Yamaha P2100 recap and upgrade: suggestions? - diyAudio
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Old 16th March 2011, 10:49 PM   #1
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Default Yamaha P2100 recap and upgrade: suggestions?

Hi all,

I'm going to recap my Yamaha P2100 (schematics here, and added as zip). It sounds very good as-is to me, nice '77 design.

In determining 'things-to-do' besides recap I was comparing it to the Yamaha P2150 (added file) and other Yamaha power amps (like this website does). I am wondering if I can add to the amplifier board a 220 uF decoupling from B+ to E and from B- to E, with parallel diode like in the P2150, and the R+C combination to the heat sink?

Also, I don't understand how the power supply in the P2100 works for the input side (the 10.2 VAC), how can it be that the small rectifier's plus side is connected to the B- supply?

Things I will do are:
  • increase bias for lowest distortion
  • add speaker protection kit Velleman K4700
  • new bridge rectifier (old one is only 5 A)
  • bypass cap for the large cans
  • metal film in signal path
  • MOX 10W for emitter resistors
  • new input diff. pair transistors A970
  • new binding posts
Any suggestions appreciated.
Attached Images
File Type: png P2150 amplifier PCB schematic.PNG (110.9 KB, 196 views)
Attached Files
File Type: zip Yamaha P2100 schematic.zip (468.9 KB, 43 views)

Last edited by pradigmshift; 16th March 2011 at 11:02 PM.
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Old 26th July 2011, 04:39 PM   #2
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Update: just did the recap and
  • increased bias from 33 mV to 52 mV (works well, but still have to measure best value)
  • added speaker protection kit Velleman K4700
  • new bridge rectifier (old one is only 5 A)
  • new binding posts
  • bypassed volume control
  • bypassed on/off switch
See the pictures below (red is adjustments):

Right channel diff/driver board:
Click the image to open in full size.

Right channel output board:
Click the image to open in full size.

Sounds much better! Note: there is an error in the schematic, there is a 0.01 uF missing between TR14 and TR15 (it's drawn correct on the left channel, not shown).

To do:
  • bypass cap for the large cans
  • metal film in signal path
  • MOX 10W for emitter resistors
  • new input diff. pair transistors A970
  • replace driver transistor with MJE15030/15031
Any suggestions? Not sure about what can be changed to the circuitry for better performance, but would like to know.
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Old 26th July 2011, 07:32 PM   #3
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by passing rails to a locan ground could be more bad than good and if you added clamp diodes 1N4007 is not enough /.... try something like 1N5408
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Old 26th July 2011, 07:52 PM   #4
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Thank you, 1N5408 added to parts list. Yes, the adjustments I show in the pictures I have already done, the amp does (still) work.

You are saying that, depending on topology, local psu bypass may work or not. I was assuming that local psu bypass is always good and thinking that it gives similar effect in the P2100 as it does in the P2150 (schematic added in first post)?

What else could I do to improve the design?

Last edited by pradigmshift; 26th July 2011 at 08:02 PM.
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Old 26th July 2011, 08:28 PM   #5
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yes but is grounded on the heatsink ???? ground rooting is a major issue in amplification
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Old 26th July 2011, 10:07 PM   #6
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Agreed, grounding scheme is very important. That's why I took the P2150 schematic as starting point. 220 uF is grounded to the boards earth, but the series combination 0.22 uF + 10 Ohms is grounded to the heatsink. I presume this is to prevent oscillation. There is no noise coming off the loudspeakers, almost completely silent.
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Old 10th May 2013, 03:23 PM   #7
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Quote:
Originally Posted by pradigmshift View Post
Hi all,

In determining 'things-to-do' besides recap I was comparing it to the Yamaha P2150 (added file) and other Yamaha power amps (like this website does). I am wondering if I can add to the amplifier board a 220 uF decoupling from B+ to E and from B- to E, with parallel diode like in the P2150, and the R+C combination to the heat sink?
I'm honored to have been mentioned!


Quote:
Originally Posted by pradigmshift View Post
Also, I don't understand how the power supply in the P2100 works for the input side (the 10.2 VAC), how can it be that the small rectifier's plus side is connected to the B- supply?
The idea is similar to the use of a center tap to set the reference voltage. By rectifying and connecting the + side to the -50V DC rail, it's generating a difference. That is, the new + becomes -50, and the new - becomes -62 to -64. This extra negative voltage is then used to provide a new - rail to the cascoded input and the pre-driver stage.

I'm still investigating this section myself, that's how I ran across it. From what I believe right now, they wanted to use the 2 cascoded sections for widest possible bandwidth and linearity, and the 2 extra 10.2V coils are there to allow it. It's VERY interesting that they chose 2 extra windings for this. It speaks to how important that supply is to the channel separation I think. It's also interesting that they could have also done a balanced differential input. Surely that would have been cheaper than the extra windings and custom coil designs. They really really wanted that in there.

Quote:
Originally Posted by pradigmshift View Post
Things I will do are:
  • increase bias for lowest distortion
I read forward in the thread. The manual spec's 22 mV bias. When I tested the bias voltage on the two P2100's I have, 3 channels were hot. I first noticed this because I ran dual stereo (1 amp per side of 4.0 home theater) and the right side treble seemed pretty hard by comparison to the left. Sure enough, the amp was physically hotter on that side and was around 33-35 mV. Reset the bias to spec and it sounded better.

I guess I'm just saying, without a distortion meter, I did not like the sound. I honestly preferred the original spec. Try it.

Best,

Nigel / Erik
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