Playing in the Sandbox

[debk]

Mcandmar

Mine are sitting gathering dust at the moment.  I hope to build a preamp to drive them with this winter.  I have most of ht eparts to build a Pumpkin preamp
I drove them with my 2a3 Paramounts, while it wokred with no problem, I really like the sound of my SR45/ BeePree combo the better.
As time permits I will play more with it.

Slan
Deb

 

[2wo]

Have you tried the F4 with the BeePre? That might be interesting. I have an F5 which sounds OK when I need some more power. Pretty much the only SS amp I have been able to stand for any length of time. The SR-45 is hard to beat...John 

 

[mcandmar]

Ok stupid question time. What is the SR-45?  I tried googling it and get a lot of hits for a Marantz amp which i assume is not what you are talking about?

 

[Natural Sound]

Ok stupid question time. What is the SR-45?  I tried googling it and get a lot of hits for a Marantz amp which i assume is not what you are talking about?

Shunt Regulated 45.

 

[mcandmar]

Gotcha, i've seen talk about BH working on a 45 amp, i assume a replacement for the Paramours?

I've gone ahead and ordered the F4, power supply, speaker protect, and soft start PCB's.  Currently trying to put together a BOM in Mouser, then order a transformer and case.  Anybody got any words of wisdom i should know about?    .....a decent manual wouldn't go amiss for these, especially for sizing the power supply section as i'm having to scroll through hundreds of pages to pick out bits of information here and there.  Why cant everybody do a kit like Bottlehead

Cheers,

Mark

 

[debk]

Mark

I didn't use a soft start board in my build.  I think the thermistors do a good enogh job with any inrush current.

I sent you a PM about some parts

Deb

 

[mcandmar]

Thanks to your inspiration, advice, and parts donation i have finally finished building my own little sandcastle.  It really is everything i hoped it would be, and by that i mean transparent to the point it sounds exactly like whatever you are driving it with.  My speakers are a pair of large inefficient vintage KEFs from the 70's which can fill the house with authority powered by nothing more than a humble little Quickie so volume range is not an issue. 

Vs the 5.1 Pioneer amp i was using before it really is astounding how much better the DAC/Quickie/F4 setup sounds, so smooth yet detailed, i cant wait to build a nice preamp for it now.

I still have plenty of experimentation to do with different sources to work out what gain and voltage levels i need for these speakers to operate in, given how well the Quickie drives the setup it appears they dont need very much at all. I am also really curious to try the S.E.X. amp in front of it so i need to make up a cable to make that happen.  Out of interest have you tried running yours directly from the BeePre?

Thanks again for all your help Deb!

Mark

 

[debk]

Very nice build!

Deb

 

[Skip Pack]

If you are using the SEX amp as a preamplifier (which I am) try putting power resistors across the binding posts (I'm using 16 ohm Mills 12 watt resistors). I like the result with a load close to spec paralleling the power amp input. It works without, but it's nicer with.

Skip

 

[mcandmar]

Interesting, i will give that a try.

Cheers,

Mark

 

[feeench]

Would the Mainline be able to drive the F4?

If you're using a Bottlehead pre amp with an amp, is the voltage swing higher? Or is that limited by the amp?

 

[Paul Birkeland]

Would the Mainline be able to drive the F4?

The Mainline would be a good choice to drive the F4. 

If you're using a Bottlehead pre amp with an amp, is the voltage swing higher? Or is that limited by the amp?

Unless the input impedance of the amplifier is very low (under 10K), then the voltage swing of the preamp is dependent on the output voltage of the source and the gain of the preamp itself.

 

[feeench]

So if we assume a constant source voltage, adding a Smash into a chain that goes like this Source --> Smash --> SEX...raises the voltage output at the SEX outputs (Compared to Source --> SEX), right? Due to it seeing more than 2vrms at it's input? If this is true, does this affect the frequency response/distortion levels at the output at the SEX?

How can we figure out the voltage swing of the SEX given a 2v input? This is something I can't seem to figure out properly...

