Best Choice Cab For GPA 604-8H-III

[DaveCan]

Hello all,
I'm starting this thread for an acquaintance who I sold my tube amp to. And this is specifically for the GPA 604 III driver: http://www.greatplainsaudio.com/down...604_8H_III.pdf
And the GPA crossover: http://www.greatplainsaudio.com/downloads/N604-8A.pdf

He was recommended the Stonehenge V cabinets by Bill at GPA, and I mentioned that there are some different designs that would be worth checking out, like an MLTL design. I've read some on GM's before and mentioned it to him and so here I am. I cannot seem to find and plans for them though.

Are there any already completed GPA 604 III MLTL cab plans available?

Here's some particulars:

1- He will be using a low powered valve amp. I sold him mine that is 6watts rms, but I think he has a few others as well that maybe are more powerful.
2- Listening space 22'x30' (and I think 8' ceiling height)
3- Cabs would be used near both corners of the 22' wall facing out into the 30' long room. He said he can put them close to the back wall or out a bit, or toed in etc.
4- He doesn't mind big cabs, no WAF to worry about here.
5- He can't diy, but has a good cabinet builder that will make them for him.
6- I guess the best would be an all rounder cab that's known to work well, with dims and stuffing specified that wouldn't need tweaking, as he isn't the diy type.
7- Music tastes - Jazz, classical, rock, reggae, girl and guitar, pop etc.

Any help would be appreciated as to what might be a better design for him than the Stonehenge V.

A big cab is okay and SQ is everything.

Note* My thoughts were that sealed would work well letting them roll off naturally, and use subs under them etc. Like Lynn Olson with his 416 design etc. But then I figured a one cab solution to be a better fit which could squeeze out all that the 604 has to offer, and it would also be easier for him to set up etc. He lives far away from me so I can't help tweak them, like add and reduce stuffing amounts etc.

I didn't want to steer him wrong, and thought to come here and ask for your opinions for what would be considered as a good all rounder cab for the GPA 604III specifically.

Thanks for any help,
Dave.

[LowOhms]

Hello all!,
Firstly the search function here wouldn't work for me and sent me to another page. I looked all I could to see if I could find GM's 604 design but couldn't see it.

I'm starting this thread for an acquaintance who I sold my tube amp to. And this is specifically for the GPA 604 III driver: http://www.greatplainsaudio.com/down...604_8H_III.pdf
And the GPA crossover: http://www.greatplainsaudio.com/downloads/N604-8A.pdf

He was recommended the Stonehenge V cabinets by Bill at GPA, and I mentioned that there are some different designs that would be worth checking out, like a MLTL design. I've read some on GM's before and mentioned it to him and so here I am.

Here's some particulars:

1- He will be using a low powered valve amp. I sold him mine that is 6watts rms, but I think he has a few others as well that maybe are more powerful.
2- Listening space 25'x15' (and I think 8' ceiling height)
3- He doesn't mind big cabs, no WAF to worry about here.
4- He can't diy, but has a good cabinet builder that will make them for him.
5- I guess the best would be an all rounder cab that's known to work well, with dims and stuffing specified that wouldn't need tweaking, as he isn't the diy type.
6- Music tastes - Jazz, classical, rock, reggae, girl and guitar, pop etc.

Any help would be appreciated as to what might be a better design for him than the Stonehenge V. Big is okay and SQ is everything.

Note* My thoughts were that sealed would work well letting them roll off naturally, and use subs under them etc. Like Lynn Olson with his 416 design etc. But then I thought the one cab solution to be a better fit that could squeeze out all that the 604 has to offer, and it would also be easier for him to set up etc. He lives far away from me so I can't help tweak them, like add and reduce stuffing etc.

I didn't want to steer him wrong, so wanted to come here and ask for your opinions for what would be thought of as a good all rounder cab for the new 604III

Thanks for any help,
Dave.

Hi Dave,

I don't think one can do better, for that driver, than a GOOD MLTL. Make it out of one inch Baltic Birch, NOT 3/4s. Use GMs designs, by all means, he KNOWS what he is doing there!!

