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6C33C OTL - Completion, break in, tuning and impressions

Posted 27th January 2013 at 04:08 PM by wlowes

Done! The second went much faster and was playing music in 2 weeks.

Now that they are running I will borrow from the circuit designer's own description of the sound as it really does sum it up..

"There is no substitute for power and that is what this amp has. Complex musical passages are effortlessly reproduced with a natural depth and breadth unmatched by any other amp. Subtle nuances are clearly revealed underneath pounding crescendos.

Striking imaging causes instruments to be layered in a three dimensional sound stage that recreates the experience of a live performance. The music "opens up" and leaps out of the loudspeaker eliminating any box like sound. The most minute and subtle sounds are revealed producing uncanny realism. Musical voices are warm and lifelike yet completely neutral with a razor sharp focus."

In my own words.. incredibly natural. 3D and layered sound. Deep bass with weight creates...
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F6 Clone Convertible PCB blog

Posted 27th January 2013 at 12:48 PM by Tea-Bag
Updated 29th June 2013 at 07:30 PM by Tea-Bag

Here is the F6 board rendered by CRT and some help from others.

Click the image to open in full size.

It's convertible premise is to be able to swap out transformers using daugter cardsand be able to swap out variations on the schematics Nelson Pass presented at the 2012 Burning Amp Festival.
Additionally, places for two pairs of 2SK/2SJ are here to allow GR's to be used to allow for higher than 8ma IDSS without degeneration on the front end. If you have 8ma IDSS BL grade for use here, than your all set.
You can use standard power resistors or 5MM thin film type.

Click the image to open in full size.

Here are some of the daughter cards that mount to the main board. They are available for Jensen, Cinemag and Onetics Quadfilar transformers.
These are mounted with 2 2x10 @ 2.54 mm pins. Note the PC PINs of...
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High-end chipamp build project

Posted 24th January 2013 at 07:21 AM by abraxalito
Updated 15th February 2013 at 05:12 AM by abraxalito

Go here : Possibly the most frugal high-end sounding amp?

If you have comments, feedback, critique or improvements and don't want to put it on that thread, feel free to leave it in the comments here.

Here are the first measurements - the Nitro amp being fed by the Ozone DAC with a six-tone multiple, peak digital level -20dB. Peak output power around 100mW in an 8R speaker (connected for this test). It looks from this that the datasheet is a little pessimistic on THD, though here I'm measuring the TDA8566, not the 8561. No measurement graphs are presented in the 8566 DS and the 8561 only has plots for 2R and 4R loads, not 8R.

Schematic now added. BOM here :

Additional schematic showing how to use TDA8566Q in place of TDA8561Q as the latter isn't available from Mouser. Mouser only has fewer than 300 TDA8566Q in stock so best...
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Posted in Power chip amps
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My Horn Project

Posted 21st January 2013 at 11:13 PM by DougL

I have 2 Horn projects.
I would like to try a
SEOS / Econowave style with a SEOS 12 / 15 and a Denevo 360 compression driver.

I also want to try a LTO style 3 way

I am trying t do this inexpensively.
Looking at JMLC 400 1.4" mid-ranges
Radian 636 CD
B&C DE10 or B&C DE7 CD
JMLC 1000 or JMLC 1400

Looking for an approprate woofer.
The GPA 515 is beyond my means at the moment.

JBL 2226H are also reputed to be great

The TD15M has a following.

I have a DCX2496 and 6 channels of 30W class D amplification.
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Featured VT: The 6BQ7

Posted 19th January 2013 at 07:01 PM by Miles Prower

Click the image to open in full size.

This is a small signal dual triode in the nine pin mini format. From the spec sheet:
The 6BQ7A is a miniature, medium-u, twin triode primarily designed for use as a cascode radio frequency amplifier in very high frequency TV tuners. In this application, its performance is characterized by low noise figures and high gain.
From the piccie, it's obvious that this is indeed a high frequency triode. It has the additional advantage of a high gm, made possible by the comparatively enormous cathodes. These are much larger than those of other small signal types like the 12AU7, 6FQ7, 6SN7, 6C4. The 6BQ7 also has a u-Factor that falls nicely between types like the 12AU7 or 6FQ7, and the 12AT7.

The spec sheet even includes a composite plate characteristic for cascode operation. What you don't find is any mention of any sort of audio applications. The RCA Receiving Tube Manual does make a concession...
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Boozehound Labs MM Phonostage

Posted 19th January 2013 at 05:06 PM by MagnumOpus

I needed a decent RIAA, and have found that I really like the sound of J-Fets. Maybe its purely metaphysical, maybe not. Still I am thrilled with the sound of of this thing. It it buildt with the kit from Boozehound Labs ebay listing.

