Tweeter Amp for OB or Horns

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IslandPink
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#31 Re: Tweeter Amp for OB or Horns

Post by IslandPink »

Cheers !
Also found 2-off 45's hiding amongst some 71A's - things are looking up.
Emailed Phil at Bluebell about toroids from Hammond.
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izzy wizzy
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#32 Re: Tweeter Amp for OB or Horns

Post by izzy wizzy »

Is that toroids for mains? If so, why over lam txs?

cheers,

Stephen
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#33 Re: Tweeter Amp for OB or Horns

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I was thinking less radiated field, plus I don't need extra windings ( as many of the Hammond ones are ) , prefer to use small transformers, separate, for filaments.
Open to arguments one way or the other, though. Nothing ordered yet.
Perhaps it's because the E-I Tx on the Verus motor supply radiates hum like a bastard.
Having said that I have a Hammond EI lined-up for the phono amp, although I was planning to make use of a sheet of mu-metal where required
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#34 Re: Tweeter Amp for OB or Horns

Post by izzy wizzy »

The times I've compared toroids to EI types, I've preferred the sound of EI types. For all in one box solutions and low level circuits, maybe themore contained field of toroids are an advantage but that's only for packaging reasons most of the time. I think for huge SS power amps, efficiency may be better and so relevant. Toroids let a lot more hash through and for a tweet amp, that wouldn't seem a good idea.

I have had issues with radiated fields with my phono primarily with the third chokes picking up something causing hum if they are in the main PSU box so they're in the audio box. However in my line/headphone stage, no issues at all and that is crammed in with TVCs as well. I'll put a photo on the thread with the line stage soon. All transformers by the same company. No flux bands or anything.

Your tweet amp wil be even higher level signal than line so it should be OK with a bit of care shouldn't it?

cheers,

Stephen
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#35 Re: Tweeter Amp for OB or Horns

Post by vinylnvalves »

Mark, After going through the same dilemma a while back, my application crossing at 1800hz. We concluded it doesn’t really matter what amp you use for HF. I ended up using a ACA amp, but I could as well have used a T amp or a valve amp if I could have got one with a good enough S/N ratio.
Don’t put another 5 years onto the speaker project...... :wink: :wink:
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#36 Re: Tweeter Amp for OB or Horns

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izzy wizzy wrote: Sat May 26, 2018 2:08 pm The times I've compared toroids to EI types, I've preferred the sound of EI types.
Is this for passive supplies and full-range ?
In that application I'd probably go for EI type. The toroids have poorer regulation so I'd expect that to make a difference to how the PS behaves under bass frequency loading.
I take your warning about more HF noise coming through a toroid, I want to have a chat with Nick who's obviously got noise levels down to very small numbers on some of his commercial gear - I want to chat about what the Tx and SiC diodes do and if anything else is needed.
But I think having the HF only and the shunt on there, do change the game quite a bit.
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#37 Re: Tweeter Amp for OB or Horns

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vinylnvalves wrote: Sun May 27, 2018 7:51 am Mark, After going through the same dilemma a while back, my application crossing at 1800hz. We concluded it doesn’t really matter what amp you use for HF. I ended up using a ACA amp, but I could as well have used a T amp or a valve amp if I could have got one with a good enough S/N ratio.
Don’t put another 5 years onto the speaker project...... :wink: :wink:
Steve - I love your attitude :) but I don't agree with you at all !
I've heard some pretty enamel-stripping sounds coming from T-amps and high efficiency HF units. I have a tweaked TDA7297 amp here for 'holiday' duty and it's pretty nice until you get above ~3kHz then starts to sound a bit gray and rough . It's well down the scale of what I'm used to from valve amps like 2A3 , 45, 801A etc.
Rest assured, this amp will not take 5 years. It needs doing, and this amp is relatively simple. I already have about 3/4 of the parts, I'm just finalising the circuit in my head, and have to get some PS parts.

On that theme, I realised yesterday that I have some ECC40's upstairs which I used on the 3-stage 300B amp. Those are very nice and Nick and Jono Noble are fans of the valve. Slightly more gain too, which will help with the output Tx being used at 3k>4R .
'course I still wonder if should stick to pentode driver for the HF, it was up top where I think I preferred the pentodes. You can always get enough gain without a cathode by-pass cap if you use a pentode driver .... Might be an idea to build the amp about half-way with power supply and output stage, then run a small breadboard for the driver, just mono , and try E83F or choke-loaded ECC40 ... hmm.
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#38 Re: Tweeter Amp for OB or Horns

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Mark have you tried dh pentodes? I'm sure Mr C has and he'll have the valve types to hand. I cant remember the names. They are typically from battery powered valve radios . I tried them and they were sweet. But they are intended to be pentodes. I,5 volt heaters, tiny and a tad micrphonic as I used them ( as preamp).
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#39 Re: Tweeter Amp for OB or Horns

