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In Reply to: RE: "I tried the Wima DC Link caps in my electronics and did not like them at all" posted by drlowmu on March 12, 2017 at 13:26:57
Jeff, As you know, we disagree on the matter of parallel caps or cap bypassing. In my experience, a single very high quality cap always sounds better than a cocktail mixture of different caps, no matter what their value or brand. I can always hear their individual contributions and the result is a less coherent, less organic sound. Bypass caps can make the sound seem faster and more spectacular but it's not as natural. Maybe someone with different priorities would reach different conclusions but that's what I hear.
Follow Ups:
To determine the truth in 2017, take a pair of you latest monos up to Montana, and compare them directly to Dennis' amps, on his 604 MLTLs.Multiple bypassing is an ART, and it is often expensive, to bypass with multiple caps, properly. Dennis is the only one "I" personally know of, in ALL of single ended audio amplifier building, who knows how to do it really well, and he has LOTS of experience doing so !!
Jeff Medwin `
Edits: 03/12/17
Some day, it would be nice to see the "guts" of his 2A3 monos to understand what you're saying.
I don't know how many changes Dennis has been since this picture.
Pretty damned unremarkable looking, isn't it?
I mean, for a guy who makes all kinds of grandiose claims........I expected to see something special.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 03/13/17
re-read my post below. I've added more useful
info to it.
-Dennis-
Thanks for posting the pix of one of my old amps.That one had very good bottom-end response, and
followed the musical groove with alacrity, although
further improvements have been made to date.It exhibited an extended high-end response that
was down about 1.5 to 2.0 db at 40KHZ, depending
on the output tube chosen. Rolloff STARTED at about
15KHZ, but was down very little at that point, with
a Single-Plate 2A3..Perhaps some comments on the Buddy Amp that you
post can be of some help to forum members:Here goes-- I hope I don't leave anything out!:
See that long black A.C. wiring going into the
rectifier filament transformer? Why not locate the
transformer between the A.C. and the tube sockets,
greatly shortening the Line Power leads. This keeps
crap from the line out of the aluminum chassis.Two rectifier tubes in parallel? No. Use ONE.
You can't use a 5R4. The filament has too small
a surface area, and can't deliver enough instantaneous
pulse current on top of the idling current..
Use a MODERN 5U4GB. (Example: JJ 5U4GB, or
Electro-harmonix 5U4GB.I can only guess, but it looks like the filter
cans are probably 70uf or so. C1 and C2. Choke-
input is nice here, but those caps should be
about 35uf. Oils are OK here.See that big Oil Can as C3? Better get THAT
out of there or your Highs are GONE!Looks like you have a nice Plate Choke on the
driver tube-- watch its value carefully. Make tests.
What is that red cap? Perhaps 4uf Dynamicap?
Excellent! Needs a few more small bypassers to
extend H.F., or you'll lose some highs here....Driver plate resistor. Get one that can pass
high-energy pulses accurately. I suggest the
best 2-watter that money can buy.I don't see any form of voltage regulation on the
driver plate supply-- can't tell exactly from the
picture, but it looks like only a voltage-dropping
resistor.This CANNOT work with a high plate-resistance tube
with high gain and low plate current.. The power supply
there must be stiff, and have lots of current available.
A series voltage dropper resistor KILLS the driver stage
thru voltage sag, and current starvation. You won't get
enough power to properly drive the 2A3 grid. The amp will
be a "wimp"-- both power-wise, and bandwidth-wise.Driver cathode bypass: Get that Solen out of
there and get something good-- another Dynamicap
with extensive, careful bypassing, or use an
Audionote copper foil, etc. Don't do it and kiss
your highs and musical swagger goodbye....That ground on the cathode bypass is crap--
all that other junk on that ground rail before
it gets to the driver tube, which is the most important part
in the amp! Re-locate the whole layout/grounding scheme.See the driver tube filament leads? Those run right
parallel to The cathode SIGNAL leads from the 2A3 filament
into the filament transformer. THIS layout has DESTROYED
H.F. response in the amp! Re-Do the whole layout!2A3 cathode bypassing: Get that SOLEN OUT OF THERE!
