As Salas says, experiment with either smaller output capacitor on the riaa output or load it harder by putting parallell resistors over the input load resistor in next stage or after the output cap to ground on FSP if that is simpler. If you want to keep low frequencies down to audible spectra but cut subsonics maybe a passive second order could be put in between. That would be parallell resistor after output cap on riaa, then an additional series cap then the load resistor on following stage. Would need some calculation tho.
A breaking of the low frequency feedback would probably be done with least footprint on the rest of the system by putting a high pass on the sub(s)?. I presume they are active and takes a splitted signal from a pre? How is that done, just a cable Y or with 100R resistors type? If so any extra HP loading on the sub branch would give the same loading on the mid-high branch. Best would be a buffer in front of a HP- filter to the subs, then you dont interfere with the rest of the system.
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Hi Nick,
That woofing phenomenon isn’t new and it was present in the past with my none-modified cart. Back then, my FSP was about 56bB and little more volume than now on TubePre required to create these waves on Sub. So, I’ll go and add to VTF, however and in order to save my records, I’ll not go above 2.5 grm. I probably not going to lower C4 due to its cost. I use Mundorf 2.2uF Supreme Silver/Oil now. New set will go at $100+. BTW, my TT+FSP+TubePre volume level is still just a bit lower then CD+TubePre. Maybe just one click on TubePre step attenuator (24 steps total).
I’ll go and try my build for 20Hz High Pass (0.1uF and 82k). If it will work, than done deal. If not, I go for these “20Hz High Pass” FMODs on Sub’s input. $34.50 total with shipping. Let’s see how it is. Thank you a lot.
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I'm going to try that passive second order after heavy VTF test.
RC High-pass Filter Design Tool
0.1uF cap and 82k resistor at Sub inputs.
Apparently, friend of mine has the same issue. Different Phono, TT and Pre. Also Sub is REL. Same woofing in mid-high volume. He never tried it in that volume level before…. It is not that loud, but his room in much smaller than mine.
My Sub is getting the signal from one of pre outputs. I have 3 of these and all of them are the same. They are connected to the same output on PCB.
Understood comment about buffer, but did not about grounding. Have you advised to connect FSP output RCA GNDs together and to connect these to the signal GND (today, they are insulated from FSP enclosure)?
I use 0.1uF now for C3. It is Mundorf Silver/Oil. I also measured resistance at output in FSP when PreAmp is connected. It is L-84.2k/R-83.7k.
Yes, let me try to treat the issue at the Sub level firs. If no success there, then I'll move towards C3 for 0.022uF. However, Mundorf does not have that value in Supreme product line…
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It's not all milk and honey in NA. Here in Canada a lot of stuff comes from USA. We have had a "Free Trade Agreement" with them since the 1980's, but it only seems to apply to corporations trading millions. When I order something from USA I have to pay VAT (we call it GST) and duty (if applicable), either when I order it or on delivery. Usually forced to pay for expensive courier fees (not regular mail), and then the courier companies add an arbitrary service charge, handling fee, and finally "customs brokerage fee" which sometimes exceeds the value of the goods, duties, and taxes. Funnily enough, if you pay more for "priority/expedited shipping" the brokerage fees go away, so it's often worth paying an extra $20 in shipping to avoid >$50 in brokerage, but you never know until it arrives. It is the uncertainty that drives you crazy. I think there have been some class action lawsuits filed in Canada against UPS and/or FedEx over these bogus charges.
OTOH I have had stuff come from China via Ali Express with absolutely no COD charges or shipping charges, but of course they were shipped via China Post.
I am only talking about signal ground. When and where that is refered to earthground is another issue.
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Thank you for advice, but I decided to resolve that case with very simple solution. May not the cheapest one, but simple... I replaced both Alps in 2 monoblocks with 100K Mini-V Goldpoit step attenuators. Easy mod vs. disordering resistors and creating all needed bypasses. It was a mess since all these parts were soldered on mail PCB. Thank you.
There is no earth GND in my FSP box. Only singnal GND. Two FSP PSBs GNDs and TT GND are connected to the enclusure at TT GND connection point. All RCA are insulated.
My earth GND is in PSU box insulated from signal GND by 2 Recifier Bridges and two 10R resistors (Mono Raw DC configuration).
Yes. Dont worry about earthground in this case, that is other troubles. What matters in this case is that when you make high-pass, low pass or band.pass filters you deal with networks between signal to ground, hot to cold or whatever we like to call it. So when we say put a component, in an RC or LC circuit between signal and ground it is always signal ground we refer to.
Signal ground is commonly and recommendable refered to earth ground somewhere in the chain of components. Preferably only in one point. If there are multiple active components in the chain there can be more then one reference to ground which can cause problems, ie loops of DC flowing because of close but not exact references to earth ground in the different connection points. The can sometimes be broken (fixed) with yin/yangs and other networks. But this is another story.
