Hafler DH-220 Strange "External Capacitor Bank" Mod?

[MicahVW]

Hello Everybody!
Exxtreeemely long time lurker here

Very quickly, let me introduce introduce myself.
I've been lurking on here for years, and I've gleaned so much valuable information from you guys and gals!
I just want to say thank you for the absolute treasure trove of valuable information that this community has provided for me.
You've all helped me truly understand audio.
Very much, thank you for this.

Okay... on to my question.

I found a great deal on a Hafler DH-220 that the owner said was modified by Musical Concepts.
As I was loading up the amp, the owner said.. "Hey don't forget the external Power Supply!"
(I had no idea Musical Concepts even offered this mod).
Of course the second I got home I had to open it up and see what was inside.

I need some help trying to figure out what's actually going on here. If I plug this thing in, is it going to send sparks shooting out of every outlet in my house??

When I opened up this alleged "external power supply" it just turned out to be what looks like a giant bank of recycled filter caps that connects through an extra jack that was installed on the back of the amp

Even if all of these capacitors are good, is this an advantageous mod?
I've never seen anything like this before.
I would think the in-rush current would be enough to blow things up (let alone trip my breakers).
Honestly though, I really don't have a clue.

The actual amp does appear to have upgraded caps and a toroidal power transformer.
But there also seems to be extra yellow caps everywhere.
I'm still growing my understanding of amplifier design.
But from what you can see, does this look good or bad? Are those yellow caps considered "bypass caps"?
What is the actual benefit of doing this?

I also have the corresponding DH-101 Preamp (which appears to have capacitor mods as well).

I still own my completely "stock" DH-200 and DH-101. I'll include pictures of both.
I didn't have an opportunity to listen it before the purchase (the owner did mention that everything was fully functional though).

Do you think these mods will offer any sonic improvements, or changes I should be listening for?

Thank you for reading my very long first post.
Any input/opinions are appreciated.
Thanx in advance everyone

 

[MicahVW]

Here are the pictures of the Preamp and Stock equipment

 

[hamrules]

Cool, a capacitor bank. What's that for, more bass "hit" without depleting the caps or something. Didn't Dynaco offer that for their 400 series something amplifier.

 

[llwhtt]

Dynaco C100.

 

[egellings]

Be careful about adding that much capacitance. The peak charging currents get vicious and can overheat the power transformer and melt the rectifier diodes. I feel sorry for your power ON/OFF switch if you are not using some sort of a soft-start scheme. You don't need all that capacitance; it just makes life hard on power supply components. The film bypasses may help and can be useful. If your original supply is saggy, a beefier power transformer would be the preferred way to go.

 

[Pio1980]

"POOGE", Progressive Optimization Of Generic Equipment. A DIY movement of the late 1970s into the 1980s.

 

[mcgjohn]

I used to know a guy who had one of those amps. Pretty good sounding amp. The outboard filter cap bank adds some extra slam in the bass. Won't do much for the other frequencies. But as others have noted, the peak charging currents get very high as the charging time gets very short. All the rage with outboard cap banks I think was started by a writer in the Absolute Sound who tried it, then wrote about it. You don't see too much of it today. If I were to do anything, would upgrade the quality and values of those yellow music caps on the two main filters in the amp. Those bypass caps will really affect the sound of the amp.

 

[MicahVW]

I used to know a guy who had one of those amps. Pretty good sounding amp. The outboard filter cap bank adds some extra slam in the bass. Won't do much for the other frequencies. But as others have noted, the peak charging currents get very high as the charging time gets very short. All the rage with outboard cap banks I think was started by a writer in the Absolute Sound who tried it, then wrote about it. You don't see too much of it today. If I were to do anything, would upgrade the quality and values of those yellow music caps on the two main filters in the amp. Those bypass caps will really affect the sound of the amp.

Thank you! Yeah, I think these are total sleepers.
The quality and power these amps deliver is quite impressive for how inexpensive they still are. The price of well known quality vintage gear has really gotten crazy lately, but these amps still seem to be quite affordable. It probably has something to do with kit stigma, or their aesthetics (which I personally enjoy).
Haha, so what you're saying is... I should modify the mods? What is adding bypass capacitors actually for? I know it's common, I just don't fully understand their function. And upgrading them has benefits?
I know a little about caps in the signal path, but I don't fully understand everything.... Yet

 

[Hyfi]

Cool find. I grew up watching my brother build Haflers on the kitchen table after dinner. He helped David Hafler tweak the kits by figuring out better values or parts. My first real system was Hafler 945 that I still have and it's matching 9180, although it was Fosgate by then.

 

[slimecity]

Thats pretty hilarious, especially how those additional caps are "secured" to the box. Looks like he found a whole heap of rando old caps and just stuffed them in there.

he was obviously a BIG fan of capacitor bypassing too

 

[mcgjohn]

Thank you! Yeah, I think these are total sleepers.
The quality and power these amps deliver is quite impressive for how inexpensive they still are. The price of well known quality vintage gear has really gotten crazy lately, but these amps still seem to be quite affordable. It probably has something to do with kit stigma, or their aesthetics (which I personally enjoy).
Haha, so what you're saying is... I should modify the mods? What is adding bypass capacitors actually for? I know it's common, I just don't fully understand their function. And upgrading them has benefits?
I know a little about caps in the signal path, but I don't fully understand everything.... Yet

when those amps were done, power supply bypasses were in their early stages.
Today, companies use 2, 3 or more values on the main filters as a bypass. Each value of cap will clean up a range of frequencies. from the photos you posted you can also see the purple electrolytic caps on the amp modules also have bypasses on them.

 

[infullview]

Are all those additional bypass caps original or did someone just think it was a great idea? I can see using these in circuits that create a lot of RF noise like switching circuits, but this looks totally excessive to me.

 

[gadget73]

Lower impedance at high frequencies. Usual argument is they do a better job of shunting supersonic nonsense than electrolytic caps. Film caps do have better high frequency properties and it certainly isn't going to hurt anything. How much it helps is another one of those how many angels can dance on the head of a pin things. The multiple values is probably about internal inductance, with the idea of smaller values having less L since there are less layers of material so they work better way up. Also at least partly true but a ceramic capacitor would be a better choice since they are not wrapped like a film cap.

The massive external bank of used parts I'd really question the value of though. Caps in parallel will have lower ESR than an equivalent value single capacitor so you can suck more current out of it, but that also means you need more current to charge it. Its a hell of a workout on the rectifier, transformer, and power switch. Charge it all through a long, thin wire and using a CB microphone connector that isn't really designed to carry high current and it partly defeats the purpose anyway. Old caps likely have higher ESR than new ones, so that also at least partly defeats it. I'd be a lot more concerned about those poorly secured old caps moving or failing and blowing the whole thing up than any sonic improvements it may offer.

'course its easy enough to A/B. Listen with the cap bank unhooked. Shut it off, plug it in, listen again. If you don't hear a difference, there is your answer.

 

[egellings]

POOGE originally appeared in The Audio Amateur Magazine, a DIY homebrew magazine published by the late Edward T. Dell. Another homebrew mag called Computer Smyth was also proposed, but that never got off the ground because building a competent motherboard is just not something for the audio amateur to tackle due to the severe complexity of such an undertaking. Back then, speaker projects got so popular that Dell started another magazine dedicated to just speaker construction projects called Speaker Builder. In the early 90's, vacuum tubes saw a renaissance and a third magazine, Glass Audio was born. All 3 magazines got replaced by Audio Express (Xpress?) Magazine just before Dell passed away. I subscribed to all of them and saved them.