Sound Lab. You see the distributed resonance cell grid that is sized differently from top to bottom.
As does Audio Research. My SP20 has 38 joules - more than many 100 watt power amps. Its big brother, the REF10 has 300!
Audire Audio Components
- Thread starter Bostown
- Start date
Zarathustra
Active Member
The REF10 is a two chassis pre-amp like the Krell KRS-2 I reckon?
And I made a mistake regarding the Sound Lab vs Beveridge.
I have had fullrange Acoustat 2 + 2's for twenty years and found them very tricky with amplifiers but they do sound great.
The late J. Gordon Holt founder of Stereophile had Sound Labs (A1 I believe) too with Threshold SA1's Class A mono's on them.
And I made a mistake regarding the Sound Lab vs Beveridge.
I have had fullrange Acoustat 2 + 2's for twenty years and found them very tricky with amplifiers but they do sound great.
The late J. Gordon Holt founder of Stereophile had Sound Labs (A1 I believe) too with Threshold SA1's Class A mono's on them.
Click on the hyperlinks I provided (blue text) to see photos of both Sound Labs and the REF10s.
As did I having first purchased the model X in 1977. Drove mine first with a Threshold Stasis 3. Still use 1+1s in the HT today driven by an Emotiva XPA-5.
I recently acquired an Otez that has apparently been worked on more that once, and I have discovered a few surprises. For anyone who has worked on Crescendos and Fortes, you know the circuits are very similar, with some 2N5401, 2N5550, MPS8099, and MPS8599 transistors, as well as several 1N4148 diodes and the MPQ6600. The driver and output transistors are the same. There are variations with some different resistor and capacitor values, but overall very similar circuits.
While looking at the Otez, I found that it is using 2N5551 transistors instead of 2N5550 transistors. No biggie, their characteristics are very similar. It's the diodes that surprised me. Instead of the usual batch of 1N4148 diodes, this Otez has a bunch of 1N5252 zeners! Unlike the 2N5550 and 2N5551 parts, which are virtually interchangeable, the 1N4148 and 1N5252 diodes have very different characteristics.
So, if anyone else has worked on these and/or has the schematic, please let me know if you have encountered similar traits in your Otez.
Either the Otez was designed using 1N5252 parts, or some guy just put in the diodes that he had handy.
So, any insight from someone with experience working on the Otez will be greatly welcomed and appreciated!
While looking at the Otez, I found that it is using 2N5551 transistors instead of 2N5550 transistors. No biggie, their characteristics are very similar. It's the diodes that surprised me. Instead of the usual batch of 1N4148 diodes, this Otez has a bunch of 1N5252 zeners! Unlike the 2N5550 and 2N5551 parts, which are virtually interchangeable, the 1N4148 and 1N5252 diodes have very different characteristics.
So, if anyone else has worked on these and/or has the schematic, please let me know if you have encountered similar traits in your Otez.
Either the Otez was designed using 1N5252 parts, or some guy just put in the diodes that he had handy.
So, any insight from someone with experience working on the Otez will be greatly welcomed and appreciated!
Zarathustra
Active Member
Hi Sungear,
Nice that you have an Otez also now. Does it have the single huge transformer or two smaller (dual mono) transformers?
I'm sorry can't help with the diodes but what I do know is that Julius probably switched from the Motorola MPQ6600 to the MPS8099/8599 substitutes without 'further notice' as often stated.
It seems common practice with all those small high-end audio manufacturers (and maybe also with the large ones) they just take what's available it seems.
Same could be true for the deviating diodes in your Otez you mentioned.
My Forte has now something to really chew on, the Watkins in my Infinity QLS. I've had a pair of Denon POA-8000's and their accompanying PRA-6000 pre-amp repaired/revised and although it really sounds great the POA-8000's do not like the load presented by a strapped QLS (mid/high & low terminals connected) as I stated in other posts in this forum. At high SPL's a blinking red LED in the POA-8000 starts warning for overload conditions. Enter the Audire Forte which has no trouble at all driving the double voicecoil of the Watkins 12 inch woofer and the Denon is happy also driving the mid/high section only.
Does your Otez play allright?
Attachments
My Otez is an earlier model with the single giant transformer. The single red LED on the front reminds me of HAL9000.
After further inspection, I believe that the 1N5252 diodes were a deliberate design decision, possibly due to the Otez using +/-80 volt power instead of the +/-60 volt power like you find on the Forte.
This thing was really rough when I got it. I have been working on it intermittently for over a month. I started testing the left channel assembly this afternoon, and I was gratified that nothing detonated!
I am a little concerned with the DC offset (+0.060v), but after having replaced every single semiconductor, it may just need a little burn-in time
Nice setup you have there. Those speakers are epic!
I'm glad you are enjoying the MOSFET Forte. My MOSFET Forte is starting to break in well after the rebuild and in time I hope it equals my BJT Forte.
Here is a shot of the freshly extracted Otez input board from the left channel (right channel is identical):
The first two diodes to the right of the 470uF cap ( the brown one) are the 1N5252 parts.
