[strider]

More specifically, the Tubelab Simple SE with KT88s vs the Tubelab Simple PP running EL84s. Looking to DIY my first tube amplifier, and was wondering what people's opinions were regarding the sound of these two amp/tube combinations.

Currently running 96db efficient open baffle speakers, I think the respective 9 watt and 18 watt outputs of the two designs are more or less a wash for my system as it stands. I don't want to paint myself in a corner with the type of amp, though. I feel like the canned response for the question of SE vs PP is what type of music do you listen to, "girl w/guitar in coffeeshop" or Tool cranked to eleven? I kinda like both.

What say ye?

[JakeJ]

Well I think you should build both!  Ok, just kidding.

Can you give us a bit more info about your system?  Music you like?  What speakers are you driving?  I am a self-confessed bass head so I'd probably lean towards the EL-84 pushing out 18 watts.  That is just my opinion, I really know nothing about the circuit designs.

[strider]

Gladly!

Currently my system is a USB DAC fed FLAC files via JRivers and  then to a PassDIY B1 pre. My DIY F5 amp released its magic smoke a couple weeks ago, so I've got an older Rotel in there now for power. The speakers are open baffle design based on the 15 inch Silver Iris drivers from Hawthorne Audio and are rated at 96db efficient.

Music-wise I'm all over the place. Hendrix, Beastie Boys, and Tool to Coltrane and Doc Watson. With a couple little kids and a wife that has a complete and utter hatred towards hearing bass from downstairs, I don't get the chance to crank it as much as I'd like.

[JakeJ]

Too bad about the bass hate.  I'm thinkin' you'll be just fine with the 9 Watts from the SE KT88 design and may get a bit more of the magical midrange.  Just my .02.

[rbwalt]

i think the kind of tube used is going to play into the kind or type of speaker in ones system. 88's tend to push the mids which is good for a speaker that has a hole in the mid's like many BBC speakers. linear speakers need a linear tube.

[roscoeiii]

I'd look into the damping factor on both amps, and what that Hawthorne driver needs for damping. Higher damping power (to a point) will give you tighter bass, though it is possible to overdamp some drivers. I had an Aleph 3 that I liked with my 12" Audio Nirvana drivers, with the exception of the bass, which was overdamped with that amp.

[strider]

I'd look into the damping factor on both amps, and what that Hawthorne driver needs for damping. Higher damping power (to a point) will give you tighter bass, though it is possible to overdamp some drivers. I had an Aleph 3 that I liked with my 12" Audio Nirvana drivers, with the exception of the bass, which was overdamped with that amp.

What dictates the damping factor of an amplifier or driver?

[roscoeiii]

The more technical folks will need to give you the details. But damping factor is a characteristic of an amp. Certain driver specs and maybe speaker designs (?) will determine how much damping a driver/speaker needs.

[JakeJ]

Maybe this will help.

http://en.wikipedia.org/wiki/Damping_factor

[strider]

Maybe this will help.

http://en.wikipedia.org/wiki/Damping_factor

Yes, thank you.

[strider]

The equation on the Wikipedia page is DF= Zload/Zsource, where DF is damping factor, Zload is the nominal impedance of the speaker, and Zsource is the output impedance of amp.

From the schematics of the amp, and from what I got from scanning the interweb, the output impedance of a tube amp is determined by the output transformer. Using OPT's with an 8ohm tap, I'd get a damping factor of .75 with my 6ohm nominal speakers. Using a 4ohm tap would bring the damping factor to 1.5.

Am I figuring that out correctly?

[Steve]

What dictates the damping factor of an amplifier or driver?

The damping factor is the ratio between the load resistor vs output impedance (Z) of the amplifier.
Resistor is just a standard used. Nominal impedance of the speaker is also used, although the Z of a
speaker changes.

The SET amp will have a varying damping factor due to changing of Rp (plate resistance of the tube)
in relation to signal level and thus varying output Z of the tube. The lower the volume level, the more
constant the damping factor.

Maximum damping factor variation is low to zero, 0, at maximum signal signal/power output.

PP amp will have a much more constant output Z with varying signal level, thus more constant damping factor.
It gets a little technical.

Cheers.

[roscoeiii]

The equation on the Wikipedia page is DF= Zload/Zsource, where DF is damping factor, Zload is the nominal impedance of the speaker, and Zsource is the output impedance of amp.

