Link for future reference to yet another nested/composite design using an LM3886 chipamp and an opamp in the outer loop:
http://www.diyaudio.com/forums/chip...mposite-amplifier-achieving-0-0004-thd-n.html
http://www.diyaudio.com/forums/chip...mposite-amplifier-achieving-0-0004-thd-n.html
Siva, I have simulated supplies with PSUD. I get better performance with a standard crc that has an additional small cap with higher ESR. Maybe the program is not correct. I read a paper recently extolling the virtues of a tantalum of 4.7u parallel to a low esr .1u ceramic. The high esr of the tantalum was an advantage. You use a .018 resistor in series with your cap to ground. Whats the reasoning?
I havr hundreds of the TDA equivalent of the lm1875. I would guess you tried it in this circuit. Could you audibly discern a difference?
Uriah
I havr hundreds of the TDA equivalent of the lm1875. I would guess you tried it in this circuit. Could you audibly discern a difference?
Uriah
Sorry, I didn't mark that 18 mohm resistance clearly - it is indeed the nominal ESR of a Rubycon ZL or ZLH cap, IIRC.
The last time I looked at small tantalums, I found that they weren't very linear (i.e. tan delta was all over the map, and fairly high in most cases). Sanyo Oscons and Panasonic SVP may be slightly better. There's also the Philips solid aluminium caps. In short, I don't know the best choice for audible sonics, but I believe you're correct that *higher* ESR up to a point is better for sonics and stability. Some very conventional electrolytics actually sound pretty good in bypass applications - Rubycon YXA, YXG, Nichicon UD. The last has remarkable measured tan (delta), as low or better than some Rubycon Black Gates. It's SMD, but you can straighten the leads and use it as a through-hole component.
Regarding the TDA20x0, I have a few but haven't yet tried them out - they should work as drop-in replacements. Also interesting is TDA7265, which is a dual 25W in a multiwatt 11-pin package (like the LM3886, but stereo). My local ST dealer has *lower* prices on the TDA7265, compared to the TDA2050 - the latter has been EOLed by ST, but still has demand from existing designs that use Pentawatt chipamps, so prices are rising as people hoard the stuff.
Edit: There should not be a significant audible difference between the TDA2050 and LM1875 in this topology - the sonics are mostly contributed by the outer-loop small-signal opamp and outer-loop passives, as well as the input filter, etc.
The last time I looked at small tantalums, I found that they weren't very linear (i.e. tan delta was all over the map, and fairly high in most cases). Sanyo Oscons and Panasonic SVP may be slightly better. There's also the Philips solid aluminium caps. In short, I don't know the best choice for audible sonics, but I believe you're correct that *higher* ESR up to a point is better for sonics and stability. Some very conventional electrolytics actually sound pretty good in bypass applications - Rubycon YXA, YXG, Nichicon UD. The last has remarkable measured tan (delta), as low or better than some Rubycon Black Gates. It's SMD, but you can straighten the leads and use it as a through-hole component.
Regarding the TDA20x0, I have a few but haven't yet tried them out - they should work as drop-in replacements. Also interesting is TDA7265, which is a dual 25W in a multiwatt 11-pin package (like the LM3886, but stereo). My local ST dealer has *lower* prices on the TDA7265, compared to the TDA2050 - the latter has been EOLed by ST, but still has demand from existing designs that use Pentawatt chipamps, so prices are rising as people hoard the stuff.
Edit: There should not be a significant audible difference between the TDA2050 and LM1875 in this topology - the sonics are mostly contributed by the outer-loop small-signal opamp and outer-loop passives, as well as the input filter, etc.
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Uriah, I now have a MiniRef working fine with ST TDA2050 chipamps. This is the latest schematic and layout revision (v1.04), and includes a series-shunt regulator upgrade (basically borrowed from Dario's MyRef FE, but entirely through-hole) and a few other minor build upgrades to passive components.
