Hello,
For the next step in my electronics journey I'd like to buy a "for parts or not working" amplifier for cheap and restore it. I have no formal electronics education but have been messing with audio electronics as a hobby for about 20 years. I consider myself at an intermediate level, I can read a schematic and understand most of the basic blocks. Furthermore I can count on the help of the fine folks here at diyAudio !
I have re-capped/re-biased and modded my solid state amps and designed a few vacuum tube projects although most never got past the breadboard stage. I have a good soldering station, a few DVMs, a signal generator and a couple scrappy scopes to help.
So after this lengthy preamble, what are the best makes and models for an hobbyist to attempt restoration at a reasonable cost. What are the makes and/or models to absolutely avoid, or should I forget this silly idea? I currently have my sights on the Adcom GFA-555. Vintage Naim is another I'd like to get my hands on, looked at a few schematics and they don't look that complicated.
Thanks for any advice.
- Joris
For the next step in my electronics journey I'd like to buy a "for parts or not working" amplifier for cheap and restore it. I have no formal electronics education but have been messing with audio electronics as a hobby for about 20 years. I consider myself at an intermediate level, I can read a schematic and understand most of the basic blocks. Furthermore I can count on the help of the fine folks here at diyAudio !
I have re-capped/re-biased and modded my solid state amps and designed a few vacuum tube projects although most never got past the breadboard stage. I have a good soldering station, a few DVMs, a signal generator and a couple scrappy scopes to help.
So after this lengthy preamble, what are the best makes and models for an hobbyist to attempt restoration at a reasonable cost. What are the makes and/or models to absolutely avoid, or should I forget this silly idea? I currently have my sights on the Adcom GFA-555. Vintage Naim is another I'd like to get my hands on, looked at a few schematics and they don't look that complicated.
Thanks for any advice.
- Joris
Last edited:
Adcom GFA-535 - 2 pair Sanken- 60V rails - it cranks. (80W+W) dual mono amp. (dual E-core)
Sonance 260 1/ or MK2 - 2 pair Sanken - 47V rails , good for 2.7R loads (70W)
Audiosource amp 1 - 2 pair Sanken - 55V rails , very similar to the Sonance (80W )
Audiosource amp 3 - 3pair (150W). Dual mono with the dual secondary Trafo.
All these amps have the high grade FR-4 PCB's , and the layout is mostly audiophile.
All are Common on Ebay , I've recapped and tweaked all these. The build quality is
WAY better than Sony/Kenwood/Japanese , most other vintage Hi-fi. Simple Hitachi , symmetrical , or LIN amp topologies .
Most are 25-30 years old , still work (a bit rough) , with mostly bad caps.
I don't bother with most cheaper "Vintage" OEM's with the aged phenolic cheap boards or E-core trafo's.
The way these OEM's design hot running cheap regulators , phenolic is usually burnt.
OS
Sonance 260 1/ or MK2 - 2 pair Sanken - 47V rails , good for 2.7R loads (70W)
Audiosource amp 1 - 2 pair Sanken - 55V rails , very similar to the Sonance (80W )
Audiosource amp 3 - 3pair (150W). Dual mono with the dual secondary Trafo.
All these amps have the high grade FR-4 PCB's , and the layout is mostly audiophile.
All are Common on Ebay , I've recapped and tweaked all these. The build quality is
WAY better than Sony/Kenwood/Japanese , most other vintage Hi-fi. Simple Hitachi , symmetrical , or LIN amp topologies .
Most are 25-30 years old , still work (a bit rough) , with mostly bad caps.
I don't bother with most cheaper "Vintage" OEM's with the aged phenolic cheap boards or E-core trafo's.
The way these OEM's design hot running cheap regulators , phenolic is usually burnt.
OS
Attachments
I also second ostrippers GFA 535 recommendation. I have one as my garage speaker amp. It’s a solid option
Interesting choice indeed as working units can be had for around 200USD on fleabay.
Is there a consensus as to which of the Mk. I or Mk. II is best?
Is there a consensus as to which of the Mk. I or Mk. II is best?
Probably depends on your feelings about DC servos.
If you do go the GFA-535 route, I have a thread on it that might benefit you: Adcom GFA-535-II Schematic errors and omissions
Also, user Phloodpants has many Adcom threads and runs a site with Adcom refurbishing parts and kits: Hoppe's Brain
If the Hafler DH-220 appeals to you, Bob Cordell has a article on a complete overhaul for it on his site (The DH-220C MOSFET Power Amplifier). Though this is a more advanced project.
If you do go the GFA-535 route, I have a thread on it that might benefit you: Adcom GFA-535-II Schematic errors and omissions
Also, user Phloodpants has many Adcom threads and runs a site with Adcom refurbishing parts and kits: Hoppe's Brain
If the Hafler DH-220 appeals to you, Bob Cordell has a article on a complete overhaul for it on his site (The DH-220C MOSFET Power Amplifier). Though this is a more advanced project.
Thanks Brian for these links and for taking the time to join the two schematic pages👍. I think I can handle this design, and the servo would be a learning experience. Besides I've been curious about them for some time as I may apply one to a vaccuum tube project at some point.
