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Jah Tubby preamp mods continued

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Joseph Redhemption View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Joseph Redhemption Quote  Post ReplyReply Direct Link To This Post Topic: Jah Tubby preamp mods continued
    Posted: 19 November 2008 at 8:06pm
NEWNEWS FLASH Mostec 4 way on the bench
http://www.speakerplans.com/forum/forum_posts.asp?TID=21452&PN=10

NEWS FLASH  The resluts of the new crossover at this page http://www.speakerplans.com/forum/forum_posts.asp?TID=21452&PID=219657#219657




After modding a 3 way JTS preamp by adding tubes and upgrading the parts (see link to original post) http://www.speakerplans.com/forum/forum_posts.asp?TID=19980 I decided to investigate further this preamp. In fact it is not the preamp I modded but another one from another sound from Geneva. In the future I will try to get back the modded one and make the same tests to balance the results.
The results below are made on an unmodded preamp.

I did make some measurments like frequency response, phase, distortions and some more tests. The results are sometimes very surprising.

Tests where done using a PC with EMU 1820M soundcard and RTA program.


This is the phase shifting measured from the preamp bass and mids crossover outputs.
PINK is Bass and BLUE is Mids. The problem revealed by this plot is the phase shifting that occurs around the crossover frequency set at 212Hz.


This plot shows the same problems but wiht the mids and highs output at 4330Hz
PINK is mids and BLUE is Highs


This is the frequency response plot taken at the tape output with all tone, equalizer and crossover pot at 12 o'clock. The parametric mids and bass pots are fully clockwise. For those who understand this plot no comment.
But for the neophytes this is the worst frequency plot I ever seen. An ideal plot should be flat from 30hz to 20Khz.

N.B : The signals taken at the tape output from the preamp are just the sum of the three crossover output.



This plot same as above exeption for the bass parametric that is fully anticlockwise.


this plot shows the behavior with a complex signal. Its an 1Khz sinus with harmonics up to 20Khz. In PINK the output of the sound card and in BLUE is the tape output of the preamp.


Ok this is enough for today. I will post other results this week like transient response and distortion.





Edited by Joseph Redhemption - 30 December 2008 at 5:55pm
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Matthias View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Matthias Quote  Post ReplyReply Direct Link To This Post Posted: 19 November 2008 at 8:40pm
so finally someone did it...

we measured exactly the same frequency response, i would never ever connect this to my speakers.... Bass Dead

the bredda measured chose to let them not be seen by the public as JTS is a very respected manufacturer and this tests are poison for his business.

So maybe you should remove the plots ?!

It is a bit strange, on the one side people have to know that this preamp is soo bad, otherside when people have good ears and a bit of knowledge of equing this preamp can also sound good.

In fact, it just sells by its "traditional" character, not for its perfomance

The funny thing is, it is not possible to get real subbass out of this... parametric bossts at 50hz lowest frequency, this saves a little bit your speakers but it is not what people want when they speak about 30hz scoop bins Wink

To be honest, this plot is sweeeeet against the one we made. same curve but even deeper hills and valleys ....18db.... unreal stuff, i could not believe it.

I would say lets end this thread and respect to you for not believing everything people say

let us remove these posts and for those who where fast enough they were lucky, got the chance LOL


Edited by Matthias - 19 November 2008 at 9:01pm
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RENSAAB View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RENSAAB Quote  Post ReplyReply Direct Link To This Post Posted: 19 November 2008 at 11:24pm
Fairplay to you for sharing these plots with us JR but lets be honest, i doubt whether anyone who purchases a JTS preamp is expecting audiophle quality or is even bothered about a flat response/phase differences etc.
 
I would imagine Tubbys is smart enough to realise that not many sounds play "flat", so i guess why not "tailor in " a typical response! I personally prefer equipment that can give a flat response when needed but the average sound system operator is rarely looking for that (others may disagree).
 
Just my two pennies worth  
"The secret of the Scoop, what a wonderful piece of Science" - Tony ASS.

"when the amplifier and voice coil are in complete synchronicity there is magic" - A Well Respected Amp Guru
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mykey View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mykey Quote  Post ReplyReply Direct Link To This Post Posted: 20 November 2008 at 5:44am

If you remove this, preamps will always be bad, atleast this will give the designer a kick and get things straightened out

Do agree with a lot of what Rensaab has said though

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DC View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DC Quote  Post ReplyReply Direct Link To This Post Posted: 20 November 2008 at 7:27am
Why should tubbs make it better. The pre is used by many sounds for years. I think making it better will affect the character of the pre. And still it isn't that bad... a steep dip around 220, so what...and some boost between 40 and 50 is what a sound need. Things can be adjusted with the EQ The 30Hz cut is quite convinient as it will prevent your amps from consuming power wich isn't really audible. Some cut in tops.... hmmm, most sound attendenders won't hear anything above these freqs anyways.
Regarding the phase difference, i can't see the value for the timeline so these plots don't tell you anything.
Even the most expensive preamp will have phase shifting.
BTW would be interesting to see the measurements from the modded pre with tubes. I bet the phase shifting is even more and defo no flat responce either.
And also measuring thru an emu card like that won't give you fair measurements either.
If you got a good quality oscilloscope and good quality frequency generator then you can do such things.


