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Here It Is: The All Singing All Dancing HTMCPS

If the final loading resistor (75K) is essentially there to act as a charge drain for the output blocking cap, why not put it at ca 200k instead and just let the following stage determine the output roll-off by default? If the load at the next stage was a 50k level control the actual load with the 75k would be less than half 75k, with 200k it'd be close to 50k F.I.
 
I see what he is asking and saying.

The first question is the source impedance which looks like the 75k resistor, not the unguarded output of an Op-Amp. The capacitor is there to guard your line stage from DC offset which is inevitable with battery or non-regulated supply voltages. As PIO points out, the 75k resistor is there to bleed it to common/ground. Of course the cap won't leak 30s after turn on so you could just wait 30s to turn on your line stage. The DC will have been grounded through your line stage's input resistor safely before you turn it on.

Phillip, look at your schematic and recalculate your corner frequency with a 10k amplifier input resistor in parallel with the 75k. That parallel combination of 10k and 75k controls the corner frequency.

You do want it as low as possible practically. A 1.4 Hz corner frequency is flat at 14 Hz. But in reality we don't have rooms that reproduce a flat 20 Hz. (calculate the length of a full and half wave of 20 Hz is) I'm sure in my system I don't have much flat below 50 or 60 Hz. But I have low frequency resonances. I have a room resonance excited by foot tapping in Uncommon Ritual by Edgar Meyer.

Our systems and rooms are really interactive below 100 Hz!

One last monkey wrench, the source impedance and amp input impedance also work together to form a first order filter with your cable's capacitance. This is only a factor with long cables, say over 10'.
 
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I have found that most preamps have a input impedance of 47k.

OK so with a 200k resistor instead of 75k and a 47k input (200k + 47k = 38k parallel) means a 2.7uf cap would give 1.5hz corner frequency. I will get some 2.7uf caps and try them out with the 200k resistors to see what difference it makes.

But for now it sounds fantastic as it is.

Steve have you built yours yet?
 
Not yet, I have to put together a rather large parts order for the stuff here still on hold for parts. Best supplier for most/all parts for the 3 projects?
 
Pio1980 said:
Not yet, I have to put together a rather large parts order for the stuff here still on hold for parts. Best supplier for most/all parts for the 3 projects?
Click to expand...

You can get all the parts from Mouser except the terminal blocks but they are optional. I sent you the BOM for Mouser and resistor calculator via email.
 
HypnoToad said:
You can get all the parts from Mouser except the terminal blocks but they are optional. I sent you the BOM for Mouser and resistor calculator via email.
Click to expand...
Sorry to say that the BOM & the resistor calculator never appeared, could you please resend an updated BOM for all 3 projects as well.
 
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Over the weekend I finally changed out the DC blocking capacitors and the output resistors on the HTMCPS. I put in 2.2uf Panasonic Polypropylenes in place of the 1.5uf's. I left the 0.1uf bypass caps in place.

I also removed the 75k resistors and put in 200k, this has made a difference in the bass area, with the old set up the bass was a little rolled off.

Now it extends flat (theoretically) right down to 18hz with a roll off to a -3db point at 1.8hz when connected to a preamp with 47k input impedance like my C4.

The audible difference is apparent with a more extended bass response resulting in an even more balanced sound IMO.

Others might like to try this out.
 
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HypnoToad said:
Over the weekend I finally changed out the DC blocking capacitors and the output resistors on the HTMCPS. I put in 2.2uf Panasonic Polypropylenes in place of the 1.5uf's. I left the 0.1uf bypass caps in place.

I also removed the 75k resistors and put in 200k, this has made a difference in the bass area, with the old set up the bass was a little rolled off.

Now it extends flat (theoretically) right down to 18hz with a roll off to a -3db point at 1.8hz when connected to a preamp with 47k input impedance like my C4.

The audible difference is apparent with a more extended bass response resulting in an even more balanced sound IMO.

Others might like to try this out.
Click to expand...

Nice! I will try it. I have assembled a second HTMCPS for a friend to run a new DL-103. Hope to have it in his hands later this week.

Rock on, Sir Toad! :guitar:
 
Is it still possible to purchase PCBs for this project? I'd like to compare it to my diy naim 323 phonograph stage.

Thanks
 
HypnoToad said:
Over the weekend I finally changed out the DC blocking capacitors and the output resistors on the HTMCPS. I put in 2.2uf Panasonic Polypropylenes in place of the 1.5uf's. I left the 0.1uf bypass caps in place.

I also removed the 75k resistors and put in 200k, this has made a difference in the bass area, with the old set up the bass was a little rolled off.

Now it extends flat (theoretically) right down to 18hz with a roll off to a -3db point at 1.8hz when connected to a preamp with 47k input impedance like my C4.

The audible difference is apparent with a more extended bass response resulting in an even more balanced sound IMO.

Others might like to try this out.
Click to expand...

Thanks for the update! Just to clarify on the recommendations....

Cap replacement at C5 & C19 with 2.2uF and resistors at R8 & R16 to 200k, am I correct? (there seems to be no other options I guess, but better to be sure than sorry)

I have all the parts in a bag, but I will update with new parts. I will be building few boards in next couple of weeks.

Thanks again for the update
 
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