SP 14 build finally done and....

After some trials and tribulations and a bit more confusion than my ST70, my SP14 is DONE.  Playing right now, and my initial question is does this need to "burn in" or improve over a certain amount of hours?  I'm reasonably sure that I have everything correctly wired, gain and volume work..etc.  I do notice my left channel seems a bit "weak" and I'm not sure if it's the speaker or something internal (too tired to tackle that right now, long day then finished up the SP.)  Both gain amounts at the same level there is a bias toward the right like the entire sound stage is shifted there, did not happen with the Rotel pre-amp.  

Initial, informal impression is that it's very "bright" and not what I expected.  Marantz CD (Robert Cray which I'm very familiar with), Tannoy Speakers, Cardas interconnects and Blue Jeans speaker cables.  No matter pentode or triode mode I'm already getting listeners fatigue.  Any insight appreciated.  Maybe now my  speakers sound how they're supposed to sound???  

After a bit of time and sorting this issue out I'll write a more detailed account of building it and what's involved and my experience with Roy and this product (which is a lot for the money.)

Got pics?

corndog71 wrote:Got pics?

"Oh yee of many fancy builds..." I have the aluminum case that Roy sells, nothing fancy, and some birds nest inside that passes as my wiring : )

I'm so naive and new to this that it wasn't easy for me, but not purely difficult. I'll have to figure out why my sound is off on the left speaker.

On another topic, but related, is that I was running the Marantz CD player out digitally to the processor on the Rotel, now I'm running the CD's built in D/A directly to the SP14 and I'm wondering if the SP14 is accurate (?) enough to show the flaws of the on board Marantz D/A processor. Still doesn't account for the left speaker, that is another issue.

Laminarman wrote:

corndog71 wrote:Got pics?

"Oh yee of many fancy builds..."  I have the aluminum case that Roy sells, nothing fancy, and some birds nest inside that passes as my wiring : )

I'm so naive and new to this that it wasn't easy for me, but not purely difficult.  I'll have to figure out why my sound is off on the left speaker.

On another topic, but related, is that I was running the Marantz CD player out digitally to the processor on the Rotel, now I'm running the CD's built in D/A directly to the SP14 and I'm wondering if the SP14 is accurate (?) enough to show the flaws of the on board Marantz D/A processor.  Still doesn't account for the left speaker, that is another issue.

On your SP14 try swapping the tubes around.  Left channel tubes to the right channel and vice versa.  See if the problem stays in the left channel (preamp problem) or if it follows the tube. (tube problem). I would also say Sonicaps run slightly to the brighter side of neutral which may not match well with your speakers. You may want to consider swapping those out for something warmer like Clarity Cap ESA series.

What attenuators did you use ? The ones with the kit that you have to build and solder the resistors in ? May be you have a bad resistor or a bad solder joint in one of them ?  May be a weak solder joint on the left side of the board somewere ?
I built two of these for myself  and neither sounded  overly "bright" if anything this last one  is less "bright " than my SS preamp.  I don't know about the sonicaps since I didn't use them . I used the Mundorf S/O and Russian PIO's in the first one  and Jensen and Jupiter caps in the other .   I've only about 35-40 hours on this last one I just finished  and the sound has smoothed out some from initial start up  but not a drastic change . But definatly for the better .

Go back in and double check the wiring and solder with a magnafying glass ?

I cought a couple mistakes I made on this last build , it happens.

corndog71 wrote:

Laminarman wrote:

corndog71 wrote:Got pics?

"Oh yee of many fancy builds..."  I have the aluminum case that Roy sells, nothing fancy, and some birds nest inside that passes as my wiring : )

I'm so naive and new to this that it wasn't easy for me, but not purely difficult.  I'll have to figure out why my sound is off on the left speaker.

On another topic, but related, is that I was running the Marantz CD player out digitally to the processor on the Rotel, now I'm running the CD's built in D/A directly to the SP14 and I'm wondering if the SP14 is accurate (?) enough to show the flaws of the on board Marantz D/A processor.  Still doesn't account for the left speaker, that is another issue.

On your SP14 try swapping the tubes around.  Left channel tubes to the right channel and vice versa.  See if the problem stays in the left channel (preamp problem) or if it follows the tube. (tube problem).  I would also say Sonicaps run slightly to the brighter side of neutral which may not match well with your speakers.  You may want to consider swapping those out for something warmer like Clarity Cap ESA series.

