Marantz 1030 Transistors/HFE Question

[Ak1337azn]

Hi all,

I'm about to start work on replacing some noisy transistors in the preamp section of my Marantz 1030. I was planning on moving over to the main amplifier section until I read about matching hfe readings on transistors and unsure whether this applied to this amp at all.

I was only able to pick up on the fact that hfe/gain needs to be matched when dealing with the amp's front end, but I'm not sure what that means. Is anybody able to put this into layman's terms for me? At least how any of this pertains to this particular amplifier. Thank you!

 

[Steven Tate]

It's most important to hfe match the differential pair of transistors on the front end of the power amp. They are physically tied together with shrink wrap. However, on the other boards, if there are mirror image transistors - one for each channel - it can't hurt to get them close in gain, although not as critical as the diff. pair.

 

[Ak1337azn]

It's most important to hfe match the differential pair of transistors on the front end of the power amp. They are physically tied together with shrink wrap. However, on the other boards, if there are mirror image transistors - one for each channel - it can't hurt to get them close in gain, although not as critical as the diff. pair.

So I think that's where some of my confusion is lying up until this point--identifying differential pairs of transistors. So unless I notice a couple of transistors bundled up in some way, shape or form, I don't necessarily have to worry about matching them? I get that it's still good practice got optimal results.

 

[Steven Tate]

I think that is correct. I'm not a tech, but looking at the 1030 schematic, I don't see anything that looks like a diff pair. - at least anything that looks like the diff pair on the schematics of the 22xx receivers that I'm more familiar with. My understanding of the diff pair is that it is for removing noise from the input signal of the amp. I'm not sure if the 1030 uses another method, has a diff pair I'm not seeing, or simply doesn't try to remove noise at this point in the circuit. Someone who knows better will chime in with an explanation.

 

[Ak1337azn]

Thanks, Steven. I suppose I'll go ahead and swap them out without any need for concern unless I'm told otherwise.

 

[sregor]

Usually (not always) Differential pairs are used with split supplies and direct coupled outputs. Most single supply amplifiers are cap coupled outputs, and don't (IMO) benefit very much from having differential pair input stage. 1030, 1060 and original 2230 are old single supply cap coupled units and don't have differential pairs. However, higher hfe for input is usually a plus. My 2 cents...