I knew about Hoppe's Brain and it is a strong incentive to go with an Adcom with all the support and upgrade paths it offers. Bob Cordell's project is indeed a bit too advanced for me at least for now. I like his electronics books though, he has a touch to explain things so the beginner can understand.
I knew about Hoppe's Brain and it is a strong incentive to go with an Adcom with all the support and upgrade paths it offers. Bob Cordell's project is indeed a bit too advanced for me at least for now. I like his electronics books though, he has a touch to explain things so the beginner can understand.
I was going to include that , He sells nice FR-4 "anal" upgrades for many Adcoms.
The Adcom 555 is wired. Much harder to get a wired layout/design to be as quiet as a whole PCB design.
Another amp to look at is the Behringer A-500 (below) . Dual secondary and true dual mono PS with a op-amp IC powered
type input/output stage. I'd put Badgers in that case.
Alesis-ra-500 also uses 3-pair Sanken 125W devices (150W).
I actually don't like the Behringer. NO discrete classic circuit to tweak.
The Sonance 275 is the bigger 260. But with a few device swaps , a 260 could be a 275+++
ON semi output stage swap and 60V+ rails ,the 260 could be 125W- 200W peak .01% amp.
The haflers are FET's out on wires , like the 555. You can compensate to get an amp less prone to parasitic's (wires) , fet's are picky.
NO way to get a wired amp PPM (<.001% THD).
Thats another option - Most of these cases could take a Badger or wolverine , "drop-in" replacement. Any power supply would work , 40 -
65VDC.
OS
Attachments
That is good to know, thanks.
Yeah, saw that.... I'd prefer working with BJTs.
I'm curious, are these pics all restorations you did?
Last edited:
Some of the best (wired) aren't bad at .003% , like some well made "Leach" amps. But a PCB leach is typically 1/10 that - 2-3PPM.
You most likely Couldn't tell the difference. I don't mind a good .02% amp , as long as it is dead quiet.
Fet's can be tame , 8 years ago ... someone modified the old wolverine output PCB to FET's , add ferrite beads to
the gates and bigger gate resistors , works perfect.
Some of those are my pix. Some are those I want , I'd sell the Behringer as "Behringer a-500 benchmark outputs" for 6-700$
(with Wolverine amps installed).
OS
The basis of everything to have fun and learn is a well-documented device, recognized for its reliability and operation values and which does not contain unobtainium parts. The ideal is also an amp on which it is pleasant to work.
Yes and I'll make sure I have all the schematics and ideally service manuals before buying anything. That is the appeal of Adcom products, they are recognized as very rugged and sound good plus there's a lot of information available from the DIY community.
I had to deal with very large 22,000 uF unobtainium caps when re-capping my '90s rega amp and ended up having to design a daughter board holding five 3900uF caps. It works but the complexity was high - I'd rather not have to repeat this endeavor again.
"Revolver" daughter board capacitor replacement
Would you recommend the GFA-545? It is PC-board based and its higher power than the GFA-535 appeals to me as I have power-hungry Magneplanar speakers.
Had restored an old Technics su-v7x from the 1980s, it is very well documented and relatively easy to access the main board. Results of the amplifier only (removed the preamp boards) are close to the original specs with THD<0.002% (1khz). This Technics series (7x, 10x) are supposed to be good (I believe were all made in Japan).
Anyway it very much depends on what you can put your hands on.
Anyway it very much depends on what you can put your hands on.
GFA 545 = Pretty much a DIYA Badger amp.
-3 pair TO-3P + EF3 with 55V rails !! Easy 120W with near 200W peaks. Actually better than a Badger - EF3 !
Buy a replacement power board or just give the original capacitors a real good testing.
At least replace all the small output board caps , silver mica for the compenstaion caps .... regrease the trannies.
This amp would drive even subwoofers - 4R, almost 300W Very nice circuit !
OS
Thanks for your input. We'll see what
Pardon my iognorance but what is this amplifier? Is it related to the "Honey Badger" boards availaible in the diyAudio store? I seem to understand you designed it?
That's the store amp , with TO-264 (big) outputs = 150W.
Designed it 15 years ago. Actually remember knowing about the 545 back then.
OS
Designed it 15 years ago. Actually remember knowing about the 545 back then.
OS
Just dowloaded the service manuals for both makes of the GFA-545 and while I can see the resemblance, your honey badger is much more complex, I see a cascode input stage ltp with DC offset adjustment, Vbe referenced current sources and some structures I don't understand yet... Certainly a major undertaking for a beginner like me. It may be something for the future though, who knows, with all the support available here things can be done.
I was agreably surprised by the relative simplicity of the 545 mk. I, it doesn't have the bias servo so maybe a better choice to begin with. Anyways for some reason the 555 seems to have a sort of hype around it, hiking prices up on epay.
I was agreably surprised by the relative simplicity of the 545 mk. I, it doesn't have the bias servo so maybe a better choice to begin with. Anyways for some reason the 555 seems to have a sort of hype around it, hiking prices up on epay.