my DACs opamps are getting pretty hot, is this normal?
i have connected pin 14 of CS8416 with pin 10 of PCM1798 but the device doesn't mute at all. the voltage is 0v when applying a correct audio stream and 3.3V when no audio is present. what am i missing? Vih at PCM1798 is 2V.
my mods so far:
sorry for posting 3 times...
regards,
oliver
i have connected pin 14 of CS8416 with pin 10 of PCM1798 but the device doesn't mute at all. the voltage is 0v when applying a correct audio stream and 3.3V when no audio is present. what am i missing? Vih at PCM1798 is 2V.
my mods so far:
- replaced the opamps by LME49720
- replaced the differential section as shown in the datasheet of PCM1798 (i use 180 ohms instead of the 200, 8000pF (4700//3300) instead of 8200pF and 26700pF (4700//22000) instead of 27000pF
- removed CD4053
- added 100 ohm series resistors instead of just shorting the inputs of CD4053 to the corresponding outputs
sorry for posting 3 times...
regards,
oliver
Hi,
Gigawork does not ship in Italy, but I think here the same boards are sold:
CS8416 + PCM1798 24bit/192khz DAC KIT / DIY su eBay.it Other, Home Audio, Electronics
The boards are sold without transformer. Please can you address me to a good transformer for this DAC (on Mouser or RS for instance)?
Thank you
Renato
Gigawork does not ship in Italy, but I think here the same boards are sold:
CS8416 + PCM1798 24bit/192khz DAC KIT / DIY su eBay.it Other, Home Audio, Electronics
The boards are sold without transformer. Please can you address me to a good transformer for this DAC (on Mouser or RS for instance)?
Thank you
Renato
the transformer shipped with the DAC is rated 10VA with 2x12V outputs.
however, both transformers that i received from gigawork emitted some noise (you can hear it, even without the DAC connected).
some rs-components part numbers:
the cheaper one:
347-2616
a toroidal one (should have a smaller magnetic field (can be placed closer to the DAC) and i think toroidal are less prone to emit noise):
223-9272
regards,
oliver
however, both transformers that i received from gigawork emitted some noise (you can hear it, even without the DAC connected).
some rs-components part numbers:
the cheaper one:
347-2616
a toroidal one (should have a smaller magnetic field (can be placed closer to the DAC) and i think toroidal are less prone to emit noise):
223-9272
regards,
oliver
Highfieldrebel:
Your doing (did?) what I want to do.
Unfortuneately for me, Lukas on his Lampucera site doesn't, for me, explain well enough what to do for a I out dac.
Do you do anything else to add the tube output, other than removing the op amp, and taking the output from the opamp socket?
No more resistors, caps, or transformers?
Thanks,
Paul
Your doing (did?) what I want to do.
Unfortuneately for me, Lukas on his Lampucera site doesn't, for me, explain well enough what to do for a I out dac.
Do you do anything else to add the tube output, other than removing the op amp, and taking the output from the opamp socket?
No more resistors, caps, or transformers?
Thanks,
Paul
Hi Paul, it's nearly as simple as that. Here's a site where the author has been a little neater in his schematic than Lampizator.
The Lampizator Experience
Essentially, you use a low value resistor (I used 100 ohms, this is marked * on the link) to convert the current output to a voltage: this voltage then controls the current flow through the SRPP.
All I did was pull out the 3 op-amps, stuck a wire into the vacant hole in the op-amp socket that ran to the 100 ohm resistor (one each channel, obviously). The SRPP then works as standard.
The current out DAC is balanced, to be correct I guess you should use the same polarity for both channels. I don't have the schematic to hand, there was some asymmetry in the op-amp wiring, I ended up using socket 2 for the left channel and socket 6 for the right channel. If this is unclear let me know and I'll reply with reference to the schematic.
The wire I used from the op-amp sockets was solid core so it jammed in nice and solid, if all you have is multicore you could solder it. A nice thing about not soldering is that you can reverse it and put back in the op-amps if you liked. Or maybe you could solder onto the bottom of the board, not sure if the op-amp socket pins go through or not.
One (maybe) issue is I gave nowhere to go for the other half of the current from the DAC. Would this make it upset? Should I have given it a path to ground as well? Where is the emoticon for shrugging my shoulders?
The Lampizator Experience
Essentially, you use a low value resistor (I used 100 ohms, this is marked * on the link) to convert the current output to a voltage: this voltage then controls the current flow through the SRPP.
