The JBL 4345 Club

[speakerdave]

If you are interested, a show of hands would be welcome.

Me! Me!

[Ian Mackenzie]

Understood. I am still trying figure out how to design and build a good sounding active H/P xover at 290 Hz just to simply biamp mine - the LF isn't nearly as demanding IMHO, I plan to use my Ashley's for the low pass. I'd be interested to see what you plan for the 2405 in this regard. Maybe a third order passive in front of the amp would be the way to go? Not exactly good engineering, though.

I'm just thinking out loud, here.

Chas,

If you pm me I will sent you some design details.

About the 2405 I already have a very good 3rd order HP filter using a discrete low noise opamp.

The initial idea was to upgrade it as a high power opamp with enough bias current to driver the 2405 to 3 or 4 volts. Simple enough to do but I have not had time to look too closely at it this week. It woud be along the lines of the Borbely headphone amp. As a one off add on project I think it would be very interesting and fun!

But once you start to think about that you start looking at the bigger picture and I think that would happen soon after the 2405 update was done. I would like to give members the opportunity to discover for
themselves the true musical potential of these vintage systems.

Looking more broardly we have learnt from GT some of the weaknesses of these systems and some of the simple ways of dealing with them. I hope that Porschedpm will be able to publish an outline of his upgraded 4343 to 4344 project soon that includes many of these updates and a very high quality active crossover that I provided for analysis and subjective assessment. If Porschedpm's review is favourable in his system driven by a Passlabs X250 and X150.50 power amps I would be happy to a consider a limited diy active crossover from my kitchen table specifically for the 290hz crossover point. I have thought about it but I think quad amping is way too complex with cut and dried JBL designs like these that have been worked over as there are more gains to be had with simple improvements like charge coupling the passive crossover and improvements with better power amplifiers.

Ulimately a chain is only as strong as its weakest link and for this reason it is my firm view that Class A power amp operation is absolutely essential with the fine resolution and high sensitivity of the mid / horn and uhf transducers used in these systems. The intent of Charge Coupling is analogous to Class A amplfication and the benefits are subjectively and immediately obvious.

Unfortunately most consumer audio amplifiers are least best at low drive levels and this manifests itself as a loss of resolution and sonic glare in the upper midrange and highs.

Unfortunately the larger 800 hz exponential horn and lense used with the 2420/2421/2425 in the less complex 43XX systems is renown as one of the worst offenders of abrasive signal content. The shorter 2307 horn with 2308 used in the JBL 4343, 4344 and 4345 is a far better candidate and when paired with a Class A amplifier the issues are not nearly as apparent.

When you employ all these improvements the subjective enhancements are cascaded and it is hard to imagine how you could ever endure going back to the stock system.

Frankly I think there is more fun and enjoyment to be had from carefully enhancing these systems than shelling out very serious amounts of money on the lastest hardware.

Ian

[andresohc]

I would love to get into this too as I build my psuedo 434X mutant Home theatre system.

[Ducatista47]

Ian, scratching up the money and time to build/install are the only boat anchors for me. My interest is always keen for your 4345 mods, but so far I haven't gotten to even disabling the biamp switch. Bear with me, but boy is my hand raised.
Not as handsome as Speakerdave's furry hand, though.

Clark

[porschedpm]

.... I hope that Porschedpm will be able to publish an outline of his upgraded 4343 to 4344 project soon that includes many of these updates and a very high quality active crossover that I provided for analysis and subjective assessment....

I’ve been invited by Ian Mackenzie to publish an outline of the upgrades that I’ve made to convert my 4343’s to 4344. And give my impressions of the resulting sound. This 2 ½ year upgrade process has culminated with the recent addition of custom built active and passive crossovers built specifically for my application by Ian. I cannot brag enough about these crossovers. They bring out the best of both the speakers and the components upstream. The quality of the crossovers you chose to use really can make or break your system. The outline for these upgrades and my listening impressions can be found at the 4343-to-4344 upgrade thread at:

http://www.audioheritage.org/vbullet...&postcount=228

Before anyone discounts these upgrades because they relate to mere mortal 4343’s converted to 4344 spec, and not to the highly venerated 4345’s to which this thread/club are devoted, let me just state that many of the upgrades suggested for the 4345 by GTimbers in post #27 earlier in this thread have been followed as part of the 4343-to-4344 upgrade process. Specifically:

• Eliminating the bi-amp switch.
• Bi-amp the speakers.
• Updating the crossover networks.
• Eliminating the L-Pads.
• Making sure all upgrades are reversible so as to not impair resale value.

