Conquering RFI in the 2C22/7193

Noisy and unstable 2C22/7193

Moving closer to civilization, this lovely sounding triode used as a voltage gain stage in my SE2A3 mono integrated amp had stability issues due to RFI. 

Since I persist in using these antediluvian devices, I had to find a solution.

A 150 ohm 1/2W CC resistor with the leads cut short soldered in series with the grid cap (insulate with heat shrink tubing) >> shielded cable terminated by an RCA plug (shield connected only at the RCA jack side) >> RCA jack (barrel grounded to chassis) solved the stability issue.

A well behaved 2C22/7193 

Altec 32A, 32C, Emilar EH1210, EH800, EH500 and Faital Pro STH100

+ 

This is a cumulative report on horns I listened to and tested from May 2016 until the end of 2017. All the tests were done through the mono hifi rig using the above Altec 802 compression driver fitted with a GPA 34852 diaphragm + an Altec 414A in a repurposed Altec 861 cabinet running in full-range mode tied together by a 6dB/octave high pass crossover/EQ hinged at 2500 Hz. 

Altec 32A and 32C

Altec 32A (top)
Altec 32C (bottom)

 The Altec 32A (metal) and 32C (plastic with ribs) horns are lineal descendants of the Western Electric 32A horn as found in the WE753 speaker system. I've had the plastic 32C since '09 and lived with the metal 32A for over a year and can say that these are the most sophisticated native 1" horns I've heard and owned to date.

Altec 32A

Altec 32A

Altec 32A + 802 + 414A

Altec 32C

Altec 32C

Altec 32C + 802 + 414A

Metal or plastic? 

It's ironic that the later plastic 32C sounds more vintage than the earlier metal 32A. Definitely, the longer throat of the earlier 32A and the type of material used for construction influence the sound. But in what capacity, I cannot surely define. The iPhone RTA results reinforce the cooler and more modern sound I hear from the metal 32A versus the warmer and sweeter plastic 32C.

The magnitude of difference is not great. Similar to the 20275 vs. 34852 Altec 1" aluminum diaphragms - distinct enough not to be used as a stereo pair but still excellent performers in their own right. However, those who are expecting a front-row presentation may find both these horns too laid back.

Watch out for roughly finished throat edges in the 32A which are detrimental to performance. So far all the plastic 32Cs I've seen have very smooth throats.

Emilar 

As soon as I landed in the US in May 2016, I tried to collect the Emilar horns talked up by Joe Roberts in his war against the devil's trumpets before they became unaffordable. 😉

EH1210

Emilar EH1210

Emilar EH1210 + 802 + 414A

This wasn't recommended by J-Rob but it was cheap enough to try. The EH1210 has the most extended high frequency response according to the iPhone RTA but subjectively it was the least refined sounding horn in this group. I think one can do much better with some modern offerings, see the last entry below. 

Emilar "Bowtie" EH800 and EH500

Emilar EH500 (left) + Emilar "Bowtie" EH800 (right)

WARNING: these two Emilar horns are heavy cast jobs, doing the audiophile knuckle test can result in serious injury! 😃

EH800

Emilar "Bowtie" EH800 

EH800 + 802 + 414A

If you are looking for a modern sounding horn with a more forward presentation but without the shout and distortion of the Altec 811, then this is the horn for you. Exciting sound but guaranteed not to make your ears bleed. 

I think the low end cut-off at 800 Hz spec is a bit optimistic. For maximum satisfaction start around 1200 Hz and work upwards.

EH500

EH500

EH500 + 802 + 414A

This is a native 2" horn with a finely machined 1" - 2" throat adaptor. Once again I find the 500 Hz cut-off an overestimation for a horn of this size. I'd start crossing around 900 Hz and up. 

My ears do not agree with the iPhone RTA. I found this horn to be mellower than the EH800 "Bowtie." The tonal balance of the EH500 is somewhere in between the Altec 32A/B/C and the EH800.

EH500 in Large Format Mode

EH500 sans adaptor + Renkus-Heinz SSD3301

With the JEL N1600 XO in tow, I removed the 1"-2" throat adapter and bolted the 2" exit Renkus-Heinz SSD3301 directly to the horn to sample large format tones. I got juicy mids and smooth highs from this combo.

Late addition:

Faital Pro STH100

Faital Pro STH100

I wanted to sample what can be had off the shelf at Parts Express for under $100 and ordered a pair of these small aluminum tractrix horns by Faital Pro.

STH100 + 802 + 414A*

*RTA was done at a later date in another location,
hence the difference in low frequency response 

With the Altec 414A running full range and the STH100/802 combo crossed at approximately 2500 Hz, I got very clean (if a bit dry) high frequency harmonic augmentation with no nastiness at all. To my ears, this tractrix horn is preferable to the EH1210.

CODA

For the past 4 years, I've been blogging about horns and compression drivers. Justifiably, the horn/driver combo seasons the speaker system's sonic flavor. However, these components only cover the upper three octaves of the audio band (mostly harmonic overtones). I would be remiss if I didn't stress the greater importance of the Altec 12" 414 woofer/midrange because it is tasked to reproduce most, if not all, of the fundamental notes in music from 30 Hz to 4000 Hz. That's seven octaves, practically the frequency range of a piano.  

I've been trying, but so far haven't found alternative 15" or 12" woofers that play the midrange as well as the Altec 414. The good news is, Bill Hanuschak of Great Plains Audio told me last year that they still re-cone 414s and their product page lists an Alnico 414-8B(16B). 

