Impedance Switch malfunction

[FraGGleR]

Hi there, have had a second hand S.E.X. 2.1 for a month or two now and have loved the sound I am getting.  It has the impedance switch kit and I had been listening on balanced and high impedance since that is how it came.  I tried changing it to low impedance to see how it sounded, but was greeted with a severe channel imbalance. 

Any ideas on what would cause this and what I should look for?  I am relatively handy with a soldering iron, but I am a paint by numbers DIYer and don't understand the circuits all that well.

Thanks.

 

[Paul Joppa]

Most likely a wiring error or a bad solder joint, on the board or the output transformer terminals.

The transformer terminals are embossed on the bobbin - you can't see the bottom ones, but they are numbered in the same direction as the top ones (i.e. NOT in a circle!). The terminal numbers are silkscreened on the PC board so that should be easy to check. If those are OK, it's worth the effort to dismount the PC board and inspect all the solder joints on the board - if you are handy with a soldering iron, you probably know what a good joint looks like, no blobs just smoothly wetted surfaces.

Did you get the manuals (one for the amp, another for the switch board)?

 

[FraGGleR]

Thanks for the advice.  I will try to do some checking later this week.  Something was likely knocked loose during shipping.  The guy I bought from has done over half a dozen Bottlehead kits so his work is likely good.

Yes, I did get the manuals from the seller, so I should be able to at least check proper wiring and solder joints without too much problems.  Just wanted to check in first.  Thanks!

 

[Paul Joppa]

Oh yeah - I forgot to say, welcome to the Bottlehead community!  :^)

 

[FraGGleR]

Finally had some time to poke around under the hood.  One thing that I noticed, which I am not sure would have an impact is that that the two parafeed caps are different values.  One is 1.5uF and the other is 1uF.  Well at least that is what I think I am reading.  They look like two different runs so the printing is different.  Would this impact the balance of sound at different impedances?  The boards look ok, so I am thinking something else in the chain is causing the imbalance.

As a follow up, I was going to "upgrade" the parafeed and coupling caps anyways so I will be matching the ratings going forward.  Along those lines, I am most likely not going to do the Magnequest upgrade for some time so I was wondering what value would be ideal for now.  I was going to use some Obbligato gold capacitors since they seem to have a good price/performance ratio.  For the parafeed, my options are 1.5uF and 2.2uF.  Would there be a benefit or downside to going with either.  Both are within the suitable range for stock according to a post about parafeed values posted elsewhere.  Alternatively, I was looking at the Mundorf Supremes which gives me more flexibility in values.  Would these be a an upgrade in sound? 

Thanks in advance!

 

[Paul Joppa]

I can only offer generalizations which ignore the effect of the cap on the speaker. Within that constraint, the larger cap will have slightly deeper low bass extension, at the price of slightly greater possibility of slightly reduced power margin in the deep bass. The difference by itself would be pretty small.

Different speakers will interact with the parafeed capacitor in different ways, again confined to the deep bass. That part is hard to predict. Room acoustics behave similarly, but are probably the largest of the effects - just for scoping purposes.

Deep bass means, in this context, the two octaves below 50Hz.

 

[FraGGleR]

Thanks again for the help.  I will keep the cap values as close to stock values.  I really like the sound I am getting.  I am more just curious to see if I can hear a difference.

BTW, my impedance boards are working on all switch positions now.  All I did is unmount the boards to check for bad joints (there were none) and remount them.  I do have the speaker taps connected now, although I don't know how that would have impacted things.

All in all, I am excited that I am fully functional now and loving the sound.

 

[Grainger49]

  .  .  .    All I did is unmount the boards to check for bad joints (there were none) and remount them.  .  .  .   

Sometimes, it seems, that is all it takes.  Who knows why????