Which first watt amp is right for my 95dB speakers?

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audioexplorations

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Joined 2015
First post here. Amazing community, making me get really excited about starting the build of my first FW amp! :)

My speakers are the DIY Troels Gravesen designed TQWT-mkIII speakers. They are a 95 dB high-efficiency "tapered quarter wave tube" speaker with a minimum impedance from 100 - 1000 Hz of 7 ohms and 5 ohms above 8 kHz, and described as being an overall an easy amplifier load.

TQWT_intro_1.jpg


JA8008_TW034_sin_imp_plus12dB_F_Sup-caps.jpg

(Red = impedance, blue = phase)

JA8008_TW034_sin_imp_plus12dB_D_Sup-caps.jpg

(Red = impedance with higher resolution)

These speakers seem to be a great candidate for FW amps. I listen in a medium sized room and often at loud levels with modern bass-driven music so I would like something that controls the woofers really well.

According to Nelson's guidance from his CAS '15 talk, I would need around 30-40W of power:

POWER CALCULATION
1W = 95dB speaker/normal level/small room
x 10 for loud level
x 4 for big room
= 40 watt​

This will be my first project so my preference would go for a simpler design. Based on what I have read I believe the F6 will work best, but I wanted to double check here before moving ahead with the project.

Any advice is much appreciated!

Further info:
TQWT mkII (previous generation mkII version on which measurements were taken)
TQWT mkIII (latest TQWT mkIII version, however this page describes mainly the DTQWT which is a larger variant with an additional bass driver, measurements here are of the DTQWT).
 
2 picoDumbs

2 picoDumbs

Member
Joined 2013
Very nice speakers.
With those speakers, the world is your oyster, you can build any amp you desire.
F6 would be nice so would Aleph J, so would F3, so would F5 etc.
If this is your first amp build and want to build something quickly I'd probably go with F6.
 
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2 picoDumbs

2 picoDumbs

Member
Joined 2013
Have you actually measured the voltage peaks across your speaker?
I never exceed 4V and that is pretty loud. The only time I could possibly imagine needing more than that if a group of teenagers took me hostage and decided to have a 18th birthday party and wanted everyone in the street know what music they were listening too.
 
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vdi_nenna

vdi_nenna

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Joined 2000
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You should also consider the choke loaded L'amp. 13 watts of SE bliss. Just need to find two 2sk82 vFets. Hammond 193v choke works fine.

http://www.diyaudio.com/forums/diyaudio-com-articles/202480-l-amp-simple-sit-amp-part-deux.html

I can't stop listening to the 5w CCS version with 94db FR Voigt pipes in a 20'x16' room.
The room opens to another room approx. the same size, so there's no shortage of volume/output. Works best with a preamp with some gain. Using the BA-3 pre at the moment with 15db of gain.

At any rate, Good luck!

Vince
 
A

audioexplorations

Member
Joined 2015
Thanks for all the replies. Good to hear that pretty much any FW amp will work with these speakers. Looks like it will be between the Aleph J and F6, with plenty of info here to help me make the choice. The L'Amp looks extremely interesting also... might just have to build a couple of these :).

Have you actually measured the voltage peaks across your speaker?
Click to expand...

No I have not, but I'll trust you that the 30-40W would be overkill...

I've wanted a pair of those speakers for some time! I would love to hear them, all reports is they are wonderful.
Click to expand...

I can only give these speakers my highest personal recommendation. Coming from a very high end $$$ setup and owning 5-6 different speakers (raidho/rockport/tad/pmc/b&w) I do not miss anything and haven't looked back for a second.

If this is your first build don't overlook the ACA amp either.
Click to expand...

First build. The ACA is intriguing, would be a great learning experience and I would love to see what 5W sounds like on these speakers! I will probably order one of these and build while I collect parts for an F6 or Aleph J.

What preamp do you (audioexploration) use?
Click to expand...

None, running source-direct. Currently a Chord Hugo DAC, which outputs between 0 and 4.75V via digital attenuation.
 
folkdeath95

folkdeath95

Member
Joined 2011
audioexplorations said:
First post here. Amazing community, making me get really excited about starting the build of my first FW amp! :)
[...]
Click to expand...
I was in your position a few months ago when I was looking for a FW project to drive my Petite Onken.
I didn't want to have less power than the 6L6 push-pull I was using at this moment (18W) and wanted to use it without preamp. I prefered to choose a project that was sold by the DIYAudio store, because of the universal mounting system and the possibility to buy pre-drilled chassis. It makes a first build easier, I think.
That left F4, F5 and AlephJ (the F6 was not available at this time).
The F4 was immediatly removed of the list because of its unity gain and, as was not sure the F5 will have enough gain, I choose the AlephJ.


2 picoDumbs said:
Have you actually measured the voltage peaks across your speaker?
Click to expand...
Never tried this. I just have to put a DMM in AC voltage mode across the binding posts?


vdi_nenna said:
You should also consider the choke loaded L'amp. 13 watts of SE bliss. Just need to find two 2sk82 vFets. Hammond 193v choke works fine.


Vince
Click to expand...

Aren't NOS 2SK82 hard to source? Maybe not ideal for a first DIY project?

2 picoDumbs said:
If this is your first build don't overlook the ACA amp either.
Click to expand...
Full kit is a good idea but will 5W be enough to drive his speakers?

Mikael
 
M

mc297

Member
Joined 2011
The ACA is very easy to build and sounds wonderfully with high eff spekers as in your casa. I have Klipsch RF82 that are declared 98dB (probably 94-95dB actually...) and I started with the ACA to see what a class A is. The sound is very open and you get a lot of low freq too. What I liked was the 3D image that on simple music and good recordings is very realistic. So I built the F6 in order to have an amp for all seasons, with lower distorsion and suitable to listen to big orchestra music: the result is an amp that has very large soundstage, 3D image and good estension, but with higher freq a bit sweet than the ACA.


-Alex
Sent from my iPhone using Tapatalk
 
2 picoDumbs

2 picoDumbs

Member
Joined 2013
folkdeath95 said:
I was in your position a few months ago when I was looking for a FW project to drive my Petite Onken.
I didn't want to have less power than the 6L6 push-pull I was using at this moment (18W) and wanted to use it without preamp. I prefered to choose a project that was sold by the DIYAudio store, because of the universal mounting system and the possibility to buy pre-drilled chassis. It makes a first build easier, I think.
That left F4, F5 and AlephJ (the F6 was not available at this time).
The F4 was immediatly removed of the list because of its unity gain and, as was not sure the F5 will have enough gain, I choose the AlephJ.



Never tried this. I just have to put a DMM in AC voltage mode across the binding posts?




Aren't NOS 2SK82 hard to source? Maybe not ideal for a first DIY project?


Full kit is a good idea but will 5W be enough to drive his speakers?

Mikael
Click to expand...

You'll need a pretty good Voltmeter with decent bandwidth (but most intense voltage peaks occur below 500Hz) and the ability to capture and store peak Voltage. i have a Fluke meter capable of this otherwise you will need an oscilloscope.

You don't need Sony parts to build F6

5W is plenty on 95dB speakers. Like bloody loud
 
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