From the schematics of the amp, and from what I got from scanning the interweb, the output impedance of a tube amp is determined by the output transformer. Using OPT's with an 8ohm tap, I'd get a damping factor of .75 with my 6ohm nominal speakers. Using a 4ohm tap would bring the damping factor to 1.5.

Am I figuring that out correctly?

Won't be able to tell unless you give us the specs of your gear and let us k ow what values you entered. Sorry, not going to look that up myself.

[Steve]

The equation on the Wikipedia page is DF= Zload/Zsource, where DF is damping factor, Zload is the nominal impedance of the speaker, and Zsource is the output impedance of amp.

From the schematics of the amp, and from what I got from scanning the interweb, the output impedance of a tube amp is determined by the output transformer. Using OPT's with an 8ohm tap, I'd get a damping factor of .75 with my 6ohm nominal speakers. Using a 4ohm tap would bring the damping factor to 1.5.

Am I figuring that out correctly?

I don't think so Strider because, to simplify, the damping factor figure should be higher with 8 ohm than 4 ohm.
Damping factor is defined as the nominal output Z of the speaker divided by the output Z of the amplifier.
(Your equation is correct.)

For instance if the output Z of the amplifier is 2 ohms, damping factor with 4 ohm nominal speaker is 2,
4 divided by 2.

With 8 ohm, the damping factor is 4, 8 divided by 2.

Hope this helps.

[strider]

I don't think so Strider because, to simplify, the damping factor figure should be higher with 8 ohm than 4 ohm.
Damping factor is defined as the nominal output Z of the speaker divided by the output Z of the amplifier.
(Your equation is correct.)

For instance if the output Z of the amplifier is 2 ohms, damping factor with 4 ohm nominal speaker is 2,
4 divided by 2.

With 8 ohm, the damping factor is 4, 8 divided by 2.

Hope this helps.

Seemed too simple 

I am in the formative stages of the learning process, I do appreciate the help.

[strider]

Won't be able to tell unless you give us the specs of your gear and let us k ow what values you entered. Sorry, not going to look that up myself.

Being DIY designs, there's a few different options in regards to transformers, tubes, etc. There's not a spec sheet that I can refer to and get damping factor, among other things. That's why I'm hear asking stupid questions 

Looking at the schematic for the SE amp, for example, the 8ohm tap of the output transformer is connected to the positive terminal of the speaker binding post. From what I know so far (which could most certainly be incorrect) this would make the output impedance of the amplifier 8ohms. My speakers are 6ohm nominal. That's how I came about the damping factor of .75.

[JakeJ]

Strider, They are not stupid questions.  Like you said it's a learning process.  One thing about impedance is that it changes.  Resistance is constant but impedance changes.  At 100 Hz it may be 22 ohms and at 500 Hz it might be 10 ohms (these numbers are just an example).  Your Hawthorne may have a listed impedance of 8 ohms but that is nominal and kind of tells you to connect it to the 8 ohm tap but that may not be true with all amps.  I looked at the Hawthorne site and they do not publish an impedance curve so I will use one for another driver to give you an example.



See how the "resistance" changes over the frequency spectrum?  That's impedance.  And the curve can change slightly from one amp to the next (using the same speaker).  You might contact Hawthorne and ask if they can provide you a curve for the model you own.  Also discuss the amp designs you are considering as they may have some valuable input.

Hope that helps.

Steve - Thanks for your input as well.  I was hoping someone that understands this issue would pipe up.

[Thirsty]

Have you considered a SE KT120?, should be able to push 20-25 watts.

I just took delivery of a SE kt88 amp yesterday and even without much break in I'm liking it a lot.

[strider]

Have you considered a SE KT120?, should be able to push 20-25 watts.

I just took delivery of a SE kt88 amp yesterday and even without much break in I'm liking it a lot.

To be honest, no I haven't. Been concentrating on the two kit amps offered by Tubelab, but have started to broaden my search after some of the posts in this thread.

[Steve]

Seemed too simple 

I am in the formative stages of the learning process, I do appreciate the help.

Hi Strider,

Notice I bypassed how to figure the output Z of the amplifier. That is the more difficult part.
One can do it mathematically but I would rather do actual measurements because of DC resistances,
differences in Rp of output tubes etc.

If one considers the DC resistance of the speaker driver winding, the damping factor is actually
quite low. This was covered some time ago in another string. Anyway, let's keep it simple.

Cheers.