[anubisgrau]

Some things you can do to enhance BYOB sound:
Install a real heatsink, lower the operating temperature and elimate the distortion of thermal protection trying to kick in. The stock heatsink is just for show, it doesn't even touch the chip. With no heatsink the chip can make no power without coming into thermal protection, which sounds like you're describing. I made a post a while back with pics about a heatsink from Mouser that works great, about $10. The heatsink must touch the entire chip tab with heat grease. http://www.audiocircle.com/index.php?topic=47130.msg442242#msg442242

this is interesting: i checked a couple of times a temperature of heatsink after 5-6 hours of use and it was mild, slightly above human's temperature. so this means that chip gets warm but not the heatsinks?!

Also play it into a 4 ohm speaker, to get more current out of it (10W at clipping.) It is not happy playing into high impedance drivers like some single drivers or exotics. Output power falls to nothing and you can hear the clipping and see it easily on a scope. At 8ohms resistive load, it makes 5W at onset of clipping. I have 14.5 ohm speakers, 95dB sensitive, and it clips readily. Obviously you already have speakers. Maybe try a pad, although I thin kyou will hear it with 115dB sensitivity, wow!

well, i would certainly rather change the amp then my curent speakers. they have a mild impedance curve - 6 to 9 ohm - and should be a piece of cake to drive.

but i suspect something else: charles told me that his amp is bridged so it is forbidden that the amp sees an earth via its minus terminals.

my sub amp modules are fed via the main amp (altmann) speaker terminals and i believe that the earth of the amp is connected to the earth of the speaker cables.

i still don't know if this is correct but this is what i suspect - charles was quite surprised that the amp wasn't fried or at least a fuse blown. no such a thing here, it works normal and to my ears it just souns as an amp's character. I've heard it in different systems and everywhere the same sonic stamp.

Last thing to try is run the chip on a race car battery that gives 16V nominal, instead of 12. Or make an unregulated 16V/10A DC supply with some nice filter caps like Jensen 4 pole. The chip has good ripple rejection, so you might get by without a regulator. If you need a regulated supply, Paul Hynes can hook you up, but his stuff is ultimate high end, so be prepared to pay. Input power can never exceed 18V while it is turned on, which is why he says disconnect before charging (with normal fast chargers.)  Playing at 16V the BYOBs specs are much better than 12V. More power, less distortion. It uses a car audio chip, which is designed to run on a car battery plus alternator at the same time, which is usually about 14.5V or more.
Rich

this is against my findings in case of BYOB. for a few months i run it with blue maxxima which i eventally brought for diagnostics being unhappy with how long it kept the charge. they measured it at 10.5V which clearly showed one of the cells went carrot. i bought yellow optima and measured it immediatelly - it runs over 13V. i had big hopes but unatural midrange character of stock BYOB was now just more prominent as the new battery openned its sound even more. blah!

i will now try a few basic things: new coupling caps, changing the pot - or rather removing it completely, a new battery cable (apparently a speaker cable evidence siren is good) with banks of electrol.caps (total 50000uf), and the new heatsink. if this doesn't elevate it into a sonic orbit i would expect than i will give it up, believeing it was more a hype around it than the sound (contrary to the DAC).

whatever seriosly assembled amps i tried against it in the last weeks, it was demolished. hiraga class A, proper 6S33 SET (with these double triodes used as halves), and - last but not least - oris manufacturer bd-design made crazyA. that was the most painful as it's a common territory, it's a dual mono gainclone, probably the best solid state i've ever heard in that price range (1700E).

[ferenc_k]

a new battery cable (apparently a speaker cable evidence siren is good)

You are on something 
The Evidence Audio Siren II pro speaker cable sounds very, very good as a battery cable with the Altmanns. As a bonus it is very good speaker cable as well.

http://www.evidenceaudio.com//content/product.html#siren2

[anubisgrau]

...double post, sorry.... aa

[anubisgrau]

do you know that BYOB is actually a bridged amp? i don't see the point, there are so many sonic compromises attached to the bridged amps (IMHO, hope i'm wrong)....

[richidoo]

Sorry, I have not been watching the thread closely enough anubisgrau ...

The chip is a bipolar bridged car stereo chip, so it is designed to run @14V with engine running. Specsheet says best power lowest distortion is at the high end of the allowed input voltage. 16V is doable and should sound "better," but along with the change in magnitude of THD will also come a change in the character of the distortion. So with speakers like yours anubisgrau, you may be hearing some harmonic crud that comes in at higher power output even though the THD value is lower. On the scope the output of the BYOB looks OK at half throttle, and at clipping which most users will see more often than you it is not as pretty at all. There is a zing at PP crossover that grows in magnitude as the amps nears clipping. At clipping it is larger amplitude than the signal. My speakers are only 95dB and low impedance so I can get there quite easily. Most people prefer the lower total distortion of the higher voltage. I run mine with the slow trickle charger attached, giving me 13.5V.

