I have a pair of JBL control 5 speakers, which valve amp design you recommend? - diyAudio
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Old 20th July 2005, 11:18 PM   #1
diyAudio Member
Join Date: Apr 2005
Location: Mexico
Default I have a pair of JBL control 5 speakers, which valve amp design you recommend?

So, Im a newbee and I like music so much and I want to try to make a valve amp. I have a old marantz amp model 2265B and a pair of control 5 JBL speakers, I have to say that it sounds good (well, I think so...)

I had a engineer friend that worked with some mexican "valve amp guru" named Julian Margules and he always told me that the sound of the valve amp was awesome and nothing compares to it. Well, years had passed and now I have the time to build a valve amp because Iam a DIYer lover and... well, I dont want to pay 2000 usd for an amp .

I lost contact with my friend a year ago so I started to search for a DIY audio website and I found this awesome site. I also started to read the book "Valve amplifiers" by Morgan Jones but now, and I think this is a commun problem of newbees, is that I have a lot of information and I really dont know which amp will be the best to start with and the best for my control 5 speakers.

Please help! Well, I think youll need the specs of the speakers so here we go:

Frequency Range: 50 Hz - 20 kHz (-10dB)

Power Capacity: 175 Watts (test signal of IEC filtered random noise with a peak-to-average ratio of 6dB, 2 hrs duration)

Sensitivity: 89dB 1W, 1m

Nominal Impedance: 4 Ohms

Crossover Frequency: 3 kHz

Components: 165mm (6 1/2 in) low frequency loudspeaker 25mm (1 in) pure titanium dome tweeter.

Thank you so much, and please excuse my english... my native language is spanish.

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Old 20th July 2005, 11:51 PM   #2
Sherman is offline Sherman  United States
diyAudio Member
Join Date: Feb 2004
Location: Chicago area
Welcome Ultrapato! I also think you will love the sound of a tube amp. As for the proper amp for you that will probably require a bit more info.

First at 89dB/W your speakers are neither very efficient nor very inefficient. So some other questions are in order-

1- How loud do you like to listen to music?
2- How large is your listening room?
3- What type of music do you listen to most?
4- What aspect of music is most important to you:
* slamming bass
* crisp detailed highs
* accurate midrange

Once you have decided all that you can get a better handle on the power requirement for your amp.

But to take a stab at it anyway I would think that with 89dB/W speakers something in the range of 10-20 watts would work if you don't want the music loud enough to shake the house.

I listen to a 6 or 7 watt amp with 89dB/W speakers and am very happy with the system. But I don't listen quite as loud as I did back in the 70's.
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Old 20th July 2005, 11:57 PM   #3
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Join Date: Dec 2002
Location: Calgary, Alberta
And since you brought up Morgan Jones' book I must point out that the Bevois Valley amp in there is a good choice. I am building a version of that myself. I think it is a spectacularly fine choice for a first amp because he does a full breakdown of the design, so if you change any aspect of the design to something you prefer, or have have in your parts bin, etc., you will be able to figure out how to incorporate it into the circuit.
The whole problem with the world is that fools and fanatics are always so certain of themselves, and wiser people so full of doubts. Bertrand Russell
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Old 21st July 2005, 01:48 AM   #4
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Join Date: Oct 2004
Location: Adelaide South Oz
Ditto the above - I had a bit of an advantage being a professional Electronic Design Eng, but the Bervois Valley Amp in the Morgan Jones Book was the first valve amp I ever built.

The "recommended design" for a Newbie to build is a question that pops up here every couple of weeks and the Bervois Valley Amp SHOULD IMHO be the standard answer.

This amp has since been joined in my house by 6 other valve amps covering the range of Push Pull Ultralinear, Push Pull Triode and Single Ended Triode (845). The Bervois Valley remains one of my favourites.

Build it exactly to the circuit in the book (except perhaps to use Solid State rectification) and then you can play around with things to your hearts content once its running.

Things I found worked as "upgrades" once my BV Amp was running:
1) Modern production JJ EL84 Output Tubes were as good if not better than a raft of NOS EL84s and 6BQ5s I tried
2) 470uF/50V Blackgates for the EL84 Cathode Bypasses
3) Ultrafast rectifiers
4) Reduction of global feedback to just 6dB
5) Polyproylene Film/Foil Coupling Capacitors

Also found that no High Voltage Standby Switch was necessary (or desirable) despite using Solid State Rectifiers.

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Old 21st July 2005, 03:25 AM   #5
diyAudio Member
Join Date: Apr 2005
Location: Mexico
Originally posted by Sherman

1- How loud do you like to listen to music?
2- How large is your listening room?
3- What type of music do you listen to most?
4- What aspect of music is most important to you:
* slamming bass
* crisp detailed highs
* accurate midrange
Thank you for welcome me Sherman and here are the answers to your questions:

1- Sometimes I listen it real loud, well, when I am in the shower so in those cases I can use my old amp... but almost all the time I listen in a moderate volume when I am using my computer and working in my home (almost all the time) so thats why I want a real good sound instead of loudness.

2- My room its ok but were I listen to music is, like I said before, when I work in my home (inside my room) so my office space is like, mmm, 7 square feet.

3- Thats a complicated question because I listen to many kinds of music... I love Bjrk (what a voice, in my opinion), The Cure, Apocalyptica, Audioslave, Elan, Nirvana, Radiohead etc. but I also love big bands and classic things like Sinatra and wow, I love blues and also some "experimental music" like the Blue Man Group. I have many classic records in vynil that belong to my father, there are quite good ones like Pink Floyd, Chicago, Hubert Law, The Beatles, etc. I like them too.

4- Mmm, I really dont know the exact answer but Ill try to answer it. I love a clear and deep voice and I love to hear crisp guitar and a detailed drums and a little bass "power". I hope I answer the question.

And Leadbelly, I will check the Bevois Valley amp.. thanks for the advice.
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