A few weeks. Of course I could go ahead with some 3k9 resistors in place of the 15k's but then I gotta clean up the board...
Does your component selection on the circuit board pose more load to the OpAmp? Perhaps this is when the resistance of the R3 100 ohm resistor should be increased? The LME49729 can easily drive 600 ohms and as you said makes the circuit on the board questionable, which it is left in its original state.The LME49720 (from DigiKey) substituted for the NE5532 sounds much better. The NE5532 passes the input diode test. I guess I got a bad one.
I changed the circuit with and without the front CRDs. The current on the bases of Q7 and Q5 didn't change much. 2.5uA to 7-ish uA. The NE5532 should work unless your C3 is wonky or some damage to the Q7 and Q5 has already occurred and the LME49720 has the ability to get through that/those problems? IDK...
But it looks like the 5532 was a bad one. So there you have it. More testing for you with the LMExxxxx... excellent.
But it looks like the 5532 was a bad one. So there you have it. More testing for you with the LMExxxxx... excellent.
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Being DC coupled we bench wizards must take note of that. There is no coupling cap to save your butt.
I suspect a lot of hacks will destroy this board easily on the 1st go around without coupling caps. Such is life.😵
I suspect a lot of hacks will destroy this board easily on the 1st go around without coupling caps. Such is life.😵
If you are going down that road, stop in at the heat sink store nearest you and get some coolers for your transistors.
It may be in your best interest.
CheersView attachment 1413080
I like those heatsinks. Curious, which transistors are you advising have heatsinks added? Or are you advising heatsinks on all transistors for this board?
Q10, Q4, Q6, & Q12which transistors are you advising have heatsinks added?
Especially if they are biased harder
Even more so if they are BC550s and BC560s
Even more still if they came on the board ;-)
In my picture they are pinched * glued on ZTX 851 and 951s. Those heatsinks fit best on TO92's.
Ther Zetex transistors have that odd shape on the package.
Ther Zetex transistors have that odd shape on the package.
Appreciate it. I use this board ZTX450 / ZTX550 output, the rest of the transistors are KSC1815 / KSA1015. I will get my hands on some of those heatsinks.
Correct me if I am wrong but the KSC1845 and the KSA992 would be better?the rest of the transistors are KSC1815 / KSA1015.
I think you know a lot more than I, currently I just consider myself an advanced builder 😀
Is the logic on KSC1845 / KSA992 being better due to them being listed as low noise, slightly higher power rating, and higher voltage rating? They seem to have higher hfe and I am not sure how that affects things.
Let's say I did pick up some up, would I need to be changing any other parts out, or are you saying the 1845/992 would be a drop in with noticeable improvement?
Is the logic on KSC1845 / KSA992 being better due to them being listed as low noise, slightly higher power rating, and higher voltage rating? They seem to have higher hfe and I am not sure how that affects things.
Let's say I did pick up some up, would I need to be changing any other parts out, or are you saying the 1845/992 would be a drop in with noticeable improvement?
That makes me nervous 🙂 This website is loaded to the brim with talent. I consider myself an advanced builder, in general terms.I think you know a lot more than I
Sure, the low noise thing is nice, the voltage rating(not a major factor on your board) is excellent and yes a higher than low hfe in a preamp is typically considered a good thing for a transistor. In general terms and statistically, it would seem the KSC1845/KSA992 are a more popular selection vs the 1815/1015. Different stages use different transistors better than others.
I am not sure how that affects things but a distortion analyzer may find a percent difference. Noticeable improvement, I don't know about such things. We'd have to sit it down back to back in blind testing for me to pick a 992 over a 1015. I'm not certain I could tell a difference. Others apparently can, all the day long. No problem for them.
Since your board is shipping to you blank, you could also consider CMF Dale/Vishay resistors. They are probably the most widely used and respected resistor here on this site. I am personally a PRP non-inductive audio grade resistor type of person. I think they are PR9372 series resistors you can get from Parts Connexion in Canada. I bought $$$$.$$ in PRP so they are my go-to audio resistor. Can I tell the difference between the PRP and a 1-cent Chinese metal film resistor? I don't know for certain but a distortion test set may find some noise and a percent difference most likely according to others here who have done the measurements. So do others who do the listening, they can tell all day long. Me? Not so much.
