[JoeSlovakia]

Yes, but as I wrote, too small of a cap can cause some LF loss. Why would 220 uf cause instability on the rca inputs, but not on the XLR inputs? It's possible, but unlikely. SMSL clearly had a space issue with those 22 uf caps, so that's the obvious explanation for that value.
Of course, most users don't hear a difference between the two input types, so the 22's are not likely rolling anything off, but I'd still go larger if I was to "upgrade" them.

--------------------------

Did your Dad have a recommendation for the PSU HF bypass caps?

No, as he doesn't have an oscilloscope to measure it. But I will have a chat on Thursday or Saturday, so I will ask him! Maybe he will figure something out.

 

[Cableaddict]

Thanks, Joe.

I have another question for him, or anyone here with high level EE knowledge:

## Is there any way (even costly / difficult) to lower the output impedance of this amp?
------------------------

I have the unfortunate need to use these with both studio cans and low impedance IEM's. In fact, my favorite IEM's are the Shure SE846, and they are only 9 ohms. The SP200 output has been measured independently as being 1.3 ohms. That's not nearly as low as amps like the O2 amp, the JDS Atom, etc, and it's a HORRIBLE match with my 846's. They sound AWFUL. (harsh, no LF, etc)

I stupidly decided on my new studio amps based only on testing with 250 - 600 ohms. Now, I literally can't use my IEM's.
I may try other good IEM's that are 16 ohm or more, but I hate the idea of retiring those amazing 846's.

I tried an inline resistor network at 80 ohms, but while this brought back the LF and lowered the distortion, it also killed a significant amount of HF. (resistance is not capacitance.) Ugh .....
======================================================================================


So, I'm wondering if there's ANY hope of electronically lowering the output impedance. I know of no amp that comes close to this design, for less than 2-3X the price, so I'm willing to sink some money and time into such a mod.

Maybe change the gain structure, by lowering both the input and the output resistance?
------------------------

## Maybe a different op amp?

The two stock SP200 gain op amps are OPA1612A.

The Benchmarl HPA4, a $3,000 THX-888 design, uses 2 OPA 564 op amps. Surprisingly, (to me) It also uses a pair of OPA1612A dual op-amps as "error-correction" amplifiers.

The HP4A has a rated output impedance of “less than 1 ohm” Given my SE846’s 9 ohm impedance, that could actually make a big difference to me.

I’d LOVE to know why Benchmark used this alternate 20-pin power ic, and then used what the SP200 uses as some kind of ancillary circuit. What is “error-correction?”

And the obvious questions:

1: Can the OPA 564 be used as a direct-replacement for the SP200’s 1612A? (I suspect not)

2: Is so, might it sound better? - Maybe not. Both ic’s cost about the same $8-$9 each.

3: If so, could it possibly have a lower output impedance? - The HP4A has a rated output impedance of “less than 1 ohm” Given my SE846’s 9 ohm impedance, that could actually make a big difference to me.

 

[Forsaked]

Thanks, Joe.

I have another question for him, or anyone here with high level EE knowledge:

## Is there any way (even costly / difficult) to lower the output impedance of this amp?
------------------------

I have the unfortunate need to use these with both studio cans and low impedance IEM's. In fact, my favorite IEM's are the Shure SE846, and they are only 9 ohms. The SP200 output has been measured independently as being 1.3 ohms. That's not nearly as low as amps like the O2 amp, the JDS Atom, etc, and it's a HORRIBLE match with my 846's. They sound AWFUL. (harsh, no LF, etc)

I stupidly decided on my new studio amps based only on testing with 250 - 600 ohms. Now, I literally can't use my IEM's.
I may try other good IEM's that are 16 ohm or more, but I hate the idea of retiring those amazing 846's.

I tried an inline resistor network at 80 ohms, but while this brought back the LF and lowered the distortion, it also killed a significant amount of HF. (resistance is not capacitance.) Ugh .....
======================================================================================


So, I'm wondering if there's ANY hope of electronically lowering the output impedance. I know of no amp that comes close to this design, for less than 2-3X the price, so I'm willing to sink some money and time into such a mod.

Maybe change the gain structure, by lowering both the input and the output resistance?
------------------------

## Maybe a different op amp?

The two stock SP200 gain op amps are OPA1612A.

The Benchmarl HPA4, a $3,000 THX-888 design, uses 2 OPA 564 op amps. Surprisingly, (to me) It also uses a pair of OPA1612A dual op-amps as "error-correction" amplifiers.

The HP4A has a rated output impedance of “less than 1 ohm” Given my SE846’s 9 ohm impedance, that could actually make a big difference to me.

