Hello Richard,
I have to admit that the surface mount parts (and TO99-8) did present a challenge to me. Initially, I sourced parts from e-bay which were already soldered to adapters. Considering the source, I always questioned the legitimacy of said parts, so about 2 months ago I went about ordering genuine samples of the usual suspects from TI and AD, and then purchased a bunch of various adapters from e-bay. They are very affordable, but of varying quality.
The SMD parts (all from AD) required the most concentration to solder in place, but with only 4 pins on each side and a generous gap between pins, it is "easy enough" even for someone with limited skills (such as myself). I performed this operation on the AD8599, AD8066, AD8620 and AD823.
I have also heard great things about the LME49710/20/LM4562 parts, particularly the LME49710HA (TO99-8) "can", so when I was ordering samples from TI, I made sure to order a couple of them, along with an LME49720HA (the "dual"), an OPA2132P, etc.
Again, e-bay has both single and dual TO99-8 to single DIP8 adapters. I bought them from "Sorch Audio"*. They are excellent quality. Soldering the TO99-8 cans in place is much easier than the SMD parts, of course. Currently I am using the pair of LME49710HA (on single adapter) in my DIY DAC. I considered trying it in my VSPS but the 55Mhz GBP gave me pause and I was uncertain whether there was clearance on the VSPS (near C1, C2) for the dual TO99-8 cans on the adapter. Also, the AD8599 was just screaming at me to be put in the VSPS, so there it went.
I will likely eventually try more of these high-end parts in the VSPS, especially once I get other things in my phono chain sorted. The LME49720HA (TO99-8 in DIP8 adapter) will probably be next, as I am sure it will physically fit in the VSPS and, despite being a "dual", its specs are nearly identical to the LME49710HA.
As time goes on and I gather more experience and opinions (for what it's worth) I will post my thoughts here.
* I have no affiliation with "Sorch Audio" on e-bay, but they do make excellent adapters and the included pins are very, very good.
I have to admit that the surface mount parts (and TO99-8) did present a challenge to me. Initially, I sourced parts from e-bay which were already soldered to adapters. Considering the source, I always questioned the legitimacy of said parts, so about 2 months ago I went about ordering genuine samples of the usual suspects from TI and AD, and then purchased a bunch of various adapters from e-bay. They are very affordable, but of varying quality.
The SMD parts (all from AD) required the most concentration to solder in place, but with only 4 pins on each side and a generous gap between pins, it is "easy enough" even for someone with limited skills (such as myself). I performed this operation on the AD8599, AD8066, AD8620 and AD823.
I have also heard great things about the LME49710/20/LM4562 parts, particularly the LME49710HA (TO99-8) "can", so when I was ordering samples from TI, I made sure to order a couple of them, along with an LME49720HA (the "dual"), an OPA2132P, etc.
Again, e-bay has both single and dual TO99-8 to single DIP8 adapters. I bought them from "Sorch Audio"*. They are excellent quality. Soldering the TO99-8 cans in place is much easier than the SMD parts, of course. Currently I am using the pair of LME49710HA (on single adapter) in my DIY DAC. I considered trying it in my VSPS but the 55Mhz GBP gave me pause and I was uncertain whether there was clearance on the VSPS (near C1, C2) for the dual TO99-8 cans on the adapter. Also, the AD8599 was just screaming at me to be put in the VSPS, so there it went.
I will likely eventually try more of these high-end parts in the VSPS, especially once I get other things in my phono chain sorted. The LME49720HA (TO99-8 in DIP8 adapter) will probably be next, as I am sure it will physically fit in the VSPS and, despite being a "dual", its specs are nearly identical to the LME49710HA.
As time goes on and I gather more experience and opinions (for what it's worth) I will post my thoughts here.
* I have no affiliation with "Sorch Audio" on e-bay, but they do make excellent adapters and the included pins are very, very good.
There's nothing stopping you from trying out any op amp you like, even ones with high GBWP. Its just that without proper bypassing (the ceramic 0.1 uF caps next to the IC or across V+ V- at the socket) any evaluation is being unfair to the op amp.