The amp dissipates about as much power in heat as it does in electrical power. At 10V input and high sensitivty speakers that maybe pretty low   but in normal use playing in to 95dB speaker at high volume level, it dissipates a lot of heat! You can't feel the heat because the stock heatsink is not touching the hot part of the chip at all. The chip will protect itself with thermal excess and that sounds very bad. When I first got mine, I did not trust the heatsink. So I put a flat 3" disc of aircraft aluminum on the chip and the stock heatsink on top of that, just until I could find a real heatsink for it. Within 1 minute playing at normal volume the disc was too hot to touch but the heatsink sitting on top of the hot disc was still at ambient temperature! The heat dissipated by the chip is proportional to how much power you are asking for, so even turned up full, with no signal it will not get hot. With your speakers the amp is not being overworked, and thermal distortion may not even be an issue, but the spec sheet says don't ask for any power with no heatsink or it will thermal protect. I wouldn't take any chances, a good heatsink is only $9, see my previous post for a link. You can esily install it yourself with a screwdriver and some heatsink grease.
 
With as much attenuation as you need for your speakers you should definitely invest in a very, very good volume control, like lightspeed, dact, or goldpoint before more subtle tweaks. I assume you already have nice wires too.

Bridging doesn't have to raise the distortion, depending on the implementation, as usual. Since it is an IC, the circuit is very precise and parts tolerance is closely controlled. Output offset was only 6mV on mine, each channel same.

Did you see that low watt SET OTL from Transcendant Sound? I bet that would rock your world with 115dB speakers! I would love to hear it myself with my Feastrex single driver speakers which are still only 95dB, but extremely fast and revealling.
Rich

[anubisgrau]

thanks rich, i'll add a comment or two tomorrow as it's getting a bit late in my part of the planet, meanwhile - slightly OT but still interesting - here is a comparison between a "normal" OTL, SE-OTL and SET from one of the very few audiophiles i've heard about who actually used all 3 of these....

>>>>>>>>>>>>
In Reply to: Transcendent sound se otl posted by horny on October 18, 2004 at 13:42:22:


Hi Robert,
I own the Transcendent SE-OTL, the T16, and a completely upgraded (parts, not circuit) Sun 2A3. I also own Lowther DX3 speakers mounted in specially made (by Doc Lowther himself) Medallion II cabinets. I have extensively listened to all the amps and am very familiar with each amp's sound. The SE-OTL is very neutral sounding, almost to a fault. It might be accused of sounding somewhat like an SS amp for that reason, but still retains all the smooth grain-free liquidity of a tube design. It is very extended at both ends, and very detailed. Dimensionality and soundstaging is very good but not the best i have heard. Compared to the T16, the soundstage and images tend to bunch together between the speakers, providing a little more "intimacy" but less expansive soundfield. The fact that there really are no vendors (other than Sovtek) for the 6C19P and 6H30 tubes used in the Se-OTL, means that you really can't tailor the sound with tube-rolling. Compared to the T16, the latter is much more expansive in its soundstage - well beyond the outer edges of my speakers. Because the input/driver tubes in that amp consist of 12ax7, 12au7, and 12at7, you can play with tubes and in fact currently my T16 has some of the warmth lacking in the SE-OTL. Both amps are very fast and detailed, with fantastic bass - as you would expect from good OTL design. The problem is, I keep returning to my 2A3 amp. Yes, the 2A3 amp is not quite as detailed and a little softer/looser in the bass, but the organic nature of sound, the immediacy and physical tangibility of intruments, the naturalness and emotion simply can't be beat. I have rotated all these amps in/out of my system at least 50 times and while each has some virtues the others don't posses, I keep returning to the 2A3 because I literally relax into the music and forget about stereo-stuff while listening. Bruce's components are designed to be very nuetral and largely sound similar ( I also own the Grounded grid preamp and can equally say that this is a very neutral component). The problem with the SE-OTL is that because of its ruthless neutrality, it might not be the best match for Lowthers (others have disagreed, so this is just my opinion), whose inherent frequency nonlinearities may be exacerbated by the neutral presentation, yet because of the 1.5W output of the SE-OTL, this is exactly the kind of speaker you would generally use it with. A bit of a catch-22. In any event, I would certainly recommend trying the SE-OTL and see if it's to your liking. It is a very good amp, just neutral to the extreme. It has a low-enough cost, that buying and trying is not a big deal. I usually own 4-5 amps at any given point in time, and there is really no reason you can't own both the SE-OTL and keep your "classic" SET amps. You too may find yourself rotating them. To answer the other gentlemen's question in this thread - the SE-OTL has 9db gain and I have successfully used it with a passive volume control with my Lowthers. However, really loud volume will require the volume control to be almost all the way up (0db attentuation). It may JUST be on the cusp of insufficient gain used in a passive setup for really loud playing. Hope all this helps.
-Alex

