Is it just me or is the Simulcast kinda bright?
- Thread starter HamishR
- Start date
I got my 2N4033 transistors from Mouser. I really like 'em. What I have done now to tame the brightness is simply put a cap across the base and collector of Q2, the Ge transistor or 2N4033 depending on which one you are using. With the 2N4033 I am using an 820pF or 1nF cap. I haven't decided which I prefer. I find I can get very similar treble response to bypassed with anything from 1n5 to 2n2, but I actually prefer just a tiny treble boost. Call me fickle!
mybud
Well-known member
'Although the term Miller effect normally refers to capacitance, any impedance connected between the input and another node exhibiting gain can modify the amplifier input impedance via this effect. These properties of the Miller effect are generalized in the Miller theorem. The Miller capacitance due to parasitic capacitance between the output and input of active devices like transistors and vacuum tubes is a major factor limiting their gain at high frequencies. Miller capacitance was identified in 1920 in triode vacuum tubes by John Milton Miller.'
en.wikipedia.org
I assume that this means in plain English that there is interference between successive gain stages in an amplifier circuit which can lower the impedance of the input stage, so adversely affecting the behaviour of the circuit. IOW it's designed to function within a given impedance range and the Miller effect (stray capacitance) messes up the frequency response so that what works on paper in the design doesn't do what it ought to.
That's my story and I'm sticking to it. Perhaps a real circuit guru can confirm my layman's understanding in due course.
Miller effect - Wikipedia
I assume that this means in plain English that there is interference between successive gain stages in an amplifier circuit which can lower the impedance of the input stage, so adversely affecting the behaviour of the circuit. IOW it's designed to function within a given impedance range and the Miller effect (stray capacitance) messes up the frequency response so that what works on paper in the design doesn't do what it ought to.
That's my story and I'm sticking to it. Perhaps a real circuit guru can confirm my layman's understanding in due course.
jhaneyzz
Well-known member
I tried bridging pins C and B of Q1 with a 1nf cap and I can't hear any impact whatsoever.
I am pretty satisfied with a 560pf between pins 1 and 2 of volume however.
jhaneyzz
Well-known member
And.... of course I skimmed right over the " I'm using a 2n5088 so ignore the transistor orientation." @daeg mentioned and I was testing the wrong legs.
Still crazy subtle to me. on a whim, I grabbed the next cap in my set which was a whopping 4.7nf and tested it, and it actually sounds pretty good to. my ear. not sure what's up with that.
However, since for some forgotten reason I didn't socket ANYTHING on this build, it's going to be easier to just solder a cap on the volume pot and call it a day.
I'll use more foresight when I j build the Duocast mini as soon as they hit the store.
Thanks for everyone's support.
Still crazy subtle to me. on a whim, I grabbed the next cap in my set which was a whopping 4.7nf and tested it, and it actually sounds pretty good to. my ear. not sure what's up with that.
However, since for some forgotten reason I didn't socket ANYTHING on this build, it's going to be easier to just solder a cap on the volume pot and call it a day.
I'll use more foresight when I j build the Duocast mini as soon as they hit the store.
Thanks for everyone's support.
Harry Klippton
Well-known member
andare
Well-known member
Sorry but I am Latvian orthodox, we don't put caps on collectors.
We believe God created everything to be perfect, silicon transistors with their saintly harshness included.
What's next, using trimmers on Germanium transistors to mess with the Grand Celestial Bias? Not on our watch!
Chuck D. Bones
Circuit Wizard
I sseem to recall you saying somewhere that you left the transformer out on your Broadcast. That transformer has limited bandwidth and eats some of the treble content.
Chuck D. Bones
Circuit Wizard
Miller caps are useful, but they lower the input impedance of the stage at high freq and must be applied carefully.
Harry Klippton
Well-known member
Long press on the button
jhaneyzz
Well-known member
So what then would be the Latvian Orthodox alternative to taming the 6kish spike in the Simulcast (without inserting a lead in a solder lug) <inside joke from another thread>
Big Monk
Well-known member
I start very small and test until I get the noise reduction and/or frequency supplementation I want.
What I usually do is built the circuit stock and listen to the baseline noise floor. Then I add suppression caps until the noise floor is how I want it.
After that I typically tweak the stock frequency shaping caps down to compensate for the frequency shaping provided by the smaller caps.
I definitely don’t subscribe to generic recommendations like, “Use a 470pF cap from base to collector…”, etc.
Chuck D. Bones
Circuit Wizard
It may very well be a resonance in the transformer.
You could try removing the transformer and jumpering pins 1 & 6, or experimenting with an R-C damper across R15. Other than the transformer, I don't see anything in the circuit that wold cause a high freq peak. Putting a cap on Q2 is a band-aid.
jhaneyzz
Well-known member
I'm going to apply the band aid on this one and call it a wrap. at least for now. It's for me so I can always bust it back open if i decide to.
As well, I will definitely be building this again (on the list for the Duocast mini) and will build with sufficient sockets and such this time to allow for a more measured and flexible "finishing process"
I learn a lot of great new things every time and you all are helping with that dramatically.
As well, I will definitely be building this again (on the list for the Duocast mini) and will build with sufficient sockets and such this time to allow for a more measured and flexible "finishing process"
I learn a lot of great new things every time and you all are helping with that dramatically.
andare
Well-known member
Join our church to find out!
I have one on the bench. Pretty sure I'll try to sell it if it's as bright as everyone says.
jhaneyzz
Well-known member
I’ve only ever heard us cork sniffers bring it up. BTW the bleed cap I installed tamed the treble AND the tiny voices in my head telling me to buy a Schecter guitar went away as well… so… bonus!
I put the cap on Q2 and it works just fine. 1nF sounds good.
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