Temporary Hi Fi 2018

Set-up in the living room until I finish renovating the man cave

Altec 2-way XO Redux

This is an update on crossovers I use for the Altec 2-way speakers.

JEL N1600 Crossover

JEL N1600C + HF EQ
optimized for the 802 driver fitted with the original
16 ohm 20275 diaphragm

The above crossover circuit, as discussed in this previous post, was optimized for my cherished pair of green Hammertone Altec 802Ds fitted with the original aluminum 20275 diaphragm, which has an aluminum wound voice coil. To my ears, this diaphragm has a more prominent midrange response which necessitates rolling off the upper midrange/lower high frequencies of the 414A woofer for flatter response.

JEL Universal Altec 2-way XO

For the Altec 802 driver equipped with the 34852 (16 ohm) or 34647 (8 ohm) diaphragms, which have copper wound voice coils, I recommend the 6dB/octave crossover circuit below which is hinged at around 2500 Hz + high frequency EQ boost. This aluminum diaphragm has less energy in the upper midrange giving a tonal balance that sounds more extended in the high frequencies compared to its 20275 predecessor. In this implementation the Altec 414A woofer is connected as a full-range driver inspired by Joe Roberts. 

JEL Universal Altec 2-way XO with HF EQ circuit

Altec 414A + 32A/802/GPA 34852
+
JEL Universal Altec 2-way XO

I've also used this crossover successfully with the Altec 802 driver fitted with the Symbiotik diaphragm, Emilar EA/EC175 and Renkus-Heinz SSD1800/1400. Please take note of the different capacitor values for 16 or 8 ohm drivers.

Simplest Crossover

If you want the simplest crossover, my buddy Joe Roberts listens to his Altec 414A/802/32 set-up with the woofer in full-range mode + a 1.5uf paper in oil cap for the compression driver, no L-pad or HF peaking EQ circuit. See his Audiokarma post for more details.

Happy Holidays and a Great New Year to All!

JE Labs Loctal Preamp

Motivated by Ding's octal version of the 834P, I quickly got my hands dirty punching out and painting a chassis. 

Loctal tubes

The concept of this project was to build a full function stereo preamp utilizing loctal tubes based on the schematics below.

Preamp circuit

!!!WARNING!!! 

The voltages found in this circuit can be lethal! 
Build at your own risk!!!

Power Supply

5AZ4 rectifier = 5Y3 on a loctal base

Line Stage

Zero feedback single gain stage direct coupled to a cathode follower line stage topology featuring the two medium-mu triodes below

The 7AF7 is very similar to the 7N7 and 6SN7
but has slightly less
transconductance and inter-electrode capacitance

7N7 = loctal based 6SN7

Phono

The stock EAR 834P circuit (above) used all high-mu 12AX7s with the second stage capacitor coupled to the cathode follower stage. While preparing this blog entry, I remembered that my dearly departed friend, mono aficionado Brian monofantastico Clark, grafted his own interpretation of an EAR 834P phono stage to his SE 801 mono integrated amplifier. He was an active participant in this discussion of 834P modifications initiated by Thorsten Loesch.

Ding's octal version of the 834P uses all 6SL7s with the second stage direct coupled to the cathode follower stage. Without ever sounding harsh, Ding's octal 834P sounded brighter and had a refreshing airiness in the high frequencies compared to my darker and more midrange oriented RCA derived phono preamp. Even if I never heard an original EAR 834P, I now have a good idea why it was received with great enthusiasm.  

7F7  = 6SL7 on a loctal base

Although the 7B4 and 7B6 are high-mu loctals, they are single triodes. AFAIK, the 7F7 is the only high-mu twin triode available in loctal and was the obvious choice for the 1st and 2nd stages of the 834P circuit given my chassis configuration.

Tube rolling loctal style

I've been tweaking and listening to this preamp for the past 6 months.

During my Dyna PAS hacking days, the 12AU7 always sounded gutsier in line stage and cathode follower applications than the 12AX7 because it had lower Rp and pulled more current. Thus, there was some room to voice the 834P circuit through the cathode follower section.

Warning: 7F8 is NOT plug-in compatible
with the 7N7 and 7AF7

I initially set up the phono section to use the unique 7F8 loctal in the cathode follower position, hoping that the 7F8's greater transconductance will produce a darker and more robust sound. But ultimately, it was the ubiquitous 7N7 (loctal 6SN7) that gave me the tonal balance I wanted, with the 7AF7 as alternate.

With an amplification factor of 48, the 7F8 may not have enough gain as a phono preamp with the RIAA EQ in the negative feedback loop. However, it was too much for a zero feedback single stage line amp.

Typically, I don't split halves of twin triodes for left and right channels. I made an exception in wiring this line stage so that I could exploit the 7AF7 vs. 7N7 comparisons and usage options.

My ears finally chose the 7AF7 as the voltage amplifier for the line stage. The slightly lower transconductance and amplification factor mimics the exotic tonal qualities of its grandad, the 76. Each half of the 7AF7 is direct coupled to half of a 7N7 configured as the cathode follower. This combination is as close as I could get to my 76/6SN7 line stage.

But don't limit yourself to this report, use it as a starting point for your loctal tube rolling adventure. 😉

Which is better?

or

Both are here to stay. 😎

🎅🎅🎅 Happy holidays and merry listening! 🎄🎄🎄