Improving my La4a . . . .

GroupDIY Audio Forum

Help Support GroupDIY Audio Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

strangeandbouncy

Well-known member
Joined
Aug 8, 2004
Messages
2,112
Location
West Sussex. UK
Dear All,

I have had an La4a silverface since I was a tap-op in the 1980's. It was damaged in a fire, and I bought it for £50. I still looks awful, but worked perfectly after a little attention, and a lot of elbow grease T-cutting the front of the Meter! Now I know that many don't like these, mainly due to the crumby 4136 op-amp, but. I absolutely love mine, more for it's "Action" than it's "Sound". I do accept that it can be muddy and a little blurred, but i still use it every day as my first choice to level vocals to tape. Nothing else is so forgiving in my armoury. It rules on many other things as well, especially bass and guitars. I would use an La2 or La3a, but I don't have these puppies anymore . . . soon to be re-instated, thanks to the wonderful Mr Drip :wink: . . . I digress. I was looking at the schemo here.

http://www.waltzingbear.com/Schematics/Urei/LA_4A.htm

and it struck me that I might replace the input op-amps(ic 1 a, b+c) with a transformer, a bit like the La2a/ La3a. I also intend to replace the buffer (ic 1 d) and the output amplifier(ic 2 d and Q2+Q3) with discrete op-amps, probably TK's Gain/Fet/BigBloaks. I might even use the existing output transformer, since it appears to be a very sexy 600:600 tranny indeed!

Forgive my use of various unqualified adjectives to describe my findings, but i just don't have any other way, posessing merely a digital voltmeter, - and my ears! Today, I tried an experiment with several of the 1:1 transformers that I have in my junk box, namely Neve orange "donut"-600:600, Sowter 4652-600:600, and Gardner's 10kct:10k. There was an immediate and quite staggering improvement with all of them! Suddenly, it was like taking off some dirty sunglasses. SOOO much detail! Further comparisons showed the following. Sowter, delicate, detailed, focused, but as little lacking in the top end. Gardner's, Absolutely outstanding, detailed, bright, forward, present - just delicious! Improved only by using only one tap of the input, making 2k4:10k step up. this makes the sound thicker as well as louder. Neve Orange, on further investigation, even though it improvement over the ic input is - total dogshit! Flat, boring and lifeless, and extremely dull, with very poor top-end. Sowter is most "HiFi" with merely a slight rolloff in the top-end. Gardner's is SOOO fat! Question is, is the top end difference a function of the impedence of the relative transformers, or a function of different makes? reason why I ask is this. Simply, the Sowter is easy to fit, being wedged between the lid and chassis with screw through the lug, and the Gardner's will be a bitch to fix, being an Octal mounting. Also. I have the Gardner's earmaked for something else . . . And, I am too mean to buy another Transformer!

I ran out of time, as it is my turn to cook tonight, so I am asking questions that I can no-doubt workout tomorrow with a handful of components, but i would seriously value some advice from those "in the know". I remember CJ saying that in an La2a, if you change out the A10 step-up input tranny to a 10k:10k, you should change R5(68k) for 11k to correct freq response. Can I reduce R12 on La4a to, say, 1k or less to improve hf roll-off with a 600:600 transformer? Or should I find a way of fixing the Garner's/Buy a Sowter 3232 10k:10k or similar? If I use te Gardner's, should I reduce R12 from 22k to, say, 11k?

I cannot wait to vamp-up the buffer and amplifier next, I am sure that a vast improvement can be made!

Any advice comments would be very greatfully recieved indeed!

MAny thanks,

ANdyP[/i]
 
Hi Andy I realize this is old post, i only just discovered it and was wondering how you got on improving your LA4A....thanks.
 

Latest posts

Back
Top