I'll have to look into the adapters you mention. I feel I'm getting a bit old for "op amp rolling" though.
I'll have to look into the adapters you mention. I feel I'm getting a bit old for "op amp rolling" though.
G'day all, it's interesting that op amp supply rail 'bypassing' was mentioned in the last post, as I admit to having a bit of an epiphany about supply rail bypassing in recent times and just how important it is, and that ceramic capacitors are actually excellent in op amp supply bypassing applications.
My own bread-boarded VSPS was actually built without any op amp supply bypass capacitors (and apparently worked fine), however I have now installed .1 uf ceramic capacitors on both supply rails to chassis earth and the sound quality has improved and become more 'solid' sounding with the OPA2134 that I used in the circuit, and quieter too.
Looking at other phono preamp circuits based on op amps, I am shocked to see, to my eyes anyway, inadequate op amp supply rail bypassing. Designers of these circuits should know better, in my heartfelt opinion. Regards, Felix.
My own bread-boarded VSPS was actually built without any op amp supply bypass capacitors (and apparently worked fine), however I have now installed .1 uf ceramic capacitors on both supply rails to chassis earth and the sound quality has improved and become more 'solid' sounding with the OPA2134 that I used in the circuit, and quieter too.
Looking at other phono preamp circuits based on op amps, I am shocked to see, to my eyes anyway, inadequate op amp supply rail bypassing. Designers of these circuits should know better, in my heartfelt opinion. Regards, Felix.
I think there are two things going on. One is traditional bypassing : providing a low impedance return for load currents at high frequency. The second is RFI filtering. The ceramic caps can filter out interference riding on the power rails which would otherwise get into the op amps.
Bypassing got a bad name because people insisted on using "audio quality" film caps instead of ceramic. The results are bad. Also, if the bypass caps are incorrectly positioned or the board layout is poor, they can make things worse rather than better. Finally, in a lot of cases they really don't make any significant difference one way or the other.
My policy is: Try it. If you don't like it, just snip them out.
Most boards have pads for optional bypass caps. Haven't updated the VSPS300 yet, but you can always solder the cap between the V+ and V- pins on the op amp socket.
Bypassing got a bad name because people insisted on using "audio quality" film caps instead of ceramic. The results are bad. Also, if the bypass caps are incorrectly positioned or the board layout is poor, they can make things worse rather than better. Finally, in a lot of cases they really don't make any significant difference one way or the other.
My policy is: Try it. If you don't like it, just snip them out.
Most boards have pads for optional bypass caps. Haven't updated the VSPS300 yet, but you can always solder the cap between the V+ and V- pins on the op amp socket.
G'day mate, the results with bypass capacitors can indeed be a little variable!
Another phono stage that I built recently using an OPA2134 oscillated furiously until I added bypass capacitors on each supply rail, then it was perfectly stable.
I've never seen that sort of behaviour before! Regards, Felix.
Another phono stage that I built recently using an OPA2134 oscillated furiously until I added bypass capacitors on each supply rail, then it was perfectly stable.
I've never seen that sort of behaviour before! Regards, Felix.
Knowing that I would eventually be rolling in different opamps, I did install the optional (but included, thank you) 0.1uF ceramics. I am curious about how critical the value of these capacitors is. The reason I ask is because I have some very nice silver mica caps that I could try, but they are only 22pF.
Alas, I have not outgrown it yet. For me, it goes in stages. Any time I make a major change to my system (for example, my recent switch from tubes to Class D), I go through the process of rolling opamps till I find the one with "synergy".
My new TT cartridge arrived yesterday and I have installed it. It sounds considerably better than the old cart. Hopefully, I will have time on the weekend for an extended listening session and some opamp rolling in the VSPS.
@fap
So as you know, the op amp bandwidth is the GWP divided by the circuit gain. If this is in the low 100's of kHz, the electrolytics are more than capable of handling the return currents, which are anyway mostly in the audio band. This the thinking behind not inluding them in the Phonoclone and VSPS BOM: the bandwidth is tuned down to about 200 kHz (I forget the exact number) when using the OPA27s.