Edited by DC - 20 November 2008 at 7:30am
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Matthias View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Matthias Quote  Post ReplyReply Direct Link To This Post Posted: 20 November 2008 at 11:30am
yes fellas, maybe the people just want something like this, but this is confusing me, i dont know... there could be also a flat response and you could eq it to this curve if you want lol.

Even in a 4 way, the "crossovers" are set so badly, no 12" plays up to 4k smooth.

I still think it is selling because of its traditional character, the preamps are very expensive for this performance. For this price, a flat response should be standard.

Things like this and the sound coming from it just keep down the roots music and many people of other music do not respect the works, because most systems i heard with this pre sound weak.

DC, i dont know if any Bass speaker could manage a boost of 12db +, at 50hz ( mine would not ) , the HP filter should work in this design, i think it is written in the manual that the lowest eq should always be turned down. ( 31.5hz probably )

Flat Bass response is not possible only a one  not bassline

We measured the same, even worse frequency response and also measured our soundcard, all i know it was ultraflat. I can ask what soundcard was used.

You as a very good producer know about the needs in the low mids, this section is quite the hardest to manage speakerwise and very important for every tune... if your speakers can do it and your preamp not... i cant follow.

The steep rolloff at 10k is not that dramatically, as you said most soundmen ears do not hear it, you could only get better highs with 100 piezos ;) This preamp is not really suited for a good 1,5" f.ex.

I respect jahtubbys as sound to the max, they had a really great influence over the years, that is why i said this is poison and i dont want to be a bad influence for his business, but the truth is also important.

I see that it would loose his character, i still think that everyone can build preamps which sounds good then...



Edited by Matthias - 20 November 2008 at 11:32am
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king david View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote king david Quote  Post ReplyReply Direct Link To This Post Posted: 20 November 2008 at 12:01pm
if u have a preamp and combine scoops, folded horns, midrange horns, tweeters there is no chance for time aligment...
 
i have a jts 3way preamp and its a good unit, it has its limits, and this thread just confirm this...but it works good with a reggae sound cause it has a lot of useful things to colour the sounds and spice it.
 
everytime i play with preamp, sound isnt perfect (sometimes is very good sometimes is just good) but its great for live dubbing. with other equipment i can come close but i feel more at ease with preamp
and u dont see people at gigs doing measurements, they come to dance+have fun!
 
everytime i use the sound as a p.a....i bring out my crossover, equalizer and limiter and the sound is much much better!
 
cheers
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DC View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DC Quote  Post ReplyReply Direct Link To This Post Posted: 20 November 2008 at 12:05pm
Thing with these plots is the measured values depend on more parameters. Also gain setting is of importance, input level, what kind of input signal is being used. What is the source, etc, etc. Besides that... there's no scales on the pre sow how would you know what is the flat setting on the pre ? There's no accurate metering on the pre either.
I definatly heard some very good sound coming from the unit, but all depending on the operator. These pre's are built for soundmen who use their ears and not rely on metering.
As far as i know the so called 'Parametric EQ' is set at a fixed boost level and only shifts the freq up or down. So flat responce even not possible unless you turn down the lowend EQ.
But as said in the above plots all the EQ settings were at 12.00. So that explains the peak in the lowend.
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King Simeon View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote King Simeon Quote  Post ReplyReply Direct Link To This Post Posted: 20 November 2008 at 12:44pm
"The Truth is also important" 

The fact this is a 'roots & culture' forum means that the truth is in the history of sound system. These charts and the info seems better suited to the other parts of speakerplans. 

Tubbys pre's don't come with a booklet, they are sold according to what they do, and have been for many years. They are also sold at a reasonable rate and come with the back up that Keith can still service equipment bought 30yrs ago. Nuff new builders come and go, who is the one still around and running a successful business?

Tubbys also builds equipment for other businesses, that require the high end specifications you mention, when he builds a pre amp he builds according to his experience of playing sound.  I'm not sure i know of anyone who has more experience and 'in the arena' knowledge. 

