I have those so I should be good
To raise the output impedance I increase the output resistors correct?
I have the latest Placid HD BP. But, I have the older 30 VA transformer. Should I up it to the 50 VA?
I think R24 is wrong. The feedback cap should be placed across R22 Left and R23 Right Am I correct?
Yes - 100-221R can make a subtle difference. Some will prefer to use 0R. The effect will depend largely on the load (cables and amp etc).
30VA is certainly sufficient, but 50VA will give very slightly less ripple at the reservoir caps.
I would say less so with the new Placids, and they have significantly improved PSRR over the previous version - still it is difficult to say what people will find audible.
Another user here posted that when using a pair of LME49990 in the BAL/SE stage that they will oscillate. He says to use 100-220pf styroflex or silver mica cap for feedback compensation when you use lme49990. When looking at the schematic I should place them across R22 Left 2.2K ohms and R23 Right 2.2K Ohms am I correct?
He states a different number for the right side so I just want to be sure that was an error. Can someone confirm?
He states a different number for the right side so I just want to be sure that was an error. Can someone confirm?
Correct. MKP ( roe...ero1830 Blue color) can be used if finding styroflex or mica is difficult
And R25 and R26 was 50ohm because i used only se output.
And R25 and R26 was 50ohm because i used only se output.
Last edited:
Thanks... I got most of the parts yesterday. I just have to place a digikey order
Just to update this thread
I used PRP resistors throughout
I used Vishay Roderstein .1uF film caps for the supply decoupling
I paralleled two Amtrans 8.2 nF film/foil polypro caps for the analog filters
Used two LME49990 op amps on a brown dog adapter and added a feedback compensation cap for each channel (value and type mentioned earlier) in place of IC5 (LM4562)
I used Nichicon Muse caps for the electrolytics
You'll need longer pin headers (Digikey SAM1061-06-ND) and standoffs (Digikey 36-8404-ND) to clear the brown dog adapter and electrolytics.
My first impression once installed was not the best. The highs were great and very detailed but there was almost no bottom end. After a few hours the highs started to become shrill. I suspect it is the BAL/SE opamp and feedback cap. My plan is to remove those items an re install a LM4562 and then listen again
In the mean time I re installed a stock IVY III, then installed a 50 VA transformer for it, then swapped out the PSU for the new Placid HD BP 2.1 along with a 30 VA transformer for the BIII VD supply
Those three steps were a significant improvement in sound. The bottom end appeared while the highs stayed detailed and there was more separation between instruments. My next step is to upgrade the BIII VD supply and then listen again for a while. Once completed I'll make the changes to the IVY III again and see what happens
I used PRP resistors throughout
I used Vishay Roderstein .1uF film caps for the supply decoupling
I paralleled two Amtrans 8.2 nF film/foil polypro caps for the analog filters
Used two LME49990 op amps on a brown dog adapter and added a feedback compensation cap for each channel (value and type mentioned earlier) in place of IC5 (LM4562)
I used Nichicon Muse caps for the electrolytics
You'll need longer pin headers (Digikey SAM1061-06-ND) and standoffs (Digikey 36-8404-ND) to clear the brown dog adapter and electrolytics.
My first impression once installed was not the best. The highs were great and very detailed but there was almost no bottom end. After a few hours the highs started to become shrill. I suspect it is the BAL/SE opamp and feedback cap. My plan is to remove those items an re install a LM4562 and then listen again
In the mean time I re installed a stock IVY III, then installed a 50 VA transformer for it, then swapped out the PSU for the new Placid HD BP 2.1 along with a 30 VA transformer for the BIII VD supply
Those three steps were a significant improvement in sound. The bottom end appeared while the highs stayed detailed and there was more separation between instruments. My next step is to upgrade the BIII VD supply and then listen again for a while. Once completed I'll make the changes to the IVY III again and see what happens
The J-FET-input OPA1642 actually does a nice job in place of the LM4562/LME49720.
Be careful of added inductance with longer leads and added effective trace lengths when modding.
Be careful of added inductance with longer leads and added effective trace lengths when modding.
I will check that op amp out. I suspect using that adapter had a negative effect because of the trace lengths. I'm pretty sure it was oscillating but I have no way to measure
The J-FET-input OPA1642 is excellent. I'm pleased with the sound. I removed the compensation caps and the other opamps on the adapter. Then, I installed the OPA1642. The sound compared to an unmodified IVY III goes from a tad bright to a neutral sound. It was a step in the right direction. I feel the amtrans caps took about 24 hours to burn in so if you build an IVY like this make sure you let it settle in before you judge it.
I'm planning on ordering 0.1% 1/4 watt 50 PPM PRP 9372 resistors for the TPA Ivy III. Normally this tolerance is not stocked by anyone and the price prohibits ordering one or two sets. I started a group buy thread for it here on diyaudio. I just need 5 people to get them for a decent price. The details are in the GB thread. Is anyone interested?