My new Sp14 build

Very nice.   I'm happy to have provided you a tiny bit of inspiration.  The rear mount selector does eliminate a large quantity of wire.  

What is the thick shielded wire?

I should have done the remote selector on my other one but you built yours after mine . That would have probobly prevented me from damageing  some of the  wires when I upgraded the caps in it six months  ago .  

The  "shielded" wire  is just plastic braid that I put on the transformer wires to the board , hopeing that it would keep the wires from laying directly on the circut  board . I just used that instead of wire ties on the longer  parts of wireing . Basicly eye candy  that you can't see.

The sound of this keeps getting better  .   But unfortunatly the heat of the tubes is being a real problem .  First the polyurethene finish  that was from research was the best for heat  has started to bubble around the tubes , next  the top started to warp , I expected a little warpage but not this bad. And the last straw , the top has split the wood in three places , almost the full length of the top . 
I've stopped using it untill I can get it fixed as I'm afraid the warping might crack the circut board .
I decided to rout out the top and inset a brass plate to secure  the board too . That will not warp or be affected by heat . I figure  brass will look good with the wood and keep the antique look . And since it's not magnetic it should  cause any problems ?





 If anyone wondered why I  mounted the little circut boards  that I soldered the big Jensen caps to , I was thinking ahead  for problems that might arise later , just like this . Since I couldn't mount the big caps  to the board easily  and now that I have to remove the board to repair the cabinet  all I have to do now is unsolder the wires  from the small boards to the main board  and I don't have to worry about the caps hanging off the board and possibly breaking one of the leads , they can stay right  in the case.

Back to the work bench !

Keep a fire extinguisher handy ... and chalk it up as a learning experience.

When you do the insert plate, maybe stand it off from the wood case a bit to allow heat to escape from underneath too. I got some handy dandy threaded spacers that worked out right nice for hanging the VTA board under the chassis plate ... might work for you too?



The dress up washers make for a nice transition too.

I'd also went a quarter inch x8 holes around each power tube to allow for a good chimney effect to draw heat up.

Another thing you might try is adding socket extensions to all the tubes. You can usually find them on da bay or maybe antique radio supply. Those add another 3/4 inches of height that would help keep the height away from the case. Here you can see the difference.



You'll also notice the drivers are set down some in the chassis, so the metal plate DOES get warm during use, but not so much I figure it's a problem ... If I were to do it again, I might go to 30mm on the holes instead of 25mm like I got.

I used the socket saver on the rectifier with a 5AR4 - That GZ37 rectifier gets mighty tall with one in the socket and I was afraid the amp would tip over, so I took it out ...   

PS ... I was actually a bit worried about the side panels on mine being too close to the power tubes, but I get no heating at all. Chalk THAT up to pure dumb luck ... then again, the tall bases on the KT120 tubes help a lot I'm sure.

My board has  1/2" standoffs on it now , so plenty or air flow , plus all the holes in the case sides . I plan on removing all the wood under the plate except about 3/4" or so to bolt it down so the tubes will be more exposed  since  the 3/4" of wood will be gone between the board . The circut board will then mount directly to the brass plate .
I tried the tube repair extenders  on all the tubes  to raise them first , but I don't know if  I got a bad one or two in the bunch but  the pre hummed and buzzed VERY badly with them ! And only one channel would work no matter which sockets I placed the  adapters in .
 I think the ventilation holes I drilled around the tubes are the main reason  of the cracking .

A couple in progress pics . I need to get to the hareware and get some brass  screws  . And sand and polish the brass yet . I made the tube holes a little bigger and eliminated the vent holes around them . There should be enough  air flow without them .

Very nice!

Polish the heck out of that plate and you'll get some serious tube glow and highlights. The brass should also blend well with the wood.

I take it that's the natural color of the wood and all you'll have to do is a bit of touchup around the new work?

PS ... couldn't tell from your pics, but the knobs are polished brass also?

Skiz , The knobs are from Goldpoint & mat black . I originally bought  some mat champagne gold knobs and didn't like them . They didn't go  with the wood color .  I think I have some brass stock down the basement somewere , that might give me a reason to blow the dust off the lathe and make some polished brass knobs for it .    Thanks for the idea !

 On the finish  I just had to sand the top wood some , brush  a little shellac ( orangeish tinted )  around the edges where I routed and then put a couple coats of poly on it . I taped the sides off and just did the top and you can't even tell .
 I didn't get the  routing perfect  from the wood edge to the brass , so I put a small bead of brown silicone on the edge under between the plate and wood and where it squeezed out and smoothed down when it was tightened filled my mistakes and you can't even tell , the color matches so close . I did the silicone  for some vibration dampning  also .

I spent the other night sanding the brass all the way up to 2500 grit wet paper  and polished the heck out of it.  I also made brass  studs to mount the plate and board  and  sanded and polished the ends of them where they come up through the top too .  Now it looks like there are ten tubes in it !  The pictures don't do it justice .   I'm now kind of glad  it cracked  because it looks so much better .  I also like how the tubes stand out a little taller than before since the brass top is thinner than the wood .    

