SUT Loading

[Ali Tait]

Any advice on this peeps?

Have Hashimoto HM-3, which I'm using with Benz Gullwing SLR. Given the Benz has an internal impedance of 38 ohms, and Benz recommend a minimum of 400 ohms loading, what's the best way to load the SUT?

As usual, a lot of conflicting advice on the net. Anyone using a Zobel to damp ringing? If so, how to calculate correct values, or do I need to get the SUT on some test kit to sort this?

Using the 1:20 tap, phone stage MM input is 47k.

[Barry]

Any advice on this peeps?

Have Hashimoto HM-3, which I'm using with Benz Gullwing SLR. Given the Benz has an internal impedance of 38 ohms, and Benz recommend a minimum of 400 ohms loading, what's the best way to load the SUT?

As usual, a lot of conflicting advice on the net. Anyone using a Zobel to damp ringing? If so, how to calculate correct values, or do I need to get the SUT on some test kit to sort this?

Using the 1:20 tap, phone stage MM input is 47k.

Can't be done I'm afraid Ali.

The 1:20 turns ratio will transform the 47,000 Ohm impedance of your phono stage input to roughly 47000/(20x20) = 117.5 Ohm. I say 'roughly', since one should also take into account the resistance of both the primary and secondary windings . The transformed impedance is likely to be ~ 120 Ohm. Ideally the input presented to the cartridge ought to be at least 10x the coil impedance, which is why Benz recommend a minimum of 400 Ohm. Usina lower loading impedance can make the cartridge sound 'sat on', conversly too high a loading impedance can cause the treble to be uncontrolled and 'lively'. The exact effect will depend on the actual cartridge used.

Ideally you want a 10:1 step-up ratio, which when coupled to the 47K input impedance of the preamp will present an impedance of ~ 480 Ohm to the cartridge.

Given the circumstances I would use the 20:1 setting and see what you think of the sound.



Apropos using a Zobel network, the only way to choose suitable values is to pass a squarewave signal through the transformer and adjust the capacitance value to preserve the best shape of the top of the squarewave i.e. minimise 'ringing'.

[Ali Tait]

Thanks Barry, will take it to Nick's sometime to use his kit.

Not had a chance for a proper listen yet. Have a choice of 1:20 or 1:40, will have a good listen when I get time to see what sounds best.

[montesquieu]

A few tips from the US importer:

http://www.tube-amps.net/MC_Step_Ups.htm

specifically:

There are so many different MC cartridges in the market with wide variety of internal impedance and output levels. The HM-3 is specifically designed for those MC cartridges whose internal impedance is between 2 and 40 Ohms with the gain of either 26 or 32 dB (x20 or x40 amplification). Typical examples of MC cartridges work well with the HM-3 include Denon DL-103 and various Ortofon MC cartridges.

Looks like the Benz just scrapes in. Often used with stuff in the SPU sort of range of 2-6 ohm which is why I was interested, also fancied trying it with the 16 ohm Miyajima, see if it was any better than the HM7 (it can't be loaded to 400 either - with-without loading I have 209 ohm and 52 ohm on thehigh ratio, and 95 and 24 ohm on the low ratio as calculated by valvebloke/ampregen who put then together).

Keen to know how you get on and first dibs if you decide to sell!

[Ali Tait]

No worries Tom, first dibs to you.

Sounds pretty good on a quick listen though!

[Ali Tait]

Will try my DL S1 too..

[petrat]

Will try my DL S1 too..

That should be a great match, Ali.

[Ali Tait]

Have a Rondo Bronze too, that should be a good match too.

[petrat]

Have a Rondo Bronze too, that should be a good match too.

Yeh, there you go! :thumbsup:

[RothwellAudio]

Have a choice of 1:20 or 1:40, will have a good listen when I get time to see what sounds best.

1:10 would be a better option for the Benz, but in the absence of that I would go for the 1:20 option. 1:40 is a very high ratio and would present a load of less than 30 ohms to the cartridge. Still, there's no harm in trying the 1:40, it won't harm anything.
Also, Barry is correct about the Zobel network - a bit of experimenting on the bench is required. Ideally you need to work with the correct source impedance and also take into account the load (resistance and capacitance) which the phonostage will place on the transformer.

[Ali Tait]

Thanks, bit of a can of worms the Zobel I think, will leave it.

I may try changing the resistors in the phono stage to alter the 47k input.

[phonomac]

Wire the HM-3 primaries in parallel, to give 10:1 ratio. Load then becomes 470 ohms.

regards

Angus

[petrat]

Wire the HM-3 primaries in parallel, to give 10:1 ratio. Load then becomes 470 ohms.

regards

Angus

Not sure about that. Here is spec, with a link to a datasheet ... http://www.acoustic-dimension.com/hashimoto/hashimoto-mc-stepup-transformers.htm

Both seem to indicate that parallel connection gives 40x gain, 29 ohm loading?

[RothwellAudio]

Not sure about that. Here is spec, with a link to a datasheet ... http://www.acoustic-dimension.com/hashimoto/hashimoto-mc-stepup-transformers.htm

Both seem to indicate that parallel connection gives 40x gain, 29 ohm loading?

That data sheet shows two primary windings but only one secondary. Series connection of the primaries will give you 1:20, parallel connection will give you 1:40. 1:10 isn't an option.

[Ali Tait]

Getting a bit ahead of myself here, haven't even had a proper listen yet!

First impressions were good though.

[montesquieu]

Getting a bit ahead of myself here, haven't even had a proper listen yet!

First impressions were good though.


Personally I wouldn't worry .. in theory the HM7s have similar limitations in matching, but in actual use sound stunning, even when strictly speaking the ratios aren't ideal. I've also found they generally work better on the high (1:30) ratio than the low (1:15), even allowing for gain differences at the volume control - in fact I've never found an application where high gain didn't sound better. Obviously the HM3s may be different.

[Ali Tait]

Cheers Tom, will give both taps a good listen.

[Barry]

Cheers Tom, will give both taps a good listen.

Sound advice there!

[Ali Tait]

Arf! :-)

[phonomac]

Brain fade - I must be thinking about some other device :doh:

regards

Angus