After further inspection, I believe that the 1N5252 diodes were a deliberate design decision, possibly due to the Otez using +/-80 volt power instead of the +/-60 volt power like you find on the Forte.
This thing was really rough when I got it. I have been working on it intermittently for over a month. I started testing the left channel assembly this afternoon, and I was gratified that nothing detonated!
I am a little concerned with the DC offset (+0.060v), but after having replaced every single semiconductor, it may just need a little burn-in time
Nice setup you have there. Those speakers are epic!
I'm glad you are enjoying the MOSFET Forte. My MOSFET Forte is starting to break in well after the rebuild and in time I hope it equals my BJT Forte.
Here is a shot of the freshly extracted Otez input board from the left channel (right channel is identical):
The first two diodes to the right of the 470uF cap ( the brown one) are the 1N5252 parts.
Zarathustra
Active Member
The pre-driverboards look very similar indeed for the different Audire amps.
As said before, the Otez's outside appearance reminds me of the Levinson ML-3's I once had, big black and powerful.
How do you use your Audires in your setup?
Great that you're restoring this beautiful amplifier.
Does it have a fuse for every powertransistor and what do you think about that?
As said before, the Otez's outside appearance reminds me of the Levinson ML-3's I once had, big black and powerful.
How do you use your Audires in your setup?
Great that you're restoring this beautiful amplifier.
Does it have a fuse for every powertransistor and what do you think about that?
So, the output transistors are fairly well protected, with one 5 amp fuse for every two transistors. The transistors' collectors are connected to the power rails through the fuses, as shown below:
The power switch is a 12 amp circuit breaker, so unless there is a serious imbalance in the transistors' current consumption, it should trip before fuses start blowing!
I also figured out the DC offset problem. It didn't make sense that a pair of 1N5252 diodes in series was connected to the base of the MPS8099 but a pair of 1N4148 diodes was connected to the base of the MPS8599 transistor, probably as a result of a previous rebuild, so I replaced the pair of 1N4148 parts with 1N5252 parts. The (see below)
Now, DC offset is steady at 4 millivolts:
It's fun to work on these old amps and preamps, and I just use them to listen to my 600 or so LPs. I mix and match the Audire amps with my Legato, Diffet, Diffet 2, and NAD preamps.
I would love to get my hands on a Diffet 3, Andante, and the unicorn of preamps, the Diffet 5.
I apologize for any typos, I'm up waaaaay too late!
The power switch is a 12 amp circuit breaker, so unless there is a serious imbalance in the transistors' current consumption, it should trip before fuses start blowing!
I also figured out the DC offset problem. It didn't make sense that a pair of 1N5252 diodes in series was connected to the base of the MPS8099 but a pair of 1N4148 diodes was connected to the base of the MPS8599 transistor, probably as a result of a previous rebuild, so I replaced the pair of 1N4148 parts with 1N5252 parts. The (see below)
Now, DC offset is steady at 4 millivolts:
It's fun to work on these old amps and preamps, and I just use them to listen to my 600 or so LPs. I mix and match the Audire amps with my Legato, Diffet, Diffet 2, and NAD preamps.
I would love to get my hands on a Diffet 3, Andante, and the unicorn of preamps, the Diffet 5.
I apologize for any typos, I'm up waaaaay too late!
Zarathustra
Active Member
Great that very low DC value, and yes it is 3:18 AM in California so good night!
Hi,
I'm new to this forum, and enjoying this thread.
Julius made a set of custom full range planars for my brother about 30 years ago that contained 4 or 5 times the panels of his largest production speaker. They were enormous, and the sound was unbelievable. They were powered by an Otez, and Julius originally thought they would require 2 Otez, but they were more efficient than he had expected. Unfortunately, parts of the panel foam started to fail, and my brother made the mistake of trying to fix them himself, which destroyed them.
I don't have any Audire components, but I am trying to repair an Andante preamp that belongs to my brother, who had bought it new along with the speakers and the Otez. The preamp developed a few problems, including pushing out DC which damaged the Otez.
Rather than divert this thread, should I start a new one on the Andante?
Here are a couple of pics for those who haven't seen inside of one before.
I'm new to this forum, and enjoying this thread.
Julius made a set of custom full range planars for my brother about 30 years ago that contained 4 or 5 times the panels of his largest production speaker. They were enormous, and the sound was unbelievable. They were powered by an Otez, and Julius originally thought they would require 2 Otez, but they were more efficient than he had expected. Unfortunately, parts of the panel foam started to fail, and my brother made the mistake of trying to fix them himself, which destroyed them.
I don't have any Audire components, but I am trying to repair an Andante preamp that belongs to my brother, who had bought it new along with the speakers and the Otez. The preamp developed a few problems, including pushing out DC which damaged the Otez.
Rather than divert this thread, should I start a new one on the Andante?
Here are a couple of pics for those who haven't seen inside of one before.