I think when I do the PH16 in the future there is a brass top going on it too. As I have enough Brass , wood and inlay left over after doing this to do another one .  

For some reason the volume remote motor is not working , I don't know if a wire came off the circutboard or I tightened the connector screws down on the end of the wire or on the plastic insulation where they go into the remote board ? I'll fix that another day .



 

That's why they call it a work in progress. Nicely done! The brass looks great.

Beautiful work pigface ... looks stunning.

Well I got the remote working again , it just turned out to be a bad connection . Everything is back  working and looking good now .

After listening to the SP14 for a while now , it seems to drive my amp a little easier than the solid state pre . Meaning I don't have to turn up the volume  alot compared to my other preamp . I guess it has more output gain . Could this be from being a tube preamp or  just having more output ?  
I might even have to put some pre attenuation resistors in the volume attenuator  .  Will that effect the sound any ??

The tuner is almost too loud at three clicks on the knob  and the phono (since I switched out the GCPS for my SP15 ) which was  the lowest of all the inputs gets too loud at half volume  now . At first I thought I forgot to switch it from  MC  to MM  for this turntable, but no  .  And the CD player is somewere in the middle , I thought thatthis would be the loudest ,like before. But that could be from the db loss  going from the XLR to the rca outputs .

I always thought the old preamp didn't drive the amp enough since when I really crancked the volume  I athought it should have played louder considering the amp is 300 WPC.

This is not a complaint just an observation  It still sounds better than the solid state to me .

Good quality (not necessarily boutique) and matched resistor divider in front of the volume control shouldn't affect that sound in any meaningful way. Some claim it can and they can hear it though. You'll have to try it and judge for yourself.

Almost all modern sources have enough output signal that preamps (read gain) aren't really needed. I believe the circuit in the SP14 is providing around 10x gain, which you'll be pretty much negating with your volume control and pre-attenuation, the net result being raised noise floor.

I think it'd be beneficial to see low gain or no gain (buffer) versions of some of these preamps for folks with modern or higher output level sources who don't need much or any gain, but could use a buffer for driving long interconnects or difficult loads.

jjones3318 wrote:Almost all modern sources have enough output signal that preamps (read gain) aren't really needed.  I believe the circuit in the SP14 is providing around 10x gain, which you'll be pretty much negating with your volume control and pre-attenuation, the net result being raised noise floor.

I agree. The SP14 has a gain stage and an output buffer stage. Having one input bypassing the gain stage would make for a very flexible preamp. Maybe there is something here for Roy if he's looking for ideas for future products. Either a preamp with switchable gain/no gain, or just a (no gain) buffer line stage to complement his other fine preamp kits.

Thanks for the info . I  might try  the pre attenuation eventually . I   would just like to change it only about 2 clicks on the attenuator not alot . So I'll have to play with resistor values .

For my setup I think a no gain preamp wouldnt work on all my inputs .

The  10x gain info got me thinking  about the slightly microphonic tube clunk  noise I have when you would tap on the case . (It doesn't effect the overall sound though ) . I haven't done any tube rolling yet  but I figured I would try something , so I moved the  40's Sylvania 6SN7 tubes out of the gain section and put them in the buffer and swapped the 5692 CBS-Hytrons in their place and visa versa  and my mocrophonic noise is gone ! So I guess it was amplifying the slight microphonics as well. Now you can lightly tap on either tubes and VERY LITTLE noise is heard from either tube now .  And the Sylvanias were supposedly tested for microphonics and were supposed to be quiet !  One of these days I'll try the  JAN RCA  black glass tubes I have .

I'm wondering if the components have some part in this too since my unmodded SP14 in my other set up  is not like this one . It might be the big amplifier also . My speakers are rated  up to 250 watts . I bought the bigger 300 watt amp for some headroom as these speakers are  known to be hard to drive and killing some inferior amps . They are rated 4-6 ohms but drop to under 1 ohm at two different frequencys .

And I was being kind a sarcastic about the " Boutique " for the audiophile - audiofool crowd . 

pigface wrote:
I'm wondering if the components have some part in this too since my unmodded SP14 in my other set up  is not like this one . It might be the big amplifier also . My speakers are rated  up to 250 watts . I bought the bigger 300 watt amp for some headroom as these speakers are  known to be hard to drive and killing some inferior amps . They are rated 4-6 ohms but drop to under 1 ohm at two different frequencys  

It does sound as if your 300 watt power amp might be contributing to your problems. Have you tried swapping your two SP14's between your set ups to eliminate them from the equation?

If you do decide to use pre-attenuation, you could use the method shown on the Goldpoint website, but instead of at the attenuator, apply it only at the rear panel input jack(s) that you wish to pre-attenuate. This way the other inputs won't be effected.

http://www.goldpt.com/mods.html