Of course the upgrade process also included replacing every driver in the cabinet, with the exception of the 2405, with the drivers specified for the 4344. There is also detailed discussion about uprading the crossovers. So if you’re interested in how this all came out and how it sounds, I invite you the link over to the 4343 to 4344 thread.

[Ian Mackenzie]

Hey Ed,

I asked for just a few lines....not the ten commandments.

Thanks again for sharing this.

Ian

[Ian Mackenzie]

Okay,

It looks like Ed wants to go top shelf so it might have to be one of these.

This particular amp is a mini class A power amp with some similarities to the amps Ed is already using in his system. Ideally, all amps in the mid and high registers should be of identical design/type so this may be a precurser to other things!

Ian

[Ian Mackenzie]

I am organising parts for this project at the moment, something should emerge in a next few weeks!

Ian

[John W]

I will soon be building a bi-amp only version of the 4345 with Giskard's equivalent 3145 network.
I saw some earlier posts suggesting it was ok to remove the 3db lpad on the 2122H and add a 10 ohm zobel, like the picture below.
Has anyone tried something similar, and do you need to compensate the HF and UHF networks to account for the 3db difference? It only looks like there is +4db available on the lpad adjustments to begin with.

[Ian Mackenzie]

John,

Hi, I have not attempted this alteration but plan to soon.

What you have said appears correct. There will be only +1 db of adjustment on the horn and slot.If you are looking at the new equivalent you could mess with the fix attenuation using 10-11 ohms to model the new values.

Ian

[Ian Mackenzie]

Some parts arrived so I will start work on Slot energiser soon

Ian

[Ducatista47]

http://www.audioheritage.org/vbullet...&postcount=228

Before anyone discounts these upgrades because they relate to mere mortal 4343’s converted to 4344 spec, and not to the highly venerated 4345’s to which this thread/club are devoted, let me just state that many of the upgrades suggested for the 4345 by GTimbers in post #27 earlier in this thread have been followed as part of the 4343-to-4344 upgrade process. Specifically:

• Eliminating the bi-amp switch.
• Bi-amp the speakers.
• Updating the crossover networks.
• Eliminating the L-Pads.
• Making sure all upgrades are reversible so as to not impair resale value.

After reading this post again, I am reminded of my initial impression of Mr. Timbers' post. I thought immediately how very many JBL designs - pretty much almost all the speakers we most covet - would benefit from the suggestions made to improve the 4345 and the 250Ti. The slot had a (fifty year?) production run, L-pads are a fixture of JBL baffle boards, all crossovers have room for improvement, etc. etc. I see opportunity everywhere, at least back to the sixties.Think of an upgraded S7. Makes my mouth water. Hmm, I wonder if ring radiators would benefit from a chip amp? I always loved the S8R.

Clark in Peoria

[Ian Mackenzie]

Initial impressions of charge coupled unbypassed equivalent network.

http://www.audioheritage.org/vbullet...7&postcount=80

[Ian Mackenzie]

To CC or to not CC..I don't know YET

http://www.audioheritage.org/vbullet...0&postcount=87

[Major Petty]

Well, the rest of us do so feel free to follow our lead...

or not... it apparently takes all kinds to fill the freeway.

I'll bury a version of the DD66000 white paper for everyone as promised for 13 SEP 2006 in this thread. It runs charge coupled Solen capacitors and it "works" just fine. Note the references (yet again) to the biased capacitors in this white paper. Be mindful that the gear associated with running something like a DD66000 is usually pretty "top end". In other words, leave the Marantz 2230B for the L16 Decades... scale as necessary for a 4345...

You know the drill - Right Click - Save Target As...

Have a great day!

The DD66000 quite simply provides the most musical experience of anything in our history.

- Agreed. Fantastic accomplishment. Stunning performance. A perfect 60th Anniversary Statement.