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Hi,
I have a Monica II DAC that can be powered with a 6V battery. I want to build a DAC without an output stage that I want to plug directly into my preamp thus making the preamp an output stage. The Monica II does that but I think, unless I am wrong, it is old technology. Is there anything new and current I should be looking at?
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I would look at the Chamelion on ebay or the Metrum Octave. Both NOS.
Hi,
For pretty much any DAC Chip you can replace Analogue stages with a transformer. The precise transformer needed depends on the DAC.
Very few DAC's allow direct connections from the DAC chip. Most require at the very least some coupling device (Capacitor/Transformer) and low-pass filter.
The ones that do not require any filter/usually do not because they include build-in Op-Amp's and in many cases a small switched mode power supply to generate a negative voltage (examples ES9023, PCM510X, various others from Cirrus Logic, AKM and Wolfson Micro also fall into this group. For an antique CS4328 is also in this group but needs an external negative voltage (not generated on-chip).
Despite using "old tech" I doubt that for CD Playback much exists out there that will be much better than the TDA1545 on your DAC, presuming it is correctly set up, ignoring cost.
Ciao T
At 20 bits, you are on the verge of dynamic range covering fly-farts-at-20-feet to untolerable pain. Really, what more could we need?
Thorsten,
Thanks for the response as you always do for me.
My friend sent me the Monica II DAC board and all it needs is a 12V DC source. It has a soldering pad for the digital IC from the transport and it goes directly to outputs(L/R) then off to wherever(another analogue stage or direct to a preamp). He says it has 1V output so the gain is on the low side. In looking at it there is not transformers of any kind.
It seems easy enough to put together in some kind of chassis.
I was more or less looking at this as a small project and I liked the act that you can probably build and output stage of your own or just go direct into a preamp of choice and see how it sounds.
When he had it he built a 12B4 output for it.
Hi,
The Monica DAC uses the TDA1545 DAC. To my ears this is a great sounding DAC chip for CD Standard Audio. The Digital receiver for the Monica is not the best by todays standards and the actual implementation in the Monica/Monica2 DAC could use improved decoupling (SMD Capacitors directly on chip pins).
Yes, you can run the audio directly from the chip, but there is DC offset, so you need a coupling Cap.
There is commercial DAC using a "kissing cousin" of the TDA1545, the TDA1543 and Duelund coupling Cap's. According to some this unit is the dogs danglies... According to the same people other DAC's with lesser coupling Cap's, even using the same chip are not good...
For a 12V Supply I would probably get a surplus SLC (Sealed Lead Calcium) Battery at a few Ampere hours rating and suitable charger hard to beat for simplicity and performance at the cost.
Ciao T
At 20 bits, you are on the verge of dynamic range covering fly-farts-at-20-feet to untolerable pain. Really, what more could we need?
I was told that the output of this DAC can go directly into a preamp. Take a look and you tell me. That was supposed the whole idea of this DAC board. You were supposed to just hook it to a battery and do a little bit of wiring and off to the races. I just wanted to build a power supply for it just to never worry about a battery charge.
I am getting to think that his project should maybe not happen but I have the DAC board ready to go so I figured what the heck!
What pins would you do the extra decoupling?
Here is the schematic:
Hi,
The DAC output will have around 2.5 to 3V DC on it. I would not recommend to connect this directly.
If using a 100K Volume control I would recommend at least 0.22uF coupling cap's between DAC and Volume control.
Incidentally, I should mention that I dug out the original French scheme from l'Audiophile of the ciruit in the Monica and suggested replacing the original Batteries used (1.5V * 3) with a diode string and CCS, as shown in the schematic, that was around the turn of the century on a Gainclone board IIRC...
Bottom line, I think you and your tubes will be happier with a coupling cap.
Ciao T
At 20 bits, you are on the verge of dynamic range covering fly-farts-at-20-feet to untolerable pain. Really, what more could we need?
Thorsten,
Again, thanks form your time and response.
The consensus seems the be to use a coupling cap so I will. Now! Would there be any benefit to using I/V transformers. Someone said there is enough gain using the resistors supplied for the I/V conversion. Or maybe this DAC isn't worth the expense. I just like playing but I need a reason.
I was going to build a 12VDC supply or just buy one already assembled in place of using a 12V battery. I know using a battery is pure DC but I don't like extra maintenance(making sure of a charge is always there). Thoughts? And believe me Thorsten, I do listen to and trust your judgment.
Hi,
> Now! Would there be any benefit to using I/V transformers.
There is no such thing as an I/V transformer.
> Someone said there is enough gain using the resistors supplied
> for the I/V conversion.
If I remember right (it has been a while), the output is around 0.7V for "digital full scale", substantially lower than common DAC's and/or CD-Players.
> Or maybe this DAC isn't worth the expense.
It can be quite good.
> I was going to build a 12VDC supply or just buy one already
> assembled in place of using a 12V battery.
Depending on the quality of this supply this may or may not work well.
A batter does give a known behaviour. If you have a battery rated at 6AH/12V you can run this DAC around 100 Hours with a Battery that is in top condition. Even one that is in a very bad state can do two days straight. The typical surplus jobs pulled out of fire alarm systems because of laws and regular maintenance I used to get where usually still worth > 80% capacity and cheap.
Make the Power switch so that when the DAC is off the battery is linked to the charger (one that trickle charges a full battery) and remember to turn the DAC off when not listening and I doubt you will even notice the battery.
Ciao T
At 20 bits, you are on the verge of dynamic range covering fly-farts-at-20-feet to untolerable pain. Really, what more could we need?
Thorsten,
I thought these were I/V transformers.
Hi,
> I thought these were I/V transformers.
If someone claims they are - they need to (re)take EE101.
Transformers are physically incapable of converting current to voltage.
They can only change the ratio between impedances/voltage/current.
The current to voltage conversion is still done in a resistor.
Generally I find it preferrable to keep transformers to a sensible minimum in a chain.
As with all things - great if applied in moderation - problems if overdone.
Ciao T
At 20 bits, you are on the verge of dynamic range covering fly-farts-at-20-feet to untolerable pain. Really, what more could we need?
Search for 'AD1955 DAC review'.
I have the S.M.S.L. DAC and it appears to be very competent.
It would be nice to get a list of suitable DACs.
I hear the Wolfson's or Sabre?? DACs are good, but others say they are way too expensive for what you get, implying that it is a DAC with a lot of bells and whistles that may of no additional interest or value.
I have been using this dac with my senn 650's and a hybrid tube amp, also connects to a HarmanKardon avr 510, using these with my pc rca out.
The Metrum dacs use parallel chips and take the output right off the chip. No analog output stage. They are NOS dacs. The Hex is great
Alan
That is how the Monica II is but I was considering another DAC board because it is old technology. It will probably still sound good. I just wanted to get other ideas if there are any.
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