Of course they could be better, tighter suited to the delivery of the speakers, but dont forget, every piece of equipment sold is also the same as Tubbys himself uses when he plays. They are regularly being updated. He doesn't blow his own equipment many times and in all the time Tubbys has been back in sound runnins, since 2000, no one has made a big fuss about him having the title, 'World Sound', nuff said.

I think that modern peeps are applying info to older technology. Of all the producers i know, just about all of them have 'older' equipment, use older produced FX, reverb, flanger, delays, eq's compressors... desks..... Some desks have 'character' a warmth... well if you run tests on them you would find that it would be 'distortion', now check out the prices on this equipment and how many people are after them! Are you saying they are all stupid/should know better?  

Some of the most sought after equipment now are older units, prices have only gone up and up. I see new eq's with hundreds of frequency controls, but they are lifeless, it just feels like you are playing with air. They are sold by the stats they offer, this frequency to point this of that.... They are sold on science, but to the human ear music comes out differently. People in music know differently, which is why they use their ears. I want to hear something sweet, warm, harsh and loud, dirty and gritty. Character!!!

I look forward to hearing new pre's, all new sounds, that is the only proof i want to hear. Make people know through the works it performs.
https://www.facebook.com/KingSimeonSound?ref=stream     
https://soundcloud.com/king-simeon
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Joseph Redhemption View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Joseph Redhemption Quote  Post ReplyReply Direct Link To This Post Posted: 20 November 2008 at 6:31pm
Raspect to every one who took time to write these remarks.

The truth is the truth and that is no offence

Thanks it is very constructive.

Sorry for the bad plot. I dont know what happens because the original plots are good. I ad a link below each plot for those who are interested.

Now to part two of results

This plot shows a real surprise. I was testing transient response by injecting a 90hz square signal in the preamp and this is what I get at the mids out. I cant explain this but normaly there should be no signal at all because we are way below the xover point at 212hz.
PINK is input and BLUE is mids out.

http://www.4shared.com/file/72242073/8a99278/Mids_out_squar_in_90Hz.html

this is at the mids out with a 1Khz square in.
PINK is input and BLUE is mids out
The transient behavior is good. For shure this is no square signal at all at the output but this is not what we want and the cause are the blocking caps.


http://www.4shared.com/file/72242063/11b2a339/Mids_out_squar_in_1Khz.html
http://www.4shared.com/file/72242063/11b2a339/Mids_out_squar_in_1Khz.html

This plot shows a burst. It is at high frequencies >10Khz.
It shows that in the high frequencies some details are lost but if you believe like some who wrote that most soundmen didnt hear this freqs then it should be no problem for them.
PINK is the burst and BLUE is the tape out of the pre.

http://www.4shared.com/file/72242032/1bc267ea/Burst_tape_out.html

This is the THD (total harmonic distortion) with a 1Khz sine input. Not too bad, very acceptable. 
N.B. the signal led is not blinking look below when it blinks.

http://www.4shared.com/file/72242082/f836be21/THD_led_off_1khz.html




Same signal as above but the gain of the mids xover is raised until the corresponding led light up. Now distortion looks more like a guitar amp.
My advice is not to push the gain too much because when the led goes on the distortion become audible. This is because of the way this preamp drive the led. The signal is directly taken from the individual xover outs to drive a transistor who in turn drive the led.
It would have been better to buffer with an opamp before driving the transistor.
N.B. This can be a wanted effect to beef up the sounds.

http://www.4shared.com/file/72242105/af49cbbd/THD_Led_on_1Khz.html


Finally I want to say that I made these test to know whats happen in this preamp so I can improve them.
I'm working know on an linear phase xover to put into the JTS. For shure it will loose the actual caracter of the pre but hoping that it will sound more accurate/sharp.
I will then test this modded pre and compare the results.
Will it be better or worser? Wait and see
If everything goes well with the construction the results will be published next weekend.



Raspect



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mange View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mange Quote  Post ReplyReply Direct Link To This Post Posted: 20 November 2008 at 7:06pm
Originally posted by Joseph Redhemption Joseph Redhemption wrote:



This plot shows a real surprise. I was testing transient response by injecting a 90hz square signal in the preamp and this is what I get at the mids out. I cant explain this but normaly there should be no signal at all because we are way below the xover point at 212hz.



But a square wave is full of harmonics, getting no signal would be expected if you were injecting a sine wave. Surely a 90 hz square wave have harmonics above 212 hz.
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Joseph Redhemption View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Joseph Redhemption Quote  Post ReplyReply Direct Link To This Post Posted: 20 November 2008 at 7:20pm
Alright this explain that
Thanks
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