Old Amplifiers

lucid said:
Physical condition aside, the two caveats with older amps are noisy volume potentiometers (sometimes source switching pots too) and capacitors drying out. Neither is a terminal problem, and noise on the pots is easy to check by switching and changing volume when there's no source playing. Capacitor issues are slightly harder to pin down unless there's a dead channel. Whiz the lid off and inspect visually. Look for signs of bulging tops or bursting at the bases. However, don't be tempted to recap unless there's a definite issue and you know what you're doing.
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Just considering a refresh on my old 1998? Musical Fidelity A220 50W AB amp considering it actually gets used on the odd occasion compared to the CD player..

If they're like guitar amps then:
a) caps go and degrade - especially in the head class A and AB (the MF gets very hot!)
b) transistors also go - often those in the signal path
c) Keep in type - specifically as ceramics can add two orders of magnitude of harmonic noise in the wrong place compared to a poly for example.

I did find this place: https://www.hificollective.co.uk/catalog/components/capacitors.html which I may use to replace the Jamicon caps in the MF.
 
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I have some early 90's Pioneer amps with integrated DAC and I can't fault them, really good sound quality, priced what would be Pioneers modern equivalent and looking at £800 upwards, so I just keep running the old stuff.

Someone mentioned NAD. I also have a Proton 520 that's based on a NAD design, not ran the amp for years, but keep intending to get it out again.

One thing more. Speakers in the 80's 90's period I don't think were that great, at least not in the price range of most consumers as they are now, look at Elac at the moment, however some of the amps were very good and are still worth running. I think a valid thing to-do is run a vintage or semi-vintage amp, and combine with modern speakers.
 
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I love vintage amps. I have a soft spot for old Marantz amps and Luxman amps. Especially Marantz when Saul Marantz was at the helm. Stuff like the Model 9 and 8B amps. Of course the stuff from his time period has shot through the roof price wise. After that then stuff like the old PM15 not the Pm15 s1 or s2 Although the PM15 s2 is pretty good.

I have gotten into the bad habit of scouring the internet for old vintage stuff as well as the Luxmans and old Onkyos. There have been quite a few occasions where I had to seriously resist getting something like the Onkyo Grand integra m510 or luxmans m7 onwards.

I just recently purchased an oldish Marantz amp after waiting 4 years to get my grubby mitts on. I like the old vintage stuff as I like sound and the build and quality of it. Don't get me wrong there is nothing wrong with modern amps like Krell, Classe, Bryston etc but it doesn't appeal to me.

I guess if there was 1 amp I could have vintage or modern over any other it would be a no brainer. It would be the last ever tube amp Marantz ever made and only 50 were ever built by the chief designer at Marantz himself. The Marantz T1.
 
NickK said:
Just considering a refresh on my old 1998? Musical Fidelity A220 50W AB amp considering it actually gets used on the odd occasion compared to the CD player..

If they're like guitar amps then:
a) caps go and degrade - especially in the head class A and AB (the MF gets very hot!)
b) transistors also go - often those in the signal path
c) Keep in type - specifically as ceramics can add two orders of magnitude of harmonic noise in the wrong place compared to a poly for example.

I did find this place: https://www.hificollective.co.uk/catalog/components/capacitors.html which I may use to replace the Jamicon caps in the MF.
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Can get some decent capacitors from non-specialist dealers in most cases outside signal path Panasonic FC or Cornell Dubilier MLQ do fine and if you have to use AE caps in signal path Nichicon KZ are pretty decent. Unless you are looking for some added distortion - which is what most of the hyped up "audio" caps do.
 
GoRedwings19 said:
I love vintage amps. I have a soft spot for old Marantz amps and Luxman amps. Especially Marantz when Saul Marantz was at the helm. Stuff like the Model 9 and 8B amps. Of course the stuff from his time period has shot through the roof price wise. After that then stuff like the old PM15 not the Pm15 s1 or s2 Although the PM15 s2 is pretty good.
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Sounds remarkably familiar. I also have a “thing” for vintage amps, particularly luxman.

