I thought about that too but it seems kind of cumbersome to have 2 sets of relays. The relays are only switching ground to turn them on which goes back to my original question. If we can find a way to tie the ground of the 2 boards together, this will work fine. I am confused why this cannot be done.
The Mez uses the center tap as GND and then if I run one secondary to power the remote board and make sure the V+ is the V+ in for the Mez and GND is GND, why would this blow fuses when the relay switches?
Pass DIY Addict
Joined 2000
Paid Member
I would like to find a more elegant solution than having 2 sets of relays, but don't see an easy way with the parts I have. Most of the remote functions come from a large IC on the board, so there isn't much fiddling to do for me. The main IC provides 5v to each of the relays as you cycle through the inputs. The DCB1 only requires continuity to operate each of its relays. I don't know of another method to "just get a closed switch" for the DCB1, so the remote's relays will serve this function. I need to cut the remote relay board to separate the RCA inputs from the relays.
I have been looking at this with a buddy and we think if we power the remote board from the voltage across the 4700uF V+ cap off the bridge on the Mez board, this will work. This then properly ties the GND's of both boards which is all that is needed to switch the relays.
I'll re-wire it this way later today and report back.
BTW, it sounds like you are running the Analog Metric remote setup as well? Does your LCD display work? Mine lights up but just shows the top row as solid white blocks ...
I switched some relays recently on a Mez flawlessly but I did not try wick/braid, I put in use my continuous vacuum desoldering station. 350C and 1mm gun nozzle did alright.
No need to, cheap to get one in USA with free shipping cost
http://www.amazon.com/Aoyue-Digital...433343176&sr=1-1&keywords=desoldering+station
That isn't bad at all! Might be a good investment! When I did tech work for a living, we used the nice PACE equipment. I invested in a PACE ST 25 soldering iron but the desoldering stations are too much (~$600US)
Hakko FR300 is a better tool than that cheap decent enough station, and portable also, it will set you back $250 (but it can be more sensitive bcs compact)
http://www.amazon.com/Hakko-FR300-0...sbs_469_1?ie=UTF8&refRID=1A2DNGCWBE0CP1X19W8Q
http://www.amazon.com/Hakko-FR300-0...sbs_469_1?ie=UTF8&refRID=1A2DNGCWBE0CP1X19W8Q
the switching transistors are usually open collector.
If you can confirm that. then you can switch 12V relays using the 5V controller board.
If you can confirm that. then you can switch 12V relays using the 5V controller board.
I posted the schematic above. The transistors in question are Q5-Q8. They are 8550 PNP low voltage, small signal transistors. It is an odd board as the base is driven directly off the PIC micro with no bias resistors or series gate resistance. Poor design.
where?
post1614?
it shows Q5e to Q8e with open emitter. No good, you would need to add 4 other transistors to provide an open collector.
Last edited:
Yes, that post ... I am confused ... 2 people have told me the circuit will not work but yet it currently powers the remote relay board using these transistors just fine. The problem is it will not power the Mez relays since the GND is not common. When I hit the button to activate a relay, it shorts out the secondary of my power transformer because it creates a loop somehow through my paralleled bi-polar and single-sided bridge rectifiers. If I power the remote board from the bridge of the Mez, I will be able to share a common GND. Other than that, the circuits are identical with the exception of the remote relays being 5V and the Mez relays are 12V. This may be a problem with the junction voltages across the transistor though ... will find out shortly. 😀
Hi.
Having bought my Mezmerise 4 years back, and having left it 80% populated, figured it was about time I got around to finishing it 😉
I have a few basic questions before I order the remaining parts:
1) To get approximately 250mA would a 7R5 5W Mills resistor for the CCS be suitable?
2) Are MUR120 diodes sufficient for the above, or would MUR860 be more prudent?
3) I have a spare 50VA 12+12V transformer, but would I be better off buying a 15+15V one for 250mA Mez?
I'll be mounting it with the mosfets underneath the pcb, using the chassis as the heatsink. It's a Naim 140/Hicap case so should be more than adequate for a slightly hotrodded+ Mez.
Thank you,
John.
Having bought my Mezmerise 4 years back, and having left it 80% populated, figured it was about time I got around to finishing it 😉
I have a few basic questions before I order the remaining parts:
1) To get approximately 250mA would a 7R5 5W Mills resistor for the CCS be suitable?
2) Are MUR120 diodes sufficient for the above, or would MUR860 be more prudent?
3) I have a spare 50VA 12+12V transformer, but would I be better off buying a 15+15V one for 250mA Mez?
I'll be mounting it with the mosfets underneath the pcb, using the chassis as the heatsink. It's a Naim 140/Hicap case so should be more than adequate for a slightly hotrodded+ Mez.
Thank you,
John.
1. Yes
2. MUR860 more reliable of course. But MUR120 if placed upright on a short leg with the other leg going down to the other pad like an inverse U will get sufficiently better ventilation and will be secure enough.