Thanks, I'll try this first tonight when I get home from work. Never thought of that.

pigface wrote:What attenuators did you use ? The ones with the kit that you have to build and solder the resistors in ? May be you have a bad resistor or a bad solder joint in one of them ?  May be a weak solder joint on the left side of the board somewere ?
I built two of these for myself  and neither sounded  overly "bright" if anything this last one  is less "bright " than my SS preamp.  I don't know about the sonicaps since I didn't use them . I used the Mundorf S/O and Russian PIO's in the first one  and Jensen and Jupiter caps in the other .   I've only about 35-40 hours on this last one I just finished  and the sound has smoothed out some from initial start up  but not a drastic change . But definatly for the better .

Go back in and double check the wiring and solder with a magnafying glass ?

I cought a couple mistakes I made on this last build , it happens.

I have the Mundorf SO caps. I have the attenuators with the individual resistors and the Goldpoint volume control. I double checked everything before firing her up, but will do so again if the tube swap doesn't show it to be the tubes. I appreciate the advice.

tube swap left to right channels and see if the gain imbalance follows, if so, it's the difference in gain of the tubes, otherwise, it's a possible error of parts stuffing.
That's the nice thing though with having the dual gain/balance attenuators, you can dial out the difference, once it's set right, you won't have to change those settings.

tubes4hifi wrote:tube swap left to right channels and see if the gain imbalance follows, if so, it's the difference in gain of the tubes, otherwise, it's a possible error of parts stuffing.
That's the nice thing though with having the dual gain/balance attenuators, you can dial out the difference, once it's set right, you won't have to change those settings.

Thanks Roy. Is the gain difference an inherent built in thing that varies with each tube, or is it adjustable in any way? Even if I dial in more gain it just doesn't sound quite right out of that speaker. I'll swap tonight and see what's up.

I'm talking about manufacturing and quality differences in the tube itself. Nothing is perfect.
Typical variation in tubes is around 20%, even within the same dual triode.
You can always pay extra to buy matched and or balanced tubes.
But after you check the tubes, then you can see if something else is wrong.

Got it Roy, thanks.

Swapped the tubes, the left channel still sounds off. Next step is I'll hook up my Rotel processor/preamp. It doesn't have gain or balance controls unless they're on the onscreen menu. I'll run white noise through it and use a sound pressure meter to see if there's a big difference. If speakers are about the same I start really looking at the SP14. I looked at all the connections very carefully tonight, all looks solid. Ugh...

One thing I would try is using a one-to-two RCA y-cable to input the same white noise to both channels. If you have a scope or high input impedance ac voltmeter and a schematic you could follow the input signal by probing both sides of the ac coupling caps--comparing left channel nodes to right channel nodes to see where the attenuation is happening.

With the same input setup Use your ac voltmeter to measure the ac voltage between left out and right out. You should see about zero ac volts as you turn the volume up and down.

While you are at it, measure the dc voltage between left out and left ground, then right out to right ground to make sure that you have zero dc offset.

check your volume and balance/gain controls to make sure they are the same on each channel. Maybe a bad attenuator?
If they are, that leave resistors on the PCB, maybe a couple are in the wrong place?

tubes4hifi wrote:check your volume and balance/gain controls to make sure they are the same on each channel.   Maybe a bad attenuator?
If they are, that leave resistors on the PCB, maybe a couple are in the wrong place?

Roy, I am going to check the PCB against the wiring diagram item by item and re-check all solder connections. The resistors on the attenuators are correct as far as I can tell with a loupe and high mag/bright light. I checked ground and connection for lines in/out. Maybe if that shows nothing I'll post photos of the connections. Thank you.

A bit confused about what exactly you mean by the left channel being "off". If it's simply a balance issue, and you're using a stepped attenuator, first thing I'd do is to try swapping the connections on the attenuator itself. If the problem switches channels, then you need to replace the attenuator, or fudge the circuit with a resistor to balance it properly. Or just go with dual pots like I did on my amp build ...

As far as "bright" goes, that could be just a match up problem with your other components that could be solved with a tube swap. Simple enough, but could get expensive depending on how many tubes you go thru to get the results you want. For that, I'd maybe score some cheepies that would at least give you an idea of what's possible, or troll the boards for what folk are using and the results they're getting.

Luck wit it ... this is the point where you either grit your teeth and press on regardless, or sit in the corner talking to yourself. Possibly both ... ;-}

sKiZo wrote:A bit confused about what exactly you mean by the left channel being "off". If it's simply a balance issue, and you're using a stepped attenuator, first thing I'd do is to try swapping the connections on the attenuator itself. If the problem switches channels, then you need to replace the attenuator, or fudge the circuit with a resistor to balance it properly. Or just go with dual pots like I did on my amp build ...

