A simple A/B switch for testing.

[Taperwood]

First, my thanks to everyone for their help on this project, especially to:

Dcibel
dnsey
Panomaniac

The primary reason I built this switch was to test separate speaker prototypes, but I think it would work very well for A/B testing of amps by simply adding a Y-cable to the outputs.

The inputs take the L/R channels from any source. Each then passes through a 10k Ohm resistor (mine measured an identical 9.83k Ohm) and connects to a SPDP toggle switch, with the output going to two RCA's at the output. All RCA's maintain a common ground.

Since the inputs are combined at the switch, the signal is in mono, but if you test using reference music or somthing you are very familier with, you will at least hear the entire recording, not just what is on the left or right channel.

All parts are from Radio Shack. Parts ran about $7. They assured me the switch was a "make before break" design. In actual use, the switch adds absolutely no pops or breaks in the sound whatsoever.

I hope everyone finds this useful.

Doug

ps: I will cross post this to the Full Range forum.

Interior shot:

[Taperwood]

The box was made from a single block of quilted maple with an oil finish. It fits in the hand very comfortably.

Oh yeah, the switch works great. It's a vast improvement and makes my life much easier.

Outside shot:

[senderj]

Newbie questions: May I ask,
1. What is the purpose of the resistors?
2. Why did you made it with solid wood?

[cpemma]

Variation at Westhost, aimed at comparing amplifiers without moving from the listening position, uses a relay slaved from the operating switch to change sources.

[Taperwood]

Newbie questions: May I ask,
1. What is the purpose of the resistors?
2. Why did you made it with solid wood?

Senderj,

I'll leave #1 to far more qualfied people than myself.

As to #2: I like wood, I had the wood, I know how to work with wood. I do not believe there are any RFI or grounding issues involved. I don't think it makes any difference what enclosure you use.

Hope this answers your question.

Doug

[Taperwood]

Originally posted by cpemma
Variation at Westhost, aimed at comparing amplifiers without moving from the listening position, uses a relay slaved from the operating switch to change sources.

That's certainly a better solution than using my box for testing amps.

The single purpose of my box is to A/B test two individual speakers for listening comparison purposes. I thought you could rig it up to test two amps, but the more I think about it, the dumber it sounds.

Doug

[Bgt]

switching A/B to test various mods in power amps is done the best with relais. You will be surprised how your mind makes up things from mods. I found out after having neutral people listening tests showing no sound change and am happy now I do it with some special 4 contacts per arm relays which have a R of 10 mOhm from plug to plug(including contacts).
Did this change my opinion about mods. I only trust mods done in direct A/B tests now with a standard stereo UCD400AD amp. as reference.

[ped]

Hi Doug and Bert,

I would have to agree that a direct A/B test is the most reliable way to evaluate just about any mod. I've only been able to do it with speakers so far but hope to get a relay setup for amps at some point. It is quite sobering, differences that I believed to be huge were quickly whittled down this way

So Bert, to date what mods (UcD) have you found to make an improvement?

Perhaps this is best answered via email to prevent a threadjacking

Regards,
Paul

[Bgt]

Paul, the best mod. was the grounding/input wiring scheme which I discussed in another thread already. This is a personal experience of a mod. that turned out to be the best I could get.
But remember, I use a 1 transformer/2bridge/4caps. setup with no mains earth connected and a passive preamp.

And yes, it is quit disappointing having done a mod. and getting lyric about it to find out after doing the A/B test that there is no difference at all.

[Bgt]

After finding out the A/B comparison was the best to use, simply bypassing your mind/mood/sentiment, I did a lot of small mods. by changing caps. and psu(rectifiers,caps.) to find out the basic UCD design is extremely well thought out. I mean If I have to use such extreme speakers to get the last drop of quality out of the amps., thats just a waste of money(my view). Improving from 90% to 90,5% and pay so much money for it, it just makes no sense to me. Modding an amp. is only meaningfull for me if the basic system improves(listening with normal(1k) speakers, not 10k ones) with simple changes/little costs.