[tanchiro58]

The problem is, I keep returning to my 2A3 amp. Yes, the 2A3 amp is not quite as detailed and a little softer/looser in the bass, but the organic nature of sound, the immediacy and physical tangibility of intruments, the naturalness and emotion simply can't be beat. I have rotated all these amps in/out of my system at least 50 times and while each has some virtues the others don't posses, I keep returning to the 2A3 because I literally relax into the music and forget about stereo-stuff while listening.

This statement is absolutely true. I switched around so many times the Sun Audio (modded with input 417As) and the modded Altmann BYOB amp in my system and think that these two are very competitive in term of kind of musics they play with. It is hard to compare between them. When listening to vocals I like the Sun 2A3 but with instrumentals and classicals the modded BYOB amp outperformed the Sun 2A3. Now I can turn up the volume of BYOB amp to 12 o'clock after adding the 36K to the outputs. This would make the vocals more revealing and lively. 

[anubisgrau]

Now I can turn up the volume of BYOB amp to 12 o'clock after adding the 36K to the outputs. This would make the vocals more revealing and lively. 

have you rolled resistors before settling down on a particular?

[anubisgrau]

I've had a bit of a situation with my BYOB recently which might provide an explanation for the way it sounds, if it differs from how it should be. Therefore I would appreciate any comments.

When I connected a friends SOTA preamp to the BYOB, there was no sound coming out, although obviously both a preamp and an amp worked. We proved that by testing both of them in another systems, but when they put together something was going wrong, and I could see that the BYOB was sucking a huge amount of power from the battery as the blue led was going dim for a few seconds when the amp was switched on.

I suspected something was going wrong with ground so I decided to write to Charles and ask him if he had a similar experience and a possible explanation.

He asked me what load the BYOB sees. I told him that my speakers have fully active bass modules fed via speaker cables from the main amp (the BYOB). Otherwise the speakers should be a piece of cake to drive, nice stable impedance 6-9 ohms and a huge efficiency, over 110db.

Than he told me the BYOB is a briged amp therefore not allowed to see ground via its output terminals. Also that R and L minus terminals shouldn't be connected so I have to be sure that none of the crossovers and bass amps connect minus or any terminal to ground.

Than I wrote to the speaker designer (Bert from BD-Design) asking him how his bass amps are wired. Bert answered shortly: the bass amps have their ground connected to the ground of the input signal.

This obviously looks like a short.

But now comes a puzzle: the BYOB is not smoked and even his fuse is still intact. It seems to be working normally.

How is this possible and should I twiddle with modding it at all, given the problem?

Thanks for your thoughts! G.

[anubisgrau]

I've finally grabbed some time to start playing with the BYOB.

I've dismantled it from the spruce board, took the original Wima caps out and also dismantled the stock heatsink (btw it hardly touches the chip, i don't get what is the function of it?).

For starters, I've soldered Mundorf Supreme (plain, not silver in oil) caps, 4.7uF, 800VDC.

Though I have a gigantic heatsink which I plan to use for BYOB, I haven't installed it yet. I want to take attention to an each mod to be sure what makes sense and what doesn't.

After 45 mins of listening to the new caps, it's clear that Wimas aren't the best choice. Mundorfs, although not being in use for a long time, sound much more lifelike, fuller, punchier. A plastic overtone of timbre is gone, as well as a shouty/honky coloration on vocals. On the other hand, there's a bit of coarseness to vocals that seems to be new - let's see if this will gone with run-in.

Generally it certainly makes sense to focus on modding it, at least to suit better the rest of everyone's system. I feel like I have just open a book, with so many pages to go. I have another interesting stuff to try, vintage Siemens PIO from 1969. I have nothing with me to check how it responds to bypassing caps but I will try that too.

The next will be the heatsink.

Then I plan to completely remove a pot and convert it into a power amp to be used with my valve pre as well as a TVC.

More to follow....

[anubisgrau]

OK, 2 days later.... the new cap really started to open and difference is now rather dramatic. more music into the room, more natural flow, and i would say certainly closer to what is usually described as altmann DAC sound - neither digital nor analogue, just natural. there's plenty of detail that nicely fit into the overal soundpicture, tones hanging in the air.

very very good. thanks everyone for pointing out that this is possible, frankly i was a bit sceptical that it will be worth.