Hi All,
I'm new to this forum and new(ish) to the audio electronics world in general so please be gentle!
My Cyrus 1 amp recently fizzed then finally went pop a week or so ago leaving me using a backup amp which has no phono stage.
Not wanting to lay out for a new amp just yet (the Cyrus has done it's work) but mostly out of curiosity I have decided to try and put together a phono preamp for myself.
For a first project I've got hold of two mono preamp kits from from an electronics shop in the UK (Maplin) and they take 10V to 30V. The boards themselves are marked as 12V.
Making the things themselves doesn't seem to be too much trouble (step-by-step is provided) but I'm blowed if I can figure out how to supply 12V to the two boards from one power supply.
Could I use a computer PSU that supplies multiple 12V leads? Would I need to have the fan running?! Could I take the transformer out of an old piece of audio kit and use that? If so, how do I sort out which tags supply 12V (or thereabouts). And If I DO use a transformer, I'm still stuck with needing to supply two circuits!
Any ideas?
Matt
I'm new to this forum and new(ish) to the audio electronics world in general so please be gentle!
My Cyrus 1 amp recently fizzed then finally went pop a week or so ago leaving me using a backup amp which has no phono stage.
Not wanting to lay out for a new amp just yet (the Cyrus has done it's work) but mostly out of curiosity I have decided to try and put together a phono preamp for myself.
For a first project I've got hold of two mono preamp kits from from an electronics shop in the UK (Maplin) and they take 10V to 30V. The boards themselves are marked as 12V.
Making the things themselves doesn't seem to be too much trouble (step-by-step is provided) but I'm blowed if I can figure out how to supply 12V to the two boards from one power supply.
Could I use a computer PSU that supplies multiple 12V leads? Would I need to have the fan running?! Could I take the transformer out of an old piece of audio kit and use that? If so, how do I sort out which tags supply 12V (or thereabouts). And If I DO use a transformer, I'm still stuck with needing to supply two circuits!
Any ideas?
Matt
Well , the easiest thing to do would be to get a 12v DC adapter (assuming the preamp needs DC , if it needs AC you can also find AC wall adapters) , you can probably find one at a thrift store for $1 .... Just cut the end off and use your multimeter to measure which wire is Positive and which is negative then connect the wires to the the positive and negative on the Preamps ....
The better way would be to get a small 12v transformer and a regulated PSU board ....
You would connect each preamp in parallel to the power source ....
The better way would be to get a small 12v transformer and a regulated PSU board ....
You would connect each preamp in parallel to the power source ....
Heat buildup in parallel?
Thanks for the reply Minion,
That sounds like the route that I was heading down but I had doubts about using the transformer with the two boards (even though they're tiny).
Would I be OK connecting them in parallel or would I be putting too much pressure (resistance?) on the transformer output? Would this heat it up?
My guess is that it wouldn't as the current would be so low but I suppose that heat buildup is my biggest fear.
Thanks for the reply Minion,
That sounds like the route that I was heading down but I had doubts about using the transformer with the two boards (even though they're tiny).
Would I be OK connecting them in parallel or would I be putting too much pressure (resistance?) on the transformer output? Would this heat it up?
My guess is that it wouldn't as the current would be so low but I suppose that heat buildup is my biggest fear.
A preamp is going to draw very low current. All you need is a small tranny, bridge rectifier and cap and perhaps a 78xx type regulator to give a clean supply.
Why not have a go at fixing the Cyrus. If you have a circuit all things are possible 🙂
Why not have a go at fixing the Cyrus. If you have a circuit all things are possible 🙂
There should be a problem with heat as the current draw would be quite low , just connect them in parallel to the PSU and you should be fine ....
Keep in mind that some "wall warts" are not regulated, so 12V could mean 15 to 18 volts with light loads. That also means a lot of ripple, and if those preamps are of the minimal two-transistor variety, they won't reject much power supply noise.
It isn't the K1803 preamp, is it? Those appear to be microphone preamps, which won't have the RIAA equalization. On eBay you can find OPA2134 RIAA preamp boards for about $25 shipped which may be copies of the Bugle preamp, which is a very good preamp. Or you can buy the real thing from Hagtech.com for rather more money.
There was a good comparison of budget preamps at AudioXpress; it has been preserved for eternity at Archive.org:
http://web.archive.org/web/20080513040545/http://www.audioxpress.com/reviews/media/403hansen2090.pdf
Notice the mediocre performance of units that just use a couple of transistors. You'll find similarly lousy preamps sold at higher prices, including preamps by TCC, and even a UREI "professional" phono preamp, so if you're considering buying something readymade, beware.