As far as "bright" goes, that could be just a match up problem with your other components that could be solved with a tube swap. Simple enough, but could get expensive depending on how many tubes you go thru to get the results you want. For that, I'd maybe score some cheepies that would at least give you an idea of what's possible, or troll the boards for what folk are using and the results they're getting.

Luck wit it ... this is the point where you either grit your teeth and press on regardless, or sit in the corner talking to yourself. Possibly both ...  ;-}

Hey SkiZo. It's just "off." Like it lacks bass mostly not just "not as loud." Dialing in more gain just makes the crappy sound louder. I'm wondering if coincidentally something happened to my speaker, it sure sounds like it. Now, I hadn't noticed this before but I'll hook it back up to my SS amp and preamp tonight and if it's fine, then something is fishy with the preamp. I'm thinking that the SP14 is showing my Tannoys for what they are, or perhaps the onboard DAC of the player is likely also to blame somewhat. I'll post further results after I look again and have some mind lubricating English ale.

The RCA outputs of the preamp..  have you flip flopped them so Right is Left and vice versa?  To see if what sounds like a bad channel from what you describe follows to the other speaker as you'd expect if the Preamp was the problem?

Also check the polarity of your speaker cables at both ends.

mantha3 wrote:The RCA outputs of the preamp..  have you flip flopped them so Right is Left and vice versa?  To see if what sounds like a bad channel from what you describe follows to the other speaker as you'd expect if the Preamp was the problem?

Got called to work for an emergency didn't get to it tonight. Have not, but I will. Didn't think of this.

corndog71 wrote:Also check the polarity of your speaker cables at both ends.

I would be really embarrassed if this was the cause, but that was the very first thing I checked!

Spent some time checking all connections and resistors...etc.  I found what I think was a cold solder joint on a capacitor as it seemed loose so I redid that (not the big Mundorf, one of those little guys.)  Then I resoldered a ground wire to the Goldpoint which looked a little shaky.  I fired it up, and still had less volume in the left channel but it seemed a bit "fuller" in sound if that makes sense.  I double checked all phase connections.  Then desoldered and swapped R for L on the OUT jacks, and lo and behold the right channel is now lower in volume. Took out my sound pressure meter and the difference in the two channels is about 14 decibels.  When I equalize the gain with two full clicks it sounds fine.  So the question now is the bias difference the tubes (I think not since a tube swap did nothing), or an attenuator?  And, is this much difference in the gain between attenuators normal?

EDIT*** More info: now I resoldered so left out goes to left channel and now I have about a 25 decibel difference in volume. WTH?? I did check my speakers, they're OK and fine through my SS preamp. To give an idea, I can equalize SPL with the left knob at 1:00 and the right knob at 9:00 position. Sound is again just "off" in the left channel. SkiZo I'm about ready to start talking to myself. Is the next step posting photos or getting another attenuator?

Is the Goldpoint wired different on the left and right channels?  If you had the connections reversed on one channel then the attenuation would be a lot different versus the other.   You can also take an ohmmeter and verify the Goldpoint center tap to ground resistance.  Both channels should match within 1% or so on each click position. An in circuit test would be OK as both channels are symmetrical. (Power off and bleed caps first!).

don't forget that using a meter to check things usually works better than eyeballing something.

arledgsc wrote:Is the Goldpoint wired different on the left and right channels?  If you had the connections reversed on one channel then the attenuation would be a lot different versus the other.   You can also take an ohmmeter and verify the Goldpoint center tap to ground resistance.  Both channels should match within 1% or so on each click position.   An in circuit test would be OK as both channels are symmetrical.  (Power off and bleed caps first!).

Yes they are different which is perplexing to me (but not reversed) and follows the diagram exactly.  Roy told me these things only matter if I don't know how they work (and I don't know how they work.)  

From the Goldpoint:

Left ground goes to resistor #1 on L gain and ground on PCB
Left out goes to the PCB
Left input goes to A terminal in the center of L gain

Right ground goes to resistor #1 on R gain and ground on PCB (just like on the left channel)
Right out goes to to the PCB (just like left channel)
Right input goes to resistor #12 on R gain (instead of to the center A tab on the attenuator) Instead the center "A" tab on the R attenuator gets wired to the source/tape switch.  Seems to me and I'm likely wrong, that the center tabs of the source/tape switch should both go to the same place, namely the #12 resistor?  Don't ask me why this stupid photo won't rotate the way I want it to.  

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