A modified Gizmo - first impressions - Home Theater Forum and Systems - HomeTheaterShack.com

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post #1 of 26 Old 11-08-08, 08:55 PM Thread Starter
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A modified Gizmo - first impressions

Through the generosity of Dweekie here and on AV123, I am trying out a modified Gizmo. He had read my posts regarding the distortion I was hearing, and touched base to discuss his plans to mod this amp.

Overall, the tweaks performed are as follows:

- Bypass opamps on input (but they are still in the sub out path)
- Speaker outputs are full range, bypass x-over
- Sub out functional with front panel volume
- Replaced Electrolytic caps and input/output caps

Some specifics

Dweekie wrote:
The speaker outputs are full range, and the sub-out still goes through the opamps/crossover. You will likely get a startup pop on the sub when you first plug it in because I used some larger input/output caps on the sub portion (I didn't have the exact value I wanted to use handy). Again, this is untested by me, so I suggest using a test sub first

I was mostly held back by size constraints with part selection. Mod parts are:

Vitamin Q/Nichicon Muse input/output caps (head-fiers fav)
Elna Silmic II dc blocking caps at the speaker outputs
Panasonic FM caps for power decoupling around amp
Nichicon KZ caps for power decoupling around regulators for opamp and volume chips
Other discussions, regarding power

Dweekie wrote:
The stock power supply is 28V / 33 Watts. After reading your pm, I thought I would try out my 24V 650 Watt power supply ($800 at allied electronics ). You can clearly hear the original stock power supply limitations. My 12V / 60W power supply I sent you before will run the Gizmo at a slightly lower power output (minus the subwoofer function), although the difference in power isn't that much compared to the stock 28V supply.
So, with all that in mind, I played the Modded Gizmo (MG) off and on for a few days, listening more critically every now and then.

This weekend, I got some good time in with it, and was able to compare it a bit to the Stock Gizmo (SG). Since I have the issue of overload with line level input, I used the SG with a Belles Soloist 3 preamp. So a bit apples to oranges, but I think a useful comparison, since most would need some sort of variable output source for SG.

Is the MG a success? Absolutely! Functionally, it cured the issue of overload for me. The sub out, something Dweekie was not able to test, works fine with the front panel volume control.

For subjective results, I'd say there is a stronger and tighter bass, more transparency, and a more extended upper treble (a TINY bit harsh at times, but I fully expect this to abate with more playing time. It may be my imagination, but it already seemed better after perhaps just 20-30 hours worth of running/listening).

The bass is tough to compare, since the SG rolls off speaker output, even with bass boosted. I felt, though, that the MG had not only some expected deeper extension, but that the quality was better: tighter, more integrated with the rest of the signal. Maybe the caps that were replaced?

The Belles-driven SG was no slouch by any means. A little elss transparent/detailed, a slightly softer top end, but a slightly fuller sound with a certain weighty presence. I used to own 2 other Belles products (250i integrated, 20A preamp), and both had this presence in spades. The Soloist 3 has some family resemblance, even if not the same level as the other two products I had.

I am going to also try the 12V PS Dweekie mentioned in my quoted PM above. It has driven a NuForce Icon and a magiDAC very well. Of course, I won't be testing the sub out with it, since the opamps require higher voltage.

So first and second impressions are great, a big thanks to Dweekie for the work he did. I'm hoping the pics below show some of it well enough, though I did notice some of his wires looked to be soldered under the board, so it may not be 100% clear via the pics. Thanks, too, to Craig, I felt I should get his OK to post this, and he was fine with it.

Not sure when I'll get another good chunk of time to continue the listening, but the bottom line message I wanted to get out is that the Gizmo responds well to mods. It makes the v1.0 an even greater deal for those DIY-inclined, especially with the $50 off a future product deal for those 1.0 buyers keeping theirs.

Accessing the board is easy enough: simply remove the front 4 screws and take off the plate - careful of the small buttons, they are loose. You can or can choose not to remove the board shown in the pic below; the cover slides out, albeit with a bit of difficulty. Removing the board may make it easier.

Of course, all caveats about modding apply! IE, no way in would I try this myself... :nervous:

Misc note:

Associated equipment:
- Toshiba SD-4000 DVD player, digital out to Promitheus NOS DAC
- Oritek X-1 IC's to MG, or to Belles
- (When Belles in) DIY magnet wire IC's to SG
- Kimber 8TC speaker cable to ELT525M's
- Sub is older Infinity 10" Servo

- Loreena McKennitt - An Ancient Muse
- Ani Difranco - Up Up Up Up Up Up
- Einsturzende Neubauten - Alles Wieder Offen

Pics 1 through 4 of stock Gizmo (SG), 5 through 9 of modded Gizmo (MG) - as if one couldn't tell! Not a lot of room to do the mods, so it may not be pretty; but the sound speaks for itself.

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post #2 of 26 Old 11-09-08, 01:29 AM
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Whoa, looks like a trainwreck in there. You can notice some mistakes and poor soldering and poor wire management as I tried a few different mods. I feel like I need to do another one so these pictures can be replaced :embarass:

Thanks for the review. Did you notice a significant pop on for the subwoofer?
If anyone wants to tackle the mods themselves, I'll try to answer your questions.