All I did was pull out the 3 op-amps, stuck a wire into the vacant hole in the op-amp socket that ran to the 100 ohm resistor (one each channel, obviously). The SRPP then works as standard.
The current out DAC is balanced, to be correct I guess you should use the same polarity for both channels. I don't have the schematic to hand, there was some asymmetry in the op-amp wiring, I ended up using socket 2 for the left channel and socket 6 for the right channel. If this is unclear let me know and I'll reply with reference to the schematic.
The wire I used from the op-amp sockets was solid core so it jammed in nice and solid, if all you have is multicore you could solder it. A nice thing about not soldering is that you can reverse it and put back in the op-amps if you liked. Or maybe you could solder onto the bottom of the board, not sure if the op-amp socket pins go through or not.
One (maybe) issue is I gave nowhere to go for the other half of the current from the DAC. Would this make it upset? Should I have given it a path to ground as well? Where is the emoticon for shrugging my shoulders?
all clear except the picture I was looking at has one AD827
I see on the gigaworks picture that there are three op amps.
Pull all three, install the wires to the lampizator into the holes for the opamp closest to the DAC?
I'm at the fact gathering stage, and just about convinced I can do this, so will now order my board.
Thanks again,
Paul
I see on the gigaworks picture that there are three op amps.
Pull all three, install the wires to the lampizator into the holes for the opamp closest to the DAC?
I'm at the fact gathering stage, and just about convinced I can do this, so will now order my board.
Thanks again,
Paul
Attachments
Hi Paul, that's right, the two op-amps closest to the DAC. You should take a look at the schematic, the output stage is pretty straightforward if you're even a small bit familiar with op-amps. BTW I do not recommend removing the capacitors unless you're delicate of touch, the traces seem to be attached with angel kisses or similar. I don't think I'm particularly hamfisted, but it didn't take me long to despatch the DAC to IC heaven/valhalla/elysian fields.
I've done the same on my board, it is a only one small difference R15 and R18 is 1k5. It raises the gain of output stage from 1 to 1.5 (3,5dB) but also raises the DC offset on the output up to 0,7V (when not muted). I'll try to change R15 and R18 to 1k and measure again.
Hi pforeman
if you don't try to have the heater and B+ from the same transformer it's easier. Get a 12V DC power supply for the heaters, depending on the tubes you use they will be in series or parallel, probably cost $10.
For B+, the VA requirement at least is easy. About .01A at about 200V is only 2W. So let's say 20VA as a nice round number. The voltage is a little more awkward, you're in a 110V area I take it. A 1:1 isolation transformer, rectified gives about 150V, filter it with C-R-C and you have 130V left, should be in the right ballpark.
I tend to use scrap transformers from dead pieces of equipment, if the design I was following needed higher than this, I'd look for two transformers to use, one 18V on the secondary and the other 15V on the secondary. Connect the two secondaries, one primary connected to mains, the other primary being sent for rectification. In this example, mains -- 18V secondary -- 15V secondary -- 110*18/15 = 132V AC. Rectified, 184V before accounting for diode and filtering losses, but 170V should be fine. There is some software called PSUD that will help you check.
If you buy the transformers new, each transformer wouldn't be too expensive, digikey has them for 10$ to 15$ each.
if you don't try to have the heater and B+ from the same transformer it's easier. Get a 12V DC power supply for the heaters, depending on the tubes you use they will be in series or parallel, probably cost $10.
For B+, the VA requirement at least is easy. About .01A at about 200V is only 2W. So let's say 20VA as a nice round number. The voltage is a little more awkward, you're in a 110V area I take it. A 1:1 isolation transformer, rectified gives about 150V, filter it with C-R-C and you have 130V left, should be in the right ballpark.
I tend to use scrap transformers from dead pieces of equipment, if the design I was following needed higher than this, I'd look for two transformers to use, one 18V on the secondary and the other 15V on the secondary. Connect the two secondaries, one primary connected to mains, the other primary being sent for rectification. In this example, mains -- 18V secondary -- 15V secondary -- 110*18/15 = 132V AC. Rectified, 184V before accounting for diode and filtering losses, but 170V should be fine. There is some software called PSUD that will help you check.
If you buy the transformers new, each transformer wouldn't be too expensive, digikey has them for 10$ to 15$ each.
