conjunctive filtering

RE: conjunctive filtering, posted on August 1, 2016 at 00:22:10
Frihed89 Audiophile Posts: 15703 Location: Copenhagen Joined: March 21, 2005	Draw the filter circuit, please.

RE: conjunctive filtering, posted on August 1, 2016 at 10:58:40
dcal40@aol.com Audiophile Posts: 45 Location: NY Joined: July 30, 2016	here it is....basically an output filter across the transformer primary to flatten out HF.

RE: conjunctive filtering, posted on August 1, 2016 at 13:02:38

Paul Joppa
Industry Professional

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Location: Seattle, WA
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I think that circuit would be sensitive to the specific output transformer, and probably to the speaker as well.

It looks to me like it is there to assure stability in the presence of feedback. With beam tetrode or pentode, the plate impedance is very high, so the voltage gain increases at high frequencies due to the transformer's leakage inductance and/or the inductive component of the speaker impedance

Normally if the tube is triode-wired the plate impedance is low so this is not a bad problem. Also most SET designs have no feedback.

RE: conjunctive filtering, posted on August 1, 2016 at 16:08:16

dcal40@aol.com
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Posts: 45
Location: NY
Joined: July 30, 2016

Paul, Thanks for that great explanation. In my experience the effect of this output filter appears to have a similar effect as using a zobel network on a cone speaker. It tightens the sound at the expense of some excitement. I have used a 5K resistor in series with a .01mF cap, both in parallel with SE transformer primary. The filter seems to tame ragged frequency response and it seems that the amp can drive the load with less tubby flabby loose low end with a somewhat rolled and "tame" HF. ( does it stabilize output impedence???). I have mixed feelings about the result but overall it is somewhat beneficial with my 6SF5 RC coupled to triode strapped EL34 into a Tomiko 2.5K SE OPT into various speakers, Dayton PS220, Altec 420, infinity overture 1s etc....It seems like a useful tool for 'scrapbox' amps made from less than exotic parts. Input from other enthusiasts welcomed, Thanks, David Calvello

taming "ragged frequency response", posted on August 2, 2016 at 00:01:54

Frihed89
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Posts: 15703
Location: Copenhagen
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I have not seen the measurements for your speakers, but from my limited experience, this is mainly associated with single driver speakers. My also limited experience with zobel networks is that they induce roll-off at the high-end (some highs are lost). Is that related to the taming effect you wrote about?

On a different subject. I have single driver speakers, but they are crossed over to a ribbon tweeter and I don't hear the jaggedness in the treble. An example is Tonian Labs speakers: relatively high sensitivity (95-97dB) and flat impedance curve > 6 Ohms all the way.

RE: conjunctive filtering, posted on August 2, 2016 at 00:48:02
Lenin	Try to measure the output (loaded with 8 Ohm resistor) with a 1kHz square wave. It should be a very tight square wave. If not you can tune it with a zobel network ( or if there is any global fb in the fb circuit) It's more a test to see if the transformer is reasonable quality.

Common for guitar amps., posted on August 3, 2016 at 05:26:36
Chip647 Audiophile Posts: 2653 Location: The South Joined: December 24, 2012	Using a conjunctive filter like this will make an amp that has a very brittle tone into one that is smoother. It attenuates the high frequencies. It is just a type of RC filter.

There's an online calculator for everything, posted on August 3, 2016 at 08:18:42

kyle
Audiophile

Posts: 1839
Location: London Ontario
Joined: September 29, 1999

see link

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/rlcparc.

RE: There's an online calculator for everything, posted on August 4, 2016 at 08:03:43
Lenin	Nice link and maybe usefull but remember a truth transformer is more complicated, specially if a transformer is not so good complications will occur.

RE: Common for guitar amps., posted on August 5, 2016 at 01:52:24

Michael Samra
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Location: saginaw michigan
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Using a conjunctive filter like this will make an amp that has a very brittle tone into one that is smoother. It attenuates the high frequencies. It is just a type of RC filter.

Exactly.He is going to lose bandwidth in the upper ranges just to mute some of the harshness so now it becomes self defeating to have a tube amp.

"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

This is why test equipment such as a scope and signal generator, posted on August 5, 2016 at 02:57:46

Michael Samra
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Location: saginaw michigan
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and distortion analyzer is so invaluable in this case.If you think about harshness and what is really,its more or less a higher distortion product in the higher frequency ranges or an exaggeration in the sonic curve in the upper ranges.

You mentioned this amp was a pentode but wired as a triode.If the amp was designed as a pentode and you wired the tube as a triode by adding the resistor between pins 3 and 4 of the EL34,you now effectively lowered the plate resistance of the EL34 and assuming you did that,you may have to recalibrate the circuit values especially if you used global NFB.
This is where a sweep of the amplifier would tell you what has changed and where..This assuming that the amp had a nice flat response as a pentode in its original form.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

RE: This is why test equipment such as a scope and signal generator, posted on August 5, 2016 at 08:50:49
Hornlover Manufacturer Posts: 2529 Joined: March 8, 2002	I totally agree. I could not do this hobby without basic test equipment. You can get a decent scope, SG and multimeter for very little (relatively speaking). A good used analog scope can be had for $100 if you look around. A new SG for similar prices.

SET Asylum

conjunctive filtering

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