When they are on opposite sides of the PCB, the PCB material will provide the isolation.
Yes arjen6t8, I take PCB isolation for granted. 🙂
But can there still be an iteration between AC lines crossing each other, as happens when the insulator is air?
(...with reference to the minimum distance of 5 mm suggested).
In any case, it seems to me that this latest version meets the requirements.
Am I wrong?
But can there still be an iteration between AC lines crossing each other, as happens when the insulator is air?
(...with reference to the minimum distance of 5 mm suggested).
In any case, it seems to me that this latest version meets the requirements.
Am I wrong?
hi ansible, do you think a R input selector ( like input C selector) could be useful? ( since the cartridges on the market required definited RC loads) ...and a question:why pin 12,13 of transf are shorted?what is the reason? un saluto to everyone Ros
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Hi Masca64,
I didn't think about changing the input load because 47K ohms is a standard value for Phono preamps, but on page 5, in posts #81 and #83, stocktrader200 talks about specific load adjustments for some cartridges.
Unfortunately I don't know enough about it, but you could ask MarcelvdG, the designer of the circuit with OPA1656 and high pass filter, or Nick Sukhov, for the version with OPA2192.
But you could also take a look at this post:
It's not excluded that they have explored this aspect in depth.
About your second question, thank you.
The answer is that for this particular use (dual power supply), the secondaries are placed in series, with the central connection (pins 12 and 13 joined) becoming the GND line. But it is certainly better to keep the possibility of connecting the secondaries in parallel, as well as in series.
I therefore modified the schematic and PCB in this direction.
(Hoping it is the final one...)
Talema 25VA Encapsulated Transformer, interface board.
Revision 0.3
I didn't think about changing the input load because 47K ohms is a standard value for Phono preamps, but on page 5, in posts #81 and #83, stocktrader200 talks about specific load adjustments for some cartridges.
Unfortunately I don't know enough about it, but you could ask MarcelvdG, the designer of the circuit with OPA1656 and high pass filter, or Nick Sukhov, for the version with OPA2192.
But you could also take a look at this post:
About your second question, thank you.
The answer is that for this particular use (dual power supply), the secondaries are placed in series, with the central connection (pins 12 and 13 joined) becoming the GND line. But it is certainly better to keep the possibility of connecting the secondaries in parallel, as well as in series.
I therefore modified the schematic and PCB in this direction.
(Hoping it is the final one...)
Talema 25VA Encapsulated Transformer, interface board.
Revision 0.3
hi Ansible, good morning to everyone... I agree with you about 47k pre load (more or less), but what you are designing is a pre riaa; so there are some cartidges specifications to consider (at least the common used cartridges); I bought an AT-VM95E, reading specs it requires 47k//100-200pF load; another cartridge example ART1000 requires a 30ohm load (no capacitance): as you see the best way to design a RIAA pre, could be designing a selectable input stage R//C with 2 or 3 values 'standard' BEFORE the op amp (for example I designed my riaa equalizer with R selectable 1k, 10k, 47k and C 47pF, 100pF, 220pF so on...) In this way I've made my preamp a little more universal; It might be worth taking some time to think about this.
🙂 About transformer: in the circuit you've designed amp op with dual power supply, right? If so, it's ok transformer with double secondaries, but you do not have to connect them together, but leave them electrically separate and connect each at own rectifier bridge: after each rectifier bridge you can connect together the two GND (of the positive rail and of the negative rail, as in all dual power supplies with common ground) . Sorry for this, I understand the whole work you're doing... take the above as a suggestion added to the great suggestions you've already been given from everyone 🙂 regards e buon lavoro!
🙂 About transformer: in the circuit you've designed amp op with dual power supply, right? If so, it's ok transformer with double secondaries, but you do not have to connect them together, but leave them electrically separate and connect each at own rectifier bridge: after each rectifier bridge you can connect together the two GND (of the positive rail and of the negative rail, as in all dual power supplies with common ground) . Sorry for this, I understand the whole work you're doing... take the above as a suggestion added to the great suggestions you've already been given from everyone 🙂 regards e buon lavoro!
good evening to everyone, dear Marcel, yes, we know that a mc is less sensitive than a mm cartridge...and yes, we know therefore that the pre stage should have more gain. The concept I expressed to Ansible, is perhaps thinking of an input stage circuit with selectable load, undoubtedly makes the circuit a little more elaborate but at the end it could be an added value to the design 🙂 ...un saluto to everyone. Ros
So just wondering about the direction of this thread? Is the intent to have gerbers available for people to use or maybe board purchases? I would be interested
According to its datasheet, an OPA1656 draws typically 3.9 mA, maximally 5 mA of quiescent current per channel, so that's 7.8 mA and 10 mA, respectively, for both channels together. With signal, it may be a milliampere or two more, depending on the signal level and load impedance. If you use the preamplifier continuously, day and night, you may have to recharge the batteries every three weeks.
