The Disappointment That is the Heath W4

[Steve O]

Well, not one to let things be, I set out on a mission to 'fix' the amp, if indeed a fix is needed. I had a few goals in mind before starting this. 1) as few changes as possible so it could be an easy fix to current amps, 2) stable into 1uF, and 3) similar power outputs. <snip>

This is good work. Ultimately I wasn't satisfied with the performance of my modified W4 and was thinking along the lines of changes you've pretty much identified as dead-ends. Since the final changes are relatively easy to make, I going to try them and compare results with yours. Hopefully they'll be identical.

Although my frequency response plots seem to indicate that my OPT is OK, I still have nagging doubts about it since the rest of the circuit is OK. We'll see.

 

[Steve O]

I've never messed with a W4 before (I've had a pair for 4 years that I have never had a chance to play with) but I have to say it would shock me if Steve's square wave results are the norm. I've never seen a vintage amp with that kind of 10 khz performance. I've seen many modern off shore sourced amplifiers look like that but never a USA made vintage amp from any manufacturer. Even a cheap PA amp......

I've seen many that the 10khz square was pretty rounded but never with that kind of uncontrolled ringing.........

I think something is malfunctioning or damaged somewhere in the test amplifier.

Craig

I understand your doubt. In a later post from the original I did note that I'd found the resistor in the phase comp network was off value. I also found that raising the 5881 coupling caps off the chassis improved performance. After the changes, the sq wave performance improved but was still not quite as good as Bricktop's so a defective OPT or something else was still possible. That's why I ran the freq response and compared to Heath's spec. I also duplicated or bettered Heath's and Bricktop's distortion performance. Since the response and distortion of my amp meets or betters the Heath spec, I now assume that the OPT is probably OK. Although I haven't seen as many vintage amps as you have, the ones I have seen where the OPT was in some way defective have had obvious response and distortion issues.

Beyond what I've done, I'm not sure how to verify OPT condition short of swap out with a known good unit. If you have any suggestions, I'm listening.

 

[PakProtector]

I feel compelled to defend the Heath W4.

It really is quite a good performer when you replace the output and power transformers.

Sounds like a dealer in Abe Lincoln's axes...'seven new handles an' three new heads'.
cheers,
Douglas

oh, and no 205 data in my 177B book.

 

[bricktop]

By chance, have you run a frequency response test on the amp in its current form? It'd be interesting to see how that compared to Steve's data above!

Thanks!

Regards,
Gordon.

Here you go! Pretty much same as stock. Mine has the input coupling caps removed, so the lower end is flatter than stock. That's the only difference I really see (that manual with freq response is on my website).

 

[GordonW]

Here you go! Pretty much same as stock. Mine has the input coupling caps removed, so the lower end is flatter than stock. That's the only difference I really see (that manual with freq response is on my website).

Wow. This looks like a pretty much all-win situation.

Congrats... I think we have a winner here!!

I'll have to keep this technique in mind when I'm working on my own amp here. Though my current design is different enough that I probably wouldn't use it, if THAT doesn't work, I could use it in an improved version of the stock Berning EA-230 circuit design (the only difference being, in essence, the addition of a cathode follower stage between the diff amp and the outputs, which shouldn't, at least in theory, affect the transfer function much as it's got near "infinite" bandwidth, having unity gain)... that might allow cranking up the input stage gain a bit (allowing an increase to a more reasonable level of feedback in the EA-230, ie, somewhere between 10-20 dB total, to improve bass damping) while maintaining stability...

Regards,
Gordon.