Vacuum State RTP3C

[gingertube]

Originally Posted by sjoarnum

Hello Kim
Nice tip about the e-choke. From the paper about the E-choke it seems to outperform the ”oldfashoned” choke in a CLC filter.
As the E-choke has a cap in the input have you tried to use the e-choke in a choke input filter (LCLC where CL equals a E-choke)?

In my own RTP-project the e-choke may com in handy as a inline choke as i have a mains transformer delivering 480Vac and need to drop som voltage.

Your own build looks fantastic – I for one would like to see some more pictures:-)

Best regards
Stig

The E-Choke is not really designed for use in an LC filter. It really was intended for C-L-C use. There is nothing new about it, its just a "garden variety" gyrator with a MOSFET as the active device.

Cheers,
Ian

[Shoog]

Originally Posted by gingertube

The E-Choke is not really designed for use in an LC filter. It really was intended for C-L-C use. There is nothing new about it, its just a "garden variety" gyrator with a MOSFET as the active device.

Cheers,
Ian

i personally wouldn't touch one with a barge pole - a very weak regulator with a nasty sound signature compared to a real choke. I feel fairly confident in saying that Allen Wright would agree.

Shoog

[gingertube]

Shoog,
Is this opinion or actual listening experience?

It is not any sort of a regulator, weak or otherwise, but used within its limitations it should provide good inductive impedance and ripple suppression.

Theory is here:
Active Choke for Valve Amplifiers

This shows that the schem above acts like a choke with:
Inductance of 1M x 10R x 100nF = 1 Henry
Series resistance of 10 x (1 + 1M/1M) = 20 Ohms

PROVIDING that the Time OFF mode is selected. IN Time ON mode the gyrator action is divided by 10 by the 100nF/1uF divider and the entire circuit swaps to a mostly capacitance multiplier operation (Multiplying that 1uF).

With the 1M, 1M parallel 100nF , 15V zener arrangement in Gyrator Mode (TIME OFF) then you can see that the gyrator will tolerate a maximum of 15V pk-pk across it which means that the input voltage must be meet that spec (<15V pk-pk ripple). Thats why it won't be any good for an L-C arrangement but is good for C-L-C arrangement.

I will be trying them out in the next power amp build. for my current SVP2 clone preamp build I have a "real" choke for an L-C style supply.
Cheers,
Ian

[Shoog]

Its a form of capacitance multiplier. Every time I tried one of those it sounded real nasty. Introduced a real bloat to the overall sound of the amp. I consistently use chokes where ever I can now and avoid power supply regulators.

Shoog

[valve5425]

Originally Posted by Alex M

Very nice.

I'm intrigued by your gain problem with the phono stage. As a quick check, you could connect a pair of reasonably well-matched BC550s to see if the solid-state devices are the cause. This design is optimised for bipolar input transistors, rather than JFETs.

Have you measured the DC voltages on the anodes and cathodes of the valves? Is the standing current correct?

Alex

Hi Alex.

Finally got the phono boards sorted! I replaced the 2SK170BL's with the SSM2212's from Farnell and, taking your advice, changed the current source resistors to 500 ohm pots. I'd originally had 330 ohm resistors in there, as per the schematic, which I'd later paralleled to 165 ohm to get more gain, without success! I have had to take the pots down to 50 ohms to get sufficient gain, around 40db, for my MM cartridge. This resistance does seem a little low for that gain but the tubes may be tired. I'll try a few different ones now it's working. Incidentally, I don't think this was the cause of the original problem as I'd tried it shorted and still didn't get the gain I needed. What resistance have you got in there?

Also replaced 330 ohm grid stoppers with 1K0's and placed 330pf caps across the input as recommended by Allen.

I also discovered that I'd had a moment of madness and put in 2 x 47K resistors at the input so I've corrected this and put in a pair of 24K9's instead. (close enough for now for the 47K0 cartridge load) The layout is more logical now with shorter paths from input to SSM2212/tubes, and I've tweaked current and pots to get 65 volts at the anodes. The voltages were slightly unbalanced before and were up around 72 volts.

All in all it's sounding good but I'll leave it to burn in a while before I try the AD797 swap in the regulators.

Having problems attaching pics to this post so I'll try later.

Regards, Dean

[valve5425]

Pics of modifications to RTP3C phono boards using pesky little SSM2212RZ. (I did some swearing soldering that!)

[herrstagl]

Hello Gents,

based on a statement of Alan "When you're done, check it. Then, let someone else check it" I like to ask if there would be someone who reviews my PCBs for SuperReg, Tape Out Buffer and Power Supply.

Many thanks for your help in advance.

regards, tom

[mishak]

Came here late, not sure if anybody watching this thread anymore, but I will shoot my question anyway.
I have built a similar to RTP3 design phono preamp (based on Lite Audio made GA31 boards, the same as Allen’s originated from old HP oscilloscope schematics as I was told). Works well, good sound, etc.
But there is a small (about -60dB) hum, which is moving from channel to channel along with different tubes as I roll them. So here is my question: how critical that differential design to the matching each half of the tube(s)? Not critical at all, needs 10% tolerance, need 1% matching?
Is it possible that some hum/noise would be originated from a different gain of the upper and lower triodes with respect to the floating ground?
Appreciate any comments.

[vtr]

if there is something strange as hum thats sometimes there or noise or microfonic tubes-its oszillating
do you have grid stoppers everywhere? try to increase to 5-10k and check if the moving hum is gone, and a clean earth layout with proper star grounding helps alot, for phone i asssume you have dc heaters, and i never matched tubes-of course i check if the node voltages are similar and adjust the cs to be identical

Originally Posted by mishak

Came here late, not sure if anybody watching this thread anymore, but I will shoot my question anyway.
I have built a similar to RTP3 design phono preamp (based on Lite Audio made GA31 boards, the same as Allen’s originated from old HP oscilloscope schematics as I was told). Works well, good sound, etc.
But there is a small (about -60dB) hum, which is moving from channel to channel along with different tubes as I roll them. So here is my question: how critical that differential design to the matching each half of the tube(s)? Not critical at all, needs 10% tolerance, need 1% matching?
Is it possible that some hum/noise would be originated from a different gain of the upper and lower triodes with respect to the floating ground?
Appreciate any comments.

[mishak]

Hi VTR,

thank you for your response. Maybe you can give more specific advise using schematics attached?
That is a printed board already grounded in one point only, heaters are DC, voltages are fine.

Key feature is it is a low hum with equal spectrum at 60, 180 and 240Hz that is changing as I replace a bulb.