I think most consider DC offset more often with power amps, but the right channel of this Andante is pushing out enough DC to blow the rail fuses on one of my amps, and throw the other into protection mode. It works for 15 seconds, albeit with distortion, then POP! My brother didn't understand what was happening, so kept trying to use the preamp and amp, but the Otez was robust enough to manage the DC on the inputs longer than my amps until ultimately, it no longer could.
When I got the preamp to work on, some of the electrolytic caps were leaking, so I decided to start by replacing all of them, which was actually fairly costly. I cleaned all of the switches and jacks, but found the right channel volume pot has a noisy trace, and I can't find a replacement, and won't bother until I can figure out the larger problem.
I've tested literally all of the passive components, but my skill set with JFETs is rather low, and without a schematic and part numbers, I've been struggling. I'm not a trained tech, though I've worked on electronics for 45 years as a hobby, built 22 tube guitar amps, 2 125-watt monoblock audio amps, and repaired tube amps, several solid state amps, and refurbished my Accuphase C200, among many other projects. Still trying to learn more about diagnosing solid state gear, and have been struggling to pinpoint and diagnose which transistor(s) have a problem. To add to the confusion, some of the part numbers on the metal can transistors are either not clear, or what numbers are visible don't seem to come up on part searches. Interestingly, the transformers are still being made. I've been sidelined with a bunch of other projects, but will have to get this one figured out.
Most of the components used were top-quality, which is not surprising. Those military-grade silver mica caps are spot on in value, for example. The main complaint is about the clamshell design - it makes testing and repair very inconvenient, because you can't get access to both sides of each board without completely removing it from the chassis and central chassis panel. Very strange design, I think. The boards are mirrored, right and left, because of the way they are stacked back to back with the central chassis panel in between them.
Last night I was watching a program on the Apollo 17 mission, and couldn't stop thinking about Julius. I wish I had known him when my brother was working with him. The stories of the creation of the speakers I mentioned is really fascinating, as are the other stories he shared with me. His were the only example of the speakers ever made, and when they needed repair, Julius was too old, and had gotten rid of the special press-table he had made to assemble the hundreds and hundreds of little magnets on either side of the mylar film panels, which he tuned for response by varying the doping along or across the mylar. Julius tuned these for the mostly classical music, primarily piano, per my brother's instructions. Jazz, of course, was also wonderfully presented. Here's a photo of one of the speakers. Listening to Miles Davis' Kind of Blue on these was a religious experience for me.
When I got the preamp to work on, some of the electrolytic caps were leaking, so I decided to start by replacing all of them, which was actually fairly costly. I cleaned all of the switches and jacks, but found the right channel volume pot has a noisy trace, and I can't find a replacement, and won't bother until I can figure out the larger problem.
I've tested literally all of the passive components, but my skill set with JFETs is rather low, and without a schematic and part numbers, I've been struggling. I'm not a trained tech, though I've worked on electronics for 45 years as a hobby, built 22 tube guitar amps, 2 125-watt monoblock audio amps, and repaired tube amps, several solid state amps, and refurbished my Accuphase C200, among many other projects. Still trying to learn more about diagnosing solid state gear, and have been struggling to pinpoint and diagnose which transistor(s) have a problem. To add to the confusion, some of the part numbers on the metal can transistors are either not clear, or what numbers are visible don't seem to come up on part searches. Interestingly, the transformers are still being made. I've been sidelined with a bunch of other projects, but will have to get this one figured out.
Most of the components used were top-quality, which is not surprising. Those military-grade silver mica caps are spot on in value, for example. The main complaint is about the clamshell design - it makes testing and repair very inconvenient, because you can't get access to both sides of each board without completely removing it from the chassis and central chassis panel. Very strange design, I think. The boards are mirrored, right and left, because of the way they are stacked back to back with the central chassis panel in between them.
Last night I was watching a program on the Apollo 17 mission, and couldn't stop thinking about Julius. I wish I had known him when my brother was working with him. The stories of the creation of the speakers I mentioned is really fascinating, as are the other stories he shared with me. His were the only example of the speakers ever made, and when they needed repair, Julius was too old, and had gotten rid of the special press-table he had made to assemble the hundreds and hundreds of little magnets on either side of the mylar film panels, which he tuned for response by varying the doping along or across the mylar. Julius tuned these for the mostly classical music, primarily piano, per my brother's instructions. Jazz, of course, was also wonderfully presented. Here's a photo of one of the speakers. Listening to Miles Davis' Kind of Blue on these was a religious experience for me.
Last edited:
I was lucky enough to pry the Diffet 3 away from Bostown.
Does anyone here know where I could find a copy of a schematic? My Diffet 3 has a small white label on the back side that says "MC". Does anyone here know how to switch it to "MM". I see a 2 dip switches on the right side of the board?
Does anyone here know where I could find a copy of a schematic? My Diffet 3 has a small white label on the back side that says "MC". Does anyone here know how to switch it to "MM". I see a 2 dip switches on the right side of the board?
The Diffet is at my local techs for a recap. He sent me that pic last night. I'll ask him to take another one this evening when he gets home