At first I thought it sounded somewhat "too fast", too dynamic, too..."bouncy"..but when settled in..I am just flabbergasted by how sweet sound so little money can buy.

The only thing is the power supply. I have tried to different wallwarts, both incredibly noisy, and both switchmode, allthough my latest is regulated it still produce a lot of noise. So, I am building a Sigma 11 to power this thing, I'll have to live with the noice for now, it will only be for a couple of months anyway.

Pictures to come when I remove it from my setup to take som gut-pictures .
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Featured VT: The 6J5

Posted 19th January 2013 at 02:37 AM by Miles Prower

This type is a singleton triode with an octal base. As nine pin mini types proliferated during the early 1950s, few singleton triodes were made, and the few that you do find are almost always VHF amp types intended for 400MHz+, running as grounded grid amps. Most triodes were made in pairs, such as the 12A*7 series, or the 6FQ7, 6DJ8, etc. If you need a singleton triode in the seven or nine pin mini format, you will either have to go with a type like the 6C4 (a type that is not recommended as an audio triode, but rather a low power, Class C RF driver/final) or make a pseudotriode from a small signal pentode. (The 6AU6 works nicely for this, and it has a u-factor that fits nicely between the medium-u triodes like the 12AU7 and the high-u types like the 12AT7 or 12AX7).

The 6J5 appeared with the Octal base, and metal envelope. There is also a glass Octal as well, but is much harder to find, and more costly to acquire. Regardless of packaging, the type is a small signal, medium-u,...
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Featured VT: The 6BQ6

Posted 18th January 2013 at 01:45 AM by Miles Prower

The 6BQ6 as an audio final came to my attention as a chance result of finding
an old article from a Portuguese (Brazilian? -- it was written in Portuguese)
ham magazine. This described a simple AM plate modulator that claimed an output
of 30W (fixed bias) or 25W (cathode bias) that used a push-pull pair of these
VTs. You would expect to see 6L6s or 807s used in this particular application.
Why 6BQ6s, and what were they?

The 6BQ6 is a large signal beam former. It has no audio pedigree
whatsoever, and the spec sheet makes no mention of its use as an audio final.
During the 1950s, screen sizes and deflection angles increased, giving a larger
viewing area, and a shorter CRT for more compact TV sets. This development meant
that the usual audio finals and RF types became increasingly unsatisfactory for
horizontal deflection duty. New types more suited to the task were developed,
and one such type was...
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Rating: 2 votes, 5.00 average.

Featured Vacuum Tube: The 807

Posted 15th January 2013 at 10:05 PM by Miles Prower

Featured VTs: The 807

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The first of the beam formers is also one of the most enduring types: the 6L6. Developed by RCA in the mid-1930s, this type was originally intended for use as an audio final. It included other, then new, features besides the elimination of an actual, physical suppressor grid required to smooth out the screen grid "kinks". This included the now standard Octal base (up to eight pins possible, and with a keyed base for proper socket alignment) and a metal envelope. The latter was made in one of two ways: a glass envelope VT slipped into a metal shield can, or using the shield can as the envelope, with a glass base to bring out the connections. Other improvements was to give the control grid and screen grid the same pitch and wire diameter. By overlaying these two grids, the negative control grid serves to "shadow" the screen, thereby reducing the useless...
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Modification of the S.M.S.L. sAp VI headphone amplifier

Posted 14th January 2013 at 11:29 AM by rjm (RJM Audio Blog)
Updated 28th January 2013 at 12:33 AM by rjm

I couldn't even build it myself for the price they are selling it at, $50 on ebay. It caught my eye for the linear, split power supply. I love the chrome 3-pin power connector, too.

As is usual when you buy cheap ultra-Chinese audio gear via eBay some adjustments are needed, however.

The basic problem seems to be a little mix up with the input coupling capacitors. It came with polar electrolytic capacitors, following the markings on the circuit board. If you lstudy the schematic I sketched up below you will notice the input signal and DC offset can swing in both positive and negative directions relative to the op amp inputs - polar capacitors in this position are a bad idea.

I recommend anyone buying this to replace the input caps with Nichicon Muse ES or similar 4.7 uF or 10 uF bipolar electrolytic caps. (I have some extra I can mail out. pm me if interested.)

Other than that it's a pretty solid circuit as far as I can see....
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Posted in The Lab
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