RF filter in the cornish LD-1?

[carboncomp]

Hi,

Anyone able to help me with understanding this circuit. it hosts:

The input impedance is identical to a high quality tube amplifier and our Class A Pre-amplifier also features a highly effective RF filter which will help prevent interference from nearby radio transmitters.

But, if I wanted a filter RF but not have a buffer, what's the best approach, can I just modify this circuit?

[carboncomp]

Hi,

Anyone able to help me with understanding this circuit. it bosts:

The input impedance is identical to a high quality tube amplifier and our Class A Pre-amplifier also features a highly effective RF filter which will help prevent interference from nearby radio transmitters.

But, if I wanted a filter RF but not have a buffer, what's the best approach, can I just modify this circuit?

[idy]

What kind of a circuit are you "inputing into"? To give a meaningful and precise answer it impedence needs to be known. To be approximate one could, say, start with a picofarad range capacitor from signal path to ground. Could be 470pf, could be smaller, could be up to 1nf. The downside is a larger value cuts treble. Only difficulty is testing. Do you live in high RF environment? Ready to take your battery powered amp over to the nearest AM radio tower and test your unboxed circuit, putting in bigger and bigger caps until the mariachis fall silent...

[antonis]

Can you locate the RF filter on the circuit posted by you..??..

[carboncomp]

What kind of a circuit are you "inputing into"? To give a meaningful and precise answer it impedence needs to be known. To be approximate one could, say, start with a picofarad range capacitor from signal path to ground. Could be 470pf, could be smaller, could be up to 1nf. The downside is a larger value cuts treble. Only difficulty is testing. Do you live in high RF environment? Ready to take your battery powered amp over to the nearest AM radio tower and test your unboxed circuit, putting in bigger and bigger caps until the mariachis fall silent...

Hi, the start of my chain is a Range master than a few older fuzzies that dont play well with buffers. Yes very near a huge radio tower and time I use a boost pedal I get the radio out my amp.

Can you locate the RF filter on the circuit posted by you..??..

No, its cornish LD-1 schematic I posted to hopefully give some context for my question, sorry I'm not very knowledgable.

[ElectricDruid]

What kind of a circuit are you "inputing into"? To give a meaningful and precise answer it impedence needs to be known. To be approximate one could, say, start with a picofarad range capacitor from signal path to ground. Could be 470pf, could be smaller, could be up to 1nf. The downside is a larger value cuts treble. Only difficulty is testing. Do you live in high RF environment? Ready to take your battery powered amp over to the nearest AM radio tower and test your unboxed circuit, putting in bigger and bigger caps until the mariachis fall silent...

+1 this. Any well-designed audio circuit ought to be filtering out everything outside the audio band anyway. That means roll-off at the bottom to remove DC rumble, and roll-off above the top of audio to remove ultrasonics and radio interference. Mostly for the roll-off at the top, all it needs is a simple lowpass RC. As IDY says, could be as simple as an extra cap from signal to ground. "What value cap?" really does depend on the details.

[antonis]

No, its cornish LD-1 schematic I posted to hopefully give some context for my question, sorry I'm not very knowledgable.

No intention to insult you..

I was just curious on exactly what you refered on..
('cause, as far as I can see, there isn't  any kind of RF filter configuration on bootstrapped emitter folower posted.. )

P.S.
IMHO, RF filter is refered on a shunt cap somewhere near Power Supply regulation..

[carboncomp]

No, its cornish LD-1 schematic I posted to hopefully give some context for my question, sorry I'm not very knowledgable.

No intention to insult you..

Oh, I did not take it as an insult, I know very little and am aware of that 

I was very confused as the RF blocking iv have seen mentioned on forums in the grounded enclosure, shielded wire, a small capacitor on the input, or thing like small cap on the collectors of a fuzz face, But could not see anything in the schismatic that look like any RF blocking iv seen......but as I said I have very limited knowledge    So is Mr Cornish not being honest about the RF filter part of the circuit?

So, maybe I should just try some small caps on a rotary switch between signal and ground?

[antonis]

So is Mr Cornish not being honest about the RF filter part of the circuit?

I can't speak on behalf of someone else..
(maybe Mr. Cornish refered on C2 for RF filter ..  capacitive reactance calculation of 1nF cap with alsmost identical voltage between its plates should be at least interesting..)

[PRR]

I don't see a great "RF filter" here. The closest is the 1nFd cap across the transistor input. Strictly this *passes* RF from input right over to output. But damps the RF on the transistor input diode so it does not demodulate the RF into the audio band. (If we didn't have the4 transistor, there's no apparent reason we need the cap....)

Let's see your real problem situation.

[r080]

It is possible Pete talks about the RF filtering because of the hybrid grounding with the 10n cap from output sleeve to the chassis.

Rob Strand had some things to say about it in this thread:

https://www.diystompboxes.com/smfforum/index.php?topic=123930.msg1173857#msg1173857

[carboncomp]

It is possible Pete talks about the RF filtering because of the hybrid grounding with the 10n cap from output sleeve to the chassis.

So we are talking about this section on the output jack's that probably doesn't make it on most clone schematics? (and does this have any effect on the pedals downstream regards RF?

[r080]

Yup, that's what I was thinking about. It shows up on the Dirk Hendrik G2 schematic. Both the input and output jacks are isolated. The input jack sleeve is connected to the chassis, and the output jack sleeve is connected to the chassis with a 10n cap.

I honestly don't know what effect it would have downstream. Intuitively, I would think anything that getting rid of RF at the first pedal (after the "antenna" of the guitar and input cable would reduce it downstream. However, the way Rob explained it, that cap is reducing RF from the output cable.

Pete Cornish has been making pedals the same way for a long time. It is possible more recent research in the EMI field would say there are other, more effective ways of reducing that noise, such as the suggestions above.