 

[Paul Joppa]

It takes about 0.62 volts RMS to drive the SEX amp to full power, which is 2 watts. That is 4v at the output for an 8 ohm load.

If you put more voltage into the SEX, it will clip at the output, increasing distortion but not voltage or power. Well, actually, if you put a LOT more voltage in, the output will be square waves and you might get close to 4 watts - but it will all be distortion, not music.

A preamp does not change the amplifiers maximum output capability.

If you had a low-output source of less than 0.62 volts, then that source would not by itself be able to drive the SEX amp to full power, and a preamp could raise the voltage closer to the clipping point (0.62v input to the SEX) and thus get more power and voltage out of the SEX.

 

[Paul Birkeland]

How can we figure out the voltage swing of the SEX given a 2v input? This is something I can't seem to figure out properly...

You can work backwards by knowing power and gain.  Power into 8 Ohms gives you voltage at the output.  The gain specification will let you calculate what voltage would need to be applied to the input to get that voltage at the output.

If you want to do the calculation without the gain specification, you have to consider the mu of the tubes at their operating points, the step-down ratio of the output transformer and other losses. 

-PB

 

[feeench]

I have a Smash on the way, and I've got the parts coming for an F4 build. I'm eager to try this out, unfortunately I won't be able to grasp these concepts until I can actually play around with the hardware it seems... But thanks for the explanation you two, it will come in handy down the road.

 

[mcandmar]

I have a Smash on the way, and I've got the parts coming for an F4 build. I'm eager to try this out, unfortunately I won't be able to grasp these concepts until I can actually play around with the hardware it seems... But thanks for the explanation you two, it will come in handy down the road.

Let us know how the smash works out with the F4.  Then input of the F4 is ~47k ohms so its not really any more difficult to drive then the S.E.X. amp. Voltage level required for normal listening levels are surprisingly low, i have a pair of vintage KEF speakers connected to mine that are easily driven into uncomfortably loud territory with a Quickie.  I measured my Quickie with ~4x gain, 2v rms in, 8v rms out.  Normal listening levels are ~1/3rd volume on the Quickie.  So in short if you have a source outputting ~4v into the F4 it will rock your socks off!

Hope that helps....

Mark

 

[feeench]

Yeah that helps Mark, thanks. I was a bit nervous at one point there that I might not get the levels I want but I've got a very good idea of what to expect now. I will certainly post results. I'm ordering a set of load resistors for the outputs of the SEX but I'm assuming, since there are no output transformers in the Smash that it's useless to load the outputs there when it's powering an F4 directly?

 

[feeench]

Okay I got it built.

The Smash with Smash-Up powers it just fine. Got it to go as loud as one would want it to go in a small room with the Orca Minis. I would have to imagine it wouldn't be up to snuff without the Smash-Up.

 

[JamieMcC]

Playing in the sandbox for beginners  :

About a month back for a little project I decided to order the Nelson Pass ACA amp pcb boards from diyaudio.  I put the two mono block amp sections in one diy enclosure and am using my Bottlehead Mainline for preamp and volume control,

Its a little pair of 6W single ended class A, mono block power amps Pass designed to be simple and inexpensive to build for newbies like me. I wanted to try it with some Fostex FX120 speakers but was also curious how it might work with my HE-6 headphones.

Its 6W is sounding good with the speaker set up so I built a little adapter and have been running the HE-6 off of the speaker taps with encouraging  results. I'm going to try some tweaking and swapping out the electrolytic signal capacitors for some film ones next, but this inexpensive little amp I am sure with a little further tweaking is potentially going to make for a really sweet combo for the notoriously difficult to drive HE6 headphones. Its also sounding ok with the HD800 but have a little low level volume noise to chase down with it on them. I am pretty certain its from my unshielded adapter cabling picking up interference (I just used the cabling I had to hand in the parts box).

Its up and running but still requires some feet and a little finishing off plus some experimental tweaking I expect I will swap out the unshielded signal wires for shielded and try a few different film cap options. Any thoughts or tips on optimising and making a little more headphone friendly would be welcome.