Go on line and look at my friend Dennis' Serious Stereo MLTL offerings, out of Montana. That was done, some years ago, with GM's help and input I hear this type of design every year, last ten years, when I go to RMAF shows, for three days- each year. Last year, I heard fabulous bass out of the unit, with a GOOD 3 Watt Jj J 2A3-40 tube amp on them, and good wiring inside and to them. Jaw dropping good bass,that I can't get out of my mind!!

Adding a sub woofer, would be a huge mistake, an unnecessary expense, and a degrade, after hearing what I have !!

Lets talk Amps and ALTECS or GPAs. Most listening on a GPA 604 speaker ( or my A7 hybrid VOTT ) is done at 1 Watt or less.

So, a 6 Watt amplifier, IF ( a huge word - my Daddy used to tell me ) the amp is executed well, and the wiring , amp-to-speakers, is well done, .... six Watts will easily work. However, most amp designs and executions are unworthy of the ALTEC or GPA drivers, and don't come close to exploiting the drivers' full potentials..

I have had a 1.3 Watt Type 46 amp, on well wired A7s, in a smallish room, over the last month, and its built right. The dynamics will easily exceed any amp , solid state or tube, that is 2 Watts to 2,000 Watts. A powerful amp usually doesn't get off dead center till its pumping out ten Watts, so its sub optimal on a ALTEC / GPA. Yes, the powerful amp is always SUB OPTIMAL at normal to high listening levels, when used with our type of speakers !! Counter-intuitive, but true !! I hear it !!

What is needed is an amp that can perform, really perform, at the sub one Watt level. That is the design challenge for our system, and the thing to look for.

The answer, for the BEST possible amp topology on an ALTEC or GPA, from my direct experience, goes all the way back to 1929, Messers Loftin and White. After that, look seriously at the design schematics of Isamu Asano and Nobu Shishido, in Japan ( both 2A3 ). It was getting better than 1929, but still had mistakes. In the USA, Sound Practices Magazine, Spring 1994 issue, did a superb article by Ciro Marzio and Christiano Jelasi " A Direct Coupled Single Triode Amplifier", which is a lovely read, 'dem Italians have a sense of style.


IspraNet Audio: Direct Coupled Single Ended Amplifier


( Necessary 2017 changes : V1 becomes a JJ or EH 5U4GB. Eliminate R1 / C1. Add a CL-80, in series with FU2. Retain L2 / C3. L1 and L2 is equal and under 10 Ohms DCR. Use two Hammond 159ZAs, 6 Ohms each, which measure about 400 mHY when lightly loaded. Adjust circuit for V2 = 1/2 12AX7, V3 = Type 46 at 22 mA. or a JJ 2A3-40 at ABOUT 43 - 47 mA. - not 60. )


In the USA, we had actual amps being offered - look at the following L-W ( Loftin White ) variants, the MOTH 2A3 by Craig Uthus , the Don Garber Fi 2A3 ( only a small window of what was possible ) , and finally, the best one of all, easily, since 1989 on, the Serious Stereo 2A3.

All of these amps I mention , spanning 1929 to 2017, have the following similarities ( a) ONLY two TRIODE stages (b) Direct Coupling of the Driver stage to the Finals stage ( c ) High mu ( 70 to 100, 100 preferred ) driver tubes ( d) Typically tube rectification (e) NO negative feedback in the circuit, the EEs crutch !!.

So WHY am I mentioning AMPs in your speaker enclosure POST David?? Because, everything works TOGETHER, and is part of a chain. It is EASY to lose what is the BEST possible from an ALTEC / GPA driver, when anything, any aspect of the chain, is not right . Well, I gave you "my " best answer about an optimal enclosure choice, in my post's first sentence!!

Thought : Instead of rushing into a design, on any expert's say - so ( Bill H, etc etc ) .........can your friend come to RMAF in October, where he'd have three days to listen to a GPA 604 in a MLTL to decide for himself, with good gear and good wiring attached ?? Or, visit Montana, even bring his six Watt amp, and give a listen, before building ??. Nothing like having a direct listening experience..... to learn from - before cutting wood..