It isn't the K1803 preamp, is it? Those appear to be microphone preamps, which won't have the RIAA equalization. On eBay you can find OPA2134 RIAA preamp boards for about $25 shipped which may be copies of the Bugle preamp, which is a very good preamp. Or you can buy the real thing from Hagtech.com for rather more money.
There was a good comparison of budget preamps at AudioXpress; it has been preserved for eternity at Archive.org:
http://web.archive.org/web/20080513040545/http://www.audioxpress.com/reviews/media/403hansen2090.pdf
Notice the mediocre performance of units that just use a couple of transistors. You'll find similarly lousy preamps sold at higher prices, including preamps by TCC, and even a UREI "professional" phono preamp, so if you're considering buying something readymade, beware.
This is all good info guys and (as expected) has shown me that this stuff is complex, deep and VERY interesting!
Most of the stuff that you all mention I've never even come across (the RIAA circuit? Ripple?) which has just spurred me on to learn more.
Guess I should start at the beginning then...
Mooly: Yes, I could have a go at the Cyrus but this is probably WAY too complicated for me to troubleshoot. I really am just a beginner.
Dangus: Yes, you're right, these ARE the K1803 circuits (I didn't even know that the RIAA specification existed before I bought them!). I'll make them anyway to see what happens. Could I insert two RIAA circuits before the two preamps?
I really am more interested in "making it go" now, rather than just replacing my Cyrus.
Apologies for the dumb questions 🙂
Matt
Most of the stuff that you all mention I've never even come across (the RIAA circuit? Ripple?) which has just spurred me on to learn more.
Guess I should start at the beginning then...
Mooly: Yes, I could have a go at the Cyrus but this is probably WAY too complicated for me to troubleshoot. I really am just a beginner.
Dangus: Yes, you're right, these ARE the K1803 circuits (I didn't even know that the RIAA specification existed before I bought them!). I'll make them anyway to see what happens. Could I insert two RIAA circuits before the two preamps?
I really am more interested in "making it go" now, rather than just replacing my Cyrus.
Apologies for the dumb questions 🙂
Matt
You think so ? 🙂
Compared to this, the Cyrus is a walk in the park 😀
http://www.diyaudio.com/forums/solid-state/233880-help-repairing-pioneer-m3.html
If it went pop then you are most likely looking at replacing output transistors, the driver transistors and perhaps one or two passives (resistors etc) that suffered along the way.
Without the RIAA equalization, music will sound pretty bad, although maybe salvageable using the tone controls.
The RIAA equalization would have to be built into the preamps, by changing the feedback from a resistor to a more complicated network of resistors and capacitors. See the schematics in the AudioXpress article.
That may have been an incomplete version of the pdf at Archive.org that I linked to. This one loads (for me): http://web.archive.org/web/20061112180327/http://www.audioxpress.com/reviews/media/403hansen2090.pdf If it doesn't load, then use the Waybackmachine at Archive.org with the original audioxpress link, and pick a date in 2006.
The RIAA equalization would have to be built into the preamps, by changing the feedback from a resistor to a more complicated network of resistors and capacitors. See the schematics in the AudioXpress article.
That may have been an incomplete version of the pdf at Archive.org that I linked to. This one loads (for me): http://web.archive.org/web/20061112180327/http://www.audioxpress.com/reviews/media/403hansen2090.pdf If it doesn't load, then use the Waybackmachine at Archive.org with the original audioxpress link, and pick a date in 2006.
Thanks for that Dangus.
It seems that I'm going to have to sort our the RIAA question! No problem, just more learning for me.
I've now got that review PDF that you sent which has been a great help in deciding what I need to achieve to make the project worthwhile but I guess that it's going to take a couple of attempts!
Matt
It seems that I'm going to have to sort our the RIAA question! No problem, just more learning for me.
I've now got that review PDF that you sent which has been a great help in deciding what I need to achieve to make the project worthwhile but I guess that it's going to take a couple of attempts!
Matt
The RIAA preamp is only needed if the source is Vinyl records. If you are simply wanting to input radio / CD / MP3 player etc. then no RIAA circuit is needed.
alan
alan
Hi Alan,
Yes, I'm experimenting with vinyl and so far it's all gone well! Thanks for the info.
Matt
So far, so good.
Hi all,
Thanks to you all I've got the thing working and making a noise, which is nice.
I've decided to knock up two simple RIAA stages and pop them after the gain stages and, to this end, I've started another thread concerning RIAA in the Analogue-Source forum (here). Let's see if I can make this fly!
Cheers,
Matt
Hi all,
Thanks to you all I've got the thing working and making a noise, which is nice.
I've decided to knock up two simple RIAA stages and pop them after the gain stages and, to this end, I've started another thread concerning RIAA in the Analogue-Source forum (here). Let's see if I can make this fly!
Cheers,
Matt
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