Tham you think that you may had system gain dynamic deficiency before from CD source with buffer control preamp as Andrew suspects? You have very efficient speakers I believe.
I can make those mods over time. Including moving R4,R5 in DCG-3 to 33R as well from 51R.
MKS2 is currently used as C5. It is what fits
With my system, it simply does not need a lot of gain, so not being able to open up the ALPS pot all that much may be limiting too (plus it's a fairly inexpensive pot. But I honestly have no complaints at this point.
MKP2 63V DC or 100V DC for C5 also fits. I have the 100V 5% type in my hand and I can see it does because there is some free space around the MKS2. Indeed fatter and taller but same pitch. 5.5x11.5x7.2mm. No real problem with MKS2 but no problem investigating for better too.
Had also moved Cb Cc decoupling caps underneath PCB and soldered from above to could extract and change op-amps during the many done tests without drama. TL072 TLE2082 OPA2604 OPA2134 LM4562 NE5532 NJM4580 OP275 AD823
*1206 alternative surface pads for 0.1uF 50V C0G Cb Cc are already added for the future.
Had also moved Cb Cc decoupling caps underneath PCB and soldered from above to could extract and change op-amps during the many done tests without drama. TL072 TLE2082 OPA2604 OPA2134 LM4562 NE5532 NJM4580 OP275 AD823
*1206 alternative surface pads for 0.1uF 50V C0G Cb Cc are already added for the future.
Attachments
I also built a prototype, as Salas showed, with capacitor outputs for line and headphones.
I have to confess that due to work and kids, had not a lot of time for testing.
Initially tested as line amp with 3X gain and liked it a lot! Of course I could hear the coloration of the capacitor coupling (russian petp bypassed by FT_-3) but as I use long cables to drive two amplifiers, dcg3 could cope with cable capacitance with ease.
I have now change the gain to 2X (increased the feedback) and put a bigger capacitor for headphones, but I am still short of time. I also now have all the parts to built the servo and hope to find some time next month to play around.
Some new headphones are on their way too!
I have to confess that due to work and kids, had not a lot of time for testing.
Initially tested as line amp with 3X gain and liked it a lot! Of course I could hear the coloration of the capacitor coupling (russian petp bypassed by FT_-3) but as I use long cables to drive two amplifiers, dcg3 could cope with cable capacitance with ease.
I have now change the gain to 2X (increased the feedback) and put a bigger capacitor for headphones, but I am still short of time. I also now have all the parts to built the servo and hope to find some time next month to play around.
Some new headphones are on their way too!
You will only need 1.78V RMS for 110dB with your AKG K712 PRO (50mW for 62 Ohm 105dB/V transducer). So 2X may serve you right for line and hp duty. Tea could also do that to can move up his Alps pot a little further. By making R6 ~500R he will have 2X gain. Still a welcome boost for when using the turntable but it could compromise his headphones loudness range on the other hand if they are not as sensitive as yours.
Then again because this preamp can drive low impedance with ease, an output voltage divider can cater for both situations. Keeping the internal gain as is but making the 50R series line output resistor (R15) to 100R and moving that original 50R across the output RCA will divide the line signal by 3 or -10dB. That restores his system gain to unity and keeps 3X for his headphones too. Will cut the line out noise level by 10dB as well. Can bring more THD though. If audible and how only he could tell.
Then again because this preamp can drive low impedance with ease, an output voltage divider can cater for both situations. Keeping the internal gain as is but making the 50R series line output resistor (R15) to 100R and moving that original 50R across the output RCA will divide the line signal by 3 or -10dB. That restores his system gain to unity and keeps 3X for his headphones too. Will cut the line out noise level by 10dB as well. Can bring more THD though. If audible and how only he could tell.
P2P DCG3 built ready for boxing
Ayrton-Perry hand wound R6 and R15 speak traditional DIY
Can do!
A few questions, for R4,R5 - I get the impression now they are part of the signal path and maybe should be decent resistors?
Also, how limiting is the Alps pot here? It's worth purchasing a Goldpoint or better attenuator, I am interested in that as well.
R4 R5 are gate-stoppers i.e dampers. Signal is there but no real current and no drop due to high MOSFET gate impedance. On the oscilloscope 33R gives slightly smoother corner on very high frequencies and amplitudes square wave tests than 51R, but generators, probes, and layouts can change this. Even with 10R it was stable and even smoother but I prefer bit more anti layout inductance damping to be there as good general practice. I got Dale RN60s for all signal associated resistors to use at a point but I always keep the initial test board as generic as possible in order to make sure its basically alright without fancy parts. No difficult tonal problems as for now. Stick an AD823 first which is very easy to do. Tham says he can easily prefer his DIY LDR over a Tocos. I use $1.5 carbon Alpha pot for tests
Its an SE preamp. Possible though. Must simply build two boards for balanced stereo, i.e. four channels, one channel for each signal phase.
The first p2p beta tester (Michael) has American magnetic panel speakers of low sensitivity and got attracted to the same aspects as you do. He never connected headphones ever, has not even a jack for that. Nonetheless it became his line preamp of choice. He uses gain of four. He even made one copy for his best friend.
The first p2p beta tester (Michael) has American magnetic panel speakers of low sensitivity and got attracted to the same aspects as you do. He never connected headphones ever, has not even a jack for that. Nonetheless it became his line preamp of choice. He uses gain of four. He even made one copy for his best friend.