3. 15-0-15VAC is better but if the specific 12-0-12VAC gives 13VAC or more per side on your mains and never below 12VAC when your mains are at their lowest hour, then its still good. Many Tx are stronger than nominal when on UK mains. So test it before spending for a new one.
2. MUR860 more reliable of course. But MUR120 if placed upright on a short leg with the other leg going down to the other pad like an inverse U will get sufficiently better ventilation and will be secure enough.
3. 15-0-15VAC is better but if the specific 12-0-12VAC gives 13VAC or more per side on your mains and never below 12VAC when your mains are at their lowest hour, then its still good. Many Tx are stronger than nominal when on UK mains. So test it before spending for a new one.
Thanks for your help Salas - much appreciated.
Our nominal mains voltage around Hampshire in England is often around 248V, but I'll measure the transformer secondary voltages when under load once the Mez is completed.
Quite strong mains indeed. The test will possibly prove satisfactory. Is it an imported transformer or domestic? I.e. is the Tx primary specified for 230VAC or 240 VAC?
I have three locations for the current setting resistors. Does your PCB have the same?
Insert one resistor leave the leads a bit too long on the bottom side, ready to attach a fourth resistor later. Power up the completed PCB and measure the voltage across the resistor. Calculate the CCS current.
Add a second resistor. re-measure the voltage and calculate the new current.
Add a third resistor.......
Add a fourth resistor......
Add a fifth resistor......
Add a sixth resistor.....
Start with ~ 33r to 27r, 0.6W
check the temperature of the 8A diode after each resistor addition. You may find that after the third to sixth resistor, that you might need to add a clip on heat sink to each of the diodes.
12Vac will work when mains voltage is high, as in during the night when no one is using lot's of power. during high demand the mains voltage and frequency falls and the regulator starts to enter a non CCS phase where performance is not as good. to overcome this you need at least 5Vdc drop across the CCS and preferably >=7Vdc across the CCS when worst voltage conditions exist.
Chassis cooling is OK for a low CCS current. Check the FET temperatures at each stage of adding an extra resistor.
"out of range" matched sets
Matching 2sk170 devices provides many that are outside of the "preferred range"
Are there compromises that result if those closely matched sets are used in the DCB1?
I ask to promote an open discussion. I have hesitated to provide those sets out of fear that an inferior project would result.
Thanks
Matching 2sk170 devices provides many that are outside of the "preferred range"
Are there compromises that result if those closely matched sets are used in the DCB1?
I ask to promote an open discussion. I have hesitated to provide those sets out of fear that an inferior project would result.
Thanks
There is a caution not to use more than 15mA IDSS (extending to grade V territory). Having 10V across each one in the audio path quartet means 150mW dissipation each. Which I consider just about long term reliable. But not that much reassuring, passable. Others would say 200mW is still alright, but I am conservative. The higher the temp the easier they can fail out of the blue sometime. Don't allocate very high IDSS ones where voltage across can be say 15V or 0.6V. Like in the PSU sections. Too much self dissipation, or too high Vgs(off) for the better Vref functioning, or too much current through the error amp BJT effects are possible. Low IDSS BL ones or even GR are good there. Up to medium BL. Non matched is still alright. Relatively batched even better. For the LEDS to match Vf easier since governed by those JFETS currents.
K170 JFETS won't see Ta=25C in a real box with powered up stuff, especially not all around the year, maybe 40C++, so this 400mW at 25C ambient specified JFET device must be well derated when we don't sink it or blow air on it. There is a positive side effect that higher IDSS band BL or lower IDSS band V units provide higher Yfs which translates to bit more circuit linearity. And more current drive for interconnects of course. Below 6mA we cross into GR and alright, can still do the job, but no less Yfs than 30mS would be preferable if possible. Talking about the quartet JFETs.
K170 JFETS won't see Ta=25C in a real box with powered up stuff, especially not all around the year, maybe 40C++, so this 400mW at 25C ambient specified JFET device must be well derated when we don't sink it or blow air on it. There is a positive side effect that higher IDSS band BL or lower IDSS band V units provide higher Yfs which translates to bit more circuit linearity. And more current drive for interconnects of course. Below 6mA we cross into GR and alright, can still do the job, but no less Yfs than 30mS would be preferable if possible. Talking about the quartet JFETs.
Only the PASS B1 jFETs need to be selected for same Idss.
There are two per channel. Try to get all 4 within 0.1mA, but two pairs each within 0.1mA are OK.
All the jFETs and BJTs in the regulator are non critical. You are just trying to get ~+-10Vdc to supply to the B1 section.
There are two per channel. Try to get all 4 within 0.1mA, but two pairs each within 0.1mA are OK.
All the jFETs and BJTs in the regulator are non critical. You are just trying to get ~+-10Vdc to supply to the B1 section.