Maestrobation - part 3

Let me start by thanking carlo, the master of the Maestrobator. Without his guidance, I would never have attempted to create my little beast.

I want to thank Canman for selling me his SHA/Gold Reference and Gopher for selling me his HP-1s without which I would never have thought about doing this.

I want to thank Chris and Vicki at Parts Connexion and Craig at Reference Audio Mods for getting me all of the parts in a timely fashion.

I know that this is nothing that is really special but hey, I'm no engineer so to do this kind of stuff is something special to me.

So without further ado, here's the latest Maestrobator.



I wanted a dedicated single input headphone amp so I dispensed with the front board containing the remote, photentiometer, balance and mute circuits. Unlike some of the earlier versions, I also disabled the pre-amp stage (hence the missing pre-amp caps in front and yeah I know, I have to get rid of that stubborn glue).

All signal path resistors (Tantalums and Rikens) and caps (Auricaps) are standard issue mods.

I was able to scare up a matched pair of Mullard 7308 to replace the Amperex Bugle Boys that came with the amp.

I replaced the 100uF cap (under the left red Blackgate) with a Blackgate version in the high voltage PS (standard issue mod). The other caps (the two large ones on the left side of the board) are Rubycons (they make Blackgates) that came with the amp. The high voltage rectifier was replaced by a Harris FRED bridge (so changing the large caps wouldn't buy much).

The biggest difference is in the low voltage PS. The original 6800uF Rubycons right after the rectifier were replaced with 470uF Blackgates (the two small ones on the left of the left red Blackgate). The 470uF Nichicons were replaced with 1000 Blackgate NXs (the red ones). The 10000uF Rubycons were replaced by 2200uF Blackgates (the two medium ones on the right). This is a change from previous versions which used bigger caps after the rectifier (the other 2 sets are the same).

Now the interesting experiment is the caps run in parallel. carlo and I took this to the extreme with this amp and paralleled all 3 sets of low voltage caps.

The 470uFs are paralleled with the original 6800uF Rubycons. The 1000uFs are paralleled with the 10000uF ELNA Cerafines lying down on the left (which are shunted by the 8.2uF Solens I took from the pre-amp stage). The 2200uFs are paralleled with the original 10000uF Rubycons. Space was tight so I took the 4 1uF Solens from the signal path and shunted the 1000uFs and 2200uFs under the board. I had spare 1uF Auricaps and shunted the 470uFs, 6800uFs and 10000uFs caps (all of that mess at the top of the board and under the disconnected input and output jacks).

Before adding the parallel caps and shunts (except the ELNAs which I put in when I changed the main caps), I tried the 2200uF, 6800uF and 10000uF in the same spot on the right. The 2200uF were FAST but it was also a bit light in the bass (they still need burn-in) and sounded a bit shrill and it got worse during heavy passages. It would congest and sound muddy. The 6800uF was a bit slower and seemed a little more distant and less immediate than the 2200uF. Bass was good, no real shrillness and it never seem to run out of steam. The 10000uF sounded slow and thick but would be a basshead's wet dream.

After adding the parallel caps, the amp seemed to be just as fast as with the 2200uF alone. It might be a shade slower but it's still really fast in my books. Tonal balance sounds about right to me. Nothing sounds recessed. The sound is immediate but not overly forward. Grabs and holds my attention. Detail is miles ahead of the original Gold Reference. Attack and decay sound very natural. Soundstaging is pretty good for headphones. Not too much like 3 blobs. There seems to be decent "depth" (drums behind vocalist and other instruments, backing vocals behind lead vocals, etc, etc).

Tasks left:
1) replace low voltage rectifier with another FRED bridge
2) replace transformer with BIG one that's on order
3) rewire using Cardas (currently using the wire that came with the amp)
4) decide if I want to replace the temporary TKD pot with a DACT
5) find a decent headphone jack
6) replace the cheap power switch, IEC connector and fuse holder
7) replace input jacks with nice Cardas ones
8) convince binary_digit to machine a custom faceplate with "The Maestrobator" and "Sound by carlo" on it

How does it sound? Well, the Blackgates need a long burn-in time so it's premature to really say much. But I will say that I don't impress easily. I've auditioned a lot of the best audio gear in existence and I'm impressed. carlo tells me that it's only going to get better when all of the caps are done burning in. I can't wait.

Is it the best amp out there? Probably not. But it's probably one of the best for my HP-1s. For the money ($800 or so for the Gold Reference and then $400 in parts), I might have gotten something else that rivals it. But now that I am building a familiarity with the amp, I'm looking forward to experimenting further to tailor the sound. Something that I would probably not try with another amp.

Well that's it. I've got listening to do.

The front board spanned pretty much the entire front part of the amp so there was no way I could get the ELNAs in there with the standard transformer and the large Solen shunt. It's going to get even more crowded when the larger transformer arrives.

I wasn't that crazy with having the balance control and the auto-mute circuit and it was going to be too difficult to separate out the circuit for the photentiometer from the others.

I have a love/hate relationship with stepped attentuators. I seem to always want to set the volume in between the steps. It isn't so bad for speaker systems but for headphone systems, when it is just a bit too loud, it really isn't good for one's hearing.

I'm guessing that it'll be at least 200 hours before the Blackgates start coming around. It's sounding very nice already but carlo said that the bass usually will take a while to really solidify and the treble to really open up. carlo and I both came to the same theory that the paralleled caps are helping to make it sound good despite the lack of burn-in for the Blackgates/Auricaps.

I've been doing a fair bit of listening to make sure I don't hear anything bad so I've been using the Mullards. They are by far better than the Amperex (and the Sovteks). They are supposed to be NOS so they'll need some burn in time as well. I'll let it run for the next few days (burn-in track when I'm not listening).

The Hammond that I'm getting is 4.5" diameter and 1.75" tall so it will fit where I've got the transformer right now. I can move the Solens over to the right to make room same with the voltage regulator if I need to (it's hiding underneath the transformer wires in the photo).

I haven't hear enough amps to really say how it compares to the rest but I'm guessing that it's up there.

I'm using a 100K TKD (50dB) at the moment and running the plate voltage at 85V gives me pretty good range for volume. I'll probably get the DACT once I've finished most of the rest of the tasks. I don't want to risk damaging it with any heavy work.

Even while I was working on it last week, I was thinking that it might not do the job and I was contemplating getting Omega IIs and building a KGSS. I still might but I know that I really like what I'm hearing out of this amp.

I'm only thinking of the Omega IIs because the price is pretty good out of Japan and building a KGSS isn't too expensive. The R10s (even out of Japan) is more than I can justify given that I'm unemployed at the moment.

I haven't had a chance to compare to the HR-2. I need to give both units enough burn-in before I really sit down with them.

As for the stepped attenuators, I did a bit of reading and I'm not sure that I like 2 dB increments. The best that I could find is the TKD attenuator with 40 steps so that is closer to 1 dB steps but it's also $359. The Goldpoint ladder type is $241 and the DACT CT2 is $151.

Now the question before me is: do I go to the complete extreme?

Since I'm feeling less of a need to get Omega IIs and build a KGSS, I've got a big chunk of money free to look into upgrading all of the parts. I've been curious about trying paper-in-oil caps like Audio Note copper foils.

It would be fun trying to make the ultimate Maestrobator with very few stock parts.