Rroff said:
Can get some decent capacitors from non-specialist dealers in most cases outside signal path Panasonic FC or Cornell Dubilier MLQ do fine and if you have to use AE caps in signal path Nichicon KZ are pretty decent. Unless you are looking for some added distortion - which is what most of the hyped up "audio" caps do.
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Best AE caps you can use in the signal path are bipolar as they have significantly less distortion even if they have greater ESR. If I can fit them in, I usually go for nichicon ES. If there is space, I try to squeeze plastic film in for smaller values.

As to ceramic, modern MLCC parts are actually considered excellent for audio purposes. It’s the old ceramics from pre 90’s stuff that can be awful.
 
Kei said:
Sounds remarkably familiar. I also have a “thing” for vintage amps, particularly luxman.


Best AE caps you can use in the signal path are bipolar as they have significantly less distortion even if they have greater ESR. If I can fit them in, I usually go for nichicon ES. If there is space, I try to squeeze plastic film in for smaller values.

As to ceramic, modern MLCC parts are actually considered excellent for audio purposes. It’s the old ceramics from pre 90’s stuff that can be awful.
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I generally avoid AC coupled designs anyhow never been a fan of AEs in the signal path.

Sometimes not much option but to use ceramics due to high frequency requirements but I've generally got away with WIMA polypropylenes - the new version MKP4 released late last year are excellent as an alternative to ceramics.
 
I’ve been reading up - doubling up (as long as the voltages work) can drop the impedance for audio PSUs.

Seems the MF A220 has a single rectifier based design that feeds a 50V 10Kuf for each rail for smoothing the +ve and -Ve rails into the main power amps (quad per channel) to handle as heavily biased AB.

So there’s serious options for improvement given reports (with before and after signal testing).

The PSU doesn’t even have a line conditioner in the 240v..

My old Myryad MC100 is completely different (runs A class style preamp) with a complete separate PSU filtering board and uses Rubicon caps, etc throughout.

Don’t get me wrong - not being audiophile but the difference is getting a fast capacitor for improving output, but as a signal chain there’s lots to look at to improve.
 
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So my thinking is to keep with the sound but add clarity rather than change the 'A' warmth of the amp - typically the main power transistor and preamp are selected because of their audio sound. This means keeping with the current power transistors and op-amp but focus on the power to produce a solid clean steady supply and the clean signal path.

The current bridge rectifier has 6.2 amp fuses and from web discussions the output is documented as 4-6amps, the current main power caps have a ripple current of 4A. This limits

Here a couple of options I'm mulling over:

Option 1:
* Add a line conditioning IEC socket to replace the current IEC socket
* Switch out Bridge Rectifier to a IXYS FRED ECOPAC Single Phase 600V 40A 35ns switching speed bridge. The nice thing is as it's a complete bridge the substrate should ensure that there's no differences in the diodes compared to using fast singular diodes in a bridge structure. It has enough oomph and is fast switching
* Switch out main per-rail Jamicon 50V 10000uF caps for something with a high ripple current capability. I may actually double the capacity.
* Replace pre-amp level signal path caps and resistors with tighter tolerance components
* Replace the power amp signal path caps with higher tolerance and use wire wound resistors.

+ it's easy to perform a bit at a time, although you don't want to keep taking the circuit board out given the attachment to the heatsink!
+ the changes can be copied over for option 2.
- the current toroidal transformer is a specific size, and would cope with inrush but doubling capacity may cause problems, plus being A biased the power draw is continuous.

Option 2 - the more complex, it involves changing the power feeds
* remove the existing power supply from the main board - this means unsoldering the common components so only the power stages are left.
* build two high current PSUs - one for each channel to supply channel's the power rails, each channel then has toroidal transformers, it's own bridge rectifier, twin 50V 10K caps.
* then as above look at the signal paths in pre-amp and power stages.

+ each channel has a full capacitor bank set, so rails will be less impacted by
- complicated power changes for components in the preamp stage - instead perhaps a small third power supply and simply cut the power lines from the old power section. Would have to be extremely careful in ensuring that all the power circuits are independent but share the same ground reference level.
- longer distance from caps to the power transistors in the power stage
- more power supplies = tight space, heat and weight.

The more I think of it - if I wanted option 2.. I may as well build my own mono blocks with a small pre-amp stage! The component cost would almost be the same (16x£4 for a power amp would be the main difference in cost).
 
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