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andrew Ivimey wrote: Sun May 27, 2018 5:28 pm Mark have you tried dh pentodes? I'm sure Mr C has and he'll have the valve types to hand.
I've longer got anything like that Andrew. I sold off 99% of my valves to our Steve S almost a year ago now.
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#40 Re: Tweeter Amp for OB or Horns

Post by izzy wizzy »

IslandPink wrote: Sun May 27, 2018 4:32 pm Is this for passive supplies and full-range ?
In that application I'd probably go for EI type. The toroids have poorer regulation so I'd expect that to make a difference to how the PS behaves under bass frequency loading.
I take your warning about more HF noise coming through a toroid, I want to have a chat with Nick who's obviously got noise levels down to very small numbers on some of his commercial gear - I want to chat about what the Tx and SiC diodes do and if anything else is needed.
But I think having the HF only and the shunt on there, do change the game quite a bit.
I couldn't remember the break down of what exactly but I remember better connection with the music. Not very helpful but it made an impression on me the times I've done it.

cheers,

Stephen
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#41 Re: Tweeter Amp for OB or Horns

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andrew Ivimey wrote: Sun May 27, 2018 5:28 pm Mark have you tried dh pentodes? I'm sure Mr C has and he'll have the valve types to hand. I cant remember the names. They are typically from battery powered valve radios . I tried them and they were sweet. But they are intended to be pentodes. I,5 volt heaters, tiny and a tad micrphonic as I used them ( as preamp).
I haven't tried small ones Andrew ( have looked at the data though ) . My main amp does use 4P1L pentode into 300B ( or GK-71 also v.good ) so I like DHP very much. For this amp as planned now, it'll take up too much space to add the additional 2x DHT filament supplies though.
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#42 Re: Tweeter Amp for OB or Horns

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izzy wizzy wrote: Sun May 27, 2018 7:40 pm I couldn't remember the break down of what exactly but I remember better connection with the music. Not very helpful but it made an impression on me the times I've done it.
cheers,
Stephen
Tend to think it's the bass end then, if your PS is better regulated it does make the music more organised and the complex stuff fits together more meaningfully. I may be wrong though !
The upshot of my discussions with Nick was that the Cree's are a very good start as they have negligible reverse current. Then the thing is to have a Morgan Jones style snubber ( cap + zobel) across the secondary before it gets to the rectifiers. With an old-school choke, and Black Gate cap after ( they work up to pretty high frequencies unlike many electros ) it should be pretty quiet. Then I can add a shunt ( see below ) . For the toroid we talked a bit about DC blocking and the input mains voltage too - might require holding down to 230V input as some of the Tx's get noisy with 248V. This would work ( also see below ) with scheme 3 .
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#43 Re: Tweeter Amp for OB or Horns

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Just to try & explain the PS options, have had a couple of things going through my head, had to backtrack at the weekend slightly, here's a picture to help.
TweeterPS_options.jpg
Circuit no.1 doesn't work. The VR tubes just saturate as there no control of the current through them.
Circuit no.2 is what I was thinking until the weekend. Same as my phono. Here a CCS running the total current of circuit, plus 20ma , gives 20ma through the OD3's ( to ground ) which is approx. their mid-point. The problem with this is the 45's run at 30 to 35ma. The shunt will swing +/-20ma, but then it hits a brick wall as the Zout of the PS goes to the CCS resistance, ie. near-infinity. The current swing limit here will basically limit the power output from the 45's to maybe half their normal output at best. It is however a VERY quiet B+.
Circuit 3 is more complicated but basically can be configured in a more versatile way and can run direct off the end of the passive PS. If you run say 20ma in the ECL82, it will be a very low Z-out and very clean until you go towards full power, at which point the shunt gives up and you revert to the Zout and cap return path of the passive PS section. I've run the 'T-Rex' supply for years , which only runs 50ma in the shunt for a pair of 300B's and drivers, and it seems to work very well, including at Owston where the power would be closer to the 8wpc.
Ok this supply is not as quiet as option2 , the noise from passive PS comes through the shunt, so care required in design and implementation, hopefully the main residual will be 100Hz hum ( ~ 30mV ) and some way from the operating frequencies for this amp.

I need to read-up on Broskie's 'Janus' PS though - which may be better and he's done examples for the ECL82.
ps. PCL82's are cheaper ( 16V fil supply )
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#44 Re: Tweeter Amp for OB or Horns

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Then I went and had a bath, and started thinking about ESR vs. shunt Zout, and whether any of the AC return would actually go through the shunt valve at 5000Hz .... :confused3:
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#45 Re: Tweeter Amp for OB or Horns

Post by izzy wizzy »

LCLC and be done ;)
Glow tubes for the driver.
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