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McBride 135 clones- help needed

Retro

Retro

pfm Member
Hi all,

I Have just started out on making some 135 clones inspired by the Neil McBride site. Courtesy of a recent Maplin Sale, Chris Allan and the generous Chiily, I have main power toroidal transformers, the power supply electrolytics and the recommended output and driver transistors. A fortunate start I think.
However, I would like to try and pull together all the experience here in building these amps before I go on with mine. I have been searching this forum and have many pieces of useful info, but the nuggetts are very widely spread and logical searches do not always produce the results you hope for. I am particularly interested in any advice surrounding successful component choices, particularly in critical feedback and signal path locations. Other areas such as separate Vas regulation (ashleyD?), cascode replacement for Q4 (Fretless Eric?) and another JFET mod also sound interesting. I have found references to all of the above, but few conclusions.
I have also been surprised by how many people are posting in McBride related threads and it seems to me that a single thread pulling together all the developments to date could be useful to others as well as myself. If this seems like a good idea, I will gladly compile a summary document, fom the responses received, that could perhaps be posted in the FAQS section.

Regards,

Graham. :)
 
Graham,
I tried PMing you but you're full up. Anyway, if I get a short break from covering myself in sawdust I'll email you a parts list with some supplier references if you want, but some people like to do their own parts number searches.

The VAS regulation (actually input and VAS stages) was a great mod and well worth doing.

Similarly replacing the resistors in the long tail pairs on the regulator board with active current sources was good.

Laterly I've cascoded the current source for the VAS and after a bit of fettling this has also produced good results.

I'll try and get all the details together and email them to you.

The info on the McBride site is very accurate, both my amps worked first time so you shouldn't have any worries there.

Ashley
 
Hi Ashley,

Why don't you post the details here, they sound interesting, I'm sure lots of members would enjoy reading them. Including me. :)

Regards,

Mus
 
Are you making you own pcbs or are you using Les' NCC200 pcbs for the amps? - the circuits are very similar I think - especially if you are doing away with the output protection circuitry as Neil recommends.
 
It's not difficult to make your own boards. I used press 'n' peel and ferric chloride cyrstals from Maplins, together with a couple of cat litter trays it produced excellent results.

I think Fretless Eric has updated the McBride PCB's to include the VAS CCS Cascode mod.

I believe the NCC200? circuit is very similar to Neil's, but there are bound to be differences, for instance the NCC200 circuit uses emitter resistors in the diff pair whereas Neil's (and Naims) don't.

Ashley
 
Originally posted by AshleyD
the NCC200 circuit uses emitter resistors in the diff pair whereas Neil's (and Naims) don't.
Click to expand...
Just a quick note - I added the emitter resistors (I used 100R 1/8w ) in the NAP-140 and it seems to work fine.
I'm now struggling with another Avondale mod - the front end supply decoupling, which is also absent from NMB and Naim's. Hope I can get it done tonight.
Yair.
 
Glad to hear that your on with the McBrides.
One of my McBride regulators failed and Les kindly had a look - there were parts missing on the pcbs! So much for my bargain amp. Havent got the amps and regs back yet, so dunno whether the projects a goer.
Let me know how it works out.
 
I was planning to make my own PCB's. The peel and stick system seems to get pretty good reports and is cheap enough.
I am interested in including some of the 'go faster' modifications, such as VAS & input regulation along with the Cascode addition. Maybe even to add to the original artwork (I understand that Fretless may have completed some of this work already) and produce combined power and regulation circuits, including the above mods, on one PCB. Clearly, this will cut down on interconnecting wire, but not necessarity make the circuit any more robust. Am I off on a wacky tangent here, or might it be an idea worth persuing?

Any thoughts?

Regards,

Graham.
 
Sorry for the delay in response and missing your PM.

I have revised the artwork to reflect the changes but I do really need to check it thoroughly before sending it out.

I have plans to build one as well but not in the near future.

I'll start checking it this week. The mod is definitely worth doing for little expense.

I take it you found the old thread with all the pictures? This also links back to the old forum.

I can see you're going to have fun with this.

Cheers,;)
 
Eric,

Correct me if I'm wrong but doesn't your modified artwork include the cascode mode only?

The reg active current source uses a daughter board sitting over the reg board and the VAS reg is a separate circuit board and heatsink, I'm afraid there will be a few interconnecting wires. All worthwhile though.

Ashley
 
Ah, Ashley. Thanks for the clarification.

There are a few mods we have carried out as well as selecting components:

Firstly the splitting of the Vas and input stage power supply from the rear end. This follows the principle of trying to isolate the low current stages from the high current and potentially noise inducing power stages and in addition providing a separate supply for the input side.

What we have implemented is a straight forward tracking reg supply; this has got some development to go, in that it could be vastly improved by using a more sophisticated design [see Andy’s site for options and then think what something along the lines of a Super-reg, if they were available at the required voltage, could do].

Secondly the Cascode. This is a separate daughter board replacing components on the main board, conveniently using the Cascode component legs passing through the vero and connecting to the relevant holes in the main board. I subsequently reworked the artwork to include this on the main board. This is the bit that I need to check [busy times] and I would like to build one or two as well.

The reg boards have also seen a bit of attention but I’m not sure if we went public on these. This is the active current source to which Ashley refers.

I am strapped for time right now but if you search on “McB” I’m sure the old thread will turn up.

Must go.
Edit - found the old thread quickly:-
http://www.pinkfishmedia.net/forum/showthread.php?s=&threadid=939&highlight=mcbride
Cheers,
 
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