SInce your board is naked, you could consider Wima capacitors and low ESR electrolytics. Sometimes ESR in power supply caps helps filter noise but it depends on the circuit. Typically resistance in a cap is not your friend. But an RC filter is your friend. Go figure...Ha
Brand name relays are nice. One tends to think a brand name relay sourced in the Americas will last long and have many cycles. I see a motorized volum pot on that motherboard of a preamp you purchased. I can't help you sourcing that part but I can tell you I personally have had the most terrible experiences in the past with Chinese-made motorized volume potentiometers. I got myself into some terrible situations repairing & building other equipment with the torture devices. If you look up 'Greatest ancient torture devices known to man in all of time', you will find Chinese motorized volume pots. I have no other advice on those things.
Most tiny little switches like yours in the red on your motherboard(and sometimes blue or black body) from China are deplorable. You touch a solder iron to the switch lug to make a connection and the metal lug falls off like the switch was made from wax! Or even worse it survives the build and shortly after you are finished assembly the switch just quits. In general I like C & K Switches but I love to hate their prices. There are other brands but I stick to C&K whenever I can. In these past few years I have had a string of bad switch purchases from Digikey. Just terrible stuff that cost $30 to $60 per switch and it is pure trash. The quality of switch building seems to have become a random process with little control. I'm glad Digikey takes care of those problems.
Now I'm really off topic. Rats. I'll send it in a PM and the Mods can delete this if they want. Cheers.
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Hi, my take on this build. I bypassed the power supply section and used some Miro regulator boards. No idea if it sounds any better or not and I have no tools to measure anything. Just me having fun. I replaced the caps with ES muse and the wima. I have tried OP1656, OPA 1612, OPA828 and Ad746 which all sound better than the 5532. Amp Camp Pre and Iron Pre from the store sound better than this one in my opinion but obviously cost alot more.
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@gsrchrisu
Just go to post #26 and observe the presence low frequency noise. (multiples of 50Hz, here in the EU, 60Hz in America). It is concievable that better power supply may improve performance of this preamplifier.
Just go to post #26 and observe the presence low frequency noise. (multiples of 50Hz, here in the EU, 60Hz in America). It is concievable that better power supply may improve performance of this preamplifier.
yes the ripple rejection(PSRR) of standard 7815/7915 ar not nice. that is the reason why peter (kleinhorn) changed at the new pcb desing to the "better" LM317.
for all regulators: especially 78xx serie - please keep the 2-3Volts more at the input to give the regulator his voltage drop otherwise the regulator is not working --> means any ripple goes unregulated through the 78xx
kr
chris
for all regulators: especially 78xx serie - please keep the 2-3Volts more at the input to give the regulator his voltage drop otherwise the regulator is not working --> means any ripple goes unregulated through the 78xx
kr
chris
Adding a 0.33uF film in parallel to the cap in the 7815 and 2.2uF film in parallel to the cap in the 7915 would make sense. The datasheet calls for a cap of low internal resistance on the input.
You can only do limited ripple reduction with a larger cap, especially considering the space limitations. If you want to reduce ripple, getting a better quality regulator would make sense. For example. a TI TL780-15KCS has 85dB typical ripple rejection. Compared to the L7815 ripple rejection of 58dB. But, I don't think there is a -15V version of that regulator. The TI LM7915CT has PSRR of only 66dB. Still better than the L7915. The TI LM7815 has 70dB ripple rejection. That would make a significant difference.
You can only do limited ripple reduction with a larger cap, especially considering the space limitations. If you want to reduce ripple, getting a better quality regulator would make sense. For example. a TI TL780-15KCS has 85dB typical ripple rejection. Compared to the L7815 ripple rejection of 58dB. But, I don't think there is a -15V version of that regulator. The TI LM7915CT has PSRR of only 66dB. Still better than the L7915. The TI LM7815 has 70dB ripple rejection. That would make a significant difference.
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