Now in a circuit with a bandwidth of 1-2 MHz or more, its a different story: the electrolytics don't work for you anymore, you need additional low impedance caps to properly bypass the amplifier.
However, as I noted above the ceramic caps might also act as an RFI filter, so even if the bandwidth is sufficiently low that they are not needed there may still be an audible improvement when they are used.
/R
So as you know, the op amp bandwidth is the GWP divided by the circuit gain. If this is in the low 100's of kHz, the electrolytics are more than capable of handling the return currents, which are anyway mostly in the audio band. This the thinking behind not inluding them in the Phonoclone and VSPS BOM: the bandwidth is tuned down to about 200 kHz (I forget the exact number) when using the OPA27s.
Now in a circuit with a bandwidth of 1-2 MHz or more, its a different story: the electrolytics don't work for you anymore, you need additional low impedance caps to properly bypass the amplifier.
However, as I noted above the ceramic caps might also act as an RFI filter, so even if the bandwidth is sufficiently low that they are not needed there may still be an audible improvement when they are used.
/R
G'day mate, thanks for that. Interesting on the RF filter aspects. Indeed this is exactly what I've found that since installing ceramic bypass capacitors in lieu of MKT's in one case.
I no longer experience any RF breakthrough from my 100 watt SSB Amateur Radio transceiver, where I did previously. Regards, Felix (vk4fuq).
I no longer experience any RF breakthrough from my 100 watt SSB Amateur Radio transceiver, where I did previously. Regards, Felix (vk4fuq).
Indeed. I have done some reading and essentially the smaller the cap value, the higher the filter frequency. I also found some interesting info on using parallel bypass caps of different values. I am quite intrigued by all of this, and will consider installing some bypass caps in my DAC.
Thank you for all the info and advice.
Thank you, Richard. Yes, I have already abandoned any urge to use the 22 pF caps. I have seen other examples that use a combination of values (such as 1.0 uF, 0.1 uF and 0.01 uF to effectively increase the bandwidth of the filtering.
At least, that is how I understood it. http://www.intersil.com/content/dam/Intersil/documents/an13/an1325.pdf See page 6.
I am not saying I think I need to do this, but I find it very interesting.
I built a power supply for both Phonoclone and VSPS, but I would like to know if my reading from the rectifier is normal. I built the bridge rectifier using Fairchild stealth II Diode with two TRIAD 50VAC transformers with dual 12V secondaries.
The reading from the BR is 12.40VDC from both Transformers, is that normal?
The reading from the BR is 12.40VDC from both Transformers, is that normal?
Thanks. I had just finished my Phonoclone built, and was just wondering about that.
The other issue I am having, is that the PC3 have "white noise" when I turn my volume to half or full. Do you know how I can get rid of it?
I have no hum, just that noise.
Thanks in advance.
Richard
An RIAA accuracy question with the VSPS.
G'day all, when I built my bread-boarded VSPS some years ago I used 2.7 nF capacitors in lieu of the 3 nF as listed in the public article in the RIAA equalisation network.
So today from my local electronics hobbyist store I bought a stack of 1nF MKT's and using my capacitance meter I found two sets of accurately matched of 3x1 nF MKT's which I've successfully soldered into my VSPS circuit.
I wonder if anyone can please model the circuit using 2.7 nF capacitors, and please tell me what the effect on the RIAA equalisation would be? For what it's worth, the sound quality sounds slightly different now (slightly less treble?) and the stereo imaging seems much better. Regards, Felix.
G'day all, when I built my bread-boarded VSPS some years ago I used 2.7 nF capacitors in lieu of the 3 nF as listed in the public article in the RIAA equalisation network.
So today from my local electronics hobbyist store I bought a stack of 1nF MKT's and using my capacitance meter I found two sets of accurately matched of 3x1 nF MKT's which I've successfully soldered into my VSPS circuit.
I wonder if anyone can please model the circuit using 2.7 nF capacitors, and please tell me what the effect on the RIAA equalisation would be? For what it's worth, the sound quality sounds slightly different now (slightly less treble?) and the stereo imaging seems much better. Regards, Felix.