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DIY audio: what are you building?


Paul Spencer

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24 minutes ago, Rob181 said:

Would be...if it was true...

 

24 minutes ago, Rob181 said:

Would be...if it was true...

So you have the same driver in the same box?

 

With the stereophile warble tones in my system in my room there is no reduction in volume until 40hZ. At 40hZ the bass slot, the bottom of the speaker, goes off and the driver stops emitting. I'm on a wooden floor and the floor vibrates in sympathy to the tone. 40hZ!

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Guest Muon N'

@mwhouston Was a shot, I had no luck finding those caps specifically with google-fu, so resorted to acronym finder.

https://www.acronymfinder.com/VMP.html

 

If they sound acceptable, that's what matters :thumb:

 

 

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After some conflab with others the caps are probably metalised polypropylene. Even better.

A nearby friend in audio DIY crime did some testing for me on Lagoon. This is a 4S 12AU7 single stage tube preamp. The results are good.

Distortion is quite low at 0.05% with the second harmonic predominant as expected. There was 50hz and 100hz hum there but low down and not audible in practice.

Frequency response was from less then 30hz to over 20K which is all the test gear goes to. BUT this was into a crippling 15K resistive load.

This leads me to question that these single stage preamps will only work into high impedance load, typically 250K!. There is an online impedance calculator in which you enter tube type, plate load resistor Rp and cathode resistor Rk and in bypassed or not. The calculator claims the output impedance should be about 13K! A lot lower than I have ever thought.


To test this out we maxed the output of the preamp just prior to clipping (30V) then loaded it down until we got half the output voltage - about 13V. This occurred at a load of 15K!!! I maybe be wrong but this indicates the output impedance is 15K. Right or wrong.


Very pleasing results all round and now I know this 4S preamp will drive SS power amps which have a input impedance of better than 15K (most will) and need less than a 13V swing - ALL WILL. Not only that the preamp sounds excellent.

Lagoon.jpg

LagoonFreqRes.jpg

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I’ve done a number of DIY projects, DC blocker, mains distribution, room diffuser panels, large refurbishment and rebuild of my NS-1000Ms, speaker stands, phonostage, turntable power supply, record clamps and mats and also my turntable. My current project is a redesign of my current turntable and is the culmination of twenty + years of experimentation and development. Here is some of the CAD I have done - I would say actual construction is about 50% complete. 

 

 

9B4138BB-DC4C-49F4-9802-3E1DF33216A1.jpeg

C11C75BD-8B22-4EC3-B87E-23A5FD7AF643.jpeg

AA1B2D05-62AB-4683-9827-0C381682112D.jpeg

EB6249B3-9B47-4E1D-9EB8-6CEDADFFDB25.jpeg

Edited by YNWaN
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@YNWaN, you should start a thread of your own.  Tell us why you are doing what you are doing and the process you have gone through to make your decisions.  The table looks great, but I for one would like to know more of the "why" and "how" if you have the time. 

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It all stated with a free JAN GE 6J6A tube. Not sure too many know the tube. It has a B7 base which means 7 pins. There is one common cathode. Fortunately my tube amp designer buddy in Seattle whipped me up a preamp based on the tube. Because of the single cathode fixed bias is applied. I may just use some batteries which will never go flat from use.

 

Here is the brd. Or more like here is the verobaord. 1uf poly input  cap, metalised poly output cap, metal film resistors and ceramic socket. The only thing I had to buy were the sockets the rest I had on hand. Also I have a finished PS from another project.

 

I need some more parts to complete the preamp but so far it's been a cheap ride.

image.jpeg

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2 minutes ago, Batty said:

Is that the same valve that is in the Headphone amp I bought from you?

By the way it really suits the HE4xx phones I recently purchased.

Yes same tube. I only ended up with one and had to do something simple with it. Could be interesting. I have so many tubes and possibly better tubes,like real expensive limited edition 6SN7s tubes but just thought how many people do you know who have a 6J6A preamps?

 

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I couldn't find a cheap suitable enclosure for this little 6J6A preamp. Most were too shallow and the tube would have been hidden in anything larger or deep enough. Then I thought "move the bottom of the socket to the parts side and then the tube will stand proud on the copper strips and be easily exposed". More than that I can now use a cheaper shallow enclsoure.

 

A bit of fiddling around and a few new holes later here is the result. I have a PS ready to go and now for a couple of cheap enclosures. I have that worked out already.

image.jpeg

image.jpeg

image.jpeg

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Finally snaffled a set of 18Sound XT1086 flares at an excellent price. So it's time to utilise the drivers I have gathering dust, especially as I've calculated I can use the same enclosure for them that my ATC build will use. So I can just get 2x the timber cut and I'll likely build both pairs at the same time.

JBL 18" sealed 60-250Hz, 2 x JBL2118 (MHM), and an XT1086/ND1090 combo x-ing in at about 1500Hz. I have a bunch (8) sealed 12" units to hand off to below 60Hz. They'll be driven by a new audio only PC* and external soundcard and existing amps.

 

* Should be finished over the w/e if I get some time.

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Bought some Altec 511B horns from a fellow SNA member. I sourced some compression drivers from a local DJ store nearby. The drivers are Itallian (link to follow) and expensive compared to some others. Looking for hifi sound from the horns. 

 

Here are some old Xovers I modded to work better with the horns. Xover at 1600hz 2nd order on the woofer and 3rd order on the horn. Looks rough but should be enough to have a listen. 

image.jpeg

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2 minutes ago, mwhouston said:

Bought some Altec 511B horns from a fellow SNA member. I sourced some compression drivers from a local DJ store nearby. The drivers are Itallian (link to follow) and expensive compared to some others. Looking for hifi sound from the horns. 

 

Here are some old Xovers I modded to work better with the horns. Xover at 1600hz 2nd order on the woofer and 3rd order on the horn. Looks rough but should be enough to have a listen. 

image.jpeg

I have a pair of 811B for a hopeful project....watching what you’re doing.

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