Cheapo! Another place for a bypassed Dynmicap. Or kiss
some more highs goodbye...2A3 cathode resistor: This is a high-current pulsed
application, so use either two exactly the same resistors
(Mills, etc.) in parallel or use one 50 watt heat-sinked
inductive wirewound power resistor. Smaller sizes WILL
result in reduced dynamics and bandwidth.See the 2A3 filament transformer mounted right next to
the filament transformer for the driver tube? The 2A3
filament trans contains the cathode signal on the 2A3.
DO NOT mount ANYTHING near the 2A3 filament trans. Re-do
the layout.See how close that 120VAC pilot light is to those two
transformers? What do you think the 120V is doing to
that whole area? Re-do the layout! Put all 120VAC into
one end of the chassis, isolated from all else.Grounding system as a whole: It can't be a series string.
It needs to spread-out in increments from a center point,
that is bolted to the chassis at a strategic location only.
Re-do the layout, starting at the A.C. line ground
connection point.2A3 and driver tube sockets: These will sound better when
they have some physical means of isolation from the chassis.Aluminum chassis: This metal will sink high frequencies into
attenuation, but will also add a "whitish" (old audiophile term)
coloration to all music. This is probably a result of aluminum
reacting against the steel in transformers and chokes.For this reason, wood is becoming popular as chassis material.
Steel is better-- much better. It is the same thing as the
transformers-- that is very good, but transformers have to be
elevated above the steel on non-steel mounts. This is to prevent
transformer vibrations from shaking the steel chassis, and
smearing/reducing high frequencies.Look at my older amp picture. In it, you'll find all of these
things, and much more, done right.There is one mistake in my old chassis-- much has been improved
since then, but there is one glaring mistake in it: the H.V.
output leads from the plate transformer are twisted together.That mistake wasn't made in the Buddy Amp.
All of us can still learn... That includes myself.
-Dennis-
Edits: 03/17/17 03/17/17 03/17/17
Thanks for sharing your observations Dennis.
Re-read my post-- above. I've added more
useful info to it.
-Dennis-
This 2a3 amp uses a very similar circuit without as many bypass caps.
I think this layout is much better WRT keeping the AC away from the signal path and keeping all the wires away from....everything (something Dennis claims to be very important and I don't disagree).
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Very neat and orderly with short leads for each connection. If I recall correctly, didn't this have some pretty severe HF rolloff?
Yes but so does Dennis' amp.A 7b4 with a 280k ohm plate resistor has an output impedance of somewhere near 50k ohms.
Dennis says the HF starts to roll off at 15kHz using modern output tubes which have less interelectrode capacitance than old tubes.
Dennis said with a Sylvania 2a3 the roll off starts are 9kHz and with a RCA 2a3 the roll off starts at 11kHz.
That is pretty much in line with the math.
A 50k ohm drive impedance won't drive much output tube Miller capacitance.
The other issue is the current delivery capability (or lack there of) of a 7b4 running less than 1ma.
That Miller capacitance will need to be driven and that takes current. Current that the 7b4 is not able to deliver.
The other problem with the design (my friends and/or Dennis') is the power supply.
The low value caps and low value chokes with low DCR makes for a very unstable power supply.
It's not stable with the amp at idle. When you stat playing music through it all hell breaks loose.
But if some people like the sound of that sort of thing...... who am I to complain?
It's just that for an amp that costs 18k per pair, with "best amp ever made" verbiage surrounding it........I would expect more.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 03/13/17
No thanks. No need to travel to Montana. I am quite comfortable using a single .1uf CuTF V-Cap as a coupling cap and unbypassed 100uf BG WKZ caps in the power supply. They give me the sound I like.
Exactly! We each have different wants when it comes to musical reproduction... even when if/when we think we are simply accurately reproducing what is recorded. Hell, we listen differently to live music, let alone reproduced!
Some folks get it. Others don't, confusing their opinions for some truth...
Okay, Tuesday night rant finished. Back on topic now.
91.
"Confusion of goals and perfection of means seems to characterise our age." Albert Einstein
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