Hello,
after having already built two quite good sounding power amplifiers, I would like to start building a preamplifier.
I have already thought about how the whole thing should look like. I will list the already imagined requirements here:
- Volume, balance, and a tone control circuit (Baxandall?)
- Attenuation (1-2 steps)
- Signal switching with relays, so that a microcontroller control can be retrofitted later
- Motorised potentiometer for volume
- 3 to 4 Line Level inputs
- One switchable Tape Output
- Phono MM input stage
- dedicated subwoofer output (fc ~ 120Hz)
- Separate power supplies for relay / control circuit and audio
But some things still make me wonder:
- How do I avoid pops and clicks when switching? Is it enough here to reduce the DC part of the signal with coupling capacitors?
- Does it make sense to use a rumble filter for the phono input? If so, does it only make sense for phono, or also for other sources?
- Is it much effort to add a phono MC stage in case of a system change to MC?
- I have found that I like to use loudness correction on my old Teac amplifier, is it difficult to implement such a correction?
- On Rod Eliott's page I saw active and passive volume controls. Is one preferable to the other?
It would also be great if I could build the circuit from NE5532 and TL072 op amps, I still have some of these in my stock, which I got for free from an electronics store going out of business.
Do you have any tips for me, which literature is good for this topic, or where I can find inspiration on the internet? I already own the books on power amplifier design by Bob Cordell and Douglas Self.
I thank you in advance for your answers to my many questions!
Regards
Lukas
after having already built two quite good sounding power amplifiers, I would like to start building a preamplifier.
I have already thought about how the whole thing should look like. I will list the already imagined requirements here:
- Volume, balance, and a tone control circuit (Baxandall?)
- Attenuation (1-2 steps)
- Signal switching with relays, so that a microcontroller control can be retrofitted later
- Motorised potentiometer for volume
- 3 to 4 Line Level inputs
- One switchable Tape Output
- Phono MM input stage
- dedicated subwoofer output (fc ~ 120Hz)
- Separate power supplies for relay / control circuit and audio
But some things still make me wonder:
- How do I avoid pops and clicks when switching? Is it enough here to reduce the DC part of the signal with coupling capacitors?
- Does it make sense to use a rumble filter for the phono input? If so, does it only make sense for phono, or also for other sources?
- Is it much effort to add a phono MC stage in case of a system change to MC?
- I have found that I like to use loudness correction on my old Teac amplifier, is it difficult to implement such a correction?
- On Rod Eliott's page I saw active and passive volume controls. Is one preferable to the other?
It would also be great if I could build the circuit from NE5532 and TL072 op amps, I still have some of these in my stock, which I got for free from an electronics store going out of business.
Do you have any tips for me, which literature is good for this topic, or where I can find inspiration on the internet? I already own the books on power amplifier design by Bob Cordell and Douglas Self.
I thank you in advance for your answers to my many questions!
Regards
Lukas
I'd say take a look at Douglas Selfs Small Signal Audio Design book as well as the Preamps he published in Linear Audio and Elektor. I think the Elektor articles were even available for download in .pdf as long as their store also sold the PCBs, but now I don't see that option anymore. I am sure you can also dig them up elsewhere on the web, but you can also toss me a PM if you are interested in those. The schematics for the linear audio one were available for download from the linear audio website the last time I checked.
Absolutely necessary read and understand Bruno Putzeys article "G word"
View attachment WP_The_G_word.pdf
Why would switches pop? Blocking DC is a good first start at anti-pop. Switching live audio "must" pop; don't do that (or get complicated).
Phono will have MUCH more subsonic than any other likely source. Your digital tracks are sharply bass-cut at 50Hz or maybe a bit lower. Antique FM radio modulators can't shift phase forever so have bass-cut. Tape does have the massive bass boost of phono but far less mechanical rumble. But I have seen <10Hz from phono as strong as the music.
And yes yes yes yes: read Doug Self.
Phono will have MUCH more subsonic than any other likely source. Your digital tracks are sharply bass-cut at 50Hz or maybe a bit lower. Antique FM radio modulators can't shift phase forever so have bass-cut. Tape does have the massive bass boost of phono but far less mechanical rumble. But I have seen <10Hz from phono as strong as the music.
And yes yes yes yes: read Doug Self.
Rod Elliott's site is a GREAT tool for garnering DIY audio knowledge. He has an excellent way of explaining things and has a LOT of projects that WORK, perform excellently and can be built at home (including a preamp).
Elliott Sound Products - The Audio Pages (Main Index)
Elliott Sound Products - The Audio Pages (Main Index)
I'll order this book, hoping, it won't take to long to arrive. Thank you! I'll search up some schematics of Self's preamps.
I'll give this one a read too, thank you very much!
Thank you very much, I think, I'll put a switchable Rumble-Filter in the Tone control section. I might also add an logical AND for automatically switching the Filter on, when the Phono Input is selected.
Thats true, Eliliott's Site is indeed great, I've built his DoZ Headphone Amp and its sounding great with my AKG K240.
I've made up a block diagram, how I imagine the function blocks of the Preamp linked together. I'm not entirely shure, wheter this is the best arrangement, I'll trust your knowledge here 🙂
Regards
Lukas
Attachments
Might it be better to put the rumble filter right near or in the phono section, since that is the only signal source needing one? The filter would certainly work well placed later in the signal path, too. By having the switch near the phono section, the other signal sources don't have to be influenced by that set of switch contacts.