Inverted OTL with 6SN7/6AS7

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Wolfgang
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Re: Inverted OTL with 6SN7/6AS7

Post by Wolfgang » Sun Aug 11, 2019 11:39 pm

Ray, there are these nice positive surprises like the Maida regulator or the SLB which are like an island in the middle of struggling with strange phenomena or resolving problems.

It was fun to work with these high quality PCBs. The power transistors get hardly warm at 0,8A and there is only about 1,5V sagging at this load.
They are ready for the first test run in the amp.
SLB psu.jpg
Another update: I won't use the TVS diodes because they change the sound almost as much as the zener and regular diodes with the voltage reg. in the TS amps. This is one of those "phenomena" which I cannot explain. I was sure it would work this time as their leakage current is only in the uA range. In the beginning I even liked the smoother sound but over time I was missing the original drama of untempered InvOTL operation.

I will go with my plan A using custom made DC monitoring/protection circuits for the InvOTL.

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Nick
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Re: Inverted OTL with 6SN7/6AS7

Post by Nick » Mon Aug 12, 2019 8:47 am

I won't use the TVS diodes because they change the sound
I have tried and failed to use TVS diodes in the signal path for overload limiting. Never works, I assume there are some capacitance (and probably non linear) in there.
Resistance isn't futile it's V / I.

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Re: Inverted OTL with 6SN7/6AS7

Post by Wolfgang » Thu Aug 15, 2019 2:43 am

I knew that even a little bit of hum can already modulate the music signal with some negative effects but I didn’t expect such a dramatic change. The difference between the original CRC psu and using the SLB is like watching a movie on VHS tape on a 4:3 TV vs. a Blu-ray DVD on a 16:9 flat screen TV. This is the best comparison I can come up with.

It is nothing less than amazing how instruments are suddenly more in focus , how single tones have a much longer reverberation time, how lower mids resolution has increased in a very dramatic way, and how subtle details in general are more audible . With some songs it feels as if the speed has doubled. This is the same observation which I had made when I was listening with only one channel of the InvOTL with original CRC psus in comparison to my other OTLs. This phenomenon must have something to do with the fact that the InvOTL doesn't use NFB. Now the same thing happened again but on the next higher level when I changed the output psu to SLB. With some recordings the dynamics sound now absolutely life-like.

The only downside is that I need new transformers for the output psu with higher voltage if I want to keep my original max output swing as the SLB “eats” some volts after all.

Really, how an almost 100 year old idea of how to use tubes “inverted” can be combined with up-to-date solid state power supplies leading to this sound quality is a living proof to me that we should never give up trying new things or experimenting with new and old technology even if we think it doesn’t matter.

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Ray P
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Re: Inverted OTL with 6SN7/6AS7

Post by Ray P » Thu Aug 15, 2019 6:36 am

Good result Wolfgang. As you know, I've started collecting parts with a view to building one myself sometime so I'll be interested in how you configure the SLB - in your earlier picture it looked like you had just done a standard build with respect to the CRC element of the SLB.

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Re: Inverted OTL with 6SN7/6AS7

Post by IslandPink » Thu Aug 15, 2019 8:18 am

Umm... what's an 'SLB' ?
"The bass is the king of the instruments - it has no known natural predator" (Wobble)

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Ray P
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Re: Inverted OTL with 6SN7/6AS7

Post by Ray P » Thu Aug 15, 2019 9:15 am

IslandPink wrote:
Thu Aug 15, 2019 8:18 am
Umm... what's an 'SLB' ?
https://www.diyaudio.com/forums/group-b ... ly-gb.html

Wolfgang
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Re: Inverted OTL with 6SN7/6AS7

Post by Wolfgang » Thu Aug 15, 2019 1:46 pm

Yes, Ray. Standard build, heat sinks like in the picture (get warm after hrs but not hot).

This is the circuit:
SLB circuit.png
and this is how it's connected :

SLB circuit.png[/attachment]
Attachments
Inv OTL psu w SLB.png

izzy wizzy
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Re: Inverted OTL with 6SN7/6AS7

Post by izzy wizzy » Thu Aug 15, 2019 6:56 pm

Looks like one of those synchronous mosfet rectifier doodads followed by a cap multiplier. Seem to remember there was another diyaudio thread with this kind of rectifier. Wasn't jc going on about something like this a while ago?

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Ray P
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Re: Inverted OTL with 6SN7/6AS7

Post by Ray P » Thu Aug 15, 2019 9:53 pm

izzy wizzy wrote:
Thu Aug 15, 2019 6:56 pm
Looks like...
Yes, that's essentially it, nothing fundamentally new but a very nice implementation.

I've got a couple of the dual rail boards that I originally bought for a Hiraga build but also two single rail ones for a MoFo project. I think the dual rail boards will now be destined for the parts collection for my own inverted OTL project.

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Re: Inverted OTL with 6SN7/6AS7

Post by izzy wizzy » Fri Aug 16, 2019 9:40 am

A bit fell off the end of my post. Was wondering if anyone had played around with this type of rectification or any other diyaudio modules like this?

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Ray P
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Re: Inverted OTL with 6SN7/6AS7

Post by Ray P » Fri Aug 16, 2019 5:56 pm

izzy wizzy wrote:
Fri Aug 16, 2019 9:40 am
A bit fell off the end of my post. Was wondering if anyone had played around with this type of rectification or any other diyaudio modules like this?
People seem to rate the approach on DIY Audio.

I bought a few bare PCBs, a mixture of surface mounted and through hole, from a group buy on DIY Audio to try them out sometime - happy to donate a board if anyone wants to give the approach a try in the meantime. These will generally be limited to use with solid-state amps because of their voltage specs (IIRC max input is about 50VAC) but there is someone working on an HV version (I think around 450V). They should be fine with any current requirement we're likely to ask of them for audio projects.

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Nick
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Re: Inverted OTL with 6SN7/6AS7

Post by Nick » Fri Aug 16, 2019 8:03 pm

They should be fine with any current requirement we're likely to ask of them for audio projects.
But not voltage.
Resistance isn't futile it's V / I.

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Ray P
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Re: Inverted OTL with 6SN7/6AS7

Post by Ray P » Fri Aug 16, 2019 9:45 pm

Nick wrote:
Fri Aug 16, 2019 8:03 pm
They should be fine with any current requirement we're likely to ask of them for audio projects.
But not voltage.
Isn't that what I said?

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Nick
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Re: Inverted OTL with 6SN7/6AS7

Post by Nick » Fri Aug 16, 2019 9:56 pm

Don't think so, I was referring to the
but there is someone working on an HV version (I think around 450V).
As not covering the voltage range (for example) I may use.
Resistance isn't futile it's V / I.

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Re: Inverted OTL with 6SN7/6AS7

Post by izzy wizzy » Fri Aug 16, 2019 10:25 pm

I was thinking filaments due to voltage limit. An interesting concept maybe.

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