DCG3 is set for 6x. As for the rest, I wish I could answer but it's beyond my level... FWIW, PCM 1792 could deliver 7,8mA and 154mV RMS on 89 ohms I/V resistor- 218mV peak - as estimated by a qualified person in the past. In my gear the chip is biased for about 6mA.
Audibly more than enough. Amps are KT88 push pull about 16W - input stage gain 29x driver stage gain 13x. Speakers SPL 94 db/W/m
Is there any feedback resistors divider setting a lower fixed gain in your tubes amp? Or all that gain (minus OPT ratio) is really there because open loop? If yes its alright, except insensitive cans would be under-served with that I/V source as you mentioned. Maybe get ~32 Ohm particularly sensitive cans like Philips Fidelio X2 which give 90dB SPL with only 90mV RMS and have great cans while you save from making a second dedicated build
Here it is! Sans front and top covers but fully operational. Drilling and wiring XLRs is not what I enjoy mostly but I'm glad it works the way I did it. Please refer to the attached schematic. To be honest, I was expecting to have troubles with input XLR pin 1 connected to chassis. This is the way to connect differential amps but DCG3 isn't such. I guess signal passes through the ground lifters. I'll test it with and without SLBs.
At the time being, I've only had a brief test to confirm it delivers sound. I took the risk to connect it directly on my PCM 1792 current output DAC chip with a single 2 ohms resistor for I/V conversion. That means 11mV DC offset at the input of DCG3 but it doesn't seem to botherIt also means that the signal level is too low. I was anxious about that because DCG3 was going to sit in place of a 18x preamp. Well it does thunderus levels as line stage and, of course rather weak as headphone amp on my 600 ohms AKG K180. But neither the 18x preamp could move them in this set up. For this, another DCG3 after the first is needed
There will be intense listening seasions during the weekend, I hope!
Nice!
Does it work properly when you are using RCA SE input?
The issue I see is that when you use SE input the signal goes to the + phase of your PCB but for the - phase to work you need to connect the - Phase on the PCB to your signal reference which you have chosen as the chassis. A solution for this is to connect a wire between the -phase input on the PCB to signal reference with a switch in between. You flip the switch when using SE input which will then make a connection to chassis in your case. Flip the switch the other way when using XLR. Otherwise you will be powering up both phases but using only the + phase and will not accrue any of the benefits of this setup.
Again when using SE output the - half of your amp is not connected to anything and is in essence floating in the wind. Some work better with the output grounded. Maybe Salas can inform whether this will cause any problems.
nash
Thanks Jesper! A special top cover that may attract your attention is coming!
Amps are nothing impresive. My own design and construction for the diy satisfaction but I like the way they sound. I attach schematic.
I'm very happy that dcg3 works fine in line stage duties because this is what I wanted it for. I'm not a headphone fan. The problem with headphones - or with me - is that the soundstage is lockated behind my head and i don't like this. Even with speakers I get confused when in live recordings the audience's clapping comes from behind the musicians
I'll consider your suggestions though!Attachments
If I understand correctly you suggest to ground the negative phase so that balanced output is maintened with SE input. This is the proper way when we deal with a differential amp - LTP - but dcg3 isn't such. Do you think it will work? Anyway I would like to have options for bal in/bal out or SE in/SE out in my system. Should line out be grounded?
Yes. I do it on my BA3 bal pre. You can measure the output from both phases using SE input this way to confirm that you are getting output from each phase. However, I connect RCA signal reference to the PCB not the chassis.
Anyway I would like to have options for bal in/bal out or SE in/SE out in my system. Should line out be grounded?
You can connect the - phase output to the signal reference, or leave it floating or connect it to a resistor to signal reference of the same value as the input resistance in your power amp to simulate a balanced impedance connection, whichever sounds best. I would feel more comfortable with the resistor approach. Or you can combine both phases thru a transformer at the input of your SE power amp.
Yes, it will be using half the build only. Maybe better do that at the input than engaging the "unbal" at the power amp in case some DC transient can short through the output stage and relay. Although there is a 10 Ohm in your build across a lift bridge so not a dead sort. But I don't know, maybe simply doing nothing is still noiseless and sounds exactly the same in your set up. You will have to examine the practicalities because no experience for that config from the rest of us with dcg3.
MagicBus rethinking this I feel I may have confused you a bit with the switch etc.
Basically with a SE input you need to connect the + of the incoming signal to the + phase of the PCB and the incoming signal reference to the - phase of the PCB. Doing this will result in output from both + and - phases. Hope this helps.
nash