It's Apples vs. Oranges, but my preliminary impression is that this particular MiniRef prototype with TDA2050s sounds even better than the previous one with LM1875s. I'll give an update later with pics and audible impressions, after I listen to some more tracks.
OK, here's a pic of the prototype MiniRef v1.04 with TDA2050 chipamps (it can also interchangeably use LM1875 chipamps):
The main upgrades are the improved series-shunt regulator for the opamp, and an inductor AC-decoupled small-signal ground. The BoM is otherwise nearly identical to the previous versions.
An externally hosted image should be here but it was not working when we last tested it.
The main upgrades are the improved series-shunt regulator for the opamp, and an inductor AC-decoupled small-signal ground. The BoM is otherwise nearly identical to the previous versions.
Attachments
I haven't taken the decision on uploading the full schematic here. However, as a broad hint, it's basically the same as the published v1.02 schematic, with the addition of the series-shunt regulator from the MyRef FE, for the op-amp rails. Other changes are minor.
TL072 (dual) will work without any changes - practically any moderately slow opamp will work in the outer loop. Some relatively fast opamps (LT1361, etc.) also happen to work.
Is this a turn-on pop? It depends a bit on the opamp that you use in the outer loop also - you may want to try a generic slow opamp like an NE5532 or TL072 to check if the turn-on pop persists.
If it still persists, post the values of the relay driver components here, and I'll see if it can be changed to delay the startup.
Hi
I think there might be some further upgradation in the passive components which need be to evaluate also and/or may be he has not yet received those components. This could be the reason for the delay.
Regards
Suman
A couple of upgrades to passives in the premium kit:
1) Main PSU filter caps C3, C8 etc.: Upgraded to Elna RW5 4700uF/25V. It has more air and definition compared to the earlier defaults at this location. Some Japanese blogs have suggested using a 0.1uF/50V Panasonic ECHU to bypass these in PSU filter applications, but I'm skipping that and going with the pure, unbypassed form, a la Mauro.
(Elna has shamelessly copied the colour and visual design of the Rubycon BG Standard for these caps - Gold markings on Black, with chevrons on the gold band denoting the -ve terminal. Text is aligned to be read in the longitudinal direction. There is no series designation, just CE and 105c marked in text. This is one of those rare audio-grade caps that is rated for 105c - leads are ferromagnetic, like Rubycon ZL and Panasonic FM, but it's good to have an affordable, compact-sized alternative to both of those that measures and sounds better.)
2) Input series resistors (R12, R62) upgraded to Welwyn W21, 4.5k/3W. It appears not to have a significant effect on sonics compared to the Dale non-magnetic RNC50 or similar at that location. The W21 has magnetic leads and non-magnetic body, so I'll take a call on whether to replace the Dales in the kit after listening a bit more.
(Pending kit shipments will definitely receive the first upgrade).
1) Main PSU filter caps C3, C8 etc.: Upgraded to Elna RW5 4700uF/25V. It has more air and definition compared to the earlier defaults at this location. Some Japanese blogs have suggested using a 0.1uF/50V Panasonic ECHU to bypass these in PSU filter applications, but I'm skipping that and going with the pure, unbypassed form, a la Mauro.
(Elna has shamelessly copied the colour and visual design of the Rubycon BG Standard for these caps - Gold markings on Black, with chevrons on the gold band denoting the -ve terminal. Text is aligned to be read in the longitudinal direction. There is no series designation, just CE and 105c marked in text. This is one of those rare audio-grade caps that is rated for 105c - leads are ferromagnetic, like Rubycon ZL and Panasonic FM, but it's good to have an affordable, compact-sized alternative to both of those that measures and sounds better.)
2) Input series resistors (R12, R62) upgraded to Welwyn W21, 4.5k/3W. It appears not to have a significant effect on sonics compared to the Dale non-magnetic RNC50 or similar at that location. The W21 has magnetic leads and non-magnetic body, so I'll take a call on whether to replace the Dales in the kit after listening a bit more.
(Pending kit shipments will definitely receive the first upgrade).