Beresford Caiman output filter

[robyonekenoby]

Hello folks,

new owner of a caiman, previously owned a modded tc 7510
After a first quick listen session; I noticed an improvement in mid and highs, more refined, but still a little harsh and pronounced sibilance

SO I couldn't resist and tried the passive mod:

I took away opamp PCB, yes, REMOVED
jumper from opamp pcb socket to rca, no need for caps here, my amp has two nice DC blocking input cap inside, 3.3uF audyn film&foil

Never heard something similar, the most refined and detailed sound so far, clean, airy, not fatiguing at all, no trace of harshness or sibilance

but

bass lack of power, I mean, is tight and deep, but with the opamp in place has more energy, more slam, it's not just a matter of lower output level

So I'm wondering if increasing value for input cap would enhance the bass; my pot is 50k, so the corner point is around 1Hz, maybe the lack of bass is just a matter of mere insufficient current drive capability by the WM8716

So I have to restore the opamp, but want to make it smoother

I noticed the output stage board is missing feedback caps; Stan told me he doesn't install them because the sound seem to be better without

If I'm not wrong, in this way the opamp is working just as a line preamp, linear gain, no HF filtering

SO, if want to experiment to drop in some feedback cap to smooth out some harshness, which value range should I consider?

I'm not able to calculate filter curve for a given cap value for that circuit

I already have some nice wima MKP 150p, 220p, 330p

Hope someone here could help me

[DSJR]

That's where the Gator comes in - a better output buffer which apparently sounds as good as the cap mod, but with full functionality and none of the matching issues.

[robyonekenoby]

yes, probably

but, maybe I'm wrong, in my mind the best opamp is always no opamp

Math is math, and 3.3uF on a 47k load gives 1hz corner, so bass should not be an issue, but just to be sure I tried to swap amp input cap from 3.3uF to 22; a test CD with a 40Hz tone, revealed absolutely no gain in bass depth

someone could explain me why the signal coming from a DAC chip is so thin and poor in bass?

Maybe that bass weigth is just the analogue stage sonic signature, something added to the music and not natural at all?

I must admit that is nice such a visceral sound pressure, but with no opamp details arer amazing

I like 'The rite of spring', Stravinskji, I heard that disc hundred times, but Today for the first time I was able to capture also ambience sound, I mean a musician that adjust is position on the chair, another one that turn a page, a flutist inhaling a breath before play a note ....

Is like to sit among the orchestra....crazy

[Reid Malenfant]

You are only taking into account the filtering caused by the 3.3uf capacitor & the amplifier input impedance ;) What you aren't taking into consideration is the output impedance of the DAC chip coupled to this. Yes it may well be fine driving a high impedance amplifier such as a valve pre amp which is quite likely to have an input impedance of up to 1Meg ohm. Quite a few people on here tend to use such kit & i have no doubt that the passive mod works a treat with such gear.

But if the impedance is lower such as your 47K ohm input then it may well give the effect you are describing & as Dave says, this is what the Gator board is for - to give a much better drive.

Not only that but it has the ultimate output topology, single ended class A & it's low global feedback to boot :) Something you need to consider is that in the case of the Gator the op amp will always run in class A as well because the output transistor base will require so little current the the op amp output transistors will never go over to AB as per usual :eyebrows:

[robyonekenoby]

Thanks for your reply

yes, I was thinking about dac output impedance vs amp input impedance when I saw your reply

I have an amp based on a tripath 3020, a true marvel, but the input impedance should be in the range of 10-20 kilo ohms, so the current could be the issue

The 47k load I was referring to is just the volume pot

I've ordered my caiman last week, did know anything about the gator, otherwise I would have ordered together

I've already modded the opamp pcb :eyebrows:

swapped coupling cap for audyn mcap film & foil, noticeable improvement, bass faster and tighter, more controlled, and more refined highs

but anyway I will end to order my gator ;)