Hi,
I am new to sound equipment, so I figured I should ask advice from more experienced people.
My project is to upgrade my old Sony TA-242 amplifier to have tubes in the input stage. The amp has Low and High Tone regulators and I want to utilize them for tube pre-amp as well. I am aware that EQ will not fix all the sound related problems like room acoustics, speaker quality, source/DAC quality, incorrect studio recording, etc. I think it will still be a neat feature to have in my amp.
Looking at professional equipment, I found that Makie mixers use what they call Perkins EQ, which is based on Wien Bridge Equalizer according to this forum: Mackie "Perkins EQ" - the schematic.
I then did little research and found this schematics:
https://www.dropbox.com/s/wbo4mt3p4coieoh/eq7.gif?dl=0
It allows +-9dB on 100Hz and 8kHz.
I might increase 8kHz to 10kHz which is pretty much standard for audio EQ. I kind of wondering what frequencies will be the best to use for EQ??? Makie mixers have 80Hz and 12kHz as Lo and High respectively...
For preamp, I was looking at Marshall preamp schematics:
https://www.dropbox.com/s/31job8j0sjcxvil/1266951502_lampovyj-predvaritelnyj-usilitel-firmy-marshall.jpg?dl=0
with modification of the cathode repeater like this:
https://www.dropbox.com/s/5c3kx8s1xp8gnvd/temp.PNG?dl=0
For input levels I want to be able to hook up amp with my DVD player and with my headphones output from iPhone. Not sure what are the levels for those? For output level, I need to feed it to STK460.
Considering all three schematics, I wonder how I would connect Wien Bridge Equalizer with the tube schematics??? If I understand correctly, it is connected in the feedback loop of operating amp, but how I would connect it without feedback loop in tube amp?
Thank you for your help.
I am new to sound equipment, so I figured I should ask advice from more experienced people.
My project is to upgrade my old Sony TA-242 amplifier to have tubes in the input stage. The amp has Low and High Tone regulators and I want to utilize them for tube pre-amp as well. I am aware that EQ will not fix all the sound related problems like room acoustics, speaker quality, source/DAC quality, incorrect studio recording, etc. I think it will still be a neat feature to have in my amp.
Looking at professional equipment, I found that Makie mixers use what they call Perkins EQ, which is based on Wien Bridge Equalizer according to this forum: Mackie "Perkins EQ" - the schematic.
I then did little research and found this schematics:
https://www.dropbox.com/s/wbo4mt3p4coieoh/eq7.gif?dl=0
It allows +-9dB on 100Hz and 8kHz.
I might increase 8kHz to 10kHz which is pretty much standard for audio EQ. I kind of wondering what frequencies will be the best to use for EQ??? Makie mixers have 80Hz and 12kHz as Lo and High respectively...
For preamp, I was looking at Marshall preamp schematics:
https://www.dropbox.com/s/31job8j0sjcxvil/1266951502_lampovyj-predvaritelnyj-usilitel-firmy-marshall.jpg?dl=0
with modification of the cathode repeater like this:
https://www.dropbox.com/s/5c3kx8s1xp8gnvd/temp.PNG?dl=0
For input levels I want to be able to hook up amp with my DVD player and with my headphones output from iPhone. Not sure what are the levels for those? For output level, I need to feed it to STK460.
Considering all three schematics, I wonder how I would connect Wien Bridge Equalizer with the tube schematics??? If I understand correctly, it is connected in the feedback loop of operating amp, but how I would connect it without feedback loop in tube amp?
Thank you for your help.
Last edited:
The TA-242 lacks the very important preamp out/amp in feature. That means you can't isolate the power O/P section from the built in preamp section, in a simple manner. 
The best you can do with that unit, without extensive "surgery", is to insert some "simple" tubed electronics in a tape monitor loop. Doing so is (IMO) not likely to buy you much.
The best you can do with that unit, without extensive "surgery", is to insert some "simple" tubed electronics in a tape monitor loop. Doing so is (IMO) not likely to buy you much.
Cutting into PCBs is not for the faint of heart. In any event, scan and post the schematics, when they arrive. Scheming and plotting do no harm. Once you cut, things can go belly up in a hurry.
As is the case in many situations, engage brain before opening mouth. Plan things out carefully and quadruple check the plan, before the scalpel goes in.
BTW, post some photos, from several angles, of the innards. Members may have some good ideas on how to proceed.
As is the case in many situations, engage brain before opening mouth. Plan things out carefully and quadruple check the plan, before the scalpel goes in.
BTW, post some photos, from several angles, of the innards. Members may have some good ideas on how to proceed.
I'm not a fan of power ICs, with their (at best) mediocre sound. However in this case, the presence of a STK460 may make retrofitting the preamp out/amp in feature reasonably straightforward.
What goes in the chassis opening? It would be great if it's just sheet metal or even plastic. What else is on the small PCB the RCA jack set and phono grounding post are associated with?
Unless it's 100% defeatable, signal shaping circuitry is best forgotten. Few recordings benefit from signal shaping, while many recordings are damaged by signal shaping stuff.
The recording O/Ps of the unit allow access to the phono section and source selection capability, before the line section gets into the act.
What goes in the chassis opening? It would be great if it's just sheet metal or even plastic. What else is on the small PCB the RCA jack set and phono grounding post are associated with?
Unless it's 100% defeatable, signal shaping circuitry is best forgotten. Few recordings benefit from signal shaping, while many recordings are damaged by signal shaping stuff.
The recording O/Ps of the unit allow access to the phono section and source selection capability, before the line section gets into the act.
Well, I am just starting with tube preams now, but plan to make my own tube power amp later. For now I am having trouble calculating cathode follower.
This is the schematics I want to use:
The tube will be 12AU7.
I have 90V supply.
What would be values of resistors, and how in the world they are determined?
This is the schematics I want to use:
An externally hosted image should be here but it was not working when we last tested it.
The tube will be 12AU7.
I have 90V supply.
What would be values of resistors, and how in the world they are determined?
And I decided to go with LM3886 instead of STK, just because I have them for free. The power supply and case from Sony ta242 is perfect for them. I am going to use inverting input schematics, and will need cathode follower as a buffer to match the resistance.
Here is schematics for LM3886:
Here is schematics for LM3886:
An externally hosted image should be here but it was not working when we last tested it.
For now I opt out from balance and tone controls. Only the volume control before cathode follower.
From the schematics that I got, the amp has such ins/outs:
Tuner input - RCA,
Phono input - RCA,
Tape input - RCA, Jack,
Rec out - RCA,
Headphones out - Jack
Speakers out
Tuner and Tape inputs go to signal switch, then volume control, then balance control, then to STK460.
Phono input goes to OPAMP that is located on the board soldered to RCA connectors. Then goes signal switch.
The tone controls are in the feedback loop of STK460. I think this is really bad on sound, but I'm not sure on that one.
From the schematics that I got, the amp has such ins/outs:
Tuner input - RCA,
Phono input - RCA,
Tape input - RCA, Jack,
Rec out - RCA,
Headphones out - Jack
Speakers out
Tuner and Tape inputs go to signal switch, then volume control, then balance control, then to STK460.
Phono input goes to OPAMP that is located on the board soldered to RCA connectors. Then goes signal switch.
The tone controls are in the feedback loop of STK460. I think this is really bad on sound, but I'm not sure on that one.
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