound of a product in a commercial situation.

But as a hobbyist I have the freedom to let my ears potentially mislead me and waste time this way, and I think I'd rather do this than conduct a confusing double blind test where I have to listen hundreds of times over .

I must admit I'm not convinced that a formal double blind test is really necessary to prove an audible difference - if anything these seem designed to confuse the listener but I am probably showing my ignorance here and won't go on.

Whether it seems like it or not I'm really not trying to prove or even say that there is a problem with this design, simply trying to be honest about my subjective impressions and trying to find out why I'm not happy with the sound. Anyone who is 100% convinced that there cannot be a difference unless it is measureable in terms of THD or proven in a double-blind test, should ignore my ramblings (as I'm sure they already are), but really in that case why would they bother reading this forum at all?
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Old 29th June 2012, 11:29 AM   #416
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Originally Posted by owdeo View Post
Hi currentflow,

Good idea, but it would leave me with no gain in the preamp and reversed phase. I also don't like using a pot on the output as the higher output impedance could have an effect, so overall I'm not sure the comparison would be that worthwhile done that way.
There should be sufficient overall gain to perform a reasonable test. For the purpose of the test, if you were concerned about phase, you could simply reverse your loudspeaker leads. The pot can be positioned at the input if you are concerned about output impedance.

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The only way I can see to really compare apples with apples is to desolder the volume pot and short between the input and wiper pins on the board, and use a 10k log pot at the input before the input buffer. This leaves the max gain and phase the same and every opamp still in circuit, but will be a pain and I will risk damaging the pot and or PCB.
But you're still feeding the signal through the active volume stage. If you unplugged all of the output opamps, the existing pot would have no influence and you wouldn't need to de-solder it. Taking the output from IC9B and IC18A would give a sample of the audio before the final stages and should allow you to determine whether the active volume stages are responsible for the sound modification you perceive.
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Old 29th June 2012, 11:45 AM   #417
Mooly is offline Mooly  United Kingdom
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Originally Posted by owdeo View Post
At the risk of getting into phillosophy I'm not sure that I entirely agree.

Yes it absolutely comes down to a matter of personal taste, but I think there's more to it than that. Being true to the original sound is what "hifi" is supposed to be about. Obviously if you only listen to music of electronic origin or artificially recorded music (ie pop/rock) the concept has no meaning and you can merrily change your components or whatever to achieve the sound you like.

But I'm looking for sound quality that gets me as close as possible to the real sound of an acoustic group, whether it be a small jazz ensemble or string quartet or a full symphony orchestra. This shouldn't be as much a matter of taste if you regularly attend concerts and play instruments.

I would say more that what I'm finding out is that the merit of the conventional set of measurements, eg THD curves and SNR etc could be missing the point somewhat in terms of how they relate to our perception of reproduced sound. These parameters are of course essential for verifying that a design is working properly and I am by no means suggesting they are irrelevant, just that perhaps there are other things we could or should also measure. This would make the whole thing awfully complicated though and it's easy to see why a designer would focus only these parameters.

I agree that I should try bypassing the Active Gain Control somehow - probably by bypassing the pot and buffer and keeping a fixed inverting gain stage at the output to keep the phase right and provide some gain. I'll need to put a pot on the input before the input buffer to control the volume then. I guess a 10k log should do.

I liked the OPA2604 in another conventional preamp circuit I tried it in, but not as much as the 5532, and also as an IV converter in a DAC output, where I think it was the best of all those I tried. Whether it's a good choice in this design seem doubtful but I guess I can try it and see.
Well I play an acoustic piano (as in traditional... it hasn't even got a din socket on it )

What works for me in amplifiers and source components are the systems and choices that allow me to close my eyes and be transported to another world.

I wanted to like some of the ultra low distortion designs, I have wanted to like the NE5534/2 but more often than not find that other approaches and choices work better.

When I settle down to really listen and then find my mind wandering as to whether I could be doing something else instead then the set up isn't right.

When I find myself reluctant to be torn away, when I want to get many different recordings of the same music to explore the different interpretations, then I know the system is working well whatever its technical shortcomings may (or may not) be.

It doesn't have to be loud or capable of putting the windows through or rattling the floorboards... what it has to do is pull off that magical trick of letting you get immersed in the music. And that is something that even a pair of 2N3055's and a few other components can do.

When it comes to low level circuitry such as opamps there is something going on audibly that can't be explained by measurement. Some configurations and devices have the magic, some don't. Quite why we can pick up on these miniscule differences always amazes me but some of us can.

Spec wise there isn't much difference between a $ 15.00 portable CD player and a $ 1500 one but when you listen there certainly is. Both could be considered blameless. This is where audio engineering for the purpose of musical enjoyment becomes as much an art as a science.

As to your preamp... you have to eliminate that gain stage to prove to yourself whether or not it is to blame. The suggestions of getting someone to throw the switch are great but just as valid is long term listening by you. You will know if it is right or not. It's no good listening after immediately swapping parts because you are not in the right frame of mind. Yes listen but listen again tomorrow and the day after and the day after that.

You Will know.
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Old 29th June 2012, 12:10 PM   #418
owdeo is offline owdeo  Australia
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Me too, the acoustic ones make a much nicer sound even though the electric ones are probably considered blameless now

Thanks Mooly, I'm 100% with you on all that
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Old 29th June 2012, 12:15 PM   #419
owdeo is offline owdeo  Australia
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Originally Posted by currentflow View Post
But you're still feeding the signal through the active volume stage. If you unplugged all of the output opamps, the existing pot would have no influence and you wouldn't need to de-solder it. Taking the output from IC9B and IC18A would give a sample of the audio before the final stages and should allow you to determine whether the active volume stages are responsible for the sound modification you perceive.
Agreed, but by removing the pot and shorting those pins it's no longer a variable gain stage and there's no feedback from the output right back to the buffer input, so it becomes just a unity gain buffer followed by a fixed gain inverting amp. But since your suggestion is so much easier maybe I'll do it that way and try to equalise things as your suggest. Thanks
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Old 29th June 2012, 12:35 PM   #420
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Originally Posted by owdeo View Post
Agreed, but by removing the pot and shorting those pins it's no longer a variable gain stage and there's no feedback from the output right back to the buffer input, so it becomes just a unity gain buffer followed by a fixed gain inverting amp. But since your suggestion is so much easier maybe I'll do it that way and try to equalise things as your suggest. Thanks
As Mooly said, being in the right frame of mind is essential during auditions. When swapping and selecting the best sounding op-amps for my own pre-amp (a different design to that in this thread) I found that I would be going round in circles some evenings if I wasn't careful. Listening over an extended period - several days in my case to different music tracks was the key it seemed.
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