Yaqin SD-CD3 Tube Buffer - upgrading caps - Page 3 - diyAudio
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Old 13th September 2011, 08:11 PM   #21
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Join Date: Feb 2010
Location: London
Hello all, does anybody know when the time is to change the valves ? Not sure what the symptoms of telling would be.
Midrange has become rather grainy and glary of late, especially with vocals, perhaps down to my ageing ears. Would the mid sound glary if the valves were on their way out ?

Thanks
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Old 28th January 2012, 04:49 AM   #22
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Default Yaquin CD3 schematic

Hi folks:
Just bought the CD3 buffer and have access to the schematic, which I thought you boys would like. But I have a vexing issue and some observations to follow in my next message.
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File Type: jpg Yaquin schematic 3.jpg (638.0 KB, 586 views)
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Old 28th January 2012, 05:22 AM   #23
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Default Yaquin SD CD3 tube buffer, a vexing issue

Hello again. Hope you like the schematic.
I'm not a tech, though I've built some kits in my time. I'd appreciate some observations and corrections from the techs in residence.

First, judging from the schematic I've submitted, I'd say that all the capacitors and the 680 & 100K resistors are in the signal path. I concluded that the 20K resistor is not. I'd appreciate any corrections.
Second, in the interest of properly orienting any capacitor upgrades, could someone point out the source and destination or ground sides of the capacitor positions judging from the supplied schematic?

Third, a very vexing issue. There's no damn difference whether my unit is on or off. That is, the system continues to play music when I shut off power to the Yaquin. There's no sonic difference whether on or off. When the unit is turned on, it's 'instant on' with no tube warm up, or turn-on thumps, and likewise when I turn the Yaquin off, there is no shut-down thump and the music continues to play merrily along.

Is it plausible that this unit acts as a 'straight wire' connection when powered down? Or have we been scammed? It just seems improbable that an active circuit would behave like this.
My connection scheme is DAC > Yaquin buffer > passive stepped attenuator > amp.

Any help is more than appreciated.
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Old 28th January 2012, 09:13 AM   #24
Cookj is offline Cookj  Belgium
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Simplistically its a straight piece of wire. If you have a source impedance of say 1K, you have effectively 1K//100K and 20k to gnd ie a potential divider with 1k and 20k. The input is to the 1k and the output from the centre tap.

When powered on, the input inpedance is Zin = Rg / (1 - Av * (Rl / Rl + Rb))

For a better explanation see

The Valve Wizard -Cathode Follower

Regards

John
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Old 28th January 2012, 04:53 PM   #25
Cookj is offline Cookj  Belgium
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I screwed up - see see attachment, this is the equivalent - but its still abit of wire

Similar : Tube Buffer 6J1 / 5654 (6AK5)
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File Type: jpg 1-28-2012 6-45-00 PM.jpg (21.8 KB, 487 views)
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Old 28th January 2012, 09:02 PM   #26
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Default More on the Yaquin

Cookj, thank you for the response.

I originally began this little experiment with the idea that I could add a dusting of powdered sugar to my strawberries. That is, that I could get a bit of the classic tube magic added to the sound of an otherwise very revealing and transparent system. [Bryston 28bSST2 amps, “Ultimate Attenuators,” ([/SIZE][/FONT]http://www.tweakaudio.com/Ultimate%20Attenuators.html[FONT=Arial][SIZE=4]) and a Monarchy DAC which still serves up red book CDs as well as anything else I’ve heard, and Volent Paragon 3.5 speakers. The system is not bright by any means, but I wanted the ability to go back and forth, with or without the buffer as dictated by mood or by software.

Is the Yaquin AC or DC coupled? If I am not jumping to conclusions, judging by your comments and this quotation from the article you referred me to, the tube buffer stage is solely and only for impedance matching and will not impart the same qualities to the signal as a tube circuit with gain: “The cathode follower is an excellent buffer stage for driving a tone stack or effects loop, or any circuit which would otherwise present a heavy load to a "normal" stage. In addition, the DC-Coupled cathode follower can also be used to produce a unique compressive quality, and is to be found in most of the classic amp designs. The AC-coupled version is not so useful for this, since the input-coupling cap prevents the flow of quiescent grid current. The AC-coupled version is therefore used as a tonally transparent stage, usually.”
It would therefore be essentially useless to engage in tube rolling with expensive classic tubes, or to upgrade caps and resistors.[/U] I don’t mind being told I’m barking up the wrong tree. I’ve wasted more money on bad CDs and records. But have I reached the right conclusions? As I’ve stated in my previous post, I hear no difference with the buffer on or off, so why not eliminate the added circuitry? There are no impedance matching problems with my system in a simple ‘passive preamp’ mode.
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Old 30th January 2012, 08:48 PM   #27
fp2000 is offline fp2000  United States
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Quote:
Originally Posted by Foolish Pleasure View Post
Hi folks:

Just bought the CD3 buffer and have access to the schematic, which I thought you boys would like. But I have a vexing issue and some observations to follow in my next message.
what is the purpose of having 2x0.47uF caps in parallel instead of a single 0.22uF on the output?
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Old 30th January 2012, 10:14 PM   #28
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Quote:
Originally Posted by fp2000 View Post
what is the purpose of having 2x0.47uF caps in parallel instead of a single 0.22uF on the output?
Parallel capacitance doubles, series halves. That's the rule of thumb.

So 2x.47uF is .94uF, so you could say about 1uF.
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Old 31st January 2012, 12:21 AM   #29
fp2000 is offline fp2000  United States
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Quote:
Originally Posted by mace1337 View Post
Parallel capacitance doubles, series halves. That's the rule of thumb.

So 2x.47uF is .94uF, so you could say about 1uF.

Yeah, you're right! that's what I really wanted to get to. Can I just replace the two caps for a single 1uF without problem?
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Old 31st January 2012, 10:37 AM   #30
DF96 is offline DF96  England
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A well-designed circuit is not meant to impart any qualities, just pass on the signal with as little damage as possible. This is a simple cathode follower, dressed up to look important (and expensive, I bet). There is nothing particularly wrong with the circuit, apart from missing ground leak resistors at the outputs. As you have found, it still passes some signal even when switched off! In most setups, it should have almost no effect on the signal apart from adding a tiny bit of noise and distortion, probably too little to notice. In most setups it is unnecessary, as there is no impedance problem to solve so it can only be used for cosmetic reasons.

Given the relatively high input impedance (the 100K resistors are bootstrapped, so look much higher in value), changing the input caps will not affect the sound unless you go to much lower values. The output caps need to be big enough to cope with whatever follows. 1uF with a 20K input impedance next will give 8Hz rolloff.

This circuit is AC coupled at both input and output.
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