Thanks! I' ll be following...Its an SE preamp. Possible though. Must simply build two boards for balanced stereo, i.e. four channels, one channel for each signal phase.
The first p2p beta tester (Michael) has American magnetic panel speakers of low sensitivity and got attracted to the same aspects as you do. He never connected headphones ever, has not even a jack for that. Nonetheless it became his line preamp of choice. He uses gain of four. He even made one copy for his best friend.
Few words about power
Lets talk two examples. One is wanting to drive 2.2VRMS into a 32 Ohm headphone*. The other is wanting to drive 2.2VRMS into a 600 Ohm line. Say at the standard 100mA output stage DC bias choice.
The two graphs show output voltage, M3 drain pin current, M1/M2 drain pin current (identical) and M1 source pin current. Its the same PSU drawn current amount just shown reversed phase at source pin. The output stage will only pull steady DC bias from the negative rail because its current source M3 resides alone there while it can pull double that pk-pk from the positive rail before progressively squashing the below zero going part of a waveform. Will drive 200mA pk-pk on 32 Ohm but only 15mA pk-pk is demanded on 600 Ohm for that same output voltage. 33V pk-pk (11.7VRMS) with 55mA pk-pk can be done on 600 Ohm. A 10K amplifier will be driven to 33V pk-pk with just 3.3mA pk-pk.
So the about +/-17.5V PSU should be capable of at least 200mA on the positive and 100mA on the negative to cover the demanding load example. There is little more to add for the input stage and the servo.
If using double mono BIB shunt regulators a 250mA CCS limit for the positives and 150mA CCS limit for the negatives would be the economic choice heatwise. Double that when with common between channels mono regulators. If using the double mono DC stabilizer there is nothing to set. Its just a low noise non amplified voltage reference with a compound current pass transistor (Sziklai) of high enough amperage.
When not planning to use headphones, or at least not below 70 Ohm impedance ones, then 150mA CCS per rail limit for double mono regulators will suffice. When planning to use much insensitive low impedance headphones then more DC current bias and higher super shunt PSU CCS limits can be calculated.
*That is 120 dBSPL on a Grado. Will blow your head
Lets talk two examples. One is wanting to drive 2.2VRMS into a 32 Ohm headphone*. The other is wanting to drive 2.2VRMS into a 600 Ohm line. Say at the standard 100mA output stage DC bias choice.
The two graphs show output voltage, M3 drain pin current, M1/M2 drain pin current (identical) and M1 source pin current. Its the same PSU drawn current amount just shown reversed phase at source pin. The output stage will only pull steady DC bias from the negative rail because its current source M3 resides alone there while it can pull double that pk-pk from the positive rail before progressively squashing the below zero going part of a waveform. Will drive 200mA pk-pk on 32 Ohm but only 15mA pk-pk is demanded on 600 Ohm for that same output voltage. 33V pk-pk (11.7VRMS) with 55mA pk-pk can be done on 600 Ohm. A 10K amplifier will be driven to 33V pk-pk with just 3.3mA pk-pk.
So the about +/-17.5V PSU should be capable of at least 200mA on the positive and 100mA on the negative to cover the demanding load example. There is little more to add for the input stage and the servo.
If using double mono BIB shunt regulators a 250mA CCS limit for the positives and 150mA CCS limit for the negatives would be the economic choice heatwise. Double that when with common between channels mono regulators. If using the double mono DC stabilizer there is nothing to set. Its just a low noise non amplified voltage reference with a compound current pass transistor (Sziklai) of high enough amperage.
When not planning to use headphones, or at least not below 70 Ohm impedance ones, then 150mA CCS per rail limit for double mono regulators will suffice. When planning to use much insensitive low impedance headphones then more DC current bias and higher super shunt PSU CCS limits can be calculated.
*That is 120 dBSPL on a Grado. Will blow your head
Attachments
Listened to Peter Gabriel's Scratch My Back version of Heroes over the DCG-3 the other night.
It's a slowly sung song, seems close mic and it ramps up to a kind of chilling end with strings if you let it.
The lower mids of his voice never sounded so strong. The presence of him in the room was both strong, almost uninvited after a certain point. You may get this emotional reaction when you realize the sound can really have a visceral affect on you like that. This is one of the reasons I like audio - to get this experience from music. Sometimes you can only get that when the equipment is crisp and spot on. Like the low-noise of the folded, this pre allows you to squeeze a little more information out of your gear, and push it at you. It's not even a spectacular recording, but it's well delivered.
I felt like sharing this part of it. That the circuit may kick your butt if you let it.
I am very interested in what VGeorge and Salas have to say with their headphone shoot out.
It's a slowly sung song, seems close mic and it ramps up to a kind of chilling end with strings if you let it.
The lower mids of his voice never sounded so strong. The presence of him in the room was both strong, almost uninvited after a certain point. You may get this emotional reaction when you realize the sound can really have a visceral affect on you like that. This is one of the reasons I like audio - to get this experience from music. Sometimes you can only get that when the equipment is crisp and spot on. Like the low-noise of the folded, this pre allows you to squeeze a little more information out of your gear, and push it at you. It's not even a spectacular recording, but it's well delivered.
I felt like sharing this part of it. That the circuit may kick your butt if you let it.
I am very interested in what VGeorge and Salas have to say with their headphone shoot out.