Is it Edcor model XPWR094-120? This will easily do the job for this project, and because it's overspec'd you could reuse it later for another project, even small power tubes. For the B+, rectify, CRC filter and size the R so you hit the voltage you want. Because you're placing such a small load on the transformer, it probably will be higher than 170 VAC on the secondary, at a guess 180 VAC, this will rectify to ~250 VDC. If the SRPPs need 5 mA each, and you're looking for 180 VDC, then the filter resistor will be (70V/.01A)=7kOhm. You'll need to try it out to find the correct resistor value. Power in the example above would be 7x10^3X(.01^2)=.7W, so either a large resistor or several smaller ones. Also, you'll need filter capacitors that can handle the 250V.
For the heater winding, it only gets a little complicated if either the Shigaclone or the heaters need 12 VDC. Many builders wouldn't use AC heating for a preamp or DAC. Then the 12 VAC (probably more like 13 VAC because of the small loading) becomes about 17 VDC. So we need to drop the voltage somehow. The tube heaters will need about 350 mA, I don't know what a Shigaclone needs, let's say it's 150 mA at 12 VDC. Total current 0.5 A, 5 V drop, power dissipated 2.5W, not too bad. If I use the R in the CRC filter for this, a problem could occur is the Shigaclone is off. The draw drops to 370 mA, the heater voltage is now 13.3 VDC. That might be bad, so you could use a diode string to drop the voltage independent of load, it's a lot of diodes though! Another fix is to use the one 12 VAC secondary to feed two separate rectification and CRC filtering stages.
For the heater winding, it only gets a little complicated if either the Shigaclone or the heaters need 12 VDC. Many builders wouldn't use AC heating for a preamp or DAC. Then the 12 VAC (probably more like 13 VAC because of the small loading) becomes about 17 VDC. So we need to drop the voltage somehow. The tube heaters will need about 350 mA, I don't know what a Shigaclone needs, let's say it's 150 mA at 12 VDC. Total current 0.5 A, 5 V drop, power dissipated 2.5W, not too bad. If I use the R in the CRC filter for this, a problem could occur is the Shigaclone is off. The draw drops to 370 mA, the heater voltage is now 13.3 VDC. That might be bad, so you could use a diode string to drop the voltage independent of load, it's a lot of diodes though! Another fix is to use the one 12 VAC secondary to feed two separate rectification and CRC filtering stages.
yes thats the tranny I was looking at.
and yes, i planned to have an all in one unit with one on/off switch
yes, I thought parallel feeds off of the 12V. One to the shigaclone one to the heaters, each independantly rectified.
The cost of this one transformer will be about the same as all the others, and I thought it might not be a good idea to have all those various transformers together?
Thanks again
Paul
and yes, i planned to have an all in one unit with one on/off switch
yes, I thought parallel feeds off of the 12V. One to the shigaclone one to the heaters, each independantly rectified.
The cost of this one transformer will be about the same as all the others, and I thought it might not be a good idea to have all those various transformers together?
Thanks again
Paul
V out better
I didn't bother to pursue the 1798 chip to try to get rid of the hum. I find that a V out dac chip such as CS4397 or AK4395 running direct offers better transparency.
I didn't bother to pursue the 1798 chip to try to get rid of the hum. I find that a V out dac chip such as CS4397 or AK4395 running direct offers better transparency.
I changed 7812 and 7912 for 7815 and 7915.
Better +-15 V. than +-12 V with 820 original resistor I / V .
Best option R27, R28, R29 and R30: 300 Oh. (470 / / 820 Oh. Vol. OK for + -12 V.).
300 Oh. resistor +-15 V. similar to + -12 V. but hot temperature , +-15 V. is no a good idea.
I tried several OPA: AD827, OPA2134, OPA2604, AD 8620, AD825, Burson,
2x OPA2134 1xAD825 better measure, all very similar except OPA AD827 is bad, came from China with the DAC Gigawork
Maybe it original?
Better +-15 V. than +-12 V with 820 original resistor I / V .
Best option R27, R28, R29 and R30: 300 Oh. (470 / / 820 Oh. Vol. OK for + -12 V.).
300 Oh. resistor +-15 V. similar to + -12 V. but hot temperature , +-15 V. is no a good idea.
I tried several OPA: AD827, OPA2134, OPA2604, AD 8620, AD825, Burson,
2x OPA2134 1xAD825 better measure, all very similar except OPA AD827 is bad, came from China with the DAC Gigawork
Maybe it original?
Last edited:
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