For a different mod, I've been trying to convince some people to run dual mono power amps with these. The crossover and volume control will be rendered useless, but it will sound a lot better. It should match well with a DacMan in a triple stack since it has volume functions. If you have a pair or want to get a pair done for the cost of parts, send me a message. I'm pretty sure you will be very surprised at how good these things can sound. At $200 - $100 in credit for a pair, it is one of a deal before supplies run out.
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post #3 of 26 Old 11-09-08, 07:19 AM Thread Starter
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No worries, Dweekie, the sound is what matters first! :thumbsup: To be able to fit anything of good quality in there is a small miracle.

In regards to sub popping noise, I kept the volume of the sub down when first plugged in, so no issue. I did get a pop with the stock, and just this minute tried the modded one without turning the sub down. Yes, a pop; not really much worse than stock. I'd still recommend turning sub down before powering, just in case (for modded AND stock, actually).
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post #4 of 26 Old 11-09-08, 07:24 AM
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Dweekie ... Thank you for not only starting this, but for being willing to support this.

This Mono-Bloc idea is outstanding. Waf-1's are going to be an honest 50 Hz bookshelf speaker ... and DAC-Man, Waf-1's and 2 Mono Blocks modded will be ... let's use a "high estimate" for the DAC-Man and Waf-1's ... with shipping

Two Gizmos............ $215
Pair of WAF-1's ...... $229
DAC-Man .............. $199

Total ................... $643
Credit ................. $100

Net for a true High end system ... $543.

Plus of course, the cost of the mods.
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post #5 of 26 Old 11-09-08, 07:28 AM
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Todd ... Thank you for all the hard work. One thing that riled me up was the change in power supply from our OEM.

This little amp has a lot of potential, and your (with dweekie's help) tweaking also makes me excited for the 45 WPC integrated we are planning.
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post #6 of 26 Old 11-09-08, 08:02 AM
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craigsub wrote: View Post
One thing that riled me up was the change in power supply from our OEM.
This was what I played around with for fun. http://www.alliedelec.com/Search/Pro...x?SKU=800-0225

It's a bit overkill and not very cost effective, but where's the fun if you don't overdo it? :crazy: It certeinly sounded better, but I really wouldn't recommend purchasing one.......
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post #7 of 26 Old 11-09-08, 09:09 AM
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This is terrific work, dweekie! It does look like a trainwreck in there, but that's to be expected since it's the first time that you'd worked on it and there's not as much space available as you'd like. I know that some of my projects have ended up looking a lot worse.

As a thought, since it's pretty difficult to figure out what you did just by looking at the pics, is it possible to give a bit clearer instructions for those people who are interested in doing the mods?

And I'm all for the idea of modding them to be mono-blocks. Definitely be among the best cost effective monos available.
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post #8 of 26 Old 11-09-08, 09:22 AM
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I just looked at the power supply that was with the Prototype, and it is a 24 V x 3.5 Amp supply.

I have only been using the prototype ... What power supply did Stephen put into the production units ?
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post #9 of 26 Old 11-09-08, 09:55 AM
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Output is rated: 28V 2000ma
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post #10 of 26 Old 11-09-08, 02:40 PM
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Let me see if I can put some basic details out. The goal was to simplify the signal path as much as possible. What I wanted to do was to reroute the signal in this manner:

RCA - dc blocking cap - resistor - volume chip - dc blocking cap - amp chip - inductor - binding post

Starting from the beginning, I needed to isolate the RCA inputs from the rest of the circuit. I did this by removing R2 and R4 closest to the RCA sockets. Since the RCA sockets are through-hole, I soldered a wire to the left and right RCA socket legs protruding from the bottom of the board.

Next came the dc blocking caps (Vitamin Q bypassing 2.2uf Nichicon ES). I glued these to an empty spot on the board and connected them to the RCA sockets. I needed a spot to tap back into the signal path, so I removed C2 and C29 and attached a wire to the ground (striped) leads of where those caps used to be, and I connected the other end of the wire to the Vitamin Q/Muse caps. This completes the path from the RCA to the volume chip since a resistor is already in place on the board between the newly attached wire and the volume chip.

From here, the work left to do is on the underside of the board. A smd capacitor and smd resistor is already in place between the volume chip and the amplifier. What we want to do is replace these comonents with a single high quaity cap. The smd caps can be identified as the closet smd caps to the cutout portion of the board. Immediately following the caps are the resistors, then the amp chip itself. I removed these caps and resistors, and I used the input pad of the smd cap and the output pad of the resistor to put my dc blocking caps into the circuilt path (Vitamin Q bypassing 4.7uf Nichicon ES) using wire leads.

The last major cap in the signal path is the large 470uf electrolytic cap right next to the connectors for the speaker outputs (C35, C36). This is the final dc blockiing cap that needs to be addressed. The 470uf value is only good enough to be -3db at 40hz on an 8ohm speaker. Since I wanted a true full range output, I decided on 1000uf (Elna Silmic II) to get me -3db at 20hz. For 4ohm speakers at the same rolloff point, you would need 2200uf caps. A substitute for the Silmics will be the smaller Nichicon ES caps.

Because the caps were so large, I could not fit them on the board as direct replacements. I removed the orginal C35 and C36 caps and put wire links in their place. Then, I cut the red leads of the speaker output wire and put the new caps in the pathway. I used some 2.2uf and 0.001uf caps I had on hand to bypass this cap.

This sums up my method for full range conversion for the Gizmo. I'll sum up the subwoofer mod later.
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