I’d LOVE to know why Benchmark used this alternate 20-pin power ic, and then used what the SP200 uses as some kind of ancillary circuit. What is “error-correction?”

And the obvious questions:

1: Can the OPA 564 be used as a direct-replacement for the SP200’s 1612A? (I suspect not)

2: Is so, might it sound better? - Maybe not. Both ic’s cost about the same $8-$9 each.

3: If so, could it possibly have a lower output impedance? - The HP4A has a rated output impedance of “less than 1 ohm” Given my SE846’s 9 ohm impedance, that could actually make a big difference to me.

The Singxer SA-1 has less then 1 Ohm output impedance on low Z mode.
But it is an class A/AB amp which would fit in the 2-3 times price range.

 

[Cableaddict]

The Singxer SA-1 has less then 1 Ohm output impedance on low Z mode.
But it is an class A/AB amp which would fit in the 2-3 times price range.

Yeah, I'm not about to sell all six SP200's and then spend that kind of money. Ouch....

FWIW, on another thread more geared towards electronics, one member thinks that the main problem with the SP200 is the power supply, which has lots of voltage swing (good for 250 cans) but lousy current, which is bad for IEMs. I suppose a good external psu could help, but that's gonna' be expensive, and I still might have an impedance issue.

Ughh.......

 

[JoeSlovakia]

Cableaddict - have you tried the cap swap step by step and tested it? Just to make sure

 

[Cableaddict]

Cableaddict - have you tried the cap swap step by step and tested it? Just to make sure

No need. Read my post carefully.

I AM interested in also trying some bypass caps, both on the input coupling caps and (esp) on the power supply caps. - But I was hoping to first hear back from Joe, re what values his Dad would recommend. 0.1 uf might be a bight small for a 1500 uf reservoir cap.

 

[JoeSlovakia]

No need. Read my post carefully.

I AM interested in also trying some bypass caps, both on the input coupling caps and (esp) on the power supply caps. - But I was hoping to first hear back from Joe, re what values his Dad would recommend. 0.1 uf might be a bight small for a 1500 uf reservoir cap.

I wrote you, that my dad needs an oscilloscope to measure it as he told me, that it has no benefit to add them on a high grade cap as those 1500uF are

 

[Cableaddict]

I wrote you, that my dad needs an oscilloscope to measure it as he told me, that it has no benefit to add them on a high grade cap as those 1500uF are

Thanks, Joe.

I had a feeling that might be the case, esp since those super-premium caps I replaced are last in the chain. I also have no scope so can't check for ripple, but the amp sounds great so... Also I've read that sometimes those tiny caps let enough ultra HF through that it can cause oscillation & other issues.
I still have a hankering to try a 0.1 uf cog, because you know I just can't help myself (lol....) but I realize now that the chance of it helping is very small.

Thank your Dad for me.

----------------------------------

- But what about mf caps, say 15 uf? The power supply is so close to the gain circuits that again, it probably doesn't matter, and a 15 uf polyethylene cap is WAY too larger to fit, but one could squeeze a couple of Elna RFS (Simic II) electro in there. I might try that just for fun, and just using my ears to test.

 

[JoeSlovakia]

@Cableaddict

 

[TheMiddleSky]

Yeah, I'm not about to sell all six SP200's and then spend that kind of money. Ouch....

So for you to be able to work with shure 846 you need to get rid all 6pcs of SP200? How about cut to become 3pcs, and sell the rest?

Topping L30 has 0,1 ohm output impedance btw, and 3 gain settings, which is should suit any IEM.

 

[Cableaddict]

@Cableaddict

And you believe them?

C'mon Joe ....

 

[JoeSlovakia]

We can use whatever we want

 

[StarTreker]

@Cableaddict

Your a rebel, rules be damned, you shall franken amp this thing to produce 1.21 jigawatts!

 

[JoeSlovakia]

@Cableaddict I have checked the Nichicon LKG1E152MESBCK caps, but they will be available next year So I will replace the caps only on the inputs. That's sad

 

[dunring]

So for you to be able to work with shure 846 you need to get rid all 6pcs of SP200? How about cut to become 3pcs, and sell the rest?

Topping L30 has 0,1 ohm output impedance btw, and 3 gain settings, which is should suit any IEM.

I just had an SP200 last week and got an L30 in the other day. The low gain on it is so good with sensitive IEM's. The SP200 in low gain mode gives great bass dynamics, but the only IEM's I could use with it were the VE Monk 64ohm. The low ohm ones I've had on it are the perfect amount of power on the low gain setting with the L30.