If there is any chance that you connect the batteries with the wrong polarity, add some series diodes to prevent the OPA1656 from going up in smoke.
If there is any chance that you connect the batteries with the wrong polarity, add some series diodes to prevent the OPA1656 from going up in smoke.
You could consider a smaller transformer if it's only to feed the RIAA amp. I am using a 10 VA Talema toroid for my build, and I'm feeding the record table motor from it too.
Hi Freecrowder,
The direction of this thread is still the one expressed on the first page.
Build a fairly simple Pre RIAA stage (for personal use), starting from the circuit published by TI for the OPA1656.
During the discussion, two alternative versions emerged that were more interesting than the one initially proposed by me, the version by MarcelvdG with OPA1656 and high pass filter, and the more minimalist one with OPA2192, suggested by Nick Sukhov.
I therefore thought of enhancing them through a (I hope) good PCB and a particularly careful selection of SMT components.
I am still waiting for the last component ordered which should arrive in a few days, then I will print the first prototypes, I suppose in the minimum quantity allowed (5 pcs.), I am still evaluating it.
It will be outrageously expensive, even considering the fixed cost of 3 dollars for each SMT component value, for which the reel must be loaded manually (this is the case for components that belong to the extended library, so almost all of them), but I will go all the way anyway, also to give a sense to all the time spent on preparation.
The next step will be to equip them with a metal case and then move on to testing.
I assume that the two PCBs are well made, but I will be sure only after trying them.
But of course I can only decide for what I make myself.
For these two circuits I only made the PCB and chose the components, so it is a work in cooperation with the designers (and with all those who intervened with useful suggestions). Marcel and Nick have authorized me to reproduce their circuit, but there is no talk of reproduction or sale, for now.
I will have to talk to them first.
For the same reason I will not publish the Gerber or project files of these two Pre stages.
Once tested, I may be willing to put together a shopping list for those who request it, assuming Marcel and Nick are okay with it.
I'll update you on this, when I have more information.
The direction of this thread is still the one expressed on the first page.
Build a fairly simple Pre RIAA stage (for personal use), starting from the circuit published by TI for the OPA1656.
During the discussion, two alternative versions emerged that were more interesting than the one initially proposed by me, the version by MarcelvdG with OPA1656 and high pass filter, and the more minimalist one with OPA2192, suggested by Nick Sukhov.
I therefore thought of enhancing them through a (I hope) good PCB and a particularly careful selection of SMT components.
I am still waiting for the last component ordered which should arrive in a few days, then I will print the first prototypes, I suppose in the minimum quantity allowed (5 pcs.), I am still evaluating it.
It will be outrageously expensive, even considering the fixed cost of 3 dollars for each SMT component value, for which the reel must be loaded manually (this is the case for components that belong to the extended library, so almost all of them), but I will go all the way anyway, also to give a sense to all the time spent on preparation.
The next step will be to equip them with a metal case and then move on to testing.
I assume that the two PCBs are well made, but I will be sure only after trying them.
But of course I can only decide for what I make myself.
For these two circuits I only made the PCB and chose the components, so it is a work in cooperation with the designers (and with all those who intervened with useful suggestions). Marcel and Nick have authorized me to reproduce their circuit, but there is no talk of reproduction or sale, for now.
I will have to talk to them first.
For the same reason I will not publish the Gerber or project files of these two Pre stages.
Once tested, I may be willing to put together a shopping list for those who request it, assuming Marcel and Nick are okay with it.
I'll update you on this, when I have more information.
Talema 15VA and 25VA Encapsulated Transformer, interface board.
Gerber file, Revision 0.3
Gerber file, Revision 0.3
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Hi arjen6t8,
I just now realize that this pcb is also compatible with the Talema 15VA version (same size as the 25VA).
The 10VA is slightly smaller (55x55mm.), but it would not be difficult to modify the schematic for that size.
Would it be useful to have it?
(In the case of simple pcbs without components, the cost for 5 pieces is usually really low, around 5 euros including shipping)
If you are not in a hurry, I could prepare it.
I just now realize that this pcb is also compatible with the Talema 15VA version (same size as the 25VA).
The 10VA is slightly smaller (55x55mm.), but it would not be difficult to modify the schematic for that size.
Would it be useful to have it?
(In the case of simple pcbs without components, the cost for 5 pieces is usually really low, around 5 euros including shipping)
If you are not in a hurry, I could prepare it.
I bought the 10 VA version for size. The larger one(s) do not fit in my turntable. I would be much obliged if you want to design a 10 VA version PCB.
Ok arjen6t8,
Give me a couple of days.
The good work you are doing with your turntable is worth a little effort. 😉
Give me a couple of days.
The good work you are doing with your turntable is worth a little effort. 😉