I have started research for parts selection / sourcing for the RH 84 amplifier.
For the power and output transformers I am going with Edcor models.
However, I can't seem to find a 20H 50ma choke as called for in the schematic. Ideally I would like to use Edcor so that everything matches and so that I can buy / ship in one batch...but Edcor only makes the following models:
5H at 200ma
10H at 200ma
10H at 300ma
Would any of these work for this design?
Here is a link to the schematic: RH 84 - Tube Audio ...... RH DESIGN
For the power and output transformers I am going with Edcor models.
However, I can't seem to find a 20H 50ma choke as called for in the schematic. Ideally I would like to use Edcor so that everything matches and so that I can buy / ship in one batch...but Edcor only makes the following models:
5H at 200ma
10H at 200ma
10H at 300ma
Would any of these work for this design?
Here is a link to the schematic: RH 84 - Tube Audio ...... RH DESIGN
On another note: Capacitors
It seems that the critical capacitor is the .22uF in the middle of the schematic. I am going to use a Mundorf Silver Oil for this one.
For the other capacitors I am using a mixed bag of Solen MKP and Mundorf MKP (metallized polypropylene), except for the big 220uf cap for which I am using a Jensen Electrolytic. (To keep cost and sizes down.)
Any suggestions or recommendations on selection of Capacitors for best bang for the buck?
It seems that the critical capacitor is the .22uF in the middle of the schematic. I am going to use a Mundorf Silver Oil for this one.
For the other capacitors I am using a mixed bag of Solen MKP and Mundorf MKP (metallized polypropylene), except for the big 220uf cap for which I am using a Jensen Electrolytic. (To keep cost and sizes down.)
Any suggestions or recommendations on selection of Capacitors for best bang for the buck?
Any of the three chokes you noted would work fine. The more Henries, the better. Make sure you've got enough current rating for both channels. I'd think 50 mA would be sufficient for only one channel. 100 mA should do fine for both channels, but it won't hurt anything if you've got extra.
I wouldn't bother. 10H is a pretty good amount, and so is 220uF. You should have plenty of filtering. I've had good results using a 6H choke with 120uF filter cap after it, even into efficient (>100dB) speakers.
Would someone be able to explain the significance of the "frequency response" data on different transformers? What does this mean in real life performance / audio? Does it affect the frequency response?
e.g. From Edcor for 5k to 8ohm output trannies:
- Bottom of the line: XSE 10-8-5K, 70hz to 18khz, $17.22
- Middle of the line: GXSE 10-8-5K, 40hz to 18khz, $26.10
- Top of the line: CXSE 25-8-5K, 20hz to 20khz, $83.50
e.g. From Edcor for 5k to 8ohm output trannies:
- Bottom of the line: XSE 10-8-5K, 70hz to 18khz, $17.22
- Middle of the line: GXSE 10-8-5K, 40hz to 18khz, $26.10
- Top of the line: CXSE 25-8-5K, 20hz to 20khz, $83.50
This measurement is hugely important for audio.
It has to do with the frequencies that the transformers can pass.
Hi-Fi Audio frequency range is considered 20hz to 20Khz, and only the CXSE series can reproduce the entire range.
In real life the XSE will have no bass, the GXSE will have poor bass, and the CXSE will sound good, with bass as good as the circuit can pass.
In general, it's a mass thing with output transformers. Big ones are the only ones with bass.
It has to do with the frequencies that the transformers can pass.
Hi-Fi Audio frequency range is considered 20hz to 20Khz, and only the CXSE series can reproduce the entire range.
In real life the XSE will have no bass, the GXSE will have poor bass, and the CXSE will sound good, with bass as good as the circuit can pass.
In general, it's a mass thing with output transformers. Big ones are the only ones with bass.
Transformer 'Frequency Range' is not a sharp bandpass filter situation- the response 'drops off' at the low and high end. Without a spec like '-3dB' or similar, it is impossible to tell how quickly the frequency response is dropping, and how poorly the transformer will perform. You really need a graph to tell you what's happening. And, you need to know the power level that was used during the test. Response with 1mW will look a lot better than at 10W. (One reason you can use a small OT in a headphone amp and still get decent bass...) Your low-power RH84 will be less demanding in a somewhat similar way.
What's your budget?
For info on the CSXE, and Hammond equivalent see Output Transformers
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I'm not buying that story. I've used the GXSE with low plate resistance DHTs, and achieved very satisfying bass. I believe that Edcor's ratings refer to the lowest frequency that will be reproduced (within 1 dB?) at full rated power. At less than full power, my experience has been that you will get good quality low frequency reproduction - even at frequencies well below the Edcor's specifications. Even if that weren't the case, 99% of the people out there simply do not have speakers capable of extending down to the 20 Hz octave anyway.
I'm not trying to discourage anyone from buying the best transformers they can afford. I'm just saying it's ridiculous to say the XSE has "no" bass, or the GXSE has "poor" bass. I'm certain my experience is not unique, and there are many other satisfied customers out there who have had good results with the X and GX line.
I am not implying that it is a sharp bandpass. Sorry if it came out that way.
As for the other transformers having good bass, that is a distinct possibility. My question is at what power does the, for example, XSE's 70hz roll-off occur? What happens if it is only a few milliwatts? (Which I doubt) The stated bandwdith, at full power, of the CXSE will help make sure that the bass is reproduced fully, at whatever output your amp can produce.
In my experience, I have never regretted buying "too much" output transformer. I have, however, really regretted buying small ones.
As for the other transformers having good bass, that is a distinct possibility. My question is at what power does the, for example, XSE's 70hz roll-off occur? What happens if it is only a few milliwatts? (Which I doubt) The stated bandwdith, at full power, of the CXSE will help make sure that the bass is reproduced fully, at whatever output your amp can produce.
In my experience, I have never regretted buying "too much" output transformer. I have, however, really regretted buying small ones.
For any of them they are operating at such a low % of maximum design capacity (what will the RH84 produce - 3W?) that the bandwidth rating is pretty irrelevant.
Having said that, the cost difference between the G- and the bare XSE is so small, it would be a no-brainer for me - go with the GXSE...
Thank you everyone. This is now more clear.
I'm going for the GXSE model as the RH84 puts out about 3.5w.
Would the GXSE 15w model offer any advantages over the 10w model? I'm thinking not, but if the frequency performance is based on 40hz at 15w then there is more cushion for performance at 3.5w?
I'm going for the GXSE model as the RH84 puts out about 3.5w.
Would the GXSE 15w model offer any advantages over the 10w model? I'm thinking not, but if the frequency performance is based on 40hz at 15w then there is more cushion for performance at 3.5w?
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