Disclosure, I am friends with Dennis Fraker of Serious Stereo, you should be too !! :-)


Jeff Medwin.....Low Ohms

[DaveCan]

Thanks Jeff,
Yes I am aware of GM's work and was hoping for one of his MLTL designs for the GPA 604III. I've seen that cab at the Serious Stereo site before and looks nice. I am aware of the low power and the first watt concept etc. The amp I sold him was a Decware Taboo but I believe he has other tube amps as well. The Decware always sounded quite nice to me for the money that I could afford, and the new owner loves it compared to what he has. Here's the manual: http://www.decware.com/newsite/SE84T...s%20manual.pdf

Anyhow I have been doing lots of google searches, but most designs are for various other 604 drivers than the GPA 604III, and not really any complete cab designs I've come across to be had.

I'm sure he would be willing to pay a nominal fee for an MLTL that he could take to his cab builder and be easily made etc with all the dims and particulars etc. The MJK math is too complex for me to try and fudge my own, plus I wouldn't want to give a design to him from me as a novice or less at cab design etc.

[LowOhms]

Thanks Jeff,
Yes I am aware of GM's work and was hoping for one of his MLTL designs for the GPA 604III. I've seen that cab at the Serious Stereo site before and looks nice. I am aware of the low power and the first watt concept etc. The amp I sold him was a Decware Taboo but I believe he has other tube amps as well. The Decware always sounded quite nice to me for the money that I could afford, and the new owner loves it compared to what he has. Here's the manual: http://www.decware.com/newsite/SE84T...s%20manual.pdf

Anyhow I have been doing lots of google searches, but most designs are for various other 604 drivers than the GPA 604III, and not really any complete cab designs I've come across to be had.

I'm sure he would be willing to pay a nominal fee for an MLTL that he could take to his cab builder and be easily made etc with all the dims and particulars etc. The MJK math is too complex for me to try and fudge my own, plus I wouldn't want to give a design to him from me as a novice or less at cab design etc.

Hi Dave.

Steve Deckert gives a LOT of amp value, for the money charged !!

'I am in the same boat as you, as far as an inability to design a MLTL enclosure, etc etc.

I wonder, if your friend was willing to "get it right", if he could HIRE GM directly as a consultant, to do the MLTL for that specific 604 model correctly ??

Remember please, my one suggestion, ONE inch thick Baltic Birch or Europly !!


Let us all know, if you are able, what gets designed, I MAY wanna copy it one fine day, so may others !! Make it BIG, internally.

Jefrf Medwin ..... Low Ohms.

[DaveCan]

I also posted this same thread over a diy as well for anyone interested: MLTL Cab Plans For GPA 604-8H-III - diyAudio

Thanks, Dave.

- - - Updated - - -

Hi Dave.

Steve Deckert gives a LOT of amp value, for the money charged !!

'I am in the same boat as you, as far as an inability to design a MLTL enclosure, etc etc.

I wonder, if you friend was willing to get it right, if he could HIRE GM direcly as a consultant, to do the MLTL for that specific 604 model correctly ??

Remember please, my one suggestion, ONE inch thick Baltic Birch or Europly !!


Let us all know, if you are able, what gets designed, I MAY wanna copy it one fine day, so may others !! Make it BIG, internally.

Jefrf Medwin ..... Low Ohms.

Thank you and yes point taken re the Baltic Birch etc. I'm sure he'd be willing to pay for some plans specific to the driver for sure. I had thought that there were some already out there but hard to find, and also they seem to be for many other 604's.. The Billfort cab is nice but uses a different 604, and no real plans either. If worse comes to worse maybe he can just go with the Stonehenge V or the 620 cab..

[DaveCan]

Here's a Cab that was done by Scott Lindgren for the 604 III that may be a good candidate. I've messaged him but haven't heard back as of yet. Not sure if the plans are for sale or available, but seems like a good contender maybe. I believe it's 290 or 300 liters, I've read both those volumes. So 10.2413 cubic feet and 10.5944 cubic feet. Any thoughts?

[LowOhms]

I'm no enclosure expert, but I have been told ....big is GOOD !!

INTUITIVELY, I DO NOT LIKE ALL THOSE BRACES SCREWING WITH THE FLOW INSIDE THE BOX, at all !!!


One inch thick Baltic Birch. NICE